Midterm Flashcards
How do collagen fibers change with age?
Collagen fibers get thinner and smaller as we age
What do proteoglycans do?
Basically act as little brushes connected to link proteins, they respond really well to compression, little bristles in the brush push back against compressive forces
What forces do GaGs resist?
What is their charge and therefore their affinity for water?
How are they complementary to collagen?
How do they affect the flow of water in and out of cartilage?
Also resist compressive forces, have a negative charge and are hydrophilic so they have the ability to push back against compression and absorb all the water into the proteoglycan brushes, complementary to the collagen which is better at resisting tension forces, water flow in and out of the cartilage ensures that the cartilage stays healthy
What does movement bring into the cartilage?
How fast is the metabolism of cartilage?
What is immobility’s effect on cartilage?
Movement causes water and nutrients to flow in and out of the cartilage
Cartilage has a very slow metabolism
Cartilage becomes more porous and pliable, may eventually lead to bones touching each other which causes shearing forces
What are the 2 most common causes of damage to the cartilage?
- Immobility
- Excessive loading
How do mogul skiiers minimize the load on the structures of the knee?
Large eccentric contraction in quads to “brake” against gravity and avoid going into full knee flexion at any point
Where is most of the fluid in articular cartliage found?
How does the concentration change with depth?
Fluid is concentrated at the joint’s surface, decreased concentration with depth
What is an aggregan?
Combination of GaGs and link protein
How is the cartilage closest to the bone organized?
Cartilage nearest to the bones in perpendicular to the bone in order to absorb compression and to be able to directly attach to the bone
What does viscoelastic mean in the context of cartilage?
Visco refers to water
Elastic refers to cartilage
How can we describe creep and relaxation of our cartilage?
Creep-liquid goes out of the cartilage quickly when the structure is pressed and then it stabilizes over time
Relaxation-characterized by initial compression and then a relaxation phase
(ex. trying to touch your toes for a few minutes, there will be initial resistance and you will feel tight but as you give your body enough time and ease into the stretch gradually you will be able to go deeper and deeper because the fluid in the structure moves and the collagen repositions itself to accommodate the stretch, do not try to stretch ballistically)
What is the relationship between permeability and resistance to fluid?
High permeability = low resistance to fluid
Low permeability = high permeability to fluid
How porous is cartilage?
How permeable is cartilage?
What causes this level of permeability in the cartilage?
Articular cartilage is very porous
Articular cartilage has very low permeability, lets fluid come in and go out at a very slow rate
This is because of the large generation of friction from the collagen and the proteoglycans within the articular cartilage
Why is it important to retain water in the articular cartilage?
Water in the cartilage helps to absorb the compressive forces and acts as a cushion
How will fluid in the carilage react to load?
If you have a compressive force straight down, fluids will move to the sides to try and avoid the compressive force.
What structure brings water back into the cartilage once unloading takes place?
Proteoglycans bring water back into the cartilage
How does a high outside pressure applied by a load to the cartilage affect the permeability of the cartilage?
P1=pressure applied by the load to the cartilage
P2=pressure within the cartilage
When there’s a big difference between P1 and P2, there’s more compression so there will be much less permeability in the cartilage.
When theres a small difference between P1 and P2, there’s less compression so there will be much more permeability
What is the last resort protection of the cartilage?
Lubrication models,
mix of models 1 & 2, not one or the other
(liquid lubricating film and surface lubrication)
Why is osteoarthitis so prevalent?
We don’t move enough as a society, and when we do try to move we overcompensate and do big bursts of physical activity at one time and put excessive loading on the structures
how does the body receive most loads?
how long does it take for the body to receive a steady state response to the cyclical loading?
What is the ideal oscillation or variability between cycles?
When is it good to see more variability in cycles, in running for example?
Cyclical, such as walking or cycling
30 cycles
We want as small an oscillation, or variation, as possible when doing cyclical activities like walking or cycling
Trail running, don’t have a choice and need to be able to adapt to the outside environment and change variability due to instability
What property makes cartilage have a non-elastic response as opposed to an elastic response?
What is lost energy between loading and unloading cycle?
What kind of training uses this method?
What is important in plyometric training?
No, it has a non-elastic response because it is viscoelastic
Energy lost to heat when structure is deforming and forming back during loading and unloading cycles
Plyometrics, being able to absorb energy and use it again
You need to tell the client to jump up and down and jump back up again as quick as possible, faster than 1 second within touching the ground, this makes sure that energy used is hystesis energy that is stored in the muscles and that this energy is not lost to heat.
(ex. do a box jump, get down off the box, jump back down as fast as possible)
What kind of force is required to elicit an elastic response from the cartilage?
What kind of force is required to elicit a viscoelastic response from the cartilage?
Very fast force
(intracellular fluid doesn’t have time to move around)
Normal force
(intracellular fluid does have time to move around)
What does collagen look like in normal situations compared to when it is under stress/strain
collagen spread out in all different directions, changes it shape and becomes more parralel to increase the rigidity of the fibers as it reacts to the stress/strain
(moves from toe region to linear region to eventually failure)
how does collagen react to shear forces and are pure shear forces common?
What combination of forces does it not react well to?
Reacts well to pure shear forces such as translation between the bottom and top layer but the body NEVER has pure shear forces
(minimal deformation, no volume changes, no fluid movement)
Doesn’t react well to compression/
tension forces being combined with shear forces
What causes wear and tear?
repetitive movements that cause stress and strain on the same structure
How does elastic/viscoelastic response change with cyclic movements?
Response because more elastic because intracellular fluid doesn’t have time to move around
What is important to prevent cartilage damage?
How is this impacted by age?
Loading-unloading through physical activity
Young people on bedrest can recover their cartilage through physical activity after deconditioning
Older people on bedrest may not be able to fully recover their cartilage after deconditioning, may need to start physical activity in the water and progress from there
What activities lead to acute cartilage damage?
What activities lead to chronic cartilage damage?
High stress events such as bike accidents, car crashes, etc.
Daily activities performed with repeated asymmetrical loading through faulty biomechanics
Why is too much static stretching bad before a workout?
Elastic response of the muscle will be dampened and viscoelastic response will be prioritized which will change the way the structures react to high force movements like sprinting, lifting, etc.
How fast can chondrocytes replace collagen matrix in the cartilage?
Cartilage is very slow to regenerate and the chondocytes have a poor ability to synthesize new collagen matrix within the cartilage
What are 2 factors that can increase the breakdown of cartilage if they are not optimal?
1.Alignment of the structures at rest and during dynamic movements, as well as imbalances between the muscles
2.Strength of the ligaments
What is the only way to fully recover a ligament after injury?
Surgery
(surgeon needs to go in and tighten the ligament again)
What lifestyle factor is the main cause of wear and tear on the cartilage?
What is a biomechanical factor in the case of wear and tear?
Lack of physical activity
misalignment is a close second
How does the ratio between proteoglycan and synovial fluid change with age?
ratio of proteoglycan and fluid will change, less synovial fluid and more proteoglycan
What is there a lack of in the case of arthrosis and what does this lack cause a decrease in? what does this lead to?
Lack of joint space causes large decrease in range of motion and leads to two ends pinching and rubbing together
Where do knee valgus and varus cause damage?
Knee varus causes damage to inside of the knee
Knee valgus causes damage to the outside of the knee
What 2 things should be your priority if your clients wants to transition to barefoot running?
- Work on perfecting their form
- switch to barefoot running slowly and increase over time, do not go for a long barefoot run right away
How much variability should you have in joint positions?
A moderate amount
Not too much so there is not any standardization but not too little so there is too much rigidity and no flexibility
What is hysteris energy and which mechanical property is responsible for it?
Viscoelastic component creates hysteris or energy lost to heat
What is the pre-conditioned state?
What will the same load cause more of over time and how will this effect the loading/unloading curve and how does it make us more efficient?
Doing warm up before physical activity to reach the pre-conditioned state, muscle fibers/tendons/
ligaments are ready to perform task
Same load will cause more deformation over time, the difference between the loading and unloading curve will get smaller with time because we become more efficient (more elastic and less viscoelastic)
(slide 22 of lecture 4)
What type of warm-up is best for pre-conditioning?
Dynamic warm-up movements are specific to the task
(ex.high knees before you go running)
What is the issue with 30 reps of plyometrics at a time?
What is the better way to do it?
Fatigue will build up and show in the results
3-5 trials of a couple reps each and then find the average
(always do an uneven number)
How to prepare for a 1RM test?
Condition muscle to do the movement and make sure my joints are ready to perform the task, build up slowly
Why is warm-up important?
Prevent injuries and get optimal performance, injuries in your 20s from not warming up will follow you for the rest of your life
How does immobility affect tendon/ligament recovery?
1,2,3 weeks in the hospital will rapidly decrease the mechanical structures of the muscles, tendon/ligament recovery from immobility is better the younger you are.
Why does the middle part of the ligament recover faster than the part connected to the bone from immobility?
How is the structure of the ligament in the middle and at the meeting point of bone and bone different?
The middle part of the ligament has all the same structures(collagen), the structures of the ligament change when you get closer to the insertion site on the bone and take longer to recover(mix of collagen from the ligament and calcium from the bone)
(slide 23 of lecture 4)
Can ligaments go back to 100% after injury?
What is the best way to recover a ligament?
Very hard for a ligament to regain 100% of function and you never recover completely, especially near the insertion site of the ligament
Regular exercise/movement with progression and warm-ups is #1 to make the baseline strength of ligaments higher, starting with above average strength of ligaments will allow the ligaments to go back to average strength of gen pop after recovering from injury
What happens when most people get immobilized?
What are the 4 best dietary guidelines to recover from injury?
How does creatine affect injury recovery?
They gain weight and their nutrition/hydration is not optimal to recover from their injury
1.Drink a lot of water to increase the intracellular water
2.Eat a high amount of calcium to support the bones
3.Eat a high amount of protein because they support muscle tissue
4.Eat a high amount of carbs because they carry alot of water with them
Creatine was mixed with a lot of different things in the early 90’s which gave it bad press, now it can be 99% pure and it is beneficial because it will increase intracellular water
What type of activity does bone need to grow and to be healthy?
Mechanical loading of the bone through weight-bearing activity
What decreases in the ligaments as we age?
When does this decline start?
What is the most common injury in an active population?
Intracellular water
Starts in early 20s, best course of action is to start healthy habits in your 20s to start the decline at a higher point
ACL injury
Why do ACLs get injured so much?
We use them all the time, makes sure the knee doesn’t go forward and there is no anterior translation
ACL is always in tension even when your not moving around so it is always active, problem is ACL affects many other components of your knee
Why are steroids bad for the tendons?
The growth of the muscle outpaces the adaptations of the tendons and the muscle applies massive forces to the tendons
How many bones do babies have and how many bones do adults have?
What do giraffe’s necks and human’s necks have in common?
What is the smallest bone in the human body and where is it found?
Babies = 300 bones
Adults = 206 bones
A giraffe’s neck contains the same number of vertebrae as a human neck.
The smallest bone in the human body is found in the inner ear and is about 0.28 cm long (Stirrup)
What are the 3 mechanical functions of bone?
- Support
- Protection
- Levers for locomotion
What are the 2 physiological functions of bone?
- Mineral Homeostasis: storage of minerals
- Hematopoiesis: Formation of red blood cells
What 2 places can hematopoietic tissue(red bone marrow) be found in newborns?
In newborns:
* Medullary canal/cavity of long bones
* Cancellous bone (aka spongy bone)
What 4 places can hematopoetic tissue be found in adults?
In adults:
* Axial skeleton
* Heads of long bones (femur & humerus)
* Flat bones (cancellous layer)
* Some irregular bones
How does bone marrow composition change from childhood to adulthood?
Child: marrow is almost exclusively red (40% water, 40% fat, and 20% proteins)
Adult: gradual transition to yellow marrow (85% fat, 15% water and 5% protein)
What are the 2 systems of the human skeleton and how many bones total across the 2 systems?
Axial and appendicular, there are 206 bones
What are the 3 components of the axial skeleton?
i. Bones in skull/head
ii. Spine
iii. Rib cage
What are the 4 components of the appendicular skeleton?
i. Upper limb bones
ii. Lower limb bones
iii. Shoulder complex
iv. Pelvis
What is the diaphysis?
What type of bone is in the diaphysis?
What is the endosteum?
the shaft or central part of a long bone.
periosteum on the outside, compact bone in the middle and the medullary canal(containing bone marrow) on the inside
A membrane lining the inner surface of the bony wall also identified as the lining membrane of the Bone marrow cavity
What is the metaphysis?
What type of bone is in the metaphysis?
the region where the epiphysis joins the diaphysis
cancellous (or spongy) bone
What is the epiphysis?
What type of bone is in the epiphysis?
the enlarged wide end of a long bone that articulates with other bones at joints
physis (growth plate)
What type of bone is in the proximal epiphysis?
Where is the epiphyseal line?
Spongy bone
Between the proximal epiphysis and the diaphysis
What is compact bone made of?
What kind of system is a compact bone?
What is the difference between haversian canal’s and volkmann canals?
What is cancellous (or spongy) bone made of?
made up of osteons
Harvesian system
Both are found in bones: Haversian canals are located in the center of compact bones, while Volkmann’s canals are located at the edges of bones.
consist of trabeculae, arranged to optimize stress resistance
What are osteoblasts?
Osteoblasts : cells that produce and
coordinate mineralization of bone
-Synthesize and secrete collagen
fibers and initiate calcification
What are osteoclasts and what are they responsible for?
Where are they concentrated?
Osteoclasts:
cells that breakdown bone
-Concentrated in the endosteum
What are osteocytes?
Osteocytes: mature osteoblasts
surrounded in bone matrix
What are the 2 mechanisms of bone maintenance?
Deposit and resorption of minerals in the bone
What are the 2 types of bone growth and what dimension do they grow?
How are osteoblasts involved in the process of the second type and where are they located?
Interstitial Growth leads to increase in bone length
Appositional Growth leads to increase in bone thickness
Osteoblasts below the periosteum form new osteons on the external bone surface.
How does the use of a bone change it’s bone density?
What is an example of this in sports?
- Change in use = change in bone
density
– Mechanical Loading - Different bone modification depending
on location
Study on tennis players:
cortical bone density
~35% higher in active arm.
What are 7 factors that affect bones?
Disease
Genetics
Local tissue
Mechanical loading
Metabolism
Hormones
Medications
What are the 3 major contributors to bone composition and what are the percentages of each?
Bone Composition:
Minerals: 40%,
Collagen: 35%,
Water: 25%
What cells are found in bones?
What is in the extracellular matrix of bones?
What is the main type of inorganic material found in bones?
Organic Material
– Cells
* Osteoblasts, Osteoclastes & Osteocytes
– Extracellular matrix
* Collagen (type I) (~90%)
* Proteoglycanes (~5%)
* Polysaccharides/glycosaminoglycans act as cement
Inorganic Material
– Minerals: mainly calcium and phosphate
What is the distribution of weight in the extracellular matrix of bones?
What does it mean that bone is bi-phasic and which materials give that property?
- Organic material: ~ 1/3
Flexible & resilient - Inorganic material (minerals): ~ 2/3
Hardness, rigidity & strength
Mechanical property of bone = bi-phasic composite materials, with organic components being flexible & resilient/inorganic components being hard & rigid
What are 2 mechanical properties of bone tissue?
How do these 2 mechanical properties refect on the damage they sustain?
Ductile: implies large deformations
Fragile: reduced or inconsistent plasticity
Ductile = slow rupture
Fragile = brutal breaks
What are the properties of bone?
What is the material of each property of bone and what do these materials resist changes in?
What forces does ductility resist and what forces does fragility resist?
Bone is semiductile & viscoelastic
Ductile:
made up of collagen
resists changes in tension
Fragile:
made up of minerals
resists changes in compression
Viscoelastic:
made up of water
What is the definition of stress?
What is the definition of strain?
What is another name for stress-strain curve?
What are the 3 parameters of the stress-strain curve?
Stress – intensity or magnitude of
the load
Strain – deformation (change in
dimension) that occurs in a structure
in response to applied loads.
Load-deformation curve
- Maximum stress supported by bone or material
- Maximum deformation before
rupture/failure - Energy stored before rupture/failure
What are the 2 regions on the load deformation curve?
Elastic region up to the breaking point
Plastic region up to the irreversible breaking point
What is the definition of elasticity?
What is the end of the elastic region?
Capacity of a tissue to return to its initial form when load is no longer applied
Elastic region ends at the breaking point on the load-deformation curve where elastic strain can no longer be taken
What is the definition of permanent deformation?
resulting from micro ruptures and lesions in the plastic region up until the point of the irreversible breaking point
How is rigidity calculated on the load-deformation curve?
Rigidity or Modulus of elasticity
(young’s modulus):
Equation:
stress(load)
divided by
strain(deformation)
What does the area under the curve represent on the load-deformation curve?
Area Under Curve
= Force of Material
What is the equation for hooke’s law?
Fs = k * x
Fs = force exerted by material to return to original shape
k = stiffness (constant to material being
tested)
x = change in distance (deformation).
Give an example of applying hooke’s law
*Situation: we hook a mass on a spring whose spring constant (k) is 15 N/m. The spring, which had an initial length of 10 cm, is now 25 cm long.
*What will be the final length (xf) of the spring if we hook an object that has a weight of 2.0 N?
In this case, we will not take into account the orientation of the forces and the elongation. This is why we will not include the negative sign in the equation of Hooke’s law.
Fs = (0.15m * 15 N/m) + 2.0 N
k = 15 N/m
xi = 10 cm = 0.10 m
xf = ?
Fs = k * x
↕
Δx = Fs / k
Δx = 4.25 N / 15 N/m
Δx = 0.28 m
Δx = xf – xi
xf = xi + Δx
xf = 0.1 m + 0.28 m
xf = 0.38 m
What is the max deformation in the elastic response?
How does the deformation in elastic response vary?
Can bone return to original shape in this response?
When loaded…
* Deformation: max length = 3%
* Deformation graph varies linearly
* Yes, Bone still returns to its original shape/length
Which fibers give way in the plastic region?
What is the end point of the plastic region?
Can the bone return to original shape?
When loaded…
* External fibers begin to give way
(Micro-tears)
* Can go as far as fracture
* Bone cannot return to original shape/length
(permanent change)
Which type of bone resists either stress or strain?
What is the max stretching for either compact or spongy bone/
Compact Bone:
* Resistor of stress
* Max stretching: 1.5-2%
Spongy Bone:
* Resistor of strain
* Stores more energy
* Max stretching: 50%
What does the behaviour of the bone depend on?
Is bone homogenous or non-homogenous?
In which direction can bone accept more force?
- Behaviour of the bone depends on the orientation of the load being applied.
- Bone is a non-homogenous material
- Can accept more force longitudinally & less force perpendicularly
What are the 6 types of loading that the skeleton withstands?
Compression pushes inward
Tension pulls outward
Bending moves side to side
Shear creates friction
Torsion twists
Combined loading is a combination
What do compressive forces do and what effect do they have on the bone and what are they necessary for?
What joint requires special considerations when it comes to compressive forces?
-Forces that compress the ends of the bones in the direction of the length of the bone
-Shortening and widening
-Necessary for bone growth and
deposition!
Hip joint
How do vertical compression forces change moving downward along the spine?
Low at cervical vertebrae
Moderate at thoracic vertebrae
High at lumbar vertebrae
What is often the source of tensile forces on bones and what effect do they have on the bone and what do they help develop?
-Often muscle is the source
-Lengthening/narrowing
-Development of bone growth
Where do shear forces occur, what kind of deformation do they cause and which other forces do they usually come at the same time as?
What is spondylolisthesis and what type of posture does it cause and which section of the spine has increased shear forces?
Shear Forces:
– On the surface
– Angular deformation
– Present during compression & tension
loading
Spondylolisthesis:
– Vertebra slide anterior on one another
– Hyperlordosis posture
– Increased shear forces (L4/L5)
In which 2 ways do materials deform from flexion forces?
What are the 2 types of flexion forces in regards to the number of points of application?
Which type of deformation causes more injury?
– Material deforms convexly from tension and concavely from compression
– Two Types of Flexion Forces
* 3 points of application (A)
* 4 points of application deformation (B)
– Risk of injury on convex part of the bone from tension (i.e. ‘boot top’ fracture in skiers)
What axis do torsion forces occur on, what are the 2 opposing forces around this axis, what kind of deformation do they cause and what is a common injury with torsion forces?
Torsion Forces:
– Twisting about the longitudinal axis
* 2 opposing forces around the axis (Material deforms convexly from tension and concavely from compression
– Angular deformation, especially on the periphery
– Common injury, spiral fractures
What are 2 factors that affect the deformation rate and what is the important of these 2 factors?
Which one is bone failure dependent on?
Do bones have better resistance to loads applied quickly or slowly?
The bone responds differently depending on:
- Loading rate
- Loading time
-Bone failure is dependent on the loading rate
-Better resistance to loads applied quickly
How does lower or higher loading rate affect fractures?
-Lower loading rate: energy has time to
dissipate = single fracture
-Bigger loading rate: energy does not have time to dissipate = bone fragments
What are 2 factors that influence injury rate and fracture rate?
- Bone Strength Limit
* Depends on: Physical Exercise,
Conditioning, Immobilization, Skeletal
Maturation, Fatigue, Loading Rate, etc. - History of Loading
* Repetition and Load
* Microtraumas: frequency is greater than the bone repair process.
Example(During fatigue, reduced shock
absorption leads to a change in distribution of the forces in the body
What is the difference in how oblique fractures and transverse fractures occur?
Refer to slide 45 of bones lecture
What are 5 common types of fractures?
When do these fractures most commonly occur?
- Tibia
- Fibula
- Femur
- Metatarsal
- Calcaneum
Especially when walking or running long distances!
Why is physical activity important in bone remodelling? What 2 things is bone density influenced by?
Give 2 examples of people who face the repercussions of not having enough physical activity?
Physical Activity & Bone Remodeling:
- Daily stimulation is needed: bone requires mechanical stresses to grow and strengthen.
- Density is influenced by the number of
cycles and the magnitude of loading
Examples:
* Astronauts
* Persons with different mobility capacities
What is the rate of bone mass loss during immobilization?
Bone mass loss is ~1% per week during
immobilization
What is the effect of bone geometry on the ability to resist rotational forces?
What do tension & compression depend on in the case of bone geometry?
What does flexion depend on in the case of bone geometry? How does the length of bone effect flexion?
What does bending depend on in the case of bone geometry?
What 3 greater forces are long bones subject to?
What type of bone shape resists bending?
Bone geometry will affect the moment of inertia (ability to resist rotational forces)
Tension and compression: depends on the cross-section of the area of bone
Flexion: depending on the moment of inertia of the area
The length of the bone influences its strength and rigidity. The longer the bone = greater the flexion moment and less ability to resist flexion
The magnitude of the stress at the point of application of the bending moment is proportional to the length of the structure.
Long bones are subject to greater flexion
moments …therefore greater tension and compression force!
Tubular shape: resist bending moments
Which property of bone increases with age? What property decrease?
– Bone porosity increases
– Bone density decreases
When does the cortical diameter of bone max out?
What percent does bone mass decrease for men and women per year after 40?
Cortical Diameter: max at ~30-40 yrs
After 40 yrs, bone mass begins to decrease
* Less Mass = Reduced mechanics
* Women: 1.5 - 2% of mass/year
* Men: 0.5 – 0.75% of mass/year
How does menopause affect bone mass loss?
Post-menopause: bone mass loss accelerates
Ultimate compressive force decreases by 15-20% between 20-39 yrs and 60-89 yrs
Bone fails more easily to weaker forces in women
Constant difference of 17% between men and women
Higher rate of fractures in women
Refer to slide 52 of bone lecture
Which bone maintenance mechanism is dominant in the case of osteoporosis?
What happens when there is loss of trabecular or spongy bone?
Bone resorption exceeds bone deposition
Loss of rigidity in the lower area of the bone leads to higher fracture rates
What percent of men and women have osteoporosis over 50?
What are 4 risk factors for the development of osteoporosis?
Women:
50% of population over 50 years old
90% …over 75 years old
Men:
30% of population over 50 years old
Risk Factors
* Low body weight (BMI < 19)
* Low muscle mass
* Inadequate or excessive exercise
* Early menopause
What are the 4 functions of skeletal muscles?
Functions:
* Produce body movements
* Stabilize posture
* Move substances/fluids throughout the body
* Produce heat
What are the 3 methods of structure/organization of skeletal muscles?
- Arrangement
* Macroscopic
* Microscopic - Fiber organization/direction
- Muscle attachments
What is the definition of fascia?
What is the difference between superficial & deep fascia?
What are the 2 types of tissues in superficial fascia?
What are 4 roles of fascia?
Fascia: Fibrous connective tissue that envelops muscles (and other organs).
Superficial fascia:
Separates muscles from skin
Deep fascia:
Lines the muscles
- Areolar Connective
- Adipose Tissue
Roles of Fascia:
-Reduce friction
-provide blood flow and nerve supply
-coordinate muscles
-Fills gaps between muscles and provides structure
How do the epimysium, perimisyum and endomisyum stratify the muscle?
Epimysium:
Outer layer enveloping the entire muscle
Perimisyum :
Surrounds and separates muscle fibers in packs of 10-100 fibers called Fasicles
Endomisyum:
Membrane that envelops each muscle fiber
What is the sarcolemma?
What is it’s function
Where is it located?
Sarcolemma : the membrane inside the endomysium, the tissue that completely surrounds each muscle fiber and defines the limits of the muscle cell.
- Allows chemical neurotransmitters to reach contractile unit of muscle
- Directly under endomysium
Where are t-tubules located?
What is it’s function?
T-Tubules :
Run along the surface to the center of each muscle fiber
propogates the action potential across the sarcolemma
What is sarcoplasm inside of?
What 2 things is the sarcoplasm made of?
Sarcoplasm :
Fluid inside sarcolemma
(glycogen, myoglobin)
What are myofibrils and what are they inside?
What is their function within the muscle?
Thin filaments inside the sarcoplasm
contractile elements of the muscle!
What is sarcoplasmic reticulum filled with and what does it surround?
What is it’s function?
Sarcoplasmic reticulum (SR):
membranous sac filled with fluid surrounding each myofibril.
Storage of calcium to trigger action potentials
What is the terminal cistae?
What is the triad?
What is the sarcomere?
What are the 2 contractile proteins?
Terminal cisternae: ends of the sarcoplasmic reticulum that surround the T-tubules
Triad: combination of 2 terminal cisternae and a T-tubule
Sarcomere: functional unit of the contractile system of muscle
- Contractile Proteins: Actin (thin) and Myosin (thick)
What is Huxley’s ‘Sliding Filament Theory’?
During muscle contraction, actin filaments slide between the filaments of myosin
What are 3 characteristics of fusiform muscles?
What are 3 examples?
A) Fusiform Muscles
Characteristics:
* Fibers run in parrallel
* Muscle fibers shorten
* They promote speed
Ex: sartorius, biceps brachii, brachialis
What are 3 characteristics of pennate muscles?
What are 3 examples?
B) Pennate Muscles
Characteristics:
* Fibers arranged on an angle towards tendon
* High amount of fibers for a given area(dense)
* They promote strength
Ex: semimembranosus of hamstring, gastrocnemius, deltoid
What is the performance of a muscle determined by(E.C.E.E)?
Which 2 of these are protective mechanisms?
E.C.E.E
Excitability - The ability to respond to a simulation by
a neurotransmitter (action potentials)
Contractility - The ability of a muscle to shorten (50-70% of their length at rest)
Extensibility - The ability of a muscle to elongate beyond its length at rest (stretch without rupture)
Elasticity - The ability of a muscle fiber to return to its initial length
Extensibility & Elasticity
What is the contractile element of a muscle contraction and what do they cause?
What 3 things do the elastic/passive components of muscle contraction do with mechanical energy?
What are the 2 things that are apart of the elastic component in series?
What are the 2 things that are apart of the elastic component in parallel?
Contractile Element (CE)
* Myofibrils with bridges binding actin/myosin filaments
* Shortening of the muscles during contraction
Elastic and passive components
Functions: absorb, transmit, store mechanical energy
Elastic component in series (SE)
* Tendon (85%)
* Actin-myosin bridge (15%)
Elastic component in parallel (PE)
* Sarcolemma
* The connective tissue that surrounds the muscle(epi/peri/endomysium)
What are the 3 types of muscle actions?
How does each change the length of the muscle?
Types of Muscle Actions
A. Isometric - The muscle is active, No changes in length
B. Concentric - The muscle is active, Shortening of muscle
C. Eccentric - External moment > internal moment, Lengthening under the effects of gravity or antagonistic muscles
What is the benefit of eccentric contractions?
How efficient are eccentric contractions? how energy intensive are they?
Eccentric: develops same muscle strength with use of less muscle fibers when compared to Isometrics and concentrics
More efficient and consumes less energy!
What are 4 reasons that concentric contractions are less efficient?
Energy expenditure: During a concentric contraction, the muscle has to generate force to overcome resistance (e.g., lifting a weight). This requires energy in the form of ATP (adenosine triphosphate) to be used for muscle contraction. This energy expenditure can be significant, especially when lifting heavy loads.
Requires energy to overcome gravity, break inertia as well as lift the load
The muscle is at a joint angle that places it at a mechanical disadvantage so it has to generate more force
Concentric contractions can lead to muscle fatigue more quickly than eccentric contractions because of the shortening of the muscle.
Concentric contractions generate more heat within the muscle tissue compared to eccentric contractions.
What is the purpose of isometric contractions?
How are concentrics/eccentrics used together and how do they maximize energy storage/muscle performance?
Isometrics:
stabilize a part of the body
Concentrics/Eccentrics:
Used sequentially
Maximize energy storage and muscle performance through stretch/shortening cycles
What is a muscle twitch?
What is the latent period?
What is the contraction period?
What is the relaxation period?
Muscle Twitch:
Mechanical response to a single stimulation
-fundamental unit of muscle activity
Latent Period:
Short delay from when action potential reaches muscle until tension starts (~2ms)
Contraction Period:
From beginning of the action potential to the maximum tension
Relaxation Period:
From maximum tension until resting length
What is tetanus?
What happens the muscle is at max frequency?
How do the muscle twitches fuse?
Tetanus:
Prolonged contraction of a striated muscle, produced by continued stimulation at a fairly high frequency
* Max frequency, at which the force no longer increases
* Fusion of muscle twitches by increasing frequency
What are 2 influential relationships on force generation in muscles?
What is an important cycle in force generation of muscles?
What is an important angle in force generation of muscles?
- Muscle Attachment Angle
- Force-Length Relationship
- Force-Velocity Relationship
- Stretch-Shortening Cycle
At what angle is the muscle at a mechanical advantage?
What is the purpose of higher forces when the muscle is either at an obtuse angle or an acute angle?
Right angle (90 degrees)
Obtuse angle (greater than 90 degrees):
Mostly force to stabilize the joint
Acute angle (less than 90 degrees):
Mostly force to rotate the joint
What are the functional biomechanical characteristics of muscle?
Refer to slides 4-17 of lecture 6
What are the 3 types of articulations?
- Fibrous:
ex. sutures in the skull - Cartilaginous
ex. vertebral discs in the spine - Synovial
ex. synovial joints like elbow and knee
What bones have fibrous articulations?
What 2 things do these joints require?
- Bones bound by tough fibrous tissue
- In joints that require strength & stability
What is responsible for connecting bones in cartilaginous articulations?
What are 2 types?
What type of cartilage is each connected by and how movable are they?
Bones are connected by cartilage
- Synchondroses (ex. ribs)
* Connected by hyaline cartilage
* Immovable - Symphyses (ex. pubic symphysis)
* Connected by fibrocartilage
* Slightly movable
What are synovial articulations filled with? what surrounds the joint?
How common are synovial joints?
How large is their range of motion?
Fluid-filled joint within a thin fibrous capsule
Most common joint in human body
Large ranges of motion compared to other types of joints
What are the 6 types of synovial joints and where can each be found?
- Ball and socket joint (hip joint)
- Pivot joint (between cervical vertebrae)
- Hinge joint (elbow)
- Saddle joint (between carpal and
metacarpal bones in hands) - Plane joint (between tarsal bones in feet)
- Condyloid joint (between radius and carpal bones in wrist)
What are the 3 dynamic functions of cartilage?
- Transfers forces between bones
- Distribute and dissipate forces over a larger surface area to reduce stress on bone
- Minimizes friction and wear during movement of joint
- Coefficient of friction: ~ 0.0025
What is the static function of cartilage?
Where in the body is there constant tension?
- Dissipate loading
- Vertebral discs of spine (constant tension is present)
What are the planes of the human body?
Transverse plane-at the waist, dividing top half and bottom half
Frontal plane-through the body, dividing the body into front half and back half
Sagittal plane-through the body, dividing the body into left half and right half
Does cartilage have a strong blood supply?
No, Cartilage is an isolated tissue with a very slow metabolism
What are the axis’ of movement and give an example of each?
Sagittal plane about the frontal axis
(flexion/extension of the shoulder,hip)
Frontal plane about the sagittal axis
(abduction/adduction of the shoulder,
hip)
Transverse plane about the longitudinal axis
(internal/external rotation of the shoulder,hip)
What kind of cells is cartilage made of and what are it’s two functions?
What is found in the organic matrix of articular cartilage?
Which forces do Type 2 collagen and proteoglycans resist within the organic matrix of the articular cartilage?
What is the last component of articular cartilage?
What do these components of articular cartilage determine?
- Cells: Chondrocytes
– organize the extracellular matrix
– Produce proteoglycans and collagen - Organic Matrix
– Dense network of collagen fibers and proteoglycans - Collagen (Type II*) resists tension
- Proteoglycans resists compression
- Interstitial fluids
Matrix components determine the biomechanical behavior of cartilage tissue
Is cartilage stratified heterogenously or homeogenously?
What are the 2 biomechanical functions of this stratification?
Stratification: Cartilage is heterogenous = different layers or ‘zones’ in tissue
- Improves support of interstitial fluids
- Improves resistance to friction
How could the arrangement of chondrocytes and collagen in articular cartilage be described?
Anisotropic arrangement of chondrocytes and collagen
What is the meaning of articular cartilage being anisotropic? Is the cartilage uniform or varied?
behaviour of cartilage changes depending on the direction of the loading
- Varying arrangements of collagen fibers with respect to articular surface.
What percent of the articular cartilage does the superficial zone represent?
What percent of the superficial zone is made up of water?
- Superficial Zone (represents ~10-20% of the total cartilage thickness)
It is in this area that there is the most water (~80%)!
What percent of the articular cartilage does the transition/middle zone represent
How is collagen dispersed in the transition/middle zone?
- Transitional/Middle Zone (~40-60%)
Collagen fibers
* Random orientation
* More dispersed
* More homogeneous dispersion
Is there a high or low density of collagen in the superficial zone?
What force does this help resist?
Collagen fibers
* High density on the articular surface within the superficial zone
* Resists shear loading
What percent of the articular cartilage does the deep zone represent?
What component is high in this zone and which component is lower?
What area do the collagen fibers penetrate?
Deep Zone (~30%)
Proteoglycan content is high and water content is lower (~65%)
- Broad grouping of fibers in the plane of movement
- Penetrates calcified area
What percent of the articular cartilage does the calcified zone represent?
What does the tide mark within the calcified zone represent?
What do the collagen fibers attach to in this zone?
Calcified Zone (~2%)
Tide mark=transitional interface between soft cartilage and stiffer subchondral bone
Collagen fibers attach to the subchondral bone: anchoring cartilage to the cortical bone
What percent of the articular cartilage does chondrocyte cells represent?
What does the variance of their size, shape and density depend on?
What 2 things do they specialize in producing?
What do they keep organized?
How do they receive nutrients?
Cells: Chondrocytes ( 5% )
- Vary in size, shape and density according to their location
- Specialize in producing/secreting proteoglycans and collagen
- Organize and maintain the components of the extracellular matrix
- Receive nutrients through matrix diffusion
What percent of the articular cartilage does the extracellular matrix represent?
What are the 3 components of the extracellular matrix within the articular cartilage?
Extracellular Matrix ( 95% )
- Collagen
- Proteoglycans
- Interstitial fluid
What type of protein is collagen?
Is it flexible or rigid?
What type of forces is it strong at resisting?
What type of forces can it not resist?
Collagen
- Fibrous protein
- Very rigid
- Resists tension forces
- Little resistance to compressive & shear
strength
What type of proteins are proteoglycans and what do they help attach?
Are they large or small? and what shape do they resemble?
What is their affinity to water?
What type of forces is it strong at resisting?
Proteoglycans (PGs)
*‘Link protein’ for glycosaminoglycan (GaG) sugar chains to attach
- Large molecules (brush-like from chains of GaGs).
- Negative charge = affinity for water.
- Resists compressive forces
What is the main type of Glycosaminoglycans and what do they bind to?
What type of charge do they have?
Do they have an affinity for water? and what type of bond do they have?
Glycosaminoglycans (GaGs)
- Mainly aggrecan (aggregates of large proteoglycans - sugars) that bind to hyaluronic acid (protein)
- Strong negative charge
- Affinity with water (hydrophilia)
- Non-covalent bond
What does the metabolism of PGs in the articular cartilage depend on?
What 3 things does immobility lead to?
What 2 things does excessive loading lead to?
Proteoglycans
- Metabolism of PGs in articular cartilage depends on loading history
- Immobility leads to…
1. Decreased synthesis
2. Thinning of cartilage
3. Tissue water leakage - Excessive loading leads to…
1. Decreased size
2. Disorganization of
collagen fibers
What is interstitial fluid mainly made of?
What percent of the extracellular matrix do they represent?
Where are they mainly concentrated and how does their concentration change with depth?
What does the movement of fluid in and out of the cartilage depend on? and what characteristic does this give the cartilage?
What are the 2 main roles of the interstitial fluid?
Interstitial fluids
- Mostly water (gel-like substance) and
minerals (Na+, K+, Ca2+) - Represents ~ 65-80% of extracellular matrix
- Concentrated at the joint’s surface (~80%)
- Decreased concentration with
depth (Deep Zone = ~ 65%) - Fluid has the ability to freely move into/out of cartilage (depending on loading)
- Gives cartilage its sponge-like characteristic
(fills in around PGs & collagen) - Main roles:
1. maintain mechanical integrity of tissue 2. lubricate the joint
What are the 4 mechanical properties of articular cartilage?
- Viscoelasticity
- Permeability
- Dependance on Load (Loading
Profile) - ‘Wear and Tear’ of Cartilage
When does the viscoelasticity of the articular cartilage become relevant?
What are the 2 ways to describe the viscoelasticity of articular cartilage?
When does creep behaviour happen and what is an example of creep behaviour?
What does relaxation behaviour result from?
Viscoelasticity
-When stress/deformation are constant and the response varies with time
Creep & Relaxation
This behavior can be described by:
1. Creep: constant stress with deformation as a function of time= permanently deforms!
* Example: A person standing
- Relaxation: constant deformation with stress release, results from flow of interstiatial fluids in cartilage
What type of stress is present in the creep viscoelastic response and what type of response is seen?
What are the 3 steps of the creep response?
Where does the point of equilibrium occur and what is it caused by?
Viscoelasticity: Creep
- Constant stress, bi-phasic response
- Rapid initial deformation
- Slow and progressive deformation
to the point of equilibrium. - Point of Equilibrium: when the
compression stress in the matrix*
balances the external stress
*compressive stress developed in the collagen-PG matrix and friction forces due to the flow created by the output of fluids
What type of stress is present in the creep viscoelastic response and what type of response is seen?
What are the 2 phases of the relaxation response? What is the amount of stress in each phase and what is it due to?
- Constant stress, bi-phasic response
- Compression Phase (0-A):
* Stress continuously increases to the
max
* Due to dispersion of fluids - Relaxation Phase (B-E):
* Stress decreases slowly and
gradually to maintain deformation
* Due to the redistribution of the fluids
in the matrix.
What does the permeability of articular cartilage measure?
What is it inversely proportional to?
Permeability
- The measurement of the ease of a fluid passing through a porous material
- Is inversely proportional to the friction created by the liquid passing through the material
What is the relationship between permeability and resistance?
What is the equation for porosity?
How porous is articular cartilage?
High permeability = low resistance
Low permeability = high resistance
Porosity = ratio of fluid volume to total volume
(β) = Vf /Vt
Articular cartilage is very porous ~80%
What is another way to define permeability of articular cartilage?
What is this dependent on?
What is the equation for permeability?
How permeable is articular cartilage and why is it that way?
A measurement of the resistance force required to penetrate a liquid into a membrane at a given speed.
This friction resistance force is dependent on the interaction between
the fluid and the porosity of the material.
Coefficient of permeability (k) is related
to the coefficient of friction (K) & porosity (β)
k = β2 / K
Articular cartilage has very low permeability
– Large generation of friction resistance force when the fluids pass
through the matrix
What are the 2 ways to directly measure permeability?
- Ways to directly measure permeability:
– Two mechanical means
1. Effect of a load on the material/tissue
2. Pressure gradient
What are the 2 things that will happen using the “effect of a load” method of testing permeability?
Effect of a Load
If cartilage is saturated with fluids and
placed under load…
1. Fluids will escape due to compressive deformation
2. Increase in local pressure (from fluid dispersion)
What is the equation for the pressure gradient test of permeability?
What 2 things does permeability decrease exponentially with?
Pressure gradient:
(P1-P2) / h
* Coefficient of permeability (k);
volumetric discharge per unit of
time (Q); permeability area (A).
k = Qh / A(P1-P2)
- Permeability decreases
exponentially with….
– Increase in pressure gradient
– Increase in deformation
What 2 loads can occur in the pressure gradient test of permeability?
What are the 2 stages of transmission/dampening of stresses?
What 2 things does this lead to?
- Dynamic Loads
– Ensures sliding between joint
surfaces and minimizes friction - Static Loads
Transmission / damping of stresses are carried out in two stages:
1. Sudden rise in intracellular pressure (little deformation due to fibrous network)
2. Water and electrolytes migrate to lower pressure areas via pores in cartilage
Leads to…
– Increase concentration in proteoglycans
– Increase in the osmotic pressure
This 2-step process makes it possible to effectively distribute loading.
What are the 2 lubrication models of permeability and what are the key features of each?
What is the 3rd lubrication model of permeability and what 2 things is it dependent on?
- Liquid lubricating film:
-Thin lubricant film between each articular surface.
-Additional load support from pressure developed in film
If model 1 is not sufficient to reduce friction, model 2! - Surface lubrication:
-A single layer of lubricating molecules incorporated into each joint surface.
-Not effected by physical properties (i.e. lubricant’s viscosity)
-Effected by chemical properties (i.e. proteoglycans)
-Limits surface wear of cartilage - Mixed lubrication: (Combining of 1 + 2)
The lubrication mode is dependent on the load applied and the relative speed and direction of loading.
What is the definition of the “dependence on the rate and application of forces” mechanical property of articular cartilage?
How many cyclical cycles are needed for soft tissue to reach a steady state response?
What is the definition of a non-elastic response in this case?
What is hysteresis energy?
- Dependence on the rate of application of forces
- Most body loads are not constant and are cyclical in nature
- The influence of cyclic loading, most soft tissues achieve a steady state response ( ~ 30 cycles )
- NON-ELASTIC RESPONSE
- Strain during loading ≠ strain during unloading
- Hysteresis energy: energy
stored by tissues during each
cycle
In the case of the mechanical property of “dependence on the rate and application of forces”, what does the response depend on and what is the behaviour of material dependent on?
What are the 2 possible responses in cartilage and how is the fluid different in each?
- Remember…response depends on loading profile
– Behavior of material is very dependent on the rate at which a load is applied and then removed. - Two possible responses in cartilage
1. Elastic Response (independent of time: rapid loading/unloading)
– Fluid does not have time to be expelled
2. Viscoelastic Response (dependent on time: slow loading/unloading)
– During unloading, the cartilage will recover its original dimensions if it
receives enough fluid for enough time
What is the response to tension forces in articular cartilage?
Highly complex mechanical behavior leads to Highly anisotropic/
heterogeneous composition
Can interstitial fluid be tested in compression and tension?
in tension, only the collagen-PG matrix can be tested, since this test does not allow to test viscoelasticity.
Therefore, interstitial fluid can only be tested in compression
Can articular cartilage resist shear forces?
What are 3 ways that cartilage responds to shear forces?
- Unlike during compression and tension, collagen fibers have good resistance under pure shear forces.
- With minimal deformation
- No volume changes
- No fluid movement
What is wear and tear of articular cartilage due to?
What is the difference between interface wear and fatigue wear?
How is the surface layer affected by wear and what is a result of this?
After wear, the surface layer becomes softer and permeable
Wear and tear due to mechanical action: part of the material is removed from a solid surface (i.e. injury)
Interface wear: due to the interaction between the support surfaces (soft versus hard material)
Fatigue wear: due to the deformation of the bodies in contact (cyclic deformations)
↑ fluid output, ↑ surface abrasion
What is the key principle in the prevention of the “breakdown in cartilage” mechanical property?
What are 3 ways that this principle keeps articular cartilage healthy?
What is the lack of this principle associated with?
Loading – unloading is key!
This principle keeps tissues healthy by allowing…
- Entry of nutrients
- Expulsion of waste
- Lubrication of the joint
Lack of use is associated with tissue degeneration
What are the 2 different kinds of breakdown in cartilage?
In the case of chronic cartilage damage, what type of damage does each kind of wear cause?
Acute Cartilage Damage
* Local stress greater than strength of material
-High external forces (impact or active) with a small contact area
Chronic Cartilage Damage
* Following interface issues (abnormal loading/growths) and/or fatigue phenomena
-Wear at the interface = lack of lubrication
-Wear from fatigue (repeated loading) = structural damage in matrix
What is the role of chondrocytes in the prevention of “breakdown in cartilage” and what is their ability to regenerate?
Responsible for the synthesis and degradation of the matrix…
Have a very poor ability to regenerate!!
What are 6 factors that influence contact in synovial joints and ROM that are involved in the breakdown of cartilage?
Factors that influence contact in synovial
joints and range of motion:
- structure/shape of bones that articulate
- Strength and tension of ligaments
- Muscle arrangement and tension
- Soft tissues
- Hormones
-Relaxin during childbirth - Inactivity
-short- vs. long-term
What are 3 ways that aging affect the breakdown of cartilage?
What are 2 ways that articular cartilage is affected by aging and what are 2 results of that?
- Decreased production of synovial fluid
- Thinning of articular cartilage
- Shortening and loss of flexibility of soft tissues
Articular Cartilage:
1. ↓ water content & ↓ the number of chondrocytes
2. Cartilage tends to calcify/ossify
What happens to the articular cartilage now?
* Reduced mechanical function
* Increased risk for damage…and injury!
What is the biomechanical model of the breakdown of cartilage?
Refer to slide 41 of lecture 3
What is arthrosis and why is aging relevant in the process?
- Wear of the cartilage that covers the bony ends at a joint
- Aging = > decrease in the number of chondrocytes
What is the difference between incomplete and complete wear in arthrosis?
What are the 4 stages of arthrosis?
Incomplete wear
Decreased cartilage thickness =
surface becomes irregular and
hinders movement / causes pain
Complete wear
Disappearance of cartilage leads to bone
against bone = Importance of pain!
- start of erosion
- progressive pinch
- of the articular line
- complete destruction
What are 4 influential factors in arthrosis?
Influential Factors
1. Axis orientation of the lower limbs (i.e. knee valgus)
2. Excess weight
3. History of trauma (previous injury)
4. Certain sicknesses (infections, auto-immune disease)
How are cartilage grafts used in arthrosis?
Cartilage Grafts
* Take donor tissue from area of little wear/loading
* Affected area is small and surrounded by healthy tissue
* Lesion - femoral condyles
What is the difference between tendons and ligaments?
Tendons connect muscles to bone
Ligaments connect bone to bone(joints)
What are the 4 functions of tendons?
Functions:
1. Attaches muscle to the bone (myotendinous junction)
2. Transfer of forces between muscle and bone
3. Joint stability
4. Elastic energy storage
What is tropocollagen in tendons?
Tropocollagen - fundamental unit
What is the function of paratenon in tendons?
Paratenon: facilitates sliding of tendons
What is the circuit model of muscular contraction?
-Tendons are the series element and they stretch the muscle fiber to create force
-Connective tissues are the parallel element and they work to protect the muscle fiber and absorb force
-Actin & Myosin cross bridges are the contractile element and they provide the muscle contraction in the fiber
Connective tissue works in parallel with the tendon and the actin/myosin cross-bridges
Tendon works in series with the actin/myosin cross-bridges
What is the function of epitenon in tendons?
Epitenon: helps with structural integrity and provides microvasculature
What is the function of Endotenon in tendons?
Endotenon: extends from the perimysium (musculo-tendon junction) to the periosteum (osteotendinous junction.)
What are 2 types of connective tissue?
Fascia
Protective components of muscle
(perimyseum,epimyseum,endomyseum)
How do active and passive contractions change with resting length?
Active = actin & myosin crossbridges as you get close to resting length and then it will go down as the cross bridges separate
Passive = goes up as you go past the resting length on the eccentric contraction
Passive strength passes active strength once past the resting length and the total torque goes higher
When is the bicep at it’s highest tension?
At 90 degrees is where all the actin-myosin cross bridges form and where there is the highest force
Why is it important to know the length of the tendon when re-attaching it?
Need to know how long the tendon will be so you can create the right moment arm at the connection for the certain muscles
What is the significance of the internal moment for muscle contraction?
Internal moment is the force needed from the muscle on the concentric contraction to fight against gravity
Concentric creates energy,
Eccentric absorbs energy
Is there an advantage to doing isometric over concentric/eccentric?
Isometric is good for rehab because you can work the muscle and improve joint stability without shortening/lengthening the muscle
Why is there more injuries on the eccentric?
It is harder to maintain control of the weight and therefore the speed of the contraction on the eccentric, and larger loads are usually used on the eccentric than on the concentric.
Are eccentrics less fatiguing?
Body is more efficient with eccentric contractions because we’re working with gravity
What muscle prevents collapsing on a typical walking stride?
Quadriceps absorbs force and prevents collapsing
How do moments effect muscle contraction?
Concentric
(internal moment of muscle greater than external moment of gravity)
Eccentric
(external moment of gravity greater than internal moment of muscle)
Do concentrics or eccentrics have higher 02 consumption and EMG activation?
Concentrics have higher 02 consumption and EMG activation
What is the most important aspect of plyometrics?
Speed, try to perform the task in less than a second
What are the 4 periods of muscle contraction?
Muscle twitch
Latent period
Contraction period
Relaxation period
There is a latency period between all muscle contractions in sequence
If you let the twitch go completely down, you will need a latency period before the next twitch is sent
If you don’t let it go down, it will build and build until it reaches the peak
What is tetanus in muscle contractions?
Smaller latent period without fully relaxing over numerous contraction cycles until it eventually levels out at maximum tension
What is the tradeoff in muscle contraction?
Force generation to rotate around the axis of the joint at acute angles and stabilization to stabilize the joint
What do the elbows want to do when holding heavy bags in your hands?
Body system engages the bicep isometrically to make sure the joint is protected from injury and is stable and there will be slight flexion in the elbow
Where should you work the bicep isometrically to build strength?
90 degrees to become the most efficient and have the least stress on the joint
What is the best way to train to increase strength in the bicep?
Start with a full range of motion from the bottom , go slow on the eccentric and fast on the concentric
How does rotational torque change during the bicep curl?
Rotational torque is highest near the top end of the concentric when the hand is close to the shoulder
How to train somebody if they want to return from an injury
Start with isometrics at 90 degrees to give the body some proprioception, slowly build range of motion with light weight until you’re doing the full ROM and slowly add weight from there
What type of training would have the goal to be move as fast as possible rather than using slow and controlled movements?
Power training
What is the optimal zone for force generation from actin-myosin crossbridges?
2.0-2.25 nm
Do eccentrics or concentrics generate more force?
Eccentrics
What is the effect of temperature on muscles?
What range of degrees in there a linear relationship between tension & stiffness?
Warm muscles can generate the same torque in less time and the muscle is able to act faster
6-34 degrees celsius
What is sacropenia?
What should we do to prevent loss of muscle mass?
Degradation of muscle mass to a point where the patient cannot function/
perform their daily tasks
Eat a high protein intake and increase protein intake as we age
What is the myotendinous junction?
Where is it located?
Region where muscle fibers
(contractile proteins) join the
tendon (collagen).
Perimyseum
What is the osteotendinous junction?
Where is it located?
Region of connection between
bone and tendon (gradual
transition from tendinous to
bone tissue)
Periosteum
What type of cells are present in the tendons?
What are 2 of their functions?
Cells: Specialized fibroblasts called Tenocytes
– Controls metabolism within tissue
– Respond to mechanical stimuli (especially tension)
What is the main role of the tendon matrix?
What is it’s composition?
Matrix
Main Role: maintain the structure of the
tendon and facilitate the response to mechanical load.
Water (55-70%)
* Proteoglycans (<0.2%)
* Elastin (~2%)
* Other proteins (~4.5%)
* Collagen (Type 1) (60-85%)
What is the difference in parallel vs transverse arrangement in tendons?
Parallel arrangement: resists tension
Transverse arrangement: resists rotation
What is the hypothesis for the mechanotransduction pathway in tendons?
Refer to slide 6 of lecture 4
What are the 4 functions of ligaments?
Functions:
*Attachment between bones
*Maintains joint configuration
*Helps guide movement
*Sensory feedback: joint positioning
What are 3 functions of epiligaments?
Epiligament:
*Loose shell: protects against friction
*Supports neurovascular structure
*Controls the flow of water and metabolites
What is the main protein in ligaments?
Collagen
* Fibers are wavy
* Oriented along the long axis
What are the 4 functions of neural endings/mechanoreceptors in tendons & ligaments?
- Proprioception and nociception
- Allows sensation of joint positioning
- Monitors ligament tension
- Initiate protective reflexes
What is the function of blood vessels in tendons & ligaments?
Nourishes cells to help make them
metabolically active
What kind of cells are ligaments made of?
How are they organized and what do they manage?
Cells - Fibroblasts:
- sparse and scattered
- manage the prevention and
repair of microscopic damage.
What is the composition of the ligament matrix?
Matrix
* Water (~66%)
* Collagen (70%)
* Proteoglycans (1%)
* Elastin (1.5%)…but can be more
in some ligaments (depending on
function)
What are 4 similarities between tendons & ligaments?
- Cells aligned with collagen
- Collagen: Type 1
- Insertion on bone
- Minimal vascularization
What are 2 differences between tendons & ligaments?
1.Arrangement of collagen
(collagen fibers are parallel in tendons,
collagen fibers are nearly parallel in ligaments)
2.Proportion of elastin
What is a similarity and difference between the external structures of tendons & ligaments?
(paratenon & epiligament)
Similarities: Outer layers made of connective tissues.
Difference: Organization
What are the 4 layers at the insertion area of tendons/ligaments into bones?
Zone 1: Collagen Fibers
Zone 2: Fibrocartilage - non-mineralized
Zone 3: Fibrocartilage - mineralized
Zone 4: Compact Bone
What is the definition of proprioception?
your body’s ability to sense movement, actions, and location
What are 3 things that the mechanical properties of tendons & ligaments depend on?
*Architecture (arrangement) and properties of collagen fibers
*Proportion of elastin
*Substrate Foundations
– Cement-like substance between collagen microfibrils
– Stabilization of tendons/ligaments
– Contributes to the overall strength of tissues
What is the stress-strain relationship of tendons & ligaments?
Non-Linear
What are the 4 zones on the stress-strain relationship of tendons & ligaments?
Zone 1:
Rapid deformation without great force
Zone 2:
Flattening of fibers, ↑ stiffness
Zone 3:
Heterogeneous distribution - deferred
recruitment
Zone 4:
↑ tension on intact fibers = ↑ fiber breakage
What is the visco-elastic property of tendons and ligaments?
Tissue is stronger with load applied quickly (less time to disperse in viscous
component)
What are the 2 types of load-deformation curves in tendons & ligaments?
Loosening:
constant deformation
load relaxation
length held constant
Creep:
constant force
creep phenomenon
load held constant
What are 2 ways that inflammation affects the load/deformation curves in tendons & ligaments?
A:
-After several successive cycles, curve moves to the right and hysteresis
decreases.
-For the same level of force, the deformation is greater and the response
is less and less viscoelastic.
B:
-After several successive cycles, the curve moves upwards.
-For the same level of strength, the release is less and less important
What are 4 ways that exercise influences the integrity of tendons & ligaments?
- Biochemically, ligaments are modestly affected by exercise
- Increases number of collagen fibers.
- Trained ligaments fail at higher levels of loadings
- Are a bit stiffer than the untrained ones
What are 3 ways that immobilization influences the integrity of tendons & ligaments?
- Increases bone resorption and
indirectly weakens ligament
insertions - Reduction in water and
collagen - Longer immobility = increased
risk of damage/injury and longer recovery
What are the effects of age similar to in tendons & ligaments?
What 2 things do younger tissues have more of?
The effects of age are similar to those produced by immobilization!
Younger tissues have greater viscosity and a greater amount of water and collagen
What are 3 things that decrease as we age past 20, in the tendons & ligaments?
As Age Increases (after 20 years old)
↓ force before rupture
↓ storage capacity
↓ rigidity
What are 2 ways that metabolic influencers like anabolic steroids affect the integrity of tendons & ligaments?
Anabolic steroids
↓ stiffness of the tendons as
well as the ultimate strength of
the tendon.
↑ Collagen degeneration and
proliferation of small collagen
fibrils rather than large fibrils
Anabolic steroids hinder the healing of tendon injuries… predispose to injury!
The higher rate of (blank) leads to higher rates of soft tissue failure
Are collagen fibers different after injury?
What percent do tissues return to after injury?
- The higher the rate of loading = more likely to have soft tissue failure (vs bone level)
- Morphologically: 40 weeks after injury,
collagen fibrils are different from those of healthy ligaments.
Over time, the tissues return to 10-20%
compared to normal…why??
What is the most common cause of tendinitis?
What are 4 different mechanisms behind it?
What is most often related with it and what is that accompanied by?
How long does healing take?
Sports activity is the main culprit of tendonitis
variable mechanisms and locations in
body
* Excessive and repeated motions/loading(i.e. tennis elbow)
* Shock absorbance (i.e. Achilles)
* Friction on a structure (i.e. ‘lace bite’ in
hockey)
* Anatomical
Most often related to the rupture of some tendon fibers (partial rupture)
which are accompanied by local swelling (edema)
Healing takes several months!
What layer of tissue is different between tendons and ligaments?
Endotenon because it’s what allows the tissues to adhese to the correct structures (muscle to muscle or bone to bone)
Is the patellar tendon a ligament or a tendon?
It is technically a ligament because it attaches bone to bone.
Why do we call the patellar tendon a tendon then if it is technically a ligament?
It’s a continuity from the tendon that attaches to the quad muscles and it structurally resembles a tendon more than a ligament.
What is necessary in order to increase the collagen and strength of tendons?
Mechanical loading (tensile loads) through activity
What is important about the orientation of the fibers of the ligaments?
The fibers are oriented with the movement of the joint to help guide movement.
If you had to tear the fibers in the muscle, tendons, and ligaments, rank them from best to worst scenario? (Yes they’re all bad)
You’d first want to tear muscle fibers because of how much more blood flow goes to the muscle and so they are able to resynthesize those fibers.
You would then usually prefer to tear the tendon fibers as they get more blood flow than the ligaments and ligaments don’t always fully heal back to 100%. In some locations of the body you would rather tear ligaments but in general you would say tendons.
Which ligament has a lot more elastin than the others?
Ligamentum flavum which is a ligament than goes down the spine. It has more elastin to provide the spine a little bit of give without damaging the ligament too much.
How will the elastin fibers be oriented at rest (not stretched)?
The elastin fibers will be in a bundle (bowl of noodles) and they will straighten out as the tendon/ligament is stretched.
Which part of the spine is at the greatest risk when submitted to compression forces? Why?
The cervical spine because its form is based on its function (which is a lot of rotational movement). It isn’t built in a way to optimally resist compression forces.
The lumbar spine is also at some risk because it is the part of the spine that absorbs most of the forces in the body, but it was designed to do this so is less at risk than the cervical spine.
Why is it important to contract the glutes while running?
Contracting the glutes is so important because the shortening of the muscles counteracts the bending forces on the neck of the femur.
What is the most common injury in older adults?
What can you do to train these people to to avoid the fracture?
Hip fracture (which is really a fracture of the femoral neck)
Strengthen the glutes so that they can resist the bending stress on the femoral from walking/falling.
When talking about spine health, why do you need to have a strong core?
Strong core muscles are needed to resist shear forces in the spine (mainly thoracic spine)
What is Osgood Schlatter’s?
Pain/swelling on the tibial tuberosity caused by the patellar tendon pulling on this section of the bone.
What is a greenstick fracture?
A greenstick fracture is a partial thickness fracture where only the cortex and periosteum are interrupted on one side of the bone but remain uninterrupted on the other.
What tissue is normally damaged by tension forces?
Tension will normally result in damage to the muscles, ligaments, and tendons whereas bone is more likely to be damaged during compression.
What is spondylolisthesis?
What kind of forces would cause spondylolisthesis?
Spondylolisthesis is a condition that occurs when one vertebral body slips with respect to the adjacent vertebral body causing radicular or mechanical symptoms or pain. It is graded based on the degree of slippage of one vertebral body on the adjacent vertebral body.
Shear forces.
Potential exam question format: If a blank force is put on a blank bone, what types of force (compression, tension, shear, bending) will be felt at different parts of the bone?
- memorize this, no answer
What is collagen?
Collagen is the most abundant protein in your body. It accounts for about 30% of its total protein. Collagen is the primary building block of your body’s skin, muscles, bones, tendons and ligaments and other connective tissues.
They are resistant to stretch, not to compression
What part of your bone makes it hard?
Minerals (phosphate, calcium, etc.). These are the inorganic parts of the bone. The organic material (collagen) is what makes your bone flexible and resilient.
Why does our collagen in the bone go in all directions?
It allows bone to absorb tensile forces from all directions.
What is osteoporosis?
Osteoporosis is a bone disease that develops when bone mineral density and bone mass decreases, or when the structure and strength of bone changes. This can lead to a decrease in bone strength that can increase the risk of fractures (broken bones).
What can you do to prevent developing osteoporosis?
Do physical activity to put stress on the bones to encourage more bone growth.
What type of physical activity would be more beneficial, running or swimming? Why?
Running because you’ll get compressive forces from gravity as well bending forces (simultaneous tension and compression).
Is swimming still beneficial? Why?
Yes because the muscles will create tensile forces on the bones when it contracts.
What does anisotropic mean?
The behaviour/resistance of a material depends on the direction of the force being applied.
What is the problem with youth football helmets?
They’re too big so they put stress on the kid’s neck muscles
What is the problem with kid’s backpacks?
Kids with backpacks that are too big are constantly bent over to counteract their back pack so they develop a hunched over posture
What causes bone growth with running?
Contact with the ground reaction forces from the ground, which increases forces within the muscle
What is unique about astronauts?
They need wheelchairs after getting back from space because their body isn’t used to the mechanical loading from gravity
What is the rate of bone loss for immobilized patients?
1% bone loss per week
Why does osteoporosis have it’s name?
Bone becomes more porous
How does ability to withstand compressive forces change with age?
Drops with age
What is the best way to prevent osteoporosis?
Try to start with a very high bone density in 20s/30s through strength training so you can start the decline from as high of a point as possible
Why are wrist and hip fractures most common in older adults?
Outstretched hands during fall and hip will fracture if you fall on your side and aren’t able to outreach their hands
What is unique about osteoporosis in women?
In women who are not physically active, they lose both the inner and outer layer of bone because of hormonal changes with menopause but men only lose outer layer
What is the only real thing that can prevent bone loss with aging?
Physical activity, strength training specifically, is the only real thing you can do
What type of PA are both genders more likely to engage in?
Men are more likely to strength train (increase muscle) and women are more likely to do cardio (decrease fat), but crossfit has changed culture
Which piece of fitness equipment is better for asymmetries?
DBs are better than BBs and free weights are better than machines
How do reps/weight change with different goals?
High reps/low weights are better for rehab, Low reps/high weights are better for strength & power
What is it called when cartilage is calcified?
Called synostonosis, when there are lots of fibers very densely packed
Synostonosis is the change from cartilage to bone
What are the 6 types of synovial articulations?
hinge (elbow)
saddle (carpometacarpal joint)
planar (acromioclavicular joint)
pivot (atlantoaxial joint)
condyloid (metacarpophalangeal joint) ball and socket (hip joint).
What is the ROM of and type of movement of each of the 6 synovial articulations?
- Ball and Socket Joints: These joints allow for the greatest range of motion. The joint involves a ball fitting into a concave surface. Because these joints allow for more motion, they are at greater risk for instability. Ball and socket joints allow for movement in many planes, and circumduction.
The shoulder and hip are both ball and socket joints.
- Condyloid Joints: Allow for flexion, extension, and some lateral movement at the joint. There is also some circumduction that takes place. The circumduction is limited however, because the shape of the joint is oval compared to the more mobile ball and socket joints. Fingers should be able to move in a circular motion, although it is small. Condyloid joints are also referred to as ellipsoidal joints.
The base of each finger is a condyloid joint.
- Saddle Joints: These joints are made of two concave and convex surfaces that intersect. Saddle joints allow for flexion, extension, and lateral movement. Saddle joints may present as a condyloid joint, but if you try to move your thumb in a perfect circle, you will notice its movement will not be smooth like the circular movement possible with a finger.
The base of the thumb is an example of a saddle joint.
- Hinge Joints: Hinge joints allow for movement in one plane only. Think of a door hinge. It allows the door to open and close, but not move up or down.
Knees and elbows are some common examples of hinge joints.
- Pivot Joints: This type of joint allows for rotation. Unlike many other synovial joints, it does not allow for any flexion or extension.
The first two cervical bones (the atlas & axis) form a pivot joint. The atlas sits on top of the axis and enables a “no” movement of the head (left & right rotation)
- Planar joints have bones with articulating surfaces that are flat or slightly curved faces. These joints allow for gliding movements, and so the joints are sometimes referred to as gliding joints. The range of motion is limited in these joints and does not involve rotation.
What type of movement is a volleyball spike related to axis’ and planes of motion?
Moving in the sagittal plane
Shoulder is rotating around the frontal axis
Torso is rotating around the transverse axis
Legs counteract the torso in the opposite direction during the spike
What type of movement is a jumping jack related to axis’ and planes of motion?
Moving in the frontal planer, hips are rotating around the sagittal axis
Why does thinning of cartilage cause pain?
Thinning of cartilage causes pain because it leads to contact with the bones
What is a good way to maintain hip mobility?
Practicing full squats
What is usually the main problem with full squats?
Not usually an anatomical abnormality, it’s usually ankle mobility
What is the definition of functional mobility?
Functional mobility is mobility that allows you to optimally perform your daily activities
Why does cartilage need movement?
There’s no blood supply to the cartilage so it has a slow metabolism, cartilage absolutely needs movement to stay healthy and receive nutrients
What is the best way to time rehab sessions?
Try to time rehab sessions very closely to when the pain medication is given for people that are rehabbing from surgery
What does it mean that cartilage is anisotropic?
Cartilage being anisotropic means that it is aligned in all different positions so it can react to stress from different directions
When does cartilage get into a vertical position?
Cartilage gets into a vertical position within the deeper layers to prevent the surface layer from collapsing, the surface layer has more water to absorb impact, the vertical position allows the cartilage to anchor to the bone
What is the top layer of cartilage able to do?
The top layer of cartilage is filled with water and positioned in all different directions, which makes it able to collapse and absorb impact
Deep layer of cartilage is positioned vertically and is anchored to the bone and resists collapsing
What are 2 examples of orthopedic conditions that would alter your visual platform?
-Scoliosis, contorted spine will alter ability for vision
-Osteoporosis, inability to stand up or being in a wheelchair will affect vision
Why is bone spongy?
Sponginess allows the bone space to deform and return to form
Sponginess moving in all different directions allows the bone to handle forces from all different directions
Why is children’s bone marrow red and adult’s bone marrow yellow?
Adults don’t need as many red blood cells and 5% protein is enough
What kind of movements does the skull perform?
Skull has micromovements to allow for the brain to shift around in the skull
What does compact bone do while jumping?
Muscles use eccentric contraction to absorb force, one side of the bone is resisting stretch and the other side is resisting compression
What are shin splints?
How do you treat shin splints?
Inflammation of the periosteum on the tibia due to repetitive stress
Treat shin splints by reducing the intensity and load of training, as well as the RICE method
What does the periosteum pull on in the case of shin splints and what does it lead to?
Periosteum pulls on the bone and creates microfractures that lead to stress fractures in long distance runners
How can you prevent shin splints?
Prevent shin splints by making sure you have a progression in your training and you slowly increase training volume
What are dorsiflexors used for?
dorsiflexors are used for heel strike and runners that are taught with that technique have higher prevalence in shin splints
What does osteoporosis break down?
Osteoporosis breaks down osteons in compact and leads to increased air pockets leading to more breaks
Why do we have so many layers of osteons?
Circles of osteons help to distribute force, we have a lot of structures that do the same thing in case one breaks then another can take over
Why do we need a good ratio of osteoblasts and osteoclasts?
we need a good ratio of osteoblasts & osteoclasts in order to create new bone, not enough obsteoblasts leads to osteoporosis
What are osteocytes?
osteocytes are mature osteoblasts that are formed into the bone
What does pulling on the bone create?
pulling on bone creates bone matter, teenagers that run too much have tibias that are overgrown
What is a side effect of reduced physical activity?
Reduce bone density with reduce physical activity, PA will cause new bone to be created
Why does diaphysis have more remodeling than epiphysis?
Outside forces create internal forces in the bones because the bones absorb forces on the extremities(epiphysis) and causes the middle to bend(diaphysis)
What are 5 ways that the structure of bones follow their function? (chatgpt)
Here are some ways in which the structure of bones reflects their functions:
Shape and Composition: Bones have specific shapes that are suited to their functions. Long bones, like those in the arms and legs, are designed to support weight and facilitate movement. Flat bones, such as those in the skull, offer protection to underlying organs. The composition of bones, which includes a combination of collagen (for flexibility) and calcium salts (for strength), allows them to withstand mechanical stress while maintaining a degree of flexibility.
Bone Marrow and Blood Cell Production: Certain bones contain bone marrow, a soft, spongy tissue responsible for producing blood cells. The structure of bones is adapted to accommodate this function, with spaces within the bone for the proliferation and maturation of blood cells.
Joints and Mobility: The structure of bones at joints, including the shape of the bone ends, cartilage, and ligaments, reflects their role in enabling movement. Joints allow for various types of movements, such as rotation, flexion, extension, and abduction. The smooth articular surfaces and synovial fluid within joints reduce friction and allow for smooth movement.
Strength and Support: The compact and cancellous (spongy) bone tissues in different parts of the bone provide the necessary strength and support required for withstanding the forces exerted on the skeleton during various activities. The arrangement of compact and cancellous bone in specific areas caters to the need for strength while minimizing weight.
Mineral Storage and Release: Bones serve as a storage site for minerals like calcium and phosphorus. The structure of bones allows for the deposition and release of these minerals based on the body’s metabolic demands. This mechanism helps regulate the levels of essential minerals in the bloodstream, contributing to overall physiological balance.
What is the difference between creep and relaxation?
In biomechanics, creep and relaxation are both terms used to describe the behavior of materials, including biological tissues, under mechanical loading over time. While they both pertain to the response of materials to applied stress or strain, they represent different phenomena:
Creep: Creep refers to the tendency of a material to deform gradually under a constant load or stress over an extended period. In the context of biomechanics, this can apply to biological tissues such as tendons, ligaments, or other connective tissues. When a constant load is applied, these tissues may exhibit a slow increase in deformation over time. The gradual elongation or deformation occurs without an increase in the applied stress. Creep is essentially a time-dependent strain that happens in response to a constant stress.
Relaxation: Relaxation, on the other hand, refers to the gradual decrease in stress within a material when it is subjected to a constant strain over time. In the realm of biomechanics, relaxation often describes the behavior of viscoelastic materials like tendons or muscles. When a constant strain is applied, the stress within the material decreases over time, implying that the material gradually accommodates the imposed strain without any further increase in the applied strain.
In summary, while creep involves a gradual increase in strain under a constant load, relaxation pertains to a decrease in stress under a constant strain. Both phenomena are relevant in understanding the mechanical properties of biological tissues and play a significant role in the study of their behavior under various physiological conditions and mechanical loading.
What are the different types of collagen in bones/cartilage vs tendons/ligaments?
Bones/cartilage have type 2
Tendons/ligaments have type 1
Can tendons/ligaments sense proprioception? T or F
True, as well as joints and muscles
Do tendons or ligaments have more elastin?
Tendons have a very small amount of elastin and ligaments have more elastin
Are tendons & ligaments stronger with load applied fast or slow? what principle does this involve?
Visco-elastic property of tendons and ligaments
Tissue is stronger with load applied quickly (less time to disperse in viscous
component)
-Why is passive muscle force
important?
-Would it be the same in each
muscle? Why, why not?
Passive muscle force refers to the tension or force generated within a muscle when it is stretched or lengthened passively, without any active contraction or neural stimulation. This force is primarily a result of the passive properties of muscle tissue, including the elasticity and viscoelasticity of the muscle fibers and connective tissues. Passive muscle force is important for several reasons:
Joint stability: Passive muscle force helps stabilize joints, especially during movements that involve stretching or lengthening of the muscles. This passive tension assists in maintaining joint integrity and preventing excessive joint displacement.
Energy storage: Passive muscle force allows for the storage of elastic energy within the muscle-tendon unit during stretching. This stored energy can be subsequently utilized during active muscle contraction, enhancing the efficiency and effectiveness of muscular movements.
Postural support: Passive muscle force contributes to maintaining proper posture and alignment of the body, assisting in the distribution of loads and minimizing the risk of injury or strain on the musculoskeletal system.
Movement efficiency: By providing a level of resistance and support during stretching, passive muscle force aids in the control and coordination of movements, allowing for smoother and more controlled muscle actions.
While the concept of passive muscle force applies to all muscles, the magnitude of this force can vary depending on the specific characteristics of each muscle. Factors such as the muscle’s architectural design, composition of muscle fibers, arrangement of connective tissues, and the presence of muscle-tendon units influence the extent of passive muscle force generated.
Different muscles have varying proportions of muscle fibers and connective tissues, leading to differences in their passive stiffness and elasticity. Additionally, the length-tension relationship and the specific roles of muscles in different movements contribute to variations in the manifestation of passive muscle force. Thus, while the concept of passive muscle force applies universally, its expression can differ among different muscles based on their unique structural and functional properties.
-Why is there a decline before a steep incline in muscle force after the resting muscle length is passed in active muscle contraction?
The decline and subsequent steep incline observed after passing the resting muscle length during active muscle contraction can be attributed to the mechanical properties of muscle fibers, particularly the sarcomeres, which are the basic contractile units of muscle. This phenomenon is related to the force-length relationship of muscle fibers and the overlap of actin and myosin filaments within the sarcomeres.
When a muscle is stretched beyond its resting length, there is initially a decline in force production. This decline occurs because the actin and myosin filaments start to move farther apart, reducing the number of cross-bridges formed between them. As a result, the force generated by the cross-bridges decreases, leading to a decline in overall muscle force.
However, as the muscle continues to lengthen beyond the resting length, the actin and myosin filaments start to overlap more extensively. This increased overlap allows for a greater number of cross-bridges to form between the actin and myosin, leading to a steep incline in force production. The steep incline represents the increasing number of cross-bridge interactions and the enhanced force-generating capacity of the muscle fibers at longer lengths.
This pattern of decline followed by a steep incline beyond the resting muscle length is known as the descending limb and ascending limb of the force-length relationship, respectively. It highlights the complex interplay between the sliding filaments within the sarcomeres and the generation of muscle force during active contraction. Understanding this relationship is essential in the study of muscle physiology and the mechanics of muscle function, providing insights into the optimal muscle lengths for force production and the implications for muscle performance in various activities and movements.
How does velocity and force change in concentric muscle contraction?
Concentric contraction
Velocity increases = Force decreases
* Actin-Myosin bridges do not have
sufficient time to form!
How do lower velocities impact concentric contraction?
How is maximum power achieved?
For concentric force…
Lower velocities leads to the Contraction being more efficient
Power 1/3 force + 1/3 velocity = Maximum power
What is the force-velocity relationship in muscles?
External load imposed is small, the velocity of contraction is max.
Load increases, the speed of contraction
decreases
When the load is equal to the maximum force that the muscle can exert, then the contraction is isometric.
When the load is greater than the max force then the muscle stretches.
The more the load increases, the faster the speed increases.
Eccentric: the force stops abruptly at rapid speed when you can no longer control the movement.
How does temperature affect muscle force?
Muscle creates the same force but the muscle is able to produce that force in less time
What are the 3 mechanical effects of fatigue on muscle performance?
What is the chemical effect of fatigue on muscle performance?
Mechanical Effects
* Modification of the movement
* Change in the load
* Decreased ability to absorb impacts
Chemical Effects
-Decrease in ATP
How does vibration effect muscle force?
Increased force, velocity, lower
Maintains muscle structure and force at rest
Decreases sarcopenia
