Last Third of the Course

Question 1

What is the function and composition of connective tissue?

Answer 1

Stores energy (chemical and mechanical) Protects organs Supports body Connects body tissue Made up of cells that produce and maintain extracellular matrix Extracellular matrix –> ground substance for diffusion and cell support, fibers for strength and support

Question 2

What is the structure and function of adipose tissue?

Answer 2

adipocytes (contain tryglycerides) mechanical cushioning energy storage

Question 3

What is the structure and function of bone

Answer 3

Water, minerals (calcium salts) to resist compression, collagen fibers to resist tension Act as levers Produce blood cells support protect organs storage of fat and minerals

Question 4

How does stress cause bone injury and how can it be minimized?

Answer 4

Muscular activity reduces tensile loading, when muscles fatigue, ability to do this reduced. Reduce tension across epiphysial plates through increased collagen fibers, resolution of vectors

Question 5

Describe the structure and function of the two types of cartilage

Answer 5

Articular cartilage coats ends of articulating bones in synovial joints some collagen fibers for strength ground substance with gel components to resist compression, reduce deformation distributes load, reduces friction, provides shock absorption Fibrocartilage forms menisci in synovial joints Lots of collagen fibers distributes load, reduces friction, shock absorption, joint stability, increases contact area

Question 6

What are the viscoelastic properties of cartilage?

Answer 6

deformation increase elastically initially, then slow creep as fluid squeezed out. Rebounds elastically (recoil) then slow recovery as fluid soaks back in

Question 7

Describe the structure of tendons and ligaments

Answer 7

water, collagen, elastin connect muscle to bone (tendons) or bones to bone (ligaments) ligaments in wavy pattern (crimp) –> creates toe region in stress-strain curve tendons recruit fibers quickly and carry higher loads

Question 8

What are the viscoelastic properties of tendons/ligaments

Answer 8

speed-dependent response to loading Constant stress leads to creep relaxation Constant strain leads to stress relaxation

Question 9

Describe the difference between collagen and elastin

Answer 9

Collagen can handle lots of stress, but not much strain Elastin can be stretched a lot, but can’t experience much stress

Question 10

Describe repetitive loading and viscoelastic effects on ligaments

Answer 10

Repetitive loading leads to decreased stiffness, and a time dependent increase in elongation (creep) Squeezes out fluid, makes ligament less stiff (thixotropy)

Question 11

Describe ligament recovery and rehab

Answer 11

Grows back in no uniform direction, weak and less stiff. Over time, grows in direction of loading. Will have same stiffness (increased area), but much weaker than before. Slow because of lack of blood supply, don’t immobilize or tissue will degenerate. Use controlled loading to enhance rehab and promote alignment. go from biking to stair master to running. Use brace to protect against uncontrolled movement (less elongation)

Question 12

What happens during warm-up

Answer 12

decrease joint friction increase synovial fluid decrease viscosity of synovial fluid (thixotropy and increased temp) decrease stiffness (decreased viscosity) of connective tissue

Question 13

What does EMG measure? What can we use it for?

Answer 13

electrical activity in the muscle Rough correlation between isometric EMG and force Measure muscle fatigue Measure % of max voluntary contraction Which muscles are active during different phases Neural input (bilateral deficit –> loss of force and EMG if two limbs contract at same time) Strength gain –> initial strength gain due to better recruitment, later due to hypertrophy

Question 14

How does muscle, length, velocity, and fatigue affect EMG?

Answer 14

muscle/length different velocity –> higher rates of EMG/movement during concentric contraction. Eccentric has same force for less EMG fatigue –> lower tetanus, slower twitch

Question 15

What are the 4 properties of muscles

Answer 15

extensibility - can stretch passively or actively contractility - can shorten in response to stimuli irritability - can respond to stimuli elasticity - can return to resting length/shape after stretch

Question 16

What are the functions of muscles?

Answer 16

Movement: produces movement, maintains posture, stabilizes joints Non-movement: controls pressure within body cavities, entrances/exits, produces heat to maintain body temperature, protects organs

Question 17

How does muscle CSA affect force?

Answer 17

Hypertrophy - increased size of fibers hyperplasia - increased number of fibers increased CSA = increased force

Question 18

How does activation level affect force?

Answer 18

muscle can be activated non-maximally, reduces force

Question 19

How does muscle length affect force?

Answer 19

Contractile element (sarcomeres) have ideal length/amount of overlap to produce maximal force Passive tension through tendons and other connective tissue can increase total tension even when active tension declines. This reduces the likelihood of muscle damage when the muscle is pulled

Question 20

How does velocity of shortening affect force?

Answer 20

Eccentric contractions produce more force. Slower velocities increase amount of force it can produce. Extension = production

Question 21

How does muscle temperature affect force/muscle behaviour

Answer 21

Blood: decreases viscosity, increases heart rate, promotes dissociation of oxygen from hemoglobin at the cells to improve O2 delivery Muscles: decreases viscosity of muscles, fibers/connective tissue have increased elasticity and extensibility, facilitates enzyme activity, increases force and speed of contraction

Question 22

How does electromechanical delay affect produciton?

Answer 22

Delays produciton. Latency between EMG neural activation and contraction of muscle

Question 23

How does muscle fiber type affect force?

Answer 23

Fast twitch produces more/quicker force, but fatigues quicker

Question 24

What is angle of pennation and how does it affect force?

Answer 24

Angle of pennation is the physiological cross sectional area. increases surface area and force

Question 25

What are the advantages and disadvantages of long tendons?

Answer 25

Advantages: can have more muscles insert in smaller area, decreases moment of inertia, store elastic energy Disadvantages: less overall shortening for same % shortening of fiber

Question 26

What is the advantages and disadvantages of crossing multiple joints?

Answer 26

Advantages: reduces work done by single joint muscles, optimize length and velocity Disadvantages: reduces range of motion

Question 27

What is the purpose of co-contraction

Answer 27

Forces have stabilizing and dislocating components, co-contractors reduce dislocating components

Question 28

What is Lombard's paradox?

Answer 28

Hamstrings active even during knee extension. Antagonist muscles. During knee extension, quadriceps has larger moment arm, so it "overwhelms" hamstring torque.

Question 29

What are the factors of muscle torque production

Answer 29

muscle force, insertion point, joint angle, muscle line of action

Question 30

How do variable resistance machines work?

Answer 30

Change the amount of muscle torque needed depending on the difficulty at different points in the movement

Question 31

What are some examples of biomechanical pulleys and how do they help?

Answer 31

Tendons, bones, ligaments change direction of muscle pull. Patella increases the moment arm of the quadriceps around the knee COR. This also increases the patellofemoral compressive force (summation of the quad tendon and patella ligament forces). Ok because patella also increases contact area with femur to prevent high compressive stress.

Question 32

What are the factors affecting muscle force

Answer 32

Electromechanical delay length velocity of shortening muscle temperature angle of pennation activation history type of muscle fibre Activation level elastic energy stored

Question 33

What do you need to calculate and how do you calculate it for inverse dynamics?

Answer 33

segment end points --\> motion capture ground reaction force --\> force plate segment mass center of mass location moment of inertia --\> all through anthropometry

Question 34

What are we calculating in inverse dynamics?

Answer 34

Proximal and distal joint moments and joint forces Start with most distal segment because there is no distal joint moment or force, so there is only one angular and one linear unkown

Question 35

Special things to consider in inverse dynamics?

Answer 35

Muscle moment is net force, may have contributions from multiple forces, co-contractors, antagonists, etc During swing phase, there is no ground reaction force

Question 36

How do you move from distal to proximal segments?

Answer 36

Proximal end of the distal segment becomes the new distal end. Moments and forces acting on that end are opposite directions. then use these forces (already calculated) to calculate the new proximal end forces/moments

Question 37

Why is water a good environment?

Answer 37

buoyancy --\> reduces impact forces (archimedes principle: buoyant force = weight of water displaced) safety --\> stabilizing, reduces accelerations resistance --\> much more dense hydrostatic pressure --\> venous return to heart, more respiratory system effort (reduced expiratory reserve and vital capacity)

Question 38

What are the different types of drag?

Answer 38

Friction drag --\> surface roughness form drag --\> due to shape of body induced drag (lift) --\> excess force generated in opposite direction of lift force wave drag --\> interaction between fluids

Question 39

What is Bernoulli's Principle?

Answer 39

pressure is inversely proportional to velocity

Question 40

What is the Magnus Effect?

Answer 40

through spinning, one part is spinning faster than the other, this crushes air molecules and increases density, leading to a greater pressure on one side than the other, so there is a force applied Faster spin = larger differential

Question 41

What are some personal and workplace risk factors for low back pain?

Answer 41

anthropometry, experience/training, health, age, strength, health history, psychophysical load, posture, spatial constraints, protective equipment, duration and frequency, environment

Question 42

How does lumbar support and backrest inclination affect compressive stress?

Answer 42

more lumbar support, more inclination = less stress, less muscle activity more muscle activity tugs on the lower vertebrae

Question 43

How does posture affect compressive stress and moment arm?

Answer 43

standing means that there is very small moment arm between spine and pelvis, but sitting and slouching rotates the pelvis anteriorly. Different postures affect compressive stress.

Question 44

What are the 3 NIOSH criteria categories, and explain the different parts of the biomechanical

Answer 44

Biomechanical: keep compressive stress at L5/S1 L5/S1 --\> where most LBP happens, lifting limited by stress rather than strength, large moments in trunk 3.4 kN due to modelling, cadavers may not be relevant to LBP compressive --\> most data, belief that this is how vertebral end-plate fractures occur, good predictor Physiological --\> fatigue, energy expenditure (limit for repetitive tasks) Psychophysical --\> worker's perceptions (limit for all except high-frequency)

Question 45

How do spinal muscles and ligaments affect shear forces?

Answer 45

Muscles decrease shear, ligaments don't help to reduce, and may increase joint shear. Ligaments limit flexion, carry load. During fully flexed back, extensor muscles inactive, ligaments inactive during neutral back

Question 46

Why is the stretch-shortening cycle good?

Answer 46

Increases amount of work that can be done. Essentially a backswing, must be small amplitude, no delay, and high velocity. Leads to eccentric contraction of the muscle, therefore more initial force can be produced. Prior activation means less time needed to generate force, and contribution of force from the stretch reflex

Question 47

How does plyometric training help?

Answer 47

Rapid loading in eccentric and concentric contractions increases muscle power High forces increase muscle strength initiates stretch shortening cycle to enhance positive work during the movement Increased force during eccentric phase means that there is overloading on muscles/tendons/ligaments Involves very common movement patterns to promote coordination

Question 48

How do tendons increase efficiency?

Answer 48

Elasticity. Sarcomeres kept at optimal length. Plantar flexors of kangaroos work isometrically to control stretch of the tendon. Tendon stores and releases elastic energy that accounts for some of the energy required during locomotion. Elasticity can be bad: need to compress sole before generating push-off, can affect stability. Static stretching increases tendon compliance, reduces force transmission.

Question 49

Define stress, strain, strength

Answer 49

Stress: normalized force, internal forces in response to external forces Strain: normalized deformation, change in length in response to external forces Strength: maximum stress a material can withstand before failure. Greatest strength for compressive forces

Question 50

List the different types of stress

Answer 50

Compression/Tension -\> forces perpendicular to surface Shear -\> forces parallel to surface Torsion -\> torque (spiral fractures)

Question 51

What are the different properties of the curve

Answer 51

Elastic region, yield point, plastic region, failure point. Slope = stiffness (k) or elastic modulus (stress-strain) Stress strain defines material properties

Question 52

Discuss viscoelasticity

Answer 52

Resistance of fluid to shear stress Viscoelasticity --\> can withstand greater stress before deforming during fast loading, greater energy lost as heat Thixotropy --\> becomes less viscous when shaken/agitated

Question 53

What are some factors of injury? what are the different types of injury? How can injury be prevented?

Answer 53

Force, exposure time, range of motion chronic or acute (low v high loads, short v long period of time) Tissue conditioning: increases anabolism, decreases catabolism, but can be injured through overuse, can experience atrophy