Muscular Considerations for Movements Flashcards
Characteristics of Muscle
Irritability
-Ability to respond to stimulation
–Electricity from nerves
Contractility
-Ability to shorten when it receives sufficient stimulation
-Unique to muscle tissue
Extensibility
-Ability to stretch/lengthen beyond resting length
-Protective Mechanism
Elasticity
-Ability to return to resting length after being stretched
-Protective Mechanism
Atrophy/Hypertrophy - Use it or lose it!!!
When does atrophy and hypertrophy occur?
Change in size relative to use/disuse
Atrophy 2-6 weeks, Hypertrophy 3-4 weeks
Hypertrophy is highly neural, learning how to recruit the muscles again
Explain Individual Muscle Organization
Muscle -> Bundles (Fasiculi); Covered by perimysium -> Single muscle fiber (muscle cell); Myofibril -> Filaments: Actin and Myosin
More cross bridging means a stronger contraction
Can I fire a single muscle fiber? Why or why not?
Act in unison
Neurologically very difficult/nearly impossible to active only one muscle
Ex: Can’t just activate Vastus Medialis, all quadricep muscles are activated
Fascia
Sheets of fibrous tissue
Compartmentalize groups of muscles
Muscles fire with fascia group
What does fusiform mean?
Parallel fibers and fascicles
Force goes through middle of muscle
High Speed of contraction and force production
ACS = PCS
Ex: Sartorius, Biceps Brachii, Brachialis
What does ACS stand for? What does it mean?
Anatomical Cross Section (ACS)
Measure the diameter of the muscle, get cross-sectional area. Don’t care about fiber direction
Widest section
What does PCS stand for? What does it mean?
Physiological Cross Section (PCS)
Orientation of fibers for force output.
Perpendicular to the fibers
What does Penniform mean?
Muscle fibers aren’t oriented in one direction
What are the three types of penniform muscles? What is significant about them?
PCS > ACS
Unipennate
- Off one side of tendon
- Semimembranosus
Bipennate
- Off sides of tendon
- Gastrocnemius
Multipennate
- Both varieties
- Deltoid
What type of muscle shortening is this?
Longitudinal
What type of muscle shortening is this?
Bipennate
What type of muscle shortening is this?
Unipennate
What type of muscle shortening is this?
Multipennate
Why is the angle of pennation important?
Shows how much it will shorten and how much force it can generate in one direction
Vectors
Bigger Vector = Bigger Magnitude
Must make a box when creating a vector to compare lengths.
Show Force from muscle
Motor Unit
- A group of muscles innervated by the same motor neuron
- From 4 to 2000 muscle fibers per motor unit
- Action Potential
- Neuromuscular Junction
- Potential meets muscle
- Conduction Velocity
- Velocity AP is propagated along the membrane
What are the three muscle fiber types? What is their function?
- Slow-Oxidative
- Red – More mitochondria
- Endurance
- Fast-Oxidative Glycolytic
- Intermediate fast twitch
- Trainable
- Fast-Glycolytic
- White – No Oxygen
- Sprinters, Jumpers
- High Force, Fast Fatigue
Recruitment Order of Muscles for Action
- Smaller to larger
- Slow to fastest muscles
- Light load use slow twitch
- May be able to make the recruitment of more muscles quicker through ballistic training
- Progressive overload overtime important for injury recovery
What is the recruitment order for neuromuscular electrical stimulation (NMES)?
- Recruits in the OPPOSITE DIRECTION
- Fastest first then slow
- Nerves pick up electricity and contract
- Fast glycolytic nerves are larger therefore pick them up first
- May feel like a cramping sensation
Do leg muscles always lengthen or shorten a lot during a movement?
No, hamstrings and quadriceps don’t move much!
Only change roughly 2%
Why is titin important?
- Spring-like filament
- Titin is a factor in eccentric force development
- Force-dependent shortening of titin’s spring length
Mechanical Model of Muscle (3 Parts)
- Contractile (CC)
- Converts stimulation to force
- Active shortening or lengthening tasks place
- Parallel Elastic (PEC)
- Allows muscle to be stretched
- Associated with fascia surrounding muscle
- Series elastic (SEC)
- Transfers muscle force to bone (Tendon)
- PEC and SEC are passive
- CC is metabolic energy
- Ex: Neurologically can’t get CC to go, but resistance from PEC and SEC when putting them through ROM
Why is the Angle of Pull important?
Spine and Disc compression
- Most muscles are longitudinal
- For spinal stability we need compression of muscle, therefore we compress our disc
Abdominal Muscles and Spine
Abdominals not good protective factor for the spine
Transverse Abdominus has some benefits, deep, hard to train
Ultrasound can be used to train transverse abdominis
Unique Architecture - VMO/VL Ratio
Muscles largely act in combination
VMO/VL Ratio
Patellar tracking is influence by how these muscles work
Very hard to selectively train one of these muscles
Patella doesn’t move in accordance with Rectus Femoris as it pulls from both sides
Q angle has an influence in patellar tracking
What is Q angle?
ASIS to center of patella to tibial tuberosity
Women have larger Q angle
Passive Length Tension Relationship
- Muscles resting length will influence amount of tension developed
- Elastic energy storage
- Depends on type of muscle/tendon
- Increased passive stiffness with stretch
- Consider the effect of prestretching prior to active muscle
- Ex: Jumping, need to bend knee deeper to be able to jump up rather than slight stretch
- Elastic energy storage
- Surgical Implications
- Releases, tenodese, transfers
Stretch Shortening Cycle
- Pre-stretch (Some neurological but largely elastic)
- Quick lengthening of a muscle before contraction
- Generates greater force than contraction alone
- Utilizes elastic component of muscle
Plyometrics
- Conditioning protocol that utilizes pre-stretching
- Single-leg bounds, depth jumps, stair hopping
- Ex: Sport
- Involves stretch shortening cycle
Contractile component
Sliding filament theory
More stretched position, less ability for cross bridging to occur, less power output
More overlap, more power output
Can get to point of no more overlap possible
Elastic Component
Begin when stretch is presented to the system
Muscle length of the elbow flexors
- Not great data on muscle lengths beyond ROM
- Not all muscles shorten the same amount through a movement
Muscle Insufficiency
- Passive insufficency
- Multi-joint muscle stretching will not allow full ROM at each joint cross
- Finger flexion during wrist flexion
- Knee extension: Hamstring
- Multi-joint muscle stretching will not allow full ROM at each joint cross
- Active insufficency
- Multi joint muscle under active tension cannot produce full ROM at each joint crossed
- Wrist Flexion not as strong
- Knee extension: Quadriceps
- Sarcomeres are maximumly shortened, sarcomeres run into each other
- Multi joint muscle under active tension cannot produce full ROM at each joint crossed
- Why does this occur?
- Active Insufficency: Muscle can’t make cross bridges when too short
Muscle Force Output - Time
- Maximum tension (force) - not instantaneous (up to 300 ms)
- Reaction time studies (Neurology side, muscle tendon proprioceptors)
- Time to sense: 40-80ms
- Electromechanical Delay (Mechanical side, actin-myosin crossbridges)
- Time to develop tension: 7-120 ms
- Seems to depend on tendon stretch or relaxed (Elastic elements: SEC and PEC)
- Time to develop tension: 7-120 ms
- Enough to prevent injury?
- Maybe not
- Expectations matter
- Understanding what we need to turn on is important
- Anything surprising will put us at risk for injury
- Maybe not
Force-Velocity Relationship
- Eccentric (lengthen under tension) > Isometric > Concentric (shorten under tension)
- The velocity of shortening of the muscle
- Slower - the more cross bridges possible = more force
Does this mean the eccentric phase of an exercise always has a higher loading?
Depends on how the movement is performed
Muscle movement is dependent on what three things?
Muscle length
Velocity
Force Output
Force Velocity and Power
- Power = Force x Velocity
- Concentric force of muscle x velocity = Power
- Training for power don’t want to train too fast or too slow
- Sweet spot to properly train for power
Length of Moment Arm
- Torque (Moment) = Force * Perpendicular distance
- Perpendicular distance must be to vector
- This distance is called the moment arm
- Amount and location of resistance produce another vector
- Mechanical Advantage (MA)
- Describes the “potential” of the leverage system
- MA = Force arm/ Resistance arm
- Levers in the human body have poor MA
- Mechanical Advantage (MA)
- Rotary Arm is rotary torque
Change in Moment Arm through ROM
- Turning effect of muscles themselves
- Largest moment arm has best chance of rotate joint (Brachiradialis)
Moment arms of the hip
- 125 Normal
- <125 Vara
- Generates less muscle force
- >125 Valga
- Generates more muscle force
- Why?
- Less force compressing the hip components in vara
Internal and External Moments
- Directions of the moments about the joint
- Which add?
- Which subtract?
- H = Hamstring
- W = Weight (Comes from center of mass of LL)
- T = Torque from PT
- Sum of Torque = 0
- In isometric
- TH, TW, TTH = 0
Implications of Muscle Mechanics to Movement and Training
- Many different factors
- Very complicated BUT all lead to specific adaptations imposed to demands
- Get stronger relative to demands
- Specificity of movement is important
- Very complicated BUT all lead to specific adaptations imposed to demands
Muscles length influences isometric tension development
Pre-puberty
- Only ~20% of child’s body mass is muscle tissue
- Movements should not be limited
- Body weight is enough resistance to create strength
- Normal development is enough of a training stimulus
- Muscle mass increases parallel to body mass
- Children can perform resistance exercise
- Heavy resistance is generally considered to be avoided
- Don’t want to damage injury to growth plate with high impact activities
- Bone insertion stability is still happening
Puberty
- Strength gains can occur rapidly, especially in male
- Maturation, proportion of muscle mass in males
- Males and females can be trained similarly
- Muscle mass diverges by sex
- Females 90% of males at 11-12 years, 85% at 13-14%, 75% at 15-16 years
- Biological (hormonal) and societal (basis)
- Some precautions. Skeletal growth not complete. Epiphyseal damage and insertion sites are a concern.
Early Adulthood
- Greatest potential 18-30 year period.
- Most adaptable, tolerate high loads
Middle Age
- Begin to lose strength
- 2 hours of training a week may positively influence strength
Advanced Age
- Can reverse weakness in old age
- Males lose strength at greater rate than females
- Helps reduce symptoms of joint degenerative changes
- Can train for power
- Atrophy reflects disuse and not mere age-related changes
Immobilization and Disuse
- Immobilization by plaster or fiberglass cast or suspension system (sling) > strength reductions with bed rest
- In 4 weeks, see loss in cross sectional area and torque when immobilized.
