week 12 Flashcards
after eccentric exercise there is a disruption in _____
z discs
coordination of muscle force dictate ___ and ___ of the movement
quality and quantity
why do we care about skeletal muscle and joint mechanics
- predicting injury and performance
- biomechanical modelling
- understanding disease processes
- fundamental science - how muscle works
start at the sarcomere and end at the muscle
sarcomere –> myofibril –> muscle fibers –> fascicles –> muscle
how are sarcomeres arranged
longitudinally or in series
how does light defraction allow us to determine and measure sarcomere length
light can travel through the I band and the size of the I band changes with length so the defraction pattern will change
why do we want to measure sarcomere length
sarcomere length influences cross bridge binding by the overlap between actin and myosin and is defined by sarcomere length
this relationship is important for the force length relationship
what do muscles always want to do
bring the z-discs together
true or false all muscles act at an optimal length
false
why dont all muscles act at an optimal length
to balance force generation capabilities around a joint (the muscles around a joint must be balanced to act as a joint system)
what is passive force
restorative force due to the stretch of muscle to pull back towards the center
true or false all sarcomeres are the same length
false
what is the scaffolding of muscles primarily and why
collagen it is very still so it resists and is the main contributor of passive force in muscle
as stress increases so does
strain
what to we measure to measure optimal force production in the force length relationship
the plateau of force
why does it become harder to understand the force-length experiment the more it continues to lengthen
- passive force is generated
- the force transducer can’t tell or differentiate between active and passive forces produced
how do you account for passive force during the force-length experiment
stretch the muscle then measure the force before stimulation to get the passive tension
draw the force velocity relationship and explain it
what were the 2 methods for the force-velocity experiment
constant velocity and constant force
what was the constant velocity method in the f-v experiment
stimulate muscle and then shorten or lengthen the muscle at a constant velocity and re cord the force required to produce this shortening or lengthening
what is the constant force method for the force velocity experiment
stimulate muscle and then rapidly decrease or increase the force to a constant level and record the subsequent velocity of shortening or lengthening
how would the axis work for the force, length and velocity graph
force on y
sarcomere length on x
velocity on z
force is dependent on the…
instantaneous velocity and length of a muscle
true or false just because a joint is being held isometrically it does not mean the muscle isn’t changing length
true since the tendon is getting longer, muscle is shortening
what is the primary determinant of muscle function
how muscle fibers (sarcomeres) are arranged within the muscle
what are the three aspects of muscle function
how fast it can shorten or lengthen
how much force a muscle can produce
how fast muscle can contract
sarcomeres arranged in parallel ____ ______
add force
sarcomeres arranged in series _____ ______
add length
what is muscle force proportional to
physiological cross sectional area
what is the PCSA and what does it represent
physiological cross sectional area
= the total number of sarcomeres in parallel
muscle _____ is proportional to fibre length
excursion
what is muscle excursion
range of motion = how big of a length change is proportional to fiber length
what does fiber length represent
total number of sarcomeres in series
maximum contractile velocity is proportional to
fiber length
muscles with larger fibers have _____ ROM and generate force at ____ velocities
greater and higher
if you have 2 muscles one with a big PSCA the other has a lower PSCA what does it tell us
larger = can generate higher force
smaller = can generate force at high velocities
how does human movement occur
through generation of moments and angular accelerations at a joint
what would happen if humans didn’t have moment arms
couldnt generate movement
how does muscle hypertrophy affect PCSA
increases
how does muscle atrophy affect PCSA
decreases
what will larger moment arms allow for
greater ranges of motion (greater ranges of length change)
what is another word for moment
torque
muscles that start off shorter but have longer moment arms will
travel farther distance
larger length over time =
higher velocities
what is a negative thing about larger moment arms
higher likely hood a muscle will reach a more compromised point
true or false moment arms are constant
false
how are moment arms not constant
moment arms don’t usually change linearly but changes lengths in different positions of extension and flexion
why is it difficult to predict moment arms
they are changing drastically during ROM so they don’t have a linear fashion
