Muscle design Flashcards
in a work loop, what is the net work per cycle
difference betweeen shortening work and lengthening work
what does it mean if the work loop is moving CCW
net work per cycle = positive
what does it mean if the work loop is moving CW
net work per cycle = negative
what are the different roles a muscle can have in vivo and what could their work loops show
motors - positive net work
brakes - shows hysteresis
springs
struts - large length change with minimal force and large change in force over short length change
can have different roles across different conditions / tasks
why is the activation rate of fast fibres important
can impact work per cycle across cycle frequencies
what is the difference in net work and cycle frequencies between fast and slow fibres
net work is higher from fast fibres
operating range of freqeuncies is higher in fast fibres
- fast fibres do more work
what is the activation of slow and fast fibres at a cycle frequency of 1 Hz
similar for both
- fast fibres reach peak activation and deactivate quicker
what is the force of slow and fast fibres at a cycle frequency of 1 Hz
higher and decreases faster in fast fibres
takes longer to get back to zero in slow fibres
- force peaks at slowest velocity (peak length - v=0)
- velocity is highest when the length crosses the x axis (where F=0)
what is the work loop of slow and fast fibres at a cycle frequency of 1 Hz
work per cycle = higher in fast fibres
faster decline in force from fast fibres (fast activation and deactivation)
both show CCW rotation (positive net work)
what is the activation of slow and fast fibres at a cycle frequency of 3 Hz
fast fibres activate and deactivate faster
don’t get to max activation in slow fibres at that speed
muscle is active during lengthening period
- mostly in slow fibres ^ because they can’t deactivate fast enough
(don’t want the activation during lengthening)
what is the force of slow and fast fibres at a cycle frequency of 3 Hz
slow fibres
- have high force during lengthening (eccentric)
fast fibres
- more force during shortening
- can activate and deactivate fast enough
what is the work loop of slow and fast fibres at a cycle frequency of 3 Hz
slow fibres = CW rotation = negative work loop cycle
- due to slow act/deact and high force during lengthening
fast fibres = CCW rotation = positive work loop cycle
what is the difference in longer muscles
longer muscle can produce force over a greater range of absolute lengths and at higher absolute velocities
what is the difference in muscles with a greater CSA
muscle with greater CSA will produce more absolute force
(ex: doubling CSA will double the max isometric force)
- max isometric stress is fairly constant across muscles of different sizes
what is the PCSA (physiological cross sectional area)
area perpendicular to the direction of the fibres
what is caused by greater pennation in muscles
results in greater PCSA
more fibres can be packed in parallel for a muscle with a given volume
- therefore more force produced
why does pennate muscle have a greater force
there are more benefits from the increase in PCSA than the decrease in cos(theta)
what is the architectural gear ratio
= muscle belly velocity / fibre velocity
what is the result of pennation angle increasing
fibres rotating to greater angles allows the fibres to contract slower relative to the muscle belly
- allows the fibres to produce more force (force-velocity relationship)
do parallel and pennate muscles have the same muscle belly velocity
yes - same muscle belly velocity
what is the difference between the parallel and pennate muscle fibre velocity
parallel fibres = same as the muscle belly velocity
pennate fibres = velocity is slower than the belly (can stay almost the same length during rotation)
what can larger pennation help mitigate
helps mitigate the effects of greater tissue inertia that comes with increases in muscle size
what occurs to other muscle variables when length increases 2x
length, velocity, acceleration = 2x increase
force = 4x increase
volume, mass = 8x increase
what does larger muscle size result in
results in larger mass relative to force that is available to accelerate it
- less work can be done per cycle (shifts work looop down)
- net force decreases
what is the difference in work penalty for larger muscles in parallel vs pennate
parallel = greater work penalty for larger mass
pennate = lower work penalty for larger mass
