week 11 Flashcards
when do you get maximum force
at zero velocity
when do you get maximum velocity
at zero force
the slower the concentric contraction the _________ force produced
more
what type of contraction then lets us create maximum force
isometric contraction
if a muscles purpose is to contract what does it mean
it becomes less and less capable of what it needs to do which is produce force
what is the power equation
F x V = power
what is power
the rate of doing work, or the rate of change in energy
units of power
N*m/s or J/s or watts
when do you achieve max power
at moderate velocity or moderate force
when is no power produced
when velocity is zero or at maximum
what does power account for
both the amount of movement produced by a force or movement and also the time it takes to do it
what is work in words (2 definitions)
flow of energy from one body to another
amount of movement produced by a force or moment
what is work in terms of equations (3)
= Fd or Mtheta
= delta E
= delta PE + delta KE + delta SE
what is the work-power relationship
sum of all power over delta time = work
when would be an example of where you want your muscles to contract at maximum velocity
sprinting
how do we generate the ground reaction forces to move our body down a track
- push backwards on the ground (newtons 3rd law)
- brain sends aMN to use rate code and recruitment causing muscles to generate a force
- muscle has to pass a force through the tendon to the skeleton
- force - mass x acceleration
- muscles moment arm causes angular acceleration
in lab we measured vertical force what are the steps we would need to calculate power simply from this one piece of information gathered by the force plate
(vertical force –> vertical velocity)
1. need to know the subjects mass
2. use newtons second law ( )
3. we know force and mass we must now find acceleration but it will still account for gravity
4. we don’t want gravity so we subtract 9.81 to give us the acceleration of the COM
5. integrate this with respect to time to get power
6. calculate vertical acceleration
angular equivalent
power = moment * angular velocity
positive power = ____ work
positive
negative power = ___ work
negative
what does muscle work/ muscle power also tell us
the type of contraction occuring
what would the contraction be of a positive muscle power
concentric contraction
what would a negative muscle power = for a contraction
eccentric
what contraction type would give 0 power and why
zero angular acceleration so no matter the moment power = 0W and the contraction type is isometric
how is energy moving in a positive muscle power
energy generated by the muscle and is passed to the segment
how is energy moving when there is negative muscle power
energy absorbed by the muscle from the segment
what is mechanical efficiency
mechanical work / mechanical cost
are human movements efficient or inefficient
inefficient
what is mechanical work comprised of
external and internal components
what causes inefficient movements
- co-contraction or co-activation
- isometric contractions against gravity
- simultaneous generation of energy at one joint and absorption at another
- jerky movements
what is co-contraction
antagonist muscles active which is essentially fighting against the agonist muscle
is co-contraction good or bad
good for stability of a joint in a movement to ensure there is enough energy around the joint to protect it but once again it is inefficient because the muscles are working way harder and there are higher compressive forces
what is an example of isometric contractions against gravity
cerebral palsy where the person has crouched knees so an increase in quadricep activity occurs and remaining in this constant state
explain generation at joint and absorption at another
similar idea to co-contraction, with positive and negative work being cancelled out
explain how jerky movements are metabolically inefficient
smooth movements allow for energy exchange where as jerky movements require generation ad absorption of energy for each ‘jerk’
