Lecture 3: Muscle Fiber Types and Recruitment Flashcards
peak force is proportional to ____
cross sectional area
the cross sectional area in human fibers is …
type 2x = type 2a = type 1
motor unit
the smallest functional unit of muscle
characteristics of a motor unit
- ALL fibers in a motor unit are of the same type
- ALL fibers in a motor unit contract together when the brain ‘recruits’ the motor unit
Type 2x or 2b: Fast twitch Fatigable
300-800 fibers per motor unit
- greatest muscle twitch force
- fastest contraction velocity
- fatigue easily
Type 2a: Fast twitch fatigue resistant
- 300-800 fibers per motor unit
- medium muscle twitch force
- fast contraction velocity
- fatigue resistant
Type 1: Slow twitch
10-200 fibers per motor unit
- small twitch force
- slow contraction velocity
- very fatigue resistant
- typically found in postural muscles*
motor unit force is equal to ________
the sum of the forces of each muscle fiber in the motor unit
fewer fibers means less _____ for the motor unit
fewer fibers means less force for the motor unit
peak force is determined by
the total number of crossbridges in PARALLEL
peak or maximal velocity (Vo or Vmax) is a function of the ______ __ ___ ________ by the myosin ATPase.
rate of ATP hydrolysis by the myosin ATPase
what are the two important proteins on the myosin head?
- binding site where it attaches to actin
2. myosin ATPase
function of myosin ATPase
breaks down ATP and takes the energy to store it in the crossbridge of the myosin head for contraction
power
rate at which a muscle can perform work
Power equation
power= force x velocity
differences in power among fiber types is due to ?
velocity
what is the effect of endurance training on power, especially of 2a fibers?
endurance training reduces power
from the graph in the notes, an athlete with more type 2 fibers
- peak power is _____
- peak power occurs at a ______ contraction velocity.
peak power is greater
peak power occurs at a higher contraction velocity
for light to moderate exercise which muscle fiber type is recruited?
type 1 motor units
SLOW TWITCH
when are fast twitch type 2x or 2a muscle fibers recruited?
fast twitch muscle fibers are recruited only at high force requirements that are close to maximum voluntary contraction or with fatigue.
as more motor units are recruited, they contribute progressively more force due to ________.
as more motor units are recruited, they contribute progressively more force, due to greater number of fibers/motor unit
what is the size principle
start off small or slow twitch then go to bigger as the force requirements go up
when 50% of the available motor units are recruited ______________
when 50% of the available motor units are recruited, only 20% of the maximum force is generated
the peak force generated by the quadriceps at the end of an incremental test to fatigue on a cycle ergometer to determine VO2 max is only ______% of the maximum voluntary contraction
25-30%
why is the relationship between the percent of pool of motor units recruited and force developed nonlinear?
because different motor units produce different forces
what would the relationship look like if ALL the motor units were the same size?
it would be a linear relationship or straight line because every motor unit contributes equally if they were the same size
what is fiber type distribution highly determined by?
genetics determines most of a persons fiber type
effects of endurance and resistance training on a type 1 fiber
endurance : no change to small 5-6% increase
resistance: no change
effects of endurance and resistance training on a type IIa fiber
endurance: no change
resistance: increase
effects of endurance and resistance training on a type IIx fiber
endurance: decrease
resistance: decrease
decreased muscle activity can reduce ____ and increase _______ fibers.
decreased muscle activity can reduce the % of slow twitch fibers and increase the % fast twitch fibers
