Lecture 3: Muscle Fiber Types and Recruitment

Question 1

peak force is proportional to ____

Answer 1

cross sectional area

Question 2

the cross sectional area in human fibers is …

Answer 2

type 2x = type 2a = type 1

Question 3

motor unit

Answer 3

the smallest functional unit of muscle

Question 4

characteristics of a motor unit

Answer 4

• 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

Question 5

Type 2x or 2b: Fast twitch Fatigable

Answer 5

300-800 fibers per motor unit

• greatest muscle twitch force
• fastest contraction velocity
• fatigue easily

Question 6

Type 2a: Fast twitch fatigue resistant

Answer 6

• 300-800 fibers per motor unit
• medium muscle twitch force
• fast contraction velocity
• fatigue resistant

Question 7

Type 1: Slow twitch

Answer 7

10-200 fibers per motor unit

• small twitch force
• slow contraction velocity
• very fatigue resistant
• typically found in postural muscles*

Question 8

motor unit force is equal to ________

Answer 8

the sum of the forces of each muscle fiber in the motor unit

Question 9

fewer fibers means less _____ for the motor unit

Answer 9

fewer fibers means less force for the motor unit

Question 10

peak force is determined by

Answer 10

the total number of crossbridges in PARALLEL

Question 11

peak or maximal velocity (Vo or Vmax) is a function of the ______ __ ___ ________ by the myosin ATPase.

Answer 11

rate of ATP hydrolysis by the myosin ATPase

Question 12

what are the two important proteins on the myosin head?

Answer 12

1. binding site where it attaches to actin

2. myosin ATPase

Question 13

function of myosin ATPase

Answer 13

breaks down ATP and takes the energy to store it in the crossbridge of the myosin head for contraction

Question 14

power

Answer 14

rate at which a muscle can perform work

Question 15

Power equation

Answer 15

power= force x velocity

Question 16

differences in power among fiber types is due to ?

Answer 16

velocity

Question 17

what is the effect of endurance training on power, especially of 2a fibers?

Answer 17

endurance training reduces power

Question 18

from the graph in the notes, an athlete with more type 2 fibers

1. peak power is _____
2. peak power occurs at a ______ contraction velocity.

Answer 18

peak power is greater

peak power occurs at a higher contraction velocity

Question 19

for light to moderate exercise which muscle fiber type is recruited?

Answer 19

type 1 motor units

SLOW TWITCH

Question 20

when are fast twitch type 2x or 2a muscle fibers recruited?

Answer 20

fast twitch muscle fibers are recruited only at high force requirements that are close to maximum voluntary contraction or with fatigue.

Question 21

as more motor units are recruited, they contribute progressively more force due to ________.

Answer 21

as more motor units are recruited, they contribute progressively more force, due to greater number of fibers/motor unit

Question 22

what is the size principle

Answer 22

start off small or slow twitch then go to bigger as the force requirements go up

Question 23

when 50% of the available motor units are recruited ______________

Answer 23

when 50% of the available motor units are recruited, only 20% of the maximum force is generated

Question 24

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

Answer 24

25-30%

Question 25

why is the relationship between the percent of pool of motor units recruited and force developed nonlinear?

Answer 25

because different motor units produce different forces

Question 26

what would the relationship look like if ALL the motor units were the same size?

Answer 26

it would be a linear relationship or straight line because every motor unit contributes equally if they were the same size

Question 27

what is fiber type distribution highly determined by?

Answer 27

genetics determines most of a persons fiber type

Question 28

effects of endurance and resistance training on a type 1 fiber

Answer 28

endurance : no change to small 5-6% increase

resistance: no change

Question 29

effects of endurance and resistance training on a type IIa fiber

Answer 29

endurance: no change
resistance: increase

Question 30

effects of endurance and resistance training on a type IIx fiber

Answer 30

endurance: decrease
resistance: decrease

Question 31

decreased muscle activity can reduce ____ and increase _______ fibers.

Answer 31

decreased muscle activity can reduce the % of slow twitch fibers and increase the % fast twitch fibers