Muscle Fiber Type

What are the characteristics of a type 1 muscle fiber?

- high number of mitochondria - high resistance to fatigue - aerobic is the primary energy system - low ATPase activity - low Vmax (speed of shortening) - high efficiency - moderate specific tension

What are the characteristics of a type 2a muscle fiber?

- high/moderate number of mitochondria - high/moderate resistance to fatigue - anaerobic/aerobic energy systems - high ATPase activity - high Vmax (speed of shortening) - moderate efficiency - high specific tension

What happens to muscle fibers when there is detraining?

-decrease in % of type 1 fibers -increases in % of type 2a/x fibers

What are the characteristics of a type 2x fiber?

-low number of mitochondria -low resistance to fatigue - anaerobic as primary energy system - high ATPase activity - high Vmax (speed of shortening) - low efficiency - high specific tension

What motor neuron is paired with type 2a fibers and what are its characteristics?

a1 - large neuron size - fast conduction velocity - high recruitment threshold

What motor neuron is paired with type 1 fibers and what are its characteristics?

a2 - small neuron size - slow conduction velocity - low recruitment threshold

What is a way to determine fiber type and how is this done?

muscle biopsy -small piece of muscle is removed (muscle specific), then viewed under microscope

What is the size principle?

refers to the size of neural signal that must be present to enervate each fiber

What motor neuron is paired with type 2x fibers and what are its characteristics?

same as type 2a

What are the different muscle fiber types types?

slow twitch- type 1 Fast twitch- type 2A, type 2x

What is the average muscle fiber type distribution?

type 1- 50 % type 2a- 35% type 2x- 15%

What is the average MHC (myosin heavy chain) distribution for muscle fiber type? (ball state data)

type 1- 52% type 1/2a- 7% type 2a- 30% type 2a/2x- 11% type 2x- <1%

What colors are the different muscle fiber types under a microscope?

type 1- black type 2a- white type 2x- grey

Does muscle fiber type vary between people and athletes? And give some examples

yes -sprinters have higher type 2a/x fibers -long distance runners have higher type 1

Can training methods shift muscle fiber type?

yes 1. endurance training causes shift from fast twitch to slow twitch fibers 2. resistance training may causes shift to hybrid type 2A fibers