Muscle Energy Systems

Skeletal muscle fibers can be classified based on their:

• Color

• Speed

• Fatigability

• Myosin Isoforms

Select the main types of skeletal muscle fibers

• slow oxidative

• fast oxidative

• fast glycolytic

• slow glycolytic

Fast fibers hydrolyze ATP approximately twice as quickly as slow fibers

• True

• False

"White fibers" or low myoglobin

• Fast-twitch muscle fibers

• Slow twitch muscle fibers

"Red fibers" or high myoglobin

• Fast-twitch muscle fibers

• Slow-twitch muscle fibers

Slow-contracting muscle fiber is characterized by

• low myosin ATPase activity

• High capacity for ATP production via oxidative phosphorylation

• dense capillary network

• high levels of intracellular myoglobin

• function for long periods without fatigue

Fast-contracting muscle fiber 2a is characterized by

• higher myosin ATPase activity than type 1

• moderate capacity for ATP production via oxidative phosphorylation

• somewhat dense capillary network

• Moderate levels of intracellular myoglobin

• more fatigue resistant than type IIb fibers

Fast-contracting muscle fiber type IIb is characterized by

• higher myosin ATPase activity than type 1 fibers

• lower capacity for ATP production via oxidative phosphorylation than red fibers; muscle fatigue occurs sooner

• sparser capillary network

• almost no intracellular myoglobin

• quick fatigue rate

Type IIb fibers can not be converteed into type IIa fibers via resistance training.

• True

• False

Contraction Time: Slow

Resistance to fatigue: High

Max duration: Hours

Mitochondrial density:High

Activity: Aerobic

• Type 1

• Type 2a

• Type 2x

• Type 2b