types of skeletal muscle fibers

red muscle fibers

Skeletal muscle fibers that have a high myoglobin content. -appear darker (the dark meat in chicken legs and thighs) -contain more mitochondria and are supplied by more blood capillaries

Based on all these structural and functional characteristics, skeletal muscle fibers are classified into three main types:

1. slow oxidative fibers. 2. fast oxidative-glycolytic fibers. 3. fast glycolytic fibers.

Skeletal muscle fibers: Fast oxidative- glycolytic fibers. (FOG)

-intermediate in diameter. -large amounts of myoglobin and many blood capillaries, dark red appearance. -generate considerable ATP by aerobic cellular respiration. -which gives them a moderately high resistance to fatigue. -intracellular glycogen level is high, so they also generate ATP by anaerobic glycolysis. -are "fast" because the ATPase in their myosin heads hydrolyzes ATP three to five times faster than the myosin ATPase in SO fibers. -twitches of FOG fibers reach peak tension more quickly than those of SO fibers but are briefer in duration—less than 100 msec. -contribute to activities such as walking and sprinting.

Skeletal muscle fibers: Fast Glycolytic Fibers. (FG)

-largest in diameter and contain the most myofibrils. -can generate the most powerful contractions. -low myoglobin content, relatively few blood capillaries, and few mitochondria. -appear white in color. -large amounts of glycogen and generate ATP mainly by glycolysis. -large size and their ability to hydrolyze ATP rapidly, FG fibers contract strongly and quickly. -The fast‐twitch fibers are adapted for intense anaerobic movements of short duration, such as weight lifting or throwing a ball. -they fatigue quickly. -Strength training programs that engage a person in activities requiring great strength for short times increase the size, strength, and glycogen content of fast glycolytic fibers.

Skeletal muscle fibers: Slow oxidative fibers. (SO)

-smallest in diameter. -least powerful. -dark red- large amounts of myoglobin and many blood capillaries. many large mitochondria. -generate ATP mainly by aerobic cellular respiration. - "slow" because the ATPase in the myosin heads hydrolyzes ATP relatively slowly and the contraction cycle proceeds at a slower pace than in "fast" fibers. -slow speed of contraction. -Their twitch contractions last from 100 to 200 msec, and they take longer to reach peak tension. -resistant to fatigue and are capable of prolonged, contractions for many hours. -adapted for maintaining posture and for aerobic, endurance‐type activities such as running a marathon.

how to skeletal muscle fibres vary?

-they vary in structure and function. -Skeletal muscle fibers contract and relax at different speeds. -vary in which metabolic reactions they use to generate ATP. -Vary in how quickly they fatigue. -For example, a fiber is categorized as either slow or fast depending on how rapidly the ATPase in its myosin heads hydrolyzes ATP.

white muscle fibers

-those that have a low content of myoglobin are called white muscle fibers and appear lighter (the white meat in chicken breasts).