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Exercise Physiology
Muscle Structure and Function: Fiber Type Comparison
Question | Answer | Type IIa | Type IIx |
---|---|---|---|
Type Label | Type I | Type IIa | Type IIx |
Twitch Label | Slow Twitch (ST) | Fast Twitch a (FTa) | Fast Twitch (FTx) |
Energy Source Label | Slow oxidative (SO) | Fast oxidative/glycolytic (FOG) | Gast glycolytic (FG) |
oxidative copacity | high | mod high | low |
glycolytic capacity | low | high | highest |
contractile speed | slow | fast | fast |
fatigue resistance | high | mod | low |
motor unit strength | low | high | high |
fibers per motor neuron | <300 (low threshold) | >300 (high threshold) | >300 (high threshold |
motor neuron size | smaller | larger | larger |
motor neuron conduction velocity | slower | faster | faster |
contraction speed (ms) | 110 | 50 | 50 |
type of myosin ATPase | slow | fast | fast |
SR development | low | high | high |
Type I fibers during exercise | high aerobic endurance, maintain for prolonged periods, require O2 for ATP production, recruited for low intensity aerobic exercise and daily activities, efficiently produce ATP from fat and carb | ||
Type II fibers during exercise in general | fatigues quickly (poor aerobic endurance). produce ATP anaerobically. | fatigues quickly (poor aerobic endurance). produce ATP anaerobically. | |
Type IIa fibers during exercise | produce more force, fatigue faster than type I. used for short, intense exercise such as 1600m run | seldom used for everyday activities. used for short, explosive sprints (100m) |