Muscle Fiber Types Explained: Type 1 vs. Type 2a vs. Type 2x
Type 1 -Slow Twitch (slow twitch speed/ slow rate of force development)
* Small, red
* Recruited first in response to action potential
* Slow nerve conduction
* HIGHLY fatigue resistant (oxidative) good for endurance – high aerobic enzyme content
* Low Myosin ATPase (low contraction speed)
* Low power
* HIGH capillary & mitochondrial density
* Cross country, marathon
Type IIa
* Medium, white/red
* Larger motor units
* Fast contract/relax speed and nerve conduction velocity, intermediate power
* More anaerobic enzyme content
* Intermediate capillary and mitochondrial density
* Low myoglobin
Type IIx
* Largest motor units
* Largest diameter fiber, white
* High recruitment threshold
* Fast conduction and contraction
* Low fatigue resistance/ endurance
* High force and power
* Low capillary / mitochondrial density
* Large fibers
* Sprint, weightlifting
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0:00
0:06 Intro
0:29 Muscle Structure
1:05 Motor Units and Mosaic Distribution
2:15 Size Principle
3:30 Type I Fibers
5:59 Type IIa Fibers
8:52 Type IIx Fibers
10:46 Muscular Adaptations
12:00 Detraining
13:20 Muscle Fiber Hypertrophy
14:20 Myosin Isoform
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