Chapter 21 Outline
Muscle Phenotypes
- Power output determines a muscle’s contractile performance, and changes in response to use and disuse
- Endurance training elicits changes in fiber type, increased capillary density, and increased mitochondrial density
- BOX 21.1 In Endurance Training, VEGF Production Precedes Angiogenesis, and Angiogenesis Precedes Changes of Fiber Type
- Resistance training causes hypertrophy and changes in fiber type
- Both resistance-trained and endurance-trained muscles continue to remodel during taper
- Combined resistance and endurance training can improve performance
- Hypertrophy also occurs in cardiac muscles
Atrophy
- Humans experience atrophy in microgravity
- Disuse influences the fiber-type composition of muscles
- Muscles atrophy with age
- Some animals experience little or no disuse atrophy
- BOX 21.2 No Time to Lose
Regulating Muscle Mass
- Myostatin
- The PI3K–Akt1 pathway