Age & Muscle

Aging (> 65 years): Muscle Changes (Males & ? Females)¹

• Type 2 muscle fibers
  • Reduced size
  • Fewer associated satellite cells
• Mitochondrial
  • SDH+ muscle fibers: More frequent
  • COX- muscle fibers: More frequent
• Nuclei
  • Shape: More irregular
• Strength correlations
  • Muscle mass: Correlates with
    • Bioavailable testosterone levels
    • Muscle fiber size
  • Type 2 muscle fiber size
  • NOT: Age per se

Children: Muscle Features

• Muscle fibers
  • Size: Small Diameters
    • 3 months: 12 μM
    • 1-2 years: 18 μM
    • 5-10 years: 30 μM
    • 10-15 years: 35 to 45 μM
    • Adult: 50 to 60 μM
    • General: Type 2 fibers 5% smaller than type 1
  • Types: More 2C fibers in 1st year
• Nuclei
  • Larger in young children
• Capillaries
  • Lower #/Muscle fiber
  • Many muscle fibers with no adjacent capillary: 1st 3 years