Endurance training typically leads to which muscular adaptation related to mitochondria and fiber size?

Endurance training typically leads to which muscular adaptation related to mitochondria and fiber size?

• A. Endurance training increases mitochondrial density without large increases in fiber size.
• B. Endurance training increases mitochondrial density with large fiber hypertrophy.
• C. Endurance training decreases capillary density.
• D. Endurance training causes large hypertrophy of fibers.

Answer: (A)

Endurance training boosts the muscle’s ability to produce energy aerobically by increasing mitochondrial biogenesis, so more mitochondria accumulate inside each muscle fiber. This rise in mitochondrial density enhances the fiber’s oxidative capacity, allowing sustained activity over longer periods. Because endurance work relies on repeated, lower‑intensity contractions rather than heavy lifting, the stimulus for growth in muscle fiber size isn’t strong, so fiber cross-sectional area tends to stay about the same or increase only modestly. In short, endurance training increases mitochondrial density while not driving large fiber hypertrophy.

Endurance training boosts the muscle’s ability to produce energy aerobically by increasing mitochondrial biogenesis, so more mitochondria accumulate inside each muscle fiber. This rise in mitochondrial density enhances the fiber’s oxidative capacity, allowing sustained activity over longer periods. Because endurance work relies on repeated, lower‑intensity contractions rather than heavy lifting, the stimulus for growth in muscle fiber size isn’t strong, so fiber cross-sectional area tends to stay about the same or increase only modestly. In short, endurance training increases mitochondrial density while not driving large fiber hypertrophy.