Muscular System and Skeletal System Practice Test

Resistance training drives muscle fiber hypertrophy by stressing the fibers that generate the most force. Fast-twitch, Type II fibers are recruited when you lift heavy loads and push for high force, and they have a greater capacity to add contractile proteins in response to overload. That makes them the primary drivers of increases in cross-sectional area with resistance training. Type I fibers are slow-twitch and more geared toward endurance and oxidative adaptations, so they don’t hypertrophy as much under typical resistance-training programs. While some hypertrophy can occur in Type I fibers with certain protocols, the most substantial CSA increase comes from Type II fibers.