Final answer:
Skeletal muscle adaptations are determined by the type of training, with endurance exercises impacting slow-twitch fibers and strength training causing hypertrophy. Lack of muscle use leads to atrophy.
Step-by-step explanation:
Skeletal muscle adaptations and the functional consequences of these adaptations are determined by the type of training. When muscles undergo endurance exercise, the slow-twitch fibers, or Type I fibers, are predominantly used. Through training, these fibers become more efficient at aerobic metabolism, producing more mitochondria and myoglobin. In contrast, muscles also adapt through hypertrophy when subjected to strength training, which increases the diameter of muscle fibers due to an increase in structural proteins like myofibrils and sarcomeres.
Conversely, a lack of muscle use can lead to muscle atrophy, where there is a loss of myofibrils and sarcomeres, causing muscles to decrease in mass and strength. Muscle function and appearance are significantly affected by the specifics of training regimes, such as frequency, intensity, and duration. Therefore, a balanced approach is necessary to optimize muscle adaptations while minimizing the risk of overuse injuries, such as stress fractures and tendon inflammation.