Final answer:
When a weightlifter exerts muscles to 75% of their maximum tension, it stimulates muscle fibers to develop new filaments of actin and myosin, which leads to hypertrophy, or enlargement of the muscle fibers. The correct answer is B. muscle fibers developing new filaments of actin and myosin.
Step-by-step explanation:
A weightlifter's intense muscle exertion leading to muscle growth involves hypertrophy due to the accumulation of structural proteins, such as actin and myosin filaments, rather than an increase in muscle fibers or transformation into other types of muscle. This process results in the enlargement of muscles, which is essential for bodybuilders and athletes who require powerful muscle contractions. Therefore, the correct answer to the question is B. muscle fibers developing new filaments of actin and myosin.
Resistance exercises typically utilize fast glycolytic (FG) fibers that are prone to hypertrophy. These fibers have a high capacity for ATP hydrolysis and cross-bridge formation leading to powerful contractions. Unlike endurance exercises that enhance slow oxidative (SO) fibers, resistance exercises cause the muscles to increase in size by adding more myofibrils. It is also worth noting that when muscles are not used or are used less frequently, the process of atrophy occurs, resulting in muscle mass decrease, but this is not directly relevant to the question posed by the student.