AFAA Personal Trainer Certification Practice Exam

What does the sliding filament theory describe?

1. Muscle recovery after exertion

2. Muscle soreness after exercise

3. Muscle shortening during contraction

4. Muscle hypertrophy over time

The correct answer is: Muscle shortening during contraction

The sliding filament theory describes the process of muscle contraction at the molecular level, specifically how muscle fibers shorten when they contract. According to this theory, muscle contraction occurs as the thin filaments (actin) slide over the thick filaments (myosin) within the sarcomeres, which are the basic functional units of muscle tissue. When a muscle fiber is stimulated by a nerve impulse, calcium ions are released, allowing myosin heads to bind to actin filaments. This interaction pulls the actin toward the center of the sarcomere, leading to overall shortening of the muscle fiber. This concept is fundamental to understanding how muscles generate force and perform work, emphasizing the mechanical movement of muscle fibers. Other options, such as muscle recovery or soreness, relate to different physiological processes that occur post-exercise or during training adaptations and do not specifically address the contraction mechanism as the sliding filament theory does. Muscle hypertrophy, on the other hand, refers to the increase in muscle size over time due to repeated tension or mechanical overload, which also does not pertain directly to the contraction process described by the sliding filament theory.