AFAA Personal Trainer Certification Practice Exam

Which statement accurately describes muscle contraction according to the sliding filament theory?

1. Muscle fibers lengthen during contraction

2. Thick and thin filaments slide past one another

3. Muscle contraction is solely driven by calcium ions

4. Muscles contract based on neural impulses only

The correct answer is: Thick and thin filaments slide past one another

The statement that accurately describes muscle contraction according to the sliding filament theory is that thick and thin filaments slide past one another. This theory explains how muscles contract at the microscopic level. During contraction, the myosin (thick filaments) pull the actin (thin filaments) toward each other, which shortens the sarcomere—the basic unit of muscle tissue—resulting in muscle contraction. This sliding mechanism is facilitated by cross-bridges formed during the interaction between myosin heads and actin filaments, powered by ATP. In contrast, the other statements do not accurately represent the sliding filament theory. Muscles do not lengthen during contraction; instead, they shorten. While calcium ions play a crucial role in muscle contraction by enabling the interaction between actin and myosin, they are not the sole drivers; ATP is also essential. Regarding neural impulses, they are important for the initiation of muscle contraction but do not describe the mechanical process that occurs at the filament level. Thus, the correct answer provides a clear understanding of the fundamental mechanism behind muscle contraction.