YMCA Level 2 Fitness Instructor Practice Test

The hamstrings are the prime movers during knee flexion because they are a group of muscles located at the back of the thigh, which includes the biceps femoris, semitendinosus, and semimembranosus. These muscles are specifically designed to facilitate the bending of the knee joint. When the knee bends, the hamstrings contract, pulling the tibia (shin bone) backward, which effectively decreases the angle between the thigh and the leg.

In contrast, the quadriceps, located at the front of the thigh, are responsible for knee extension, which is the opposite movement of flexion. The gastrocnemius, while it plays a role in knee flexion, is primarily a muscle used for ankle movement and only assists in bending the knee. The tibialis anterior is responsible for dorsiflexion of the ankle, thus having no direct role in knee flexion. Understanding the roles of these muscles helps in comprehending basic leg movements and enhances the effectiveness of training programs for strength and rehabilitation.