ACSM Personal Trainer Certification Practice Exam 2025 - Free Personal Trainer Practice Questions and Study Guide.

The hamstrings are primarily responsible for knee flexion during running. This group of muscles, located on the back of the thigh, includes the biceps femoris, semitendinosus, and semimembranosus. When a runner lifts the leg during the recovery phase of the running stride, the hamstrings contract to bend the knee, allowing for efficient movement and preparation for the next step.

The rectus femoris, which is part of the quadriceps group located in the front of the thigh, primarily functions to extend the knee and is also involved in hip flexion but does not play a significant role in knee flexion. The tibialis anterior is mainly responsible for dorsiflexion of the foot, and the gastrocnemius crosses both the knee and ankle joints but predominantly acts to plantarflex the ankle when the foot is on the ground.

Therefore, the hamstrings are the key muscle group for knee flexion, making them crucial for running efficiency and stride mechanics. Understanding the function and role of these muscle groups is essential for recognizing proper biomechanics in physical activities like running.