Which of the following muscle groups are concentrically involved during the upward movement phase of the lead leg of the step-up exercise?

During the upward movement phase of the step-up exercise, the quadriceps play a key role in the concentric phase. As the lead leg steps up onto the elevated surface, the quadriceps contract to extend the knee, allowing for effective upward propulsion. This contraction supports the body’s weight and facilitates the movement by straightening the leg, which is essential for stabilizing and powering the upward motion. The quadriceps are primarily responsible for knee extension, making them the dominant muscle group engaged as you step up.

In contrast, while the other muscle groups mentioned have roles in various movements, they do not predominantly act concentrically during the upward phase of the step-up. The hamstrings assist in knee flexion and hip extension, the gastrocnemius is primarily involved in ankle plantarflexion rather than knee extension, and the gluteus maximus aids in hip extension. However, it is the quadriceps that are most specifically and concentrically activated during this particular action, making them the correct choice for this question.