Which of the following exercises is NOT considered an open-chain exercise?

Open-chain exercises are defined by movements where the distal segment of the limb (like the hands or feet) moves freely in space and is not fixed to a surface. This type of exercise typically isolates a specific muscle group and allows for more controlled movements.

In this context, the push-up is indeed not an open-chain exercise. During a push-up, the hands remain fixed on the ground while the body moves in and out of a plank position. This stability at the hands means that the lower body can freely move, which shifts the dynamics of the exercise away from being classified as an open-chain activity. In fact, the push-up is considered a closed-chain exercise because the feet and hands are both in contact with a surface, thereby stabilizing the body and engaging multiple muscle groups simultaneously.

On the other hand, exercises like the leg extension, squat, and pull-up involve certain characteristics of open-chain activities. The leg extension isolates the quadriceps with the lower leg moving freely. In a squat, while the feet are grounded, the movement primarily involves the hips and knees flexing and extending, where the load is primarily on the legs, but since this involves support through the lower body while the torso is free to move, it's often categorized differently depending on