The leg press is an exercise performed on a weight resistance machine. As a compound movement, your hip and knee joints flex, or bend, and extend to perform the exercise. Some leg press machines place your body in a declined position, with your head lower than your lower body. Other leg machines place your body in a horizontal position. Resistance can be in the form of weighted plates that are placed on the machine or a weight stack that uses a pin for resistance selection. While your hips and legs bear most of the resistance, the leg press is a safer alternative to the barbell squat, requiring your whole body to bear the weight.
The leg press exercise has two phases of movement. At the start of the exercise, your knees are bent at 90 degrees and your hips are bent at 90 degrees. Your feet are flat against the platform. As the exercise begins, your knees extend, pushing the platform away from your body until your legs are straight. Hold the extension and then bend your knees, bringing your legs slowly back to the starting position.
Your quadriceps muscles contract to extend your knees. The quadriceps are a group of four muscles including your rectus femoris, vastus medialis, vastus lateralis and vastus intermedius. The quadriceps are in the front of your thigh, starting from your hip and ending just below your knees. Your hamstrings contract as you bend your knees to slow down the movement of the resistance. Your hamstring group consists of your biceps femoris, semitendinosus and semimembranosus. These muscles are in the back of your thigh, starting from your hip and ending just below your knee. Your buttocks assist in the movement of extending your legs and stretch as you bend your knees. The buttocks group consists of your gluteus maximus, gluteus medius and gluteus minimus.
The leg press exercise increases lower body muscular strength and muscular endurance. For strength gains, use heavier weight, completing three or four sets of six to 10 repetitions. For endurance gains, use lighter weight, completing three or four sets of 12 to 15 repetitions. The leg press is a relatively safer alternative for strength training because your spine and upper body is supported throughout the exercise.
Unlike squats, your hips do not fully extend when performing the leg press. This limits strength and endurance gains for your hip flexors and buttocks muscles. The leg press exercise is not recommended as part of a conditioning program for improving explosive athletic movements such as the vertical jump. Squats would be a more effective alternative.