Dr. Laskowski: The leg press is an exercise you can do with a weight machine to work a variety of muscles in the lower body. Specifically, the leg press targets the quadriceps muscles in the front of the thighs, the gluteal muscles in the buttocks, the hamstring muscles in the back of the thighs, and the calves, all in an integrated fashion. Since the leg press works several muscles at once, it's an especially efficient way to strengthen your lower body.
Nicole Campbell: To do a seated leg press with a weight machine, start by sitting on the weight bench. Place your feet on the platform about shoulder-width apart, and grasp the handles with your hands. Slowly push the platform away with your legs. Keep your feet firmly planted on the platform and stop just short of full knee extension. Then slowly return to the starting position. You'll feel tension in the muscles in your legs and buttocks.
When you're doing the leg press, stop just short of full knee extension when you push on the platform. When you return to the starting position, do not let your thigh drop below the level of 90 degrees at the knee. If you dip your thighs too low, you may hurt your knees. It's also important to allow your kneecaps to follow the path of your feet during the exercise. Bringing your knees too close together could also injure your knees.
For most people, one set of 12 to 15 repetitions is adequate.
Remember, for best results, stop just short of full knee extension when you push on the platform. When you return to the starting position, do not let your thigh drop below the level of 90 degrees at the knee and keep your movements smooth and controlled.