Do Heavy Leg Presses Hurt Your Knees?

The leg press is a compound exercise that works most of the muscles in the lower body. The joint with the greatest range of motion during the press is the knee, an area of the body that is prone to stress injury. As with any weight-training exercise, the more weight you use, the higher your risk of joint injury. However, leg presses that are performed correctly with the proper equipment are not exceedingly likely to hurt your knees during the exercise.

  1. Leg Press Form

    • The form of the leg press has two phases -- eccentric and concentric. The concentric phase occurs first, when you press the foot platform upward against the pull of gravity. The eccentric phase is the second part, when you control the weight as you return it back to starting position. The press engages the quadriceps, hamstrings, calves and gluteal muscles. If you feel strain in your lower back, adjust your position on the leg press machine so the stress of the weight is on your leg muscles.

    Knee Impact

    • The knee is the primary joint in motion during the leg press. During the concentric phase, your knees extend as your upper and lower legs push the weight upward. By making sure you don’t lock your knees at the top of the motion -- between the concentric and eccentric phases -- you drastically reduce the chance of knee injury. When the knee joint is locked, it absorbs the stress of the heavy weight as you keep it in position, rather than your leg muscles. Also, while heavy weight alone won’t necessarily injure your knees, this is only true if it's an amount of weight that your leg muscles can handle. For the average person, you can safely leg press your body weight plus 20 percent. Going extremely heavy, even if you don’t lock your knees, risks injury to the knee joint.

    Equipment Variations

    • The type of leg press machine you use also plays a factor in injury risk. For example, machines that have you seated with your back to the ground, so that you push the weight directly against the pull of gravity, are more likely to cause injury. The 45-degree leg press sled requires you to push the weight at an angle to the ground, reducing the impact on your knees. Other machines that use levers and stacked weight require that you press the platform laterally, parallel to the ground. This configuration offers the least risk for the knees, but limits how much weight you can press.

    Rest

    • Another consideration for preventing knee injuries from heavy leg presses is recovery time after lifting. Just as your muscles need at least a day in between workouts to recover, so to do your joints, ligaments and tendons. Avoid working out the lower body on consecutive days, and also avoid activities that impact the knees following a leg-press workout. These include running on hard surfaces, martial arts, most sports, and activities like moving boxes and yard work.