Do Heavy Leg Presses Hurt Your Knee?

Proper Weight

Choosing a weight based on your one rep maximum ensures you’re working within a range that will encourage muscle gains without traumatizing your knees. The one rep max, or 1RM, refers to the maximum weight you can move for a single repetition. To determine your 1RM start with a challenging weight and press out three to five repetitions. Keep adding weight in small increments until you can only squeak out one rep. Once you’ve determined your 1RM, calculate 80 to 90 percent of that as your weight for the days you want to press heavy. Power-lifters garner strength by working with explosive movements in a low rep range of as little as four to six reps, but true strength gains and increases in muscle mass occur more effectively at a range of eight to 12 reps.

Proper Form

Form is key to avoiding injury in any strength training movement. When tucking yourself in the leg press, make sure your feet are no less than hip width apart. Too narrow a stance strains the knees when moving heavy weight. A wider stance provides a more solid base for heavy weight. As the sled comes down and the knees bend, make sure the knees do not go past the toes at the bottom of the range of motion and that you maintain a slow and controlled movement. Be sure to push through the heels as you straighten the legs again and keep the knees aligned with the feet rather than letting them dip inwards or outwards. Keep the lower back against the back rest and avoid arching the back up as you straighten the legs to ensure the lower body does all the work and not the lower back.

Variation

Varying your workout is another way to make sure you keep you reap the benefits from lifting heavy but avoid injury. Changing up your workout between heavy weight and fewer rep’s and lighter weight and more rep’s is a great way to keep your muscles from getting bored with the exercise. Switching to lighter weight and increased rep’s will keep your muscle and strength gains while also giving your knees a break. Changing up your training focus and varying weight, repetitions, sets and tempo every three to four weeks can provide further strength gains and be safer on the knees than just lifting heavy exclusively.

Cautions

Any leg workout is best approached well warmed up with light cardio and stretching. However, if you have any pre-existing knee tweaks it may be natural to feel strain on the knees when lifting heavy. Be sure you have clearance from your physician for any strength training activity and be conservative with the leg press until you’re confident your knees can handle the weight. Be sure to allow your legs sufficient rest between sets -- as much as three to five minutes if you’re working with maximal loads and fewer reps -- and at least two days of rest between leg workouts.