Leg curls can cause or exacerbate knee pain because they isolate the hamstrings and only use them to bend the knees. In reality, the hamstrings are responsible for much more than bending your knees. They’re also key for flexing and extending your hips. To avoid knee pain, choose hamstring exercises that incorporate natural hip flexion. Examples of these exercises include Romanian deadlifts, good mornings, single-leg deadlifts, and nordic hamstrings.
Why Are Leg Curls Damaging to Your Knees?
Leg curls are not proven to destroy your knees and they can still provide benefits to some athletes. However, it should be noted that leg curls carry a higher risk of knee injury compared to other hamstring exercises. This is due to the fact the leg curl uses the hamstring to perform only one function—bend and straighten the knee. Other hamstring exercises focus less on knee flexion and activate the hamstrings by also using them to drive the hips forward.
- Leg curls are not scientifically proven to injure your knees, but there is some evidence they cause knee stress.
- Leg curls force the hamstring to work only to bend the knee—this places shear force on the knee joint.
- Most alternative hamstring exercises focus less on knee flexion and more on using the hamstrings to flex the hips—this reduces the chance of knee injury.
Due to the fact the leg curl focuses on using the hamstring for knee flexion, more shear stress is placed on the knee. This creates a higher risk of knee injury. The leg curl also does not use the hamstring as effectively as other exercises. So, avoiding leg curls is a win-win for preventing injury and building stronger hamstrings.
4 Exercises You Should Do Instead of Leg Curls
In order to avoid the leg curl machine and keep your knees as healthy as possible, it’s important to prioritize exercises that use a natural range of motion and engage the hamstring muscles for both knee flexion and hip flexion. The following exercises are better than leg curls at working your hamstrings. Add these to your work to build more toned, stronger legs at the same time you avoid injury.
Romanian deadlifts—commonly known as RDLs—are an incredible free weight exercise that targets the hamstrings (the same muscle the leg curl is designed to activate). To perform this lift:
- Stand with your feet hip-width apart.
- Grip a barbell (or dumbbells) overhand with your hands just outside your legs.
- Begin at a standing position.
- Push your hips backwards, bending slightly at the knees.
- Bring the bar down along the front of your legs.
- Continue downward until you feel your hamstrings fully stretch (typically the barbell will be 2–3 inches below your knees at the lowest point).
- Stand up, driving your hips forward.
By stretching your hamstrings during the downward movement of the Romanian deadlift you cause your hamstrings to contract during the eccentric motion of the exercise. Then, by driving your hips forward on the upward movement you trigger your hamstrings to lift the weight. This not only takes the strain off your back, but it also provides an incredible hamstring workout on both the upward and downward movement of this exercise.
Nordic Hamstrings/Manual Hamstring Curl
Nordic hamstrings are an incredible workout alternative to the leg curl. In fact, the Nordic hamstring exercise was shown to provide better hamstring activation than the ball leg curl in this study. To do this exercise:
- Use a loaded barbell or a partner to hold your ankles down near floor level.
- Sink to your knees, with your ankles secured beneath a barbell or by your partner.
- Keep your back straight and eyes forward in the starting position.
- Lean forward slowly by straightening your legs. Use your hamstrings to slow your descent as your upper body tilts toward the floor.
- Once your hamstrings can no longer support your weight, fall forward softly and catch yourself in a push-up position.
- Push-up from the floor about ¼ of the way to upright. From there, use your hamstrings to pull yourself back to the starting position.
This exercise uses your body weight to develop strong hamstrings. It’s much easier to perform with a partner holding your ankles, but you can still do this solo. It’s one of the best leg curl replacements you can do.
One of the biggest drawbacks of the leg curl machine is that the machine handles all of the balancing and weight stabilization for you. This reduces your strength and muscle mass gains, as well as hinders your balance. The single-leg deadlift is the antidote for all these negatives. For this exercise:
- From a standing position, bring your left knee up in front of you until your thigh is parallel to the floor.
- Hinge forward at the hips as you drive your left leg straight out behind you.
- Keep your back and the raised leg straight as you hinge forward until both your torso and the raised leg are parallel to the ground.
- The knee of your planted leg may bend slightly. However, it should be as straight as possible.
- Keep your hips square and pointed to the ground.
- Hinge upward at the hips, bringing your leg forward to the starting position with your knee tucked.
- Perform your desired reps with your left leg raised, then switch to the other leg.
This exercise requires you to balance on one leg throughout the entire set. The leg that remains planted on the ground works to hinge your hips forward and back, providing an incredible hamstring workout. At the same time, it trains your balance, increasing your overall fitness. For an added challenge, you can even hold dumbbells as you perform the single-leg deadlift.
An often-neglected exercise, good mornings are incredible for training lower back and hamstring strength. Strengthening these major muscles with compound exercises is great for reducing the risk of back injury. Good mornings also protect the knees from harm, unlike the leg curl. To do this exercise:
- Stand with feet shoulder-width apart and balance the weight across the upper back, as with a barbell back squat.
- Hinge forward at the hips, driving your hips backward and bringing your chest parallel with the ground.
- Keep your back straight.
- Bend your knees slightly, between ¼ and ⅓ of the way to a squat position.
- Straighten your back by driving your hips forward, not by using your back muscles.
- Straighten your legs as you drive your hips forward.
By focusing on the hip extension movement of good mornings you activate the hamstrings. Plus, you’ll strengthen and protect both your back and knees. Just remember to start with a light weight during this leg exercise—you won’t be able to load good mornings to the same degree as squats.
Are Nordic Curls Bad for Your Knees?
The nordic hamstring exercise is typically not dangerous for your knees and is often used to rehab hamstring injuries. Because nordic curls have a similar movement pattern as a traditional leg curl machine, some believe they can cause knee injury. However, the leg curl machine often inhibits hip extension and activation. During nordic hamstring exercises, you can drive your hips forward on the upward motion, activating the hamstring much more naturally than during leg curls. This makes the nordic hamstring curl a great alternative to leg curls that won’t injure your knees.
Can Hamstring Curls Cause Knee Pain?
Hamstring curls can be responsible for knee pain and injury because the exercise machines designed for leg curls isolate the knee-flexing movement. This places additional stress on the knees while you are attempting to target your hamstrings. Instead of leg curls, choose compound exercises that work your hamstrings through a combination of knee extension and hip flexion. Romanian deadlifts, Nordic hamstring curls, single-leg deadlifts, and good mornings are all examples of knee-friendly hamstring exercises.