How to Do Leg Curls for Strong Hamstrings and Pain-Free Knees

Deadlifts get a lot of praise for their hamstring-building ability. But if you really want to give your hamstrings a muscle-twitching challenge, the leg curl is a must-try exercise — just get ready for some post-workout soreness.

• ‌What does the leg curl do?‌ It’s a hamstrings exercise that isolates and strengthens these muscles by bending your knees or “curling” your feet to your hips against resistance.
• ‌What muscles does the exercise work?‌ This exercise focuses on your hamstrings, the three long muscles across the back of your legs that connect your hips and knees, says California-based physical therapist and personal trainer Jereme Schumacher, PT, DPT.
• ‌Are leg curls bad for your knees?‌ Generally, leg curls are pretty safe for your knees, and are actually a common knee-friendly rehab exercise — so long as you’re using safe leg curl form. When you’re lying down, your knees should be flat on the floor.

A little-known leg curl benefit? They can actually help relieve knee pain, according to Schumacher. Strengthening your hamstrings helps build stability in your knees and pelvis. This helps improve your knee alignment (and reduces your injury risk) when you do other forms of exercise, like walking or running.

Most forms of activity happen in front of your body, like jogging or mowing the lawn. On their own, these exercises can make the front of your body (your anterior chain) stronger than your backside (posterior chain). These imbalances can cause poor posture and lower-back pain.

By strengthening your hamstrings and glutes, this leg curl variation can help take some of the pressure and stress off your lower back, Schumacher says. When your glutes and hamstrings are strong, your body can (and should) use these muscles, rather than your back, to perform daily activities or exercises in the gym.

During hamstring injury rehab, the goal is to prevent future re-injury. And to do so, you want to increase the strength of this muscle when it’s fully lengthened, according to a June 2012 study in the ‌International Journal of Sports Physical Therapy‌.

This is where hamstring curls come in. As you bring the dumbbell closer to the ground and straighten your knees, you challenge your hamstring muscle in its fully extended state.

Whenever you get up from a chair or get down on the floor, you’re using your hamstrings to help stabilize your hip and knee joints. Adding some hamstring-focused exercises to your workout routine can help make these daily motions even easier.

The main benefit of the lying leg curl is increased hamstring muscle strength, according to Schumacher. These muscles play a big part in producing power in other exercises you may be doing in the gym.

Deadlifts and hip thrusts, for instance, demand a lot of power and strength from your lower body, but especially your hamstrings and glutes. By isolating the hamstring muscles, leg curls can help improve your strength in these (generally) harder lifts.

For those who prefer cardio-based exercises, strong hamstrings are necessary for generating power in plyometric movements, like box jumps.

The most common mistake Schumacher sees with this exercise is an overarched lower back. When you do a lying hamstring curl, it’s really easy to let your core relax, causing your lower back to overextend. But this can add pressure and stress to your lower back, causing some painful side effects.

Even though you’re lying down on the ground, keep your core tight. In the lying-down position, tuck your tailbone slightly and squeeze your glutes a bit to help contract your abs.

If you’re swinging your legs and smacking your hips with the dumbbell, your form likely needs a tweak. After all, you want to use your muscles (not momentum) to raise and lower the weight. That’s how you build strength.

Keep your motions controlled both when you lower and raise the dumbbell, Schumacher says. You can opt to increase the weight a little bit or try an eccentric progression (more on that below), lowering the weight for a 3-second count.

You can most likely find a lying or seated leg curl machine at your gym, which is a great option if you want to really isolate your hamstrings.

The free-weight and machine versions of the leg curl exercise are pretty similar, Schumacher says. Typically, machines are set up with your torso at an angle, which can increase hamstring activation. However, the dumbbell version also develops core and inner-thigh strength, as your body works to stabilize the weight.

You don’t need to use a machine (or even a dumbbell) to try leg curls. These variations can be done with equipment you might already have at home.

When you curl against a resistance band, your hamstrings have to work harder the closer your heels get to your body (a dumbbell keeps the resistance consistent throughout the curl). Your hamstrings are naturally strongest in this position, so using a band can help your muscles stay challenged through their entire range of motion.

Nordic curls don’t actually use a weight at all — just your body. This variation definitely puts your hamstrings through the ringer. Only lower your body as low as you can with good form, maintaining a straight line between your knees, hips and head.

Whereas the other curl variations above really focus on your hamstrings, this one engages your glutes, too, as these muscles work to keep your hips up. Plus, the movement of the ball triggers your abdominals because they need to work to keep your body stable.