MariposasHow to Do the Leg Curl
By Zachary, builder of Mariposas · Reviewed against published exercise-science sources (references)
· Last updated June 2026
The leg curl is one of the few exercises that loads the hamstrings through their primary function, knee flexion, rather than hip extension. Most lower-body staples like squats and deadlifts work the hamstrings as a supporting player; the leg curl puts them center stage, forcing them to produce force without the quads or glutes picking up the slack. That isolation quality makes it especially valuable for correcting hamstring weakness relative to quad strength, a ratio that shows up in knee health and sprint mechanics alike. Track your sets and progression for free in the Mariposas app.
How to do it
- Adjust the machine's thigh pad so it sits just above your knees, and set the ankle roller so it contacts the back of your ankles just above the heel, not mid-calf.
- Lie face-down flat on the bench with your hips pressed firmly into the pad and your kneecaps just off the edge of the thigh cushion, which protects the joint and gives the hamstrings a full range to work through.
- Grip the handles lightly to anchor your upper body, but avoid pulling with your arms or shrugging your shoulders up during the movement.
- Take a breath in, brace your core gently to keep your hips from rising off the pad, then exhale as you curl the ankle roller toward your glutes in a smooth, controlled arc.
- Drive the curl until your heels are as close to your glutes as the machine allows, pausing briefly at peak contraction to maximize hamstring recruitment before returning.
- Lower the weight back down slowly, aiming for a two-to-three second eccentric, resisting gravity the entire way rather than letting the stack drop.
- Stop just short of the weight stack touching down at the bottom so tension stays on the hamstrings throughout the set, then begin the next rep without bouncing.
- After your set, step off carefully as the hamstrings may feel fatigued and cramped, especially at higher rep ranges.
Form cues
- Hips glued to the pad the entire rep.
- Squeeze hard at the top, hold one count.
- Slow on the way down, fight the weight.
- Ankles neutral, no toe flare or pigeon-toeing.
- Breathe out on the curl, breathe in on the descent.
Common mistakes
- Hips lifting off the pad: when your hips rise to help pull the weight, the glutes take over and the hamstrings get less stimulus; consciously press your hip bones into the bench before each rep to eliminate this compensation.
- Using momentum to jerk the weight up: a fast, jerky concentric shortens the effective range and increases the risk of a proximal hamstring strain; drop the load and focus on a deliberate, smooth curl instead.
- Ankle roller sitting on the mid-calf: this shifts stress up the leg and reduces ankle leverage, making the movement mechanically harder for the wrong reasons; reposition it to sit just above the heel bone.
- Cutting the eccentric short: releasing tension quickly on the way down wastes the most productive part of the rep for muscle growth; the hamstrings handle substantial load eccentrically, so controlling that phase matters.
- Going too heavy and losing range of motion: piling on weight that only allows a partial curl means the hamstrings never reach peak shortening; a full range at moderate load produces better results than a half-range at heavy load.
Why do the Leg Curl?
- Direct hamstring hypertrophy: because no other large muscle can compensate in this position, the hamstrings do all the work across the full set, making it a reliable driver of posterior thigh size.
- Quad-to-hamstring balance: many lifters accumulate far more quad volume from squats and lunges than direct hamstring work, and the leg curl fills that gap in a way that hip hinge patterns alone often do not.
- Knee joint support: stronger hamstrings contribute to the stability of the knee by counteracting anterior tibial shear, which matters for athletes returning from or trying to reduce the risk of ACL-related stress.
- Eccentric loading at a practical scale: the controlled lowering phase lets lifters accumulate meaningful eccentric hamstring work without the technical demands of exercises like the Nordic curl, making it accessible for a wide range of trainees.
Leg Curl variations
- Seated Leg Curl
- Stretches the hamstring from both the hip and the knee simultaneously, which creates a longer effective muscle length and may produce greater growth stimulus, making it a useful complement or substitute when prone machines are unavailable.
- Single-Leg Prone Curl
- Isolates each leg independently so strength imbalances become obvious and the dominant leg cannot compensate for the weaker side, useful as a corrective or finishing tool.
- Nordic Hamstring Curl
- A bodyweight regression-to-progression depending on the lifter, this floor exercise emphasizes the eccentric phase heavily and builds the hamstrings under high stretch, though it requires a partner or anchor and considerable existing hamstring strength.
- Stability Ball Leg Curl
- Replaces the machine entirely with a Swiss ball underfoot, adding a core stability demand and making it a solid option when no leg curl machine is available, though load progression is limited to bodyweight and positioning.
How to program it
The leg curl is most commonly programmed after a primary lower-body compound like a squat or Romanian deadlift, where it serves as an isolation finisher rather than a main lift. Rep ranges tend to skew moderate to high, with many coaches and lifters using somewhere in the 8 to 15 range for hypertrophy-focused work, though heavier sets of 6 to 8 are also used during strength-oriented phases. Because the hamstrings recover reasonably well from machine-based isolation work, it often appears two to three times per week across different lower-body or full-body sessions. Total weekly volume across those sessions typically falls somewhere in the range of 6 to 16 working sets depending on training history and goals.
Leg Curl alternatives
FAQ
- Should I use the seated or prone leg curl machine?
- Both train the hamstrings, but they differ in how the muscle is loaded. The seated version stretches the hamstring at the hip as well as the knee, which places the muscle under tension in a longer position. Some research suggests muscles grow better when trained in a stretched position, so the seated curl may have an edge for hypertrophy. The prone version is more widely available and still highly effective. Using both when possible covers more bases.
- Why do my hamstrings cramp during leg curls?
- Cramping usually happens because the hamstrings are being asked to work through a shortened range they're not conditioned to handle, especially at the top of the curl. Dehydration and low electrolyte levels can make it worse. Easing into the full range gradually over a few sessions, keeping well hydrated, and building hamstring flexibility through regular stretching generally reduces the cramping over time.
- How much weight should I use on the leg curl?
- Start light enough that you can complete the full range of motion with slow, controlled reps and your hips staying flat on the pad. Most people discover they've been using too much weight when they notice their hips lifting or their range collapsing. Once you can perform clean reps through the full range for your target rep count, adding small increments of weight is the straightforward path forward.
- Do leg curls actually help with athletic performance?
- The hamstrings play a major role in sprinting, deceleration, and change of direction. Isolated hamstring strength from leg curls builds a foundation of muscle that transfers to those patterns. It doesn't replace sprint training or hip hinge work, but it does address a weak link that shows up in many athletes who train the quads far more than the posterior chain.
- Can I do leg curls if I have lower back pain?
- Because you're lying prone and the movement is at the knee, the leg curl places very little direct demand on the lumbar spine compared to hip hinges or squats. Many people with back sensitivities find it comfortable. That said, anyone managing a specific injury or condition should check with a healthcare provider before assuming any exercise is safe for their particular situation.