Muscles worked
The lying leg curl isolates your hamstrings, the muscles that bend your knee: the biceps femoris, semitendinosus and semimembranosus. The short head of the biceps femoris only crosses the knee, so it is trained by bending the knee and not by hip exercises such as the Romanian deadlift. Your calf also helps, because the large calf muscle attaches above the knee joint. With your toes pulled towards your shins the weight usually feels lighter, and many coaches have you point your feet away to put more of the work on the hamstrings.
Common mistakes
- Jerking the weight into motion. A fast start from straight legs lets momentum do the work. Start every rep calmly and curl the weight up at an even speed.
- Only doing half the movement. With too much weight your heels stop well short of your bum. Choose a weight that lets you bend your knees as far as the machine allows and hold the top briefly.
- Letting the stack rest at the bottom between reps. When the plates touch down, your hamstrings get a rest mid-set. Start the next rep just before your legs are fully straight.
Variations and alternatives
- Seated leg curls are the same knee bend done seated. With your hips bent, your hamstrings work in a more stretched position, which makes them a good complement.
- Standing leg curls train one leg at a time, useful if one side is weaker.
- Nordic hamstring curls are a tough bodyweight option where you brake yourself on the way down to the floor. Start with few reps.
- Slider leg curls train your hamstrings at home, with no machine.
Sets and reps
The leg curl is an isolation exercise, best suited to building muscle and endurance. Most people do it for 8 to 15 reps over three or four sets, and 12 to 20 reps works well as a finisher on leg day. Really heavy sets of 3 to 6 reps rarely add anything here, because the movement easily turns into jerking. The guide to sets and reps explains the ranges.
One step on the weight stack can be a large share of what you lift, so for progressive overload add reps first and raise the weight once you reach the top of your range on every set. Pair the leg curl with a hip exercise such as the Romanian deadlift, so you train your hamstrings at both the knee and the hip.