Muscles worked
The seated leg curl isolates your hamstrings, the muscles that bend your knee: the biceps femoris, semitendinosus and semimembranosus. Because you sit with your hips bent, the parts of the hamstrings that also cross the hip are already stretched when the movement starts, so they work in a longer position than in the lying leg curl. Your calf helps too, since it attaches above the knee joint. Pulling your toes towards your shins usually lets the calf take a bigger share, which is why many people keep their feet relaxed.
Common mistakes
- Jerking the weight from straight legs. A fast start lets momentum take over just where your hamstrings are most stretched. Start each rep smoothly and pull at an even speed.
- Only doing half the movement. With too much weight, the ankle pad stops well short of the seat. Pick a weight that lets you bend your knees as far as the machine allows and hold briefly there.
- Your stronger leg taking over. When both legs pull the same pad, one side can do more of the work without you noticing. Train one leg at a time now and then to check both sides are equally strong.
Variations and alternatives
- The lying leg curl is the same knee bend lying face down, and a good complement.
- The standing leg curl is a one-leg machine where your hip stays straight rather than bent.
- The Nordic hamstring curl is a very demanding bodyweight version where you brake yourself down towards the floor.
- The slider leg curl is done lying down with your heels on sliders, for training at home.
Sets and reps
As an isolation exercise, the seated leg curl suits muscle and endurance best. Most people do 8 to 15 reps over three or four sets, and 15 to 20 reps works well at the end of a leg session. Heavy sets of 3 to 6 reps rarely add anything, as form easily turns into jerking. The guide to sets and reps explains more.
One step on the weight stack can be a large share of what you lift. Add reps first and raise the weight once you reach the top of your range in every set, in line with progressive overload. The machine guides the movement, so you can take your last sets close to your limit, with one rep or none left (see reps in reserve). The leg curl trains your hamstrings at the knee and pairs well with a hip exercise such as the dumbbell Romanian deadlift.