Leg Curl

What is the leg curl?

The leg curl is the dominant isolation exercise for the hamstrings. Performed on a machine in either lying or seated position, the trainee curls the heels toward the glutes by flexing the knees, isolating the hamstrings without involving the hip extension that compounds like the deadlift recruit. For trainees pursuing balanced hamstring development, leg curls are an essential complement to hip-hinge work.

Who should do leg curls?

Most lifters benefit from including leg curls in their leg program. Compound exercises like squats, deadlifts, and Romanian deadlifts train the hamstrings as part of the hip-extension pattern; leg curls train them as direct knee flexors. The two roles are different and the hamstring is uniquely active in both. Programs with only hip-hinge hamstring work tend to produce underdeveloped lower hamstrings and knee flexion strength.

How do you program leg curls?

Once or twice per week. For hypertrophy: 3 to 4 sets of 10 to 15 reps. The hamstrings respond well to moderate-to-high rep work with controlled tempo and full range of motion. The lying leg curl produces stronger hamstring engagement than the seated version because the position eliminates hip flexor involvement; some programs use both for stimulus variation.

Lying vs seated leg curl

The lying leg curl positions the trainee face-down with the hips extended; the hamstring works purely as a knee flexor. The seated leg curl has the hips flexed at 90 degrees, which lengthens the hamstring at the start; this produces a stronger stretch but partially offloads the hamstring's bi-articular nature. Both are productive; lying leg curls are typically the primary version with seated curls for variation.

Frequently asked questions

How heavy should you go?

For working sets, use weights that allow 10 to 15 strict reps with 1 to 3 reps in reserve. Going heavier than form allows produces the hip-lifting and momentum that defeats the isolation purpose. Most intermediate trainees use 20 to 50 kilograms on the leg curl; the absolute number matters less than maintaining strict form.

Why does my hamstring cramp on leg curls?

Hamstring cramping during high-rep leg curls is common and usually reflects accumulated fatigue, dehydration, or electrolyte depletion. Reduce the rep range temporarily, hydrate well before training, and ensure adequate sodium and potassium in the diet. Most cramping resolves within a few sessions of these adjustments.

Should you do nordic curls?

Nordic curls (kneeling with the heels anchored, lowering the torso forward) are an extremely productive bodyweight hamstring exercise that loads the eccentric phase very heavily. They are challenging and require building up; most trainees cannot complete a full Nordic curl initially and need to lower with assistance for several weeks. Once accessible, Nordic curls are an excellent supplement to machine leg curls.

How do leg curls compare to Romanian deadlifts?

Romanian deadlifts train the hamstring as a hip extensor; leg curls train it as a knee flexor. Both are productive but emphasize different functional aspects of hamstring development. Most balanced leg programs include both: RDLs for the hip-extension pattern and overall hamstring mass, leg curls for the knee-flexion pattern and lower hamstring development.

Frequently asked questions

Are leg curls necessary if I deadlift?

Yes for full hamstring development. The deadlift trains hip extension, which uses the hamstring's upper portion strongly. The leg curl trains knee flexion, which uses the hamstring's lower portion. Programs with only deadlifts and squats tend to produce underdeveloped lower hamstrings; adding leg curls fills this gap.