Leg Curl

Lie face down on the leg curl machine with the pad resting on your lower calves. Curl your heels toward your glutes, squeezing your hamstrings at the top. Lower with control.

Pro Tips

• Squeeze hard at the top for a full contraction
• Control the negative — don’t let the weight drop
• Avoid lifting your hips off the pad

Muscles worked

Primary: Hamstrings — all three muscles (biceps femoris long head, biceps femoris short head, semimembranosus, semitendinosus) are loaded through knee flexion (curling the heel toward the glutes). The lying leg curl is the most common direct hamstring isolation exercise and one of the few movements that loads the hamstrings exclusively through knee flexion rather than hip hinge.

Supporting: Gastrocnemius (the two-headed calf muscle crosses the knee joint and assists with knee flexion — it is active in the leg curl), popliteus (small muscle behind the knee that assists in initiating flexion).

Common mistakes

Hips lifting off the pad: The most common form error. When the hips lift, the pelvis tilts posteriorly and the hip extensors (glutes and lower back) assist the curl, reducing the hamstring demand. Keep the hips pressed firmly against the pad throughout the entire range.

Short range of motion: Not curling all the way to full hip flexion (heels toward the glutes) limits the hamstring’s contraction range. Full range — from straight legs to maximum curl — is required for complete hamstring loading.

Rushing the eccentric: The controlled lowering phase is where significant hamstring damage and adaptation occurs, particularly in the long head of the biceps femoris. Lowering in 2–3 seconds is a meaningful driver of hamstring hypertrophy.

Lying leg curl only: The lying leg curl loads the hamstrings through knee flexion with the hip extended. The seated leg curl loads them with the hip in some flexion, which changes the muscle length-tension relationship. Including both variations provides more complete hamstring loading.

Programming notes

The leg curl is the standard direct hamstring accessory in leg-focused and lower body hypertrophy programmes. Because compound hip-hinge movements (RDL, deadlift) train the hamstrings primarily through hip extension, the leg curl provides the complementary knee-flexion component needed for complete hamstring development.

Typical programming: 3–4 sets of 10–15 repetitions. In a lower body session the leg curl typically follows compound work and is paired with leg extensions or quad-dominant exercises to provide balanced leg training within the session.

Frequently asked questions

Should I use the lying or seated leg curl for hamstring growth?

Both are worth including if you have access to them. The lying leg curl works your hamstrings with the hip extended, which puts the muscle closer to a shortened position at the knee. The seated leg curl works with the hip flexed, placing the hamstring under greater stretch at the hip end — research suggests this contributes to more growth in the long head of the biceps femoris. If you can only pick one, either works well; if you want complete hamstring development, rotate or combine them.

How many sets and reps should I do on the leg curl?

For hypertrophy, 3–4 sets of 10–15 reps is a reliable starting point. Your hamstrings respond well to moderate rep ranges and are particularly sensitive to time under tension during the eccentric. Use a load that lets you reach full range of motion with control, not one that forces you to shorten the rep or let your hips lift off the pad.

Why do my hamstrings cramp during leg curls?

Cramping usually means you are curling through a shortened range repeatedly without adequate warm-up, or your hamstrings are fatigued and firing under high demand. Make sure you fully extend the leg at the bottom of each rep — cutting the eccentric short keeps the muscle in a semi-contracted state that promotes cramping. Staying well hydrated and including a light warm-up set before loading up also helps reduce cramping during the working sets.