Machine Single-Leg Lying Leg Curl
What Is the Machine Single-Leg Lying Leg Curl?
The Machine Single-Leg Lying Leg Curl is an isolation exercise that primarily targets the hamstrings. It is a beginner-level movement and a single-leg version of the Machine Lying Leg Curl, performed face down with the roller pad loading one leg at a time while the other leg rests on the bench.
Working one leg at a time is mainly a way to see and train each side on its own terms. With both legs under the pad, a stronger hamstring can take a larger share of the work and the weight still moves, so a gap between sides is easy to miss. Here each leg has to complete its own reps at its own load, which makes a difference in strength or endurance obvious and gives you something concrete to track. Training one side at a time does not correct an imbalance by itself, but it stops the stronger leg from covering for the weaker one while you work on it.
The single-leg version also makes the working hamstring easier to feel, since there is only one leg moving and nothing on the other side to mask the contraction. That is useful if one hamstring tends to stay quiet during hinges and curls. Lifters coming back from a hamstring strain or a knee injury often use it for the same reason, because the healthy leg can keep training at its usual load while the affected side builds back at its own pace.
Lying face down keeps the hip extended while the knee bends, so the hamstrings do their work from a position where they are already shortened at the hip. That is the main mechanical difference from the Machine Seated Leg Curl, where the hip is flexed and the hamstrings start each rep in a lengthened position, and a 12-week study that trained one leg seated and the other lying found the seated version added noticeably more hamstring size. Neither one replaces the other, and it is common to use both, or to pair a curl variation with a hip hinge such as the Barbell Romanian Deadlift so the hamstrings get trained at the knee and at the hip.
Muscles Worked
- Biceps Femoris
- Primary
- Semimembranosus
- High
- Semitendinosus
- High
Instructions
- Adjust the machine so the leg pad rests comfortably just above the back of your ankle.
- Lie face down on the machine, ensuring your hips are aligned with the pivot point.
- Place one leg under the pad while the other rests on the machine platform.
- Grip the handles or sides of the machine to stabilize your upper body.
- Curl the pad upward by contracting your hamstrings, bringing your heel toward your glutes.
- Slowly lower the pad back to the starting position in a controlled manner.
- Repeat for the desired reps, then switch to the other leg.
Common Mistakes
Arching the Back
Letting your hips lift off the pad and your lower back arch swings the weight up instead of curling it, taking tension off the hamstrings and straining the lumbar spine, so keep your torso flat and your hips pressed into the bench.
Using Momentum
Swinging your leg or rushing the movement reduces tension on the hamstrings. Perform each rep slowly and with control.
Incorrect Pad Placement
Placing the pad too high or too low can cause discomfort and reduce the exercise's efficiency. Adjust it to rest just above the back of your ankle.
Partial Range of Motion
Not completing the full range of motion limits hamstring activation and reduces the exercise's effectiveness. Ensure you fully curl and extend your leg for maximum benefit.
Knee Off the Machine's Pivot
Lying too far up or down the bench leaves your knee out of line with the machine's rotation point, which shortens the curl and pushes stress into the joint, so set up with your hips over the bend in the bench and your knee level with the pivot.
Overloading the Stronger Leg
Carrying your two-leg weight onto a single leg or grinding out extra reps on your better side hides the side-to-side gap this variation exists to expose, so train the weaker leg first and match its rep count with the stronger one.
Injuries
Machine Single-Leg Lying Leg Curl is a low risk exercise when performed with proper technique. The bench supports your torso and the knee is the only joint under real load, so there is little room for the movement to go wrong once the machine is set up. The strain that does occur is almost always in the hamstring itself, and it comes from the load rather than from posture. Working one leg at a time puts the whole stack on a single limb, so a weight that feels ordinary with both legs can be close to maximal here. Avoid using excessive weight, and maintain control throughout the movement to avoid jerky or uncontrolled motions, especially on the way down. Letting a heavy roller snap your leg into the fully lengthened bottom position is the most common way to strain a hamstring on this machine.
Roller pad placement decides how the rest of the set feels. It should sit just above the back of your heel, on the lower calf and clear of the Achilles tendon. Set too high on the calf it digs into the muscle belly and shortens the lever, so the weight feels heavier and the pressure becomes the limiting factor rather than the hamstring. Set too low, over the heel or onto the foot, it tends to slide as you curl and drags the ankle into the work instead of the knee. Once the pad is right, grip the handles and keep your hips pressed into the bend of the bench. Letting the hips lift is the usual way of cheating a heavy last rep up, and it takes load off the hamstring and puts it into an arched lower back. If your hips are rising, the weight is too heavy.
Hamstring cramping is common on leg curls of every kind, and it is more likely on a single leg, in higher rep sets, and when you are dehydrated or the muscle has not been warmed up. It is alarming the first time but it is not an injury: stop the set, straighten the leg slowly, and ease into a Standing Hamstring Stretch before continuing. Knee discomfort is a different signal. This curl does not press the kneecap into the joint the way a leg extension does, but the pull behind the knee can bother anyone with existing posterior knee or meniscus problems, in which case shorten the range, drop the load, and work in the 12 to 15 rep range, or switch to a Machine Seated Leg Curl. Warm up thoroughly to prepare your hamstrings and knees for the exercise; a light set or two on each leg is usually enough.
If single-leg loading feels like too much, regress to the two-legged Machine Lying Leg Curl so the weight is shared, or train the pattern unloaded with an Exercise Ball Single-Leg Hamstring Curl. To progress, add reps before you add plates, then slow the lowering phase to about three seconds or pause briefly at the top of each curl before moving the pin. A Nordic Hamstring Curl is the harder step once controlled reps here are easy. Stop the set for any sharp or pinpoint pain high in the hamstring near the sit bone, or anything that feels like a pull or a tear, and do not train that leg through it, since a hamstring strain worked through takes far longer to settle than one rested early. Knee pain that lingers after the session is worth a professional opinion before you keep loading the leg.
- Primary Focus
- Hamstrings
- Equipment
- Machine
- Modality
- Strength
- Difficulty
- Beginner
Alternative Exercises
Frequently Asked Questions
- Q: Is the Machine Single-Leg Lying Leg Curl good for beginners?
Yes. The machine fixes the path of the movement, so there is little to learn beyond keeping the hips down on the pad and curling under control, and training one leg at a time makes any side-to-side strength difference obvious. Beginners who find the pelvis twisting toward the working side can start with the two-leg Machine Lying Leg Curl and switch once the position feels stable.
- Q: How does the Machine Single-Leg Lying Leg Curl compare to the seated leg curl?
The difference is hip position rather than which part of the hamstring gets worked. Flexing the hips in the Machine Seated Leg Curl holds the three hamstrings that cross the hip at a longer length, and a direct training comparison found greater growth in those heads from the seated version, while the short head of the biceps femoris, which crosses only the knee, grew about the same in both. Lying face down keeps the hips close to straight, so if size is the goal the seated machine is the stronger first choice and this one works well as a second hamstring exercise.
- Q: What should I do if one leg is clearly weaker than the other?
Train both legs, start each set with the weaker one, and then match the stronger leg to whatever the weaker leg managed instead of pushing it to its own limit. Done consistently over a few months this gives the weaker side room to close the gap, and a difference that never budges, or that comes with pain rather than just less strength, is worth having looked at.
- Q: Is training one leg at a time worth the extra time?
It is worth it when there is a specific reason for it: a noticeable side-to-side difference, a return to training after an injury to one leg, or a set where you can feel the stronger leg taking over. Without one of those, the two-leg version gets the same work done in roughly half the time and is the better default.
- Q: Is it normal for the hamstring to cramp during this exercise?
Yes, cramping is common on leg curls, especially near the top of the curl where the hamstring is already shortened and on higher-rep sets. It is not a sign of damage, so straighten the leg out, let it settle, and come back with a lighter load, a slower tempo, or a stop just short of full knee flexion. Sharp pain, or pain behind the knee rather than in the muscle belly, is a different matter and a reason to end the set.