Single leg leg curls are an isolation exercise used to train the hamstrings one leg at a time. They are usually performed on a seated or lying leg curl machine, where one leg bends against resistance while the other stays relaxed or out of the way. This unilateral setup makes the exercise especially useful for improving hamstring strength, building muscle evenly between the legs, and exposing side to side differences that bilateral curling can hide.

They are common in bodybuilding, lower body hypertrophy routines, sports performance training, and rehabilitation style programmes because they allow direct hamstring work with controlled resistance. While compound exercises such as Romanian deadlifts and deadlifts train the posterior chain broadly, single leg leg curls focus much more directly on knee flexion, which is one of the hamstrings’ key functions. That makes them a valuable addition to a balanced leg programme.

How to Do Single Leg Leg Curls

To perform a single leg leg curl, set up on a lying or seated leg curl machine and adjust it so the pivot of the machine lines up properly with your knee joint. Position the pad against the back of your lower leg or ankle depending on the machine design, and keep the non working leg relaxed or placed according to the setup instructions of the machine.

Start with the working leg extended or nearly extended. From there, bend the knee and curl the pad through the range of motion until you reach the end of the machine’s pulling path or a strong hamstring contraction. Pause briefly at the top, then slowly lower the weight back down under control until the leg returns to the starting position.

The movement should be smooth and deliberate. Avoid jerking the pad, twisting through the hips, or rushing the lowering phase. A good single leg curl should feel controlled from start to finish, with the hamstrings clearly driving the movement rather than momentum doing the work.

Muscles Worked on Single Leg Leg Curls

Single leg leg curls primarily work the hamstrings, including the biceps femoris, semitendinosus, and semimembranosus. These muscles are responsible for bending the knee and also assist in hip extension during other lower body movements. In this exercise, their knee flexion role is trained directly.

The calves may assist slightly depending on foot position, and the glutes or core may contribute only minimally in a stabilising role depending on whether the machine is seated or lying. Compared with hinge based exercises, the leg curl is much more isolated and focused specifically on the back of the thigh.

Because the exercise is unilateral, it also gives a clearer picture of how each hamstring is functioning on its own, which can be useful for both performance and muscle balance.

Single Leg Leg Curls Difficulty

Single leg leg curls are generally considered a beginner friendly exercise. The machine guides the movement, the load can be adjusted precisely, and the movement pattern is easy to understand. This makes them accessible even for people with limited gym experience.

That said, they can still be very challenging once enough resistance is used. Because the hamstrings are being isolated so directly, even moderate loads can create a strong contraction and a serious burn in the working leg. Performing the movement one side at a time often makes it feel harder because there is no help from the stronger leg.

So while they are simple to learn, they remain highly effective for building direct hamstring strength and size.

How Common Is Single Leg Leg Curls

Single leg leg curls are fairly common, though the two leg version is still more commonly used in most gyms. Many people default to training both legs together on a curl machine, but the single leg version is well known and often used when the goal is to improve symmetry, identify weaker sides, or create a stronger mind to muscle connection with one hamstring at a time.

They are especially common in bodybuilding programmes, physiotherapy settings, and lower body routines where unilateral work matters. Personal trainers and coaches often use them because they are easy to scale and reveal side to side differences very clearly.

So while not quite as universal as bilateral leg curls, they are still a very established and practical variation.

Common Mistakes to Avoid

One of the most common mistakes is using too much weight and kicking the pad through the movement. This often reduces hamstring tension and turns the exercise into a jerky motion rather than a controlled curl. Single leg leg curls usually work best when the movement is smooth and the top position is reached through muscle effort rather than momentum.

Another common issue is poor machine setup. If the knee does not line up with the machine’s pivot point, the movement can feel awkward and less effective. Many people also rush the lowering phase, which wastes a valuable part of the rep and reduces the total time under tension. Twisting the hips or shifting in the seat to help the rep along is another frequent mistake that takes work away from the hamstrings.

Locking out too aggressively at the bottom or cutting the range of motion short are also common problems. Controlled reps almost always produce better results than heavier sloppy ones.

Sets and Reps for Hypertrophy

For hypertrophy, single leg leg curls usually work very well for around three to four sets of ten to fifteen repetitions per leg. Some lifters also do well with slightly higher reps because the exercise is stable and highly targeted.

Moderate to higher reps often suit this movement best because they allow the hamstrings to stay under tension without relying on heavy, harsh repetitions. A controlled lowering phase and a brief squeeze at the top can make the set especially effective for building the back of the thighs.

Single leg leg curls are often placed later in a lower body workout after compound movements such as squats, deadlifts, or leg presses. In that position, they work very well as direct hamstring accessory training.

Other Similar Exercises

Several exercises are similar to single leg leg curls. The standard two leg leg curl is the closest alternative and trains both hamstrings together. Sliding leg curls, stability ball leg curls, and Nordic curl regressions also train knee flexion and hamstring control, though with different setups and difficulty profiles.

Romanian deadlifts, good mornings, and hamstring biased glute bridges also train the hamstrings, but through hip extension rather than direct knee flexion. Single leg Romanian deadlifts can complement single leg curls nicely by training the hamstrings in a different function.

For anyone trying to build complete hamstring development, single leg leg curls fit well alongside hinge based posterior chain work rather than replacing it.

Injury Considerations

The main injury considerations with single leg leg curls usually involve the knees and the hamstrings themselves. The exercise is often well tolerated, but if the machine is set up poorly or the movement is overloaded, some people may feel discomfort around the knee joint or cramping through the hamstrings.

Aggressive reps and poor control can also make the movement feel rougher than it needs to be. People with active hamstring strains should be cautious, since even direct machine based curling can stress healing tissue depending on the stage of recovery. In many cases, though, the single leg version is actually useful because it allows each side to be trained with more awareness and control.

Using a sensible load, setting the machine properly, and keeping the reps smooth usually make the exercise very manageable.

Who Should Avoid This Exercise

People with active knee pain, hamstring strains, or discomfort during leg curl movements may want to avoid single leg leg curls until symptoms improve. Those who consistently feel joint pain rather than muscle tension during the movement may be better using a different hamstring exercise or adjusting the machine setup.

Individuals recovering from knee or hamstring injuries should also be cautious, even though this exercise is sometimes used in rehabilitation. In those cases, medical advice and stage of recovery matter a great deal. Beginners who are unsure how to adjust the machine properly may also need guidance before using it.

For most people, though, the exercise does not need to be avoided completely. It simply needs to match their current comfort, control, and training goal.

Summary

Single leg leg curls are a highly effective isolation exercise for training the hamstrings one side at a time. They are simple to learn, easy to adjust, and especially useful for hypertrophy, muscle control, and addressing side to side differences in leg strength.

When performed with proper machine setup, controlled reps, and sensible resistance, they can be an excellent addition to a lower body programme. They are not a substitute for larger compound posterior chain lifts, but in an exercise encyclopaedia they absolutely deserve a place as one of the most practical and direct hamstring isolation exercises available.