Seated Single Leg Knee Flexion
- Target muscle
- —
- Equipment
- Body weight
- Body part
- Thighs
- Type
- Strength
The seated single leg knee flexion is a bodyweight exercise that targets the hamstrings and knee flexors of one leg at a time through a controlled bending motion performed while seated. It is well suited for strengthening the posterior thigh, improving unilateral knee flexion strength, and serving as an accessible rehabilitation or warm-up movement that requires no equipment.
How to do the Seated Single Leg Knee Flexion
- 1Sit upright near the edge of a sturdy chair or bench so your hips are at roughly a 90-degree angle and both feet rest flat on the floor.
- 2Extend one leg out in front of you until it is nearly straight, hovering just above the floor.
- 3Engage your core lightly to keep your torso stable and avoid leaning back.
- 4Slowly curl the extended leg back by bending at the knee, drawing your heel toward the underside of the chair.
- 5Continue the movement until your knee is bent to the fullest comfortable range of motion.
- 6Hold the contracted position for one to two seconds, squeezing the hamstring at the back of your thigh.
- 7Slowly reverse the motion, extending the leg back out to the starting position under control.
- 8Complete all reps on one leg, then switch to the other side and repeat.
Form tips
- Keep your torso upright throughout the movement — do not hunch forward or lean back to compensate.
- Move at a slow, deliberate tempo (roughly two seconds on the way in, two on the way out) to maximise hamstring engagement.
- Focus on initiating the curl from behind the knee rather than just dragging the foot inward.
- Sit close enough to the edge of the seat so that your lower leg can travel freely without hitting the chair.
- If you feel tightness at the back of the knee rather than the thigh, reduce your range of motion until flexibility improves.
Common mistakes
- Leaning back as the leg curls: shifting your torso to generate momentum reduces hamstring activation and puts strain on the lower back — stay upright.
- Using a fast, swinging motion: rushing through the curl relies on momentum instead of muscle work, diminishing the training effect.
- Lifting the hip of the working leg: hiking the hip off the seat shortens the movement and shifts load away from the hamstrings.
- Holding your breath: failing to breathe normally increases unnecessary tension; exhale as you curl and inhale as you extend.
- Skipping the pause at peak contraction: omitting the brief hold at maximum knee bend removes a key stimulus for the hamstring muscles.
Frequently asked questions
What muscles does the seated single leg knee flexion work?
The exercise primarily works the hamstrings — the group of muscles at the back of the thigh — which are the main knee flexors. The surrounding thigh stabilisers assist in controlling the movement.
Is this exercise suitable for beginners?
Yes. Because it uses only body weight and is performed seated, it is low-impact and easy to learn. Beginners can focus on controlled movement and a comfortable range of motion before progressing to more demanding hamstring exercises.
How many sets and reps should I do?
A common starting point is 2–3 sets of 10–15 repetitions per leg. If you are using the exercise for rehabilitation or warm-up purposes, 1–2 sets of 10 reps with an emphasis on slow tempo is usually sufficient.
What are some alternatives to this exercise?
Exercises that also target the knee flexors and hamstrings include lying leg curls, Nordic hamstring curls, seated leg curls on a machine, and standing single leg curls. The seated single leg version is a useful starting point when equipment is unavailable.
Can I do this exercise as part of a rehabilitation programme?
It is commonly used in early-stage knee and hamstring rehabilitation because it is low-impact and easily controlled. However, if you are recovering from an injury, confirm the appropriate range of motion and load with your physiotherapist before adding it to your programme.
