# Sitting Single Leg Knee Flexion - Canonical: https://fitwill.app/exercise/10000/sitting-single-leg-knee-flexion/ - Media ID: 10000 - Primary muscle: Hamstrings - Body part: Thighs - Equipment: Bench Or Seat - Video: https://fitwill.app/videos/10000/sitting-single-leg-knee-flexion.mp4 ## Description Sitting Single Leg Knee Flexion is a simple seated movement where you bend one knee at a time by drawing your foot back toward or under the chair, working against gravity and the resistance of your own leg. It is one of the most accessible ways to load the hamstrings, the group of muscles at the back of the thigh that bend the knee, and it requires nothing more than a sturdy chair or bench with enough clearance underneath for your foot to travel backward. This exercise is especially useful for beginners, older adults, anyone returning from a layoff, and people doing desk-based rehabilitation-style training who want to strengthen the back of the thighs without lying down or using machines. Because you stay seated with your torso upright, it places very little demand on the lower back and hips, which makes it a gentle starting point before progressing to standing leg curls, stability ball curls, or a seated leg curl machine. The setup matters more than it looks. Sitting tall on the front half of the seat with both feet flat keeps your thigh fixed and your pelvis neutral, so the knee is the only joint that moves. If you slump or rock the torso, you lose the clean hinge at the knee and the hamstrings stop doing the work. Keeping the working thigh pressed lightly into the seat gives the hamstrings a stable origin, which is what makes the short range in this position feel productive. To perform it well, plant the non-working foot firmly and keep it still. Slide or lift the working foot backward along the floor until the knee bends as far as it comfortably can, pause briefly at the fully bent position, then return the foot forward with control rather than letting it drop. The return is where most of the strength benefit lives, so treat the lowering phase with the same attention as the pull back. A common use case is pairing this with a seated knee extension for balanced knee health, hitting the hamstrings and quadriceps back to back without changing position. It also fits neatly into warm-ups before squats or deadlifts, since it wakes up the hamstring-knee connection in a low-fatigue way. Keep the effort honest but modest. If you want more challenge, add an ankle weight, slow the tempo, or pause longer at the bent-knee position. Stop if you feel pinching at the back of the knee, and keep the movement smooth rather than snapping the foot backward at speed. ## Instructions 1. Sit tall on a sturdy chair or bench with enough clearance underneath, positioned on the front half of the seat with your torso upright. 2. Place both feet flat on the floor, knees bent roughly 90 degrees, and rest your hands on your thighs or the sides of the seat for support. 3. Brace your core lightly and keep your weight evenly balanced over both sitting bones so your pelvis stays level. 4. Choose your working leg and press that thigh gently down into the seat so it stays fixed throughout the set. 5. Draw the foot of your working leg backward along the floor toward or slightly under the chair, bending the knee as far as you comfortably can. 6. Pause for one to two seconds in the fully bent position, feeling the hamstrings at the back of the thigh engage. 7. Slowly slide the foot forward again until your knee returns to the starting 90-degree bend, taking about two to three seconds on the way back. 8. Exhale as you bend the knee and inhale as you return the foot forward, keeping your breathing steady. 9. Complete all repetitions on one leg, then switch to the other leg and match the rep count and tempo. 10. Reset your posture between sets so you do not carry a slouched position into the next round. ## Tips & Tricks - If your seat is too low, your knee will already be deeply bent and the movement range will be tiny; choose a chair where your thighs sit roughly parallel to the floor. - A frequent mistake is letting the working hip slide forward on the seat as the foot pulls back, which shortens the hamstring artificially; keep that thigh glued to the seat. - Avoid flicking the foot backward at speed. The hamstrings respond better to a deliberate one-second pull and a slower two-to-three-second return. - If the back of your knee feels pinched at full bend, do not force the end range; bend to about 100 to 110 degrees instead and build up gradually. - Keep the non-working foot planted. Letting it drift or lift means you are shifting weight through the torso instead of isolating the knee joint. - To add resistance once body weight feels easy, loop a light ankle weight around the working ankle or place a folded towel under the foot and drag it against mild friction. - Do not let your torso round forward to watch the movement; a tall spine keeps the pelvis neutral and the hamstring working from a stable position. - If your heel catches on the floor, switch to a smooth surface or lift the heel slightly and flex the knee in a small arc just off the floor. - Keep the toes relaxed. Gripping the floor with the foot steals effort from the actual target at the back of the thigh. ## Frequently Asked Questions ### Which muscles does Sitting Single Leg Knee Flexion work? The primary movers are the hamstrings at the back of the thigh, which bend the knee. The calf muscles, particularly the gastrocnemius, assist because they cross the knee joint, and the glutes and core work lightly to keep you stable on the seat. ### Why do this exercise seated instead of standing? Sitting removes the balance demand and keeps the hips and lower back in a supported position, so the knee can bend through its range without compensation. It is a good first step before standing leg curls or machine work. ### Can beginners do Sitting Single Leg Knee Flexion? Yes, it is one of the gentlest hamstring exercises available. Start with one or two sets of 10 to 12 slow repetitions per leg using body weight only, and add an ankle weight only when the tempo feels easy to control. ### How far should my knee bend during Sitting Single Leg Knee Flexion? Bend only as far as feels smooth and pinch-free at the back of the knee; for most people that is somewhere between 100 and 120 degrees from a seated start. Forcing the heel further back under the chair usually just pulls the hips forward on the seat. ### What is the most common mistake in this exercise? Letting the working thigh lift or the hips slide forward as the foot pulls back. Both turn a knee-only movement into a hip movement and reduce the work the hamstrings actually do. Keep the thigh pressed into the seat for every repetition. ### How is this different from a seated leg curl machine? The machine adds a padded resistance lever and a weighted stack, while this version uses only the weight of your lower leg. The joint path is similar, so the body-weight version is a sensible introduction or a substitute when no machine is available. ### Can I use resistance with Sitting Single Leg Knee Flexion? Yes. A light ankle weight around the working ankle is the simplest option, and slowing the return phase to three or four seconds increases the challenge without any equipment at all. ### How many sets and reps should I do? Two to three sets of 10 to 15 controlled repetitions per leg works well for general strength and endurance. Because the resistance is light, prioritize tempo and a clean thigh position over chasing high rep numbers. ### Should I feel anything behind my knee during this exercise? You should feel muscular effort in the hamstring belly above the knee, not sharp pain or pinching right in the joint crease. If the joint itself complains, reduce the range, slow down, and check that your thigh is staying flat on the seat. ### Can I pair Sitting Single Leg Knee Flexion with another exercise? It pairs naturally with seated knee extensions, where you straighten the leg instead of bending it, so you train the hamstrings and quadriceps from the same chair without changing your setup.