# Lying Single Leg Extension - Canonical: https://fitwill.app/exercise/9525/lying-single-leg-extension/ - Media ID: 9525 - Primary muscle: Quads - Body part: Thighs - Equipment: Body Weight - Video: https://fitwill.app/videos/9525/lying-single-leg-extension.mp4 ## Description The Lying Single Leg Extension is a bodyweight movement performed on your back, where one knee is pulled gently toward your chest while the other leg straightens fully toward the ceiling. The leg that extends has to work against gravity with no help from momentum or the other side, which makes the quadriceps do the bulk of the work through the full straightening action. Because the opposite knee is held in toward the torso, the pelvis stays anchored and the lower back is protected from arching as the working leg moves. This is a quietly demanding exercise. With no external load, the resistance comes purely from the weight of your own leg and the angle you create at the hip, so the quads, particularly the rectus femoris which crosses both the hip and the knee, are trained through a long range. The hip flexors on the bent, held leg work isometrically to keep that knee tucked, and the deep core stabilizes the trunk throughout. It is a useful way to load the knee extensors when machines, bands, or weights are not available. Setup matters more here than it looks. If the non-working leg is allowed to drift or the held knee loosens, the pelvis tilts and the lumbar spine takes on movement it should not. Pinning that knee toward your chest with both hands behind the thigh is what locks the pelvis in a neutral, supported position, letting the working leg move cleanly from a bent-knee position to a fully straight line toward the ceiling and back with control. This movement suits beginners learning to extend the knee under control, people returning to training who want a low-load reintroduction for the thighs, and anyone doing home or travel workouts with no equipment. It is also commonly used in warm-ups before squatting or lunging, and in mat-based or Pilates-style sessions where single-leg control is a priority. Keep the tempo slow and the range honest. Straighten the working leg until the knee feels fully but comfortably extended, pause briefly at the top, then lower the leg back to the bent starting position without letting it drop. If you feel pinching at the front of the hip or knee, reduce the range slightly rather than forcing the leg higher. Move one leg at a time, finish all reps on one side before switching, and stop if either knee complains with sharp pain rather than simple muscular effort. ## Instructions 1. Lie on your back on an exercise mat with your head resting on the floor and your gaze up. 2. Bend both knees, then clasp your hands behind the thigh of one leg and draw that knee in toward your chest so the pelvis stays anchored. 3. Bend the other leg so the knee points toward the ceiling and the foot hangs relaxed; this is the leg that will work. 4. Brace your midsection lightly and press your lower back gently toward the mat so the torso stays quiet throughout. 5. Extend the working knee, pushing the foot up toward the ceiling until the leg is as straight as you can make it without the hip lifting. 6. Pause for a beat at the top with the knee fully straightened and the thigh muscles engaged. 7. Bend the knee again and lower the foot back to the starting position slowly, resisting gravity on the way down rather than letting the leg fall. 8. Breathe out as you straighten the leg and breathe in as you bend it back down. 9. Complete all repetitions on one side, then switch hands to the opposite thigh and repeat with the other leg. ## Tips & Tricks - The most common mistake is letting the held knee drift away from the chest as the working leg extends, which tilts the pelvis and arches the lower back. Re-grip behind that thigh every few reps and keep the knee pulled in. - Do not chase height. The goal is a straight knee, not a leg that reaches the ceiling at any cost; if the hip on the working side lifts, you have gone past your available range. - Point the working foot in a neutral position rather than flexing or pointing hard, so the focus stays on the knee extension instead of turning into a calf and ankle exercise. - If the back of the held thigh is tight and your hands struggle to reach, loop a towel behind that thigh to keep the knee tucked without straining your shoulders. - Move deliberately on the lowering phase. Letting the bent leg drop back quickly removes most of the work from the quadriceps, which are doing their job on the way down as much as on the way up. - Keep your head and shoulders relaxed on the mat. Lifting the head to watch the leg usually pulls the upper back off the floor and makes the trunk less stable. - If the knee feels pinchy at full extension, back off to a slightly softer straightening angle and build up over sessions rather than forcing the lockout. - Start with your weaker or stiffer leg first so both sides get the same quality of work when you are fresh. ## Frequently Asked Questions ### Which muscles does the Lying Single Leg Extension work? The quadriceps on the front of the thigh are the primary movers, since they straighten the working knee against gravity. The hip flexors on the bent, held leg work statically, and the deep core stabilizes the pelvis and trunk. ### Why does one knee need to be held toward the chest during the Lying Single Leg Extension? Hugging one knee in pins the pelvis so it cannot tilt or anteriorly rotate as the other leg moves. That keeps the lower back supported and makes the working quadriceps do the job on their own. ### Is the Lying Single Leg Extension suitable for beginners? Yes. Because the only resistance is the weight of your own leg, the load is easy to regulate by adjusting speed and range. Beginners should prioritize a slow, controlled tempo over straightening the knee completely. ### How is the Lying Single Leg Extension different from a leg extension machine? The machine adds external load and supports your torso, while this version uses only the weight of your leg and requires you to stabilize your own pelvis. It trains less absolute force but more single-leg control and coordination. ### How many reps and sets of the Lying Single Leg Extension should I do? Around 8 to 15 controlled repetitions per leg for 2 to 3 sets works well, either as a warm-up before lower-body training or as part of a home session. Rest briefly between sides. ### What should I do if my hip flexor on the held leg cramps? Ease the knee slightly further from the chest, keep your grip relaxed, and shorten the set. Cramping there usually means that hip flexor is being asked to hold more tension than it is used to, so build up gradually. ### Can I substitute the Lying Single Leg Extension if lying on the floor is uncomfortable? You can perform the same single-leg knee extension sitting on a bench or chair, though you lose the pelvic anchoring that the floor and the held knee provide. A firm cushion under the head and hips also makes the floor version more comfortable. ### Should the working leg point straight at the ceiling? Aim the foot roughly toward the ceiling, but the exact angle matters less than a fully straightened knee and a stable pelvis. Stop at whatever height lets you keep the held knee tucked and the lower back flat. ### Is it safe to do the Lying Single Leg Extension with knee pain? Muscular effort in the thigh is normal, but sharp or pinching pain at the knee is not. Reduce the extension range, slow the tempo, and if the pain persists, get the knee assessed before continuing.