# Lying Alternating Legs Extension - Canonical: https://fitwill.app/exercise/9660/lying-alternating-legs-extension/ - Media ID: 9660 - Primary muscle: Hips - Body part: Hips - Equipment: Body Weight - Video: https://fitwill.app/videos/9660/lying-alternating-legs-extension.mp4 ## Description The Lying Alternating Legs Extension is a bodyweight movement performed flat on your back, where you draw one knee in toward your chest and then extend that leg back out to full length while the opposite leg stays controlled on the floor. The two legs trade roles rep by rep, so while one hip flexes and straightens, the other holds a stable, lengthened position. This alternating rhythm is what separates it from a two-leg tuck or a straight leg raise: one side is always moving, and the other is always bracing. The main work comes from the hip flexors, particularly the iliopsoas and the rectus femoris, which drive the knee toward the torso and control the leg as it extends away. The lower abs work isometrically to keep your pelvis from tipping and your lower back from arching off the floor, and the quads help lock the extended leg out straight. Because the hands can lightly assist the knee in the tucked phase, the exercise scales easily from gentle to demanding. This is a useful drill for people who sit for long hours and feel stiff through the front of the hip, for beginners building basic leg control before progressing to hanging knee raises or straight-leg raises, and for anyone warming up the hips before squats, lunges, or running. It also works well in rehab-adjacent settings because the floor supports the spine and the range can be kept small. Setup matters more than it looks. Lying flat with the low back in contact with the floor gives the hip flexors a fair starting length and stops the lumbar spine from doing the work. If your back arches the moment a leg moves, bending the support knee slightly or keeping the working leg a little less extended will fix it without losing the point of the drill. To execute it well, move one leg at a time with deliberate speed: pull the knee in, pause briefly, then let the leg travel back to full extension under control rather than letting gravity drop it. The leg that stays down should press gently into the floor and stay still. Rushing turns this into a series of uncontrolled leg swings, and the hips and abs stop getting the benefit. Keep the reps moderate and the quality high. If you feel pinching at the front of the hip, reduce the range, slow the tempo, or shorten the lever by keeping the knee more bent on the way back out. Discomfort in the low back rather than working effort in the hip is a signal to reset your position before continuing. ## Instructions 1. Lie flat on your back on an exercise mat or the floor with both legs extended straight and your arms relaxed at your sides, palms down. 2. Press your low back gently toward the floor and brace your abdominals before any leg moves, so your pelvis starts in a neutral, stable position. 3. Draw one knee up toward your chest, letting the knee bend fully; you may lightly guide the knee with one or both hands if you need the assistance. 4. Keep the opposite leg extended, thigh pressing toward the floor, and hold it still while the working leg moves. 5. Pause briefly at the top with the knee close to your chest, feeling the hip flexors of the extended leg under a mild stretch. 6. Extend the working leg back out to full length in a slow, controlled path, resisting gravity instead of dropping it. 7. Exhale as you pull the knee in, inhale as the leg extends back out, keeping the breath steady throughout. 8. Repeat the knee tuck and extension on the same leg for the planned reps, or alternate legs rep by rep depending on your program. 9. Reset your brace after each set: check that the low back stays in contact with the floor and reposition if it has lifted. 10. To finish, bring both knees in together, then lower both legs to rest, or roll to one side before standing up. ## Tips & Tricks - The most common mistake is the low back peeling off the floor as the leg extends away. Watch for a growing gap behind your waist and fix it by bracing harder or not extending the leg quite so far. - If pulling the knee in with the hands, apply gentle guidance only. Yanking the knee toward the chest shifts the effort away from the hip flexors and turns it into a passive stretch. - Keep the extended leg active, not floppy. A leg that rolls outward or drifts sideways means the stabilizing muscles have switched off and the pelvis is free to tilt. - Slow the return phase to about two or three seconds. Most people get the tuck right and then let the leg fall, which removes half the training effect on the hip flexors. - If the front of the hip pinches when the leg is fully straight, extend the leg with a slightly bent knee or reduce how far the leg travels from the body. The range should feel like work, not compression. - Point your toes of the extended leg toward the ceiling to help keep the knee straight and the quad engaged through the full length of the leg. - Keep the head and shoulders relaxed on the floor. Craning the chin to watch your legs tightens the neck and distracts from keeping the pelvis steady. - On a hard floor, use a mat. The tailbone and lower spine stay in contact with the ground the entire set, and padding makes the position comfortable enough to hold good form. - If one hip flexor feels much tighter than the other, start with the stiffer side and match the reps, so the looser side does not quietly do more volume. ## Frequently Asked Questions ### What muscles does the Lying Alternating Legs Extension work? The primary movers are the hip flexors, especially the iliopsoas and rectus femoris, which lift the knee and control the leg as it extends. The lower abs stabilize the pelvis, and the quads help keep the extended leg straight. ### Is the Lying Alternating Legs Extension suitable for beginners? Yes. The floor supports the spine and the hands can assist the knee toward the chest, so the difficulty is easy to adjust. Beginners should start with a smaller extension range and prioritize keeping the low back on the floor. ### Why does my lower back arch when one leg extends during the Lying Alternating Legs Extension? That arch means the abs are not bracing enough to hold the pelvis still while the hip flexors pull on the spine from the front. Brace harder before moving, or reduce how far the leg extends until you can keep the back in contact with the floor. ### Should I hold my knee with my hands in this exercise? You can use the hands for light guidance, which makes the movement accessible when the hip flexors are weak or stiff. Keep the pull gentle and let the hip muscles, not your arms, do most of the work. ### How is the Lying Alternating Legs Extension different from a straight leg raise? In a straight leg raise both legs move through the same path together, while here one leg tucks and extends at a time and the other holds still. That gives you a moving hip and a stabilizing hip on every rep, which trains control rather than just flexor strength. ### Can I use this exercise as a warm-up before lower body training? Yes, a set or two of slow, comfortable reps works well before squats, lunges, or running, because it takes the hips through flexion and extension under light load. Keep the tempo smooth and stop short of fatigue. ### How many reps of the Lying Alternating Legs Extension should I do? Around 8 to 12 controlled repetitions per side is a reasonable working range, or 20 to 30 seconds of continuous alternating for a warm-up. Quality of the controlled return matters more than the total count. ### What can I do if the front of my hip pinches during the movement? Reduce the extension range, keep a slight bend in the knee as the leg travels out, and slow the tempo. If pinching persists, switch to a bent-knee version or consult a qualified professional before continuing. ### Can I do the Lying Alternating Legs Extension without a mat? Yes, any firm, flat surface works, since the exercise requires no equipment. A mat simply makes the contact points at the tailbone and spine more comfortable during longer sets.