# Straight Hip Single Leg Curl On Stability Ball - Canonical: https://fitwill.app/exercise/9047/straight-hip-single-leg-curl-on-stability-ball/ - Media ID: 9047 - Primary muscle: Hamstrings - Body part: Legs - Equipment: Stability Ball - Video: https://fitwill.app/videos/9047/straight-hip-single-leg-curl-on-stability-ball.mp4 ## Description The Straight Hip Single Leg Curl On Stability Ball is a unilateral hamstring exercise performed lying on your back with one heel resting on a stability ball while the other leg is held straight and lifted off the floor for the entire set. From that position, you pull the ball toward your hips by bending the working knee, then extend back out with control. Because only one leg drives the ball, the hamstrings on the working side handle the full load, and the straight leg creates an additional demand on your trunk to keep the hips level and square. This movement is a step up from the two-leg stability ball hamstring curl. Single-leg versions expose left-to-right differences in hamstring strength and hip control, which matters for runners, field sport athletes, and anyone rehabilitating back into bilateral training after a layoff. The bent-knee knee flexion work also targets the hamstrings in a way hip extension exercises like glute bridges do not, since the knee joint does the majority of the moving. The setup is what separates a good rep from a sloppy one. Your shoulders stay flat on the floor with arms out to the sides for support, hips stay extended so your body forms a straight line from shoulders to knee, and the non-working leg stays straight and elevated. If your hips sag or rotate, the exercise loses its point and your lower back picks up work it should not. That is why the stability ball should be inflated so it sits firm rather than squishy, which makes the roll smoother and more predictable. To perform it well, think about dragging the ball in with your heel rather than lifting your hips higher. The hips should stay elevated at roughly the same height throughout the curl, and the motion happens at the knee. Exhale as you pull the ball in, pause briefly when the knee is fully bent, then lower the leg back to a long position without letting the hips drop. Expect your hamstrings to work hard and your trunk to work harder than you anticipate, especially on the side where the leg is held straight. Grip is minimal here, and the arms are only there for balance, so there is little to limit you except leg strength and body control. Most people do well with two to four sets of six to twelve reps per side, resting a minute or so between sides. Use this exercise as a progression once bilateral ball curls feel easy, or as a targeted hamstring builder on days when your lower back is not up for deadlift variations. Because it is bodyweight-driven, it is also easy to slot into home training where the only piece of equipment needed is the ball itself. Stop the set if you feel cramping in the hamstring or a loss of hip height, both of which signal fatigue rather than a need to push on. ## Instructions 1. Lie on your back on the floor with your arms out to your sides at roughly 45 degrees, palms down, for support. 2. Place one heel on top of the stability ball with the knee slightly bent, and extend that leg so your hips can lift into a straight line from shoulders to knee. 3. Raise your other leg off the floor and hold it straight, keeping it in line with or slightly above the working thigh. 4. Lift your hips toward the ceiling until your body forms a straight line from shoulders through the knee on the ball. 5. Brace your core and squeeze the glute on the working side to hold that hip height before moving. 6. Exhale and drag the ball toward your hips by bending the working knee, pulling with the heel and keeping the ball tracking straight rather than drifting sideways. 7. Continue until the knee is fully bent and the ball is tucked close to your glutes, holding a brief pause at the top. 8. Slowly extend the knee and let the ball roll back out until the leg is long again, keeping the hips lifted the entire time. 9. Inhale at the extended position, reset your brace, and repeat for the target reps before switching legs. 10. To finish a set, roll the ball out to the long position and lower your hips back to the floor with control before bringing the elevated leg down. ## Tips & Tricks - If the ball slides or drifts sideways as you curl, your hips are rotating. Point the toes of the working foot up slightly and press the heel directly into the ball rather than hooking with the top of the foot. - Hips sagging as you pull in is the most common fault. Set your hip height before the first rep and cue yourself to curl the ball without letting your torso and thigh line break. - Do not let the straight leg drop toward the floor as you fatigue. Once it drops, the exercise becomes easier and the set is effectively over, so end the rep there. - A softer, underinflated ball wobbles and makes single-leg curls much harder to steer. If reps feel chaotic, firm up the inflation before blaming your form. - Keep the shoulders pressed into the floor and resist the urge to press hard through the arms. The arms are for balance only, so pushing too hard through your hands can twist your torso. - If your hamstring cramps at the top of the curl, shorten the range slightly at first and work toward full knee bend over several sessions. Cramping is common in single-leg knee flexion when the muscle is not used to the demand. - Keep your neck relaxed and your gaze at the ceiling. Craning the head forward adds tension to the upper body and tends to tip the hips. - Slow down the extension phase rather than the curl. Letting the ball shoot back out on the way in or out is where most reps lose their value. - Master the two-leg stability ball curl first. If you cannot hold a stable bridge position with both heels on the ball, the single-leg version will expose it immediately. ## Frequently Asked Questions ### What muscles does the Straight Hip Single Leg Curl On Stability Ball work? The hamstrings are the primary movers because the knee flexes to pull the ball in, with the glutes and lower back holding the hips up. The core also works hard to keep the trunk level while one leg is held straight in the air. ### Why does one leg stay straight during this exercise? Holding the non-working leg straight keeps it out of the movement and forces the hips to stay level without a second foot on the ball. This makes each hamstring work on its own and adds a balance and trunk control challenge. ### Is the Straight Hip Single Leg Curl On Stability Ball suitable for beginners? It can be, but only after the two-leg stability ball curl feels stable. If the hips wobble or sag with both heels on the ball, build that variation first before progressing to one leg. ### How high should my hips be during the curl? Your hips should form a straight line from your shoulders to the knee on the ball and stay at that height through the whole rep. If your hips drop as you pull in or extend out, the set is losing its hamstring focus. ### Should I press hard with my arms on the floor? No, the arms are only there for balance. Pressing hard through your hands tends to twist the torso and shift work away from the legs, so keep the contact light and let the heel drive the ball. ### The ball keeps drifting to one side. What should I fix? This usually means the hips are rotating or the heel is hooking the ball instead of pressing into it. Square your hips, point the working toes up, and pull the heel straight back toward your glutes. ### Can I substitute the Straight Hip Single Leg Curl On Stability Ball with anything at home? Yes. Glute bridges with the heel dug into the floor, sliding leg curls using a towel on a smooth floor, or lying hamstring curls with a band around the ankles cover similar ground when no ball is available. ### How many reps should I do per side? Two to four sets of six to twelve controlled reps per leg is a reasonable range. Because single-leg knee flexion fatigues quickly, stop the set when hip height or form starts to slip rather than grinding out extra reps. ### Is it safe for my lower back? For most people it is a back-friendly hamstring exercise because it is done lying down with bodyweight load. Keep the hips supported by the glutes rather than arching the lower back, and if you feel strain in the lumbar area, reduce the range or return to the two-leg version.