Leg Curl (Stability Ball)
The Stability Ball Leg Curl is a hamstring-dominant exercise that involves curling a stability ball towards your glutes while maintaining a bridge position. This movement builds posterior chain strength and core stability by forcing you to balance on an unstable surface.
Since hamstrings are notoriously slow to recover and prone to cramping, our AI analyzes your recent leg training volume and sleep quality to prescribe the perfect rep range for today's session. If you struggle with maintaining hip height (a sign of fatigue), the app detects RPE spikes and can adjust upcoming sets to prevent form breakdown. Additionally, if you have a history of lower back tightness, the system can suggest regressions like machine curls to isolate the hamstrings without stressing the lumbar spine.
Form Cues
- Keep your hips elevated and glutes squeezed throughout the entire set
- Dig your heels firmly into the ball to engage the hamstrings
- Curl the ball in until your knees are bent at 90 degrees
- Control the release phase slowly as you roll the ball back out
- Don't let your hips sag towards the floor as you curl the ball in
- Don't hyperextend your lower back to compensate for weak hamstrings
- Don't let the ball wobble side-to-side; keep your core braced
- Don't rush the extension phase; keep tension on the muscles
Common Mistakes
- Sagging hips during the curl
- Relying on momentum to move the ball
- Hyperextending the lumbar spine
- Insufficient range of motion
- Relaxing the core
Muscles Worked
This exercise primarily strengthens the hamstrings through knee flexion while simultaneously challenging the glutes to maintain hip extension. Unlike machine curls, it forces the core and stabilizer muscles to work overtime to keep the unstable ball steady, providing a functional boost to your posterior chain.
Primary
Secondary
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