Jack knife on Ball
Perform the Jack knife on a stability ball to engage your core and improve balance.
- Start by lying on your back on the stability ball, with your feet on the ground.
- Extend your arms overhead and legs straight.
- Simultaneously lift your upper body and legs, bringing them together above the ball.
- Lower back to the starting position and repeat.
How to perform the Jack knife on Ball
- Set up. Set up in a stable, balanced starting position appropriate for the Jack knife on Ball using your stability ball.
- Brace and execute. Brace your core, control the descent, and move through a full pain-free range of motion while emphasizing your abdominals.
- Reset. Reverse the movement under control and reset between repetitions, keeping your form crisp on every rep.
Coaching cues
- Move with intent — every rep should feel deliberate, not rushed.
- Drive force through your abdominals rather than momentum.
- Keep your breathing steady: exhale on the hard part, inhale on the reset.
Common mistakes
- Using too much weight and losing positional control.
- Cutting the range of motion short and missing the target muscle.
- Letting your spine round or hyperextend instead of staying neutral.
Detailed cues, common mistakes, and demonstration video are available in the Fitly app.
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