BOSU Crunch
A crunch on the BOSU dome that opens up a deeper range of motion through the rectus abdominis than the flat floor allows.
Level: Beginner
Primary: Abs
Movement: Isolation
Tags: Balance / Stability
Type: Strength (Weight Lifting)
Equipment: Balance Trainer
Target muscles
The rectus abdominis does the work, shortening to pull your ribcage toward your pelvis. Because the dome lets your spine extend slightly below horizontal at the bottom, the abs are loaded through a longer range than a floor crunch, which raises the tension at full stretch. The transverse abdominis and obliques fire isometrically to keep you centred on the unstable surface.
How to perform
Setup
Sit on the centre of the BOSU and walk your feet out until your lower back is draped over the dome and your hips are slightly below your knees. Plant your feet flat, hip-width apart. Cross your hands on your chest or cup them lightly behind your ears without pulling on your neck.
Execution
Exhale and curl your sternum toward your hips, peeling your upper back off the dome one vertebra at a time. Stop when your shoulder blades clear the surface — this is a short-range spinal flexion, not a sit-up. Pause for a beat at the top and squeeze, then inhale as you lower under control until your back wraps the dome again and you feel the stretch through your abs. Keep the movement smooth; let the curve of the BOSU dictate the range rather than throwing yourself up.
Common mistakes
- Hauling on the head and jutting the chin forward, which strains the neck instead of loading the abs.
- Hinging from the hips like a sit-up rather than flexing the spine segment by segment.
- Sliding too far back so the dome supports the hips, which removes the lengthened-position advantage.
- Rushing the eccentric and bouncing off the dome to start the next rep.
Progressions and regressions
Regress by reducing the range or moving to a flat-floor crunch until the balance demand feels manageable. Progress by holding a light plate or dumbbell across the chest, extending the arms overhead for a longer lever, or pausing for two seconds at the top of each rep. A decline-style BOSU crunch with the feet elevated raises the difficulty further.
Programming notes
Treat this as accessory core work at the end of a session, 2-3 sets of 12-20 controlled reps. The unstable base makes high-rep grinding messy, so stop a couple of reps shy of failure where form stays crisp. It pairs well with an anti-extension hold like a plank to train both the shortening and the bracing roles of the abs.
