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  5. Core & Abs
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  7. Crunch On Bosu Ball

Exercise guide

Crunch On Bosu Ball

  • Intermediate
  • Compound
  • Rep-based
  • Waist

The Bosu ball crunch utilizes the dome's curvature to increase the range of motion, allowing for a deeper abdominal stretch and greater muscle fiber recruitment. It isolates the rectus abdominis while the unstable surface forces the obliques to work harder for stabilization.

Reviewed by the Crucible Fit team · Updated June 2026

Watch the Crunch On Bosu Ball demonstrationVideo and instructions for every movement are in the Crucible Fit app.

Muscles worked

Primary

  • Abs
  • Obliques

Secondary

  • Erector spinae

Equipment

  • Bosu ball

Setup

  1. Sit on the forward slope of the Bosu ball with your feet flat on the floor and knees bent at 90 degrees.
  2. Lean back so your lower back is centered on the dome, allowing your spine to follow the ball's curve.
  3. Place your hands lightly behind your ears or cross them over your chest.

How to do it

  1. Exhale and contract your abdominals to curl your ribcage toward your pelvis, lifting your upper back off the ball.
  2. Squeeze your abs at the peak of the movement for one second, ensuring you aren't using momentum.
  3. Inhale as you slowly lower your torso back down, following the contour of the ball to a full stretch.
  4. Maintain a controlled 2-1-2 tempo (2 seconds up, 1 second hold, 2 seconds down).

Form checklist

  • Keep your neck neutral and avoid pulling on your head with your hands.
  • Ensure your lower back stays in contact with the ball throughout the movement.
  • Keep your feet firmly planted to stabilize your base.
  • Focus on the 'crunching' motion of the ribs toward the hips rather than sitting all the way up.

Pro tips

  • At the bottom of the rep, allow your spine to extend slightly over the ball to maximize the eccentric stretch of the abdominal wall.
  • Visualize pulling your belly button toward the ball to ensure deep transverse abdominis engagement.

Make it harder

  • Extend your arms straight overhead to increase the lever length and resistance.
  • Lift one foot off the floor to significantly increase the stability demand on the obliques.

Frequently asked

What muscles does the crunch on bosu ball work?
The crunch on bosu ball primarily targets the abs and obliques, and also works the erector spinae as secondary muscles.
What equipment do you need for the crunch on bosu ball?
The crunch on bosu ball uses bosu ball.
Is the crunch on bosu ball good for beginners?
The crunch on bosu ball is rated intermediate. Build a base with simpler variations first, then progress to it with light load and strict form.

Related exercises

  • 3/4 Sit-UpBeginner · abs and obliques
  • 45 Degree Bicycle Twisting CrunchIntermediate · abs and obliques
  • 45 Degree Lean Back Alternate Knee RaiseBeginner · abs and obliques
  • 45 Degrees Arms PlankIntermediate · abs, deltoids, obliques, and pectorals

Train it with Crucible Fit.

Every movement in this library is in the app with video and instructions, ready for your own sessions on the days between Crucibles. Your first Crucible is on us.

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