Core · Bodyweight
Knee in and Out Crunch
How to do the knee in and out crunch, the muscles it works, and the mistakes to avoid. Pulled straight from the Kovo app's exercise library.
- Equipment
- Bodyweight
- Difficulty
- Beginner
- Logged as
- Reps
- Movement
- Flexion
- Mechanic
- Isolation
How to do it
Sit on the floor or a bench and lean back slightly, hands behind you for support and legs extended out front. Crunch your knees in toward your chest by bending at the hips and waist, then extend your legs back out without letting your feet touch the floor. Keep tension on your abs the whole set.
- 1Your lower abs pulling your knees in to your chest
- 2Constant tension on your core as your legs extend out
- 3A controlled tempo in both directions
Common mistakes
- Don't let your feet rest on the floor between reps
- Avoid rounding through your lower back to yank the knees in
- Don't use momentum; keep the motion deliberate
Muscles worked
The knee in and out crunch mainly works the lower abs, with the upper abs, hip flexors, and obliques assisting.
- Lower AbsPrimary
- Upper AbsSupport
- Hip FlexorsSupport
- ObliquesSupport
- TricepsMinor
- ForearmsMinor
- QuadsMinor
Kovo programs the knee in and out crunch for you and tracks it every session.
We build your whole program, drop the right lifts into each workout, and adjust your weights as you get stronger. Free on iOS and Android.
More abs & core exercises
- How to do the ab wheel rollout
- How to do the ankle tap plank
- How to do the ankle taps
- How to do the resistance band dead bugs
- How to do the resistance band pallof press
- How to do the rollout
Last reviewed June 2026.