Seated Knee-to-chest Crunch
The seated knee-to-chest crunch is a chair-based core exercise that targets the abs through a knee drive from a seated position. It engages the hip flexors and lower abdominals, making it an accessible crunch variation for those seeking a seated core workout.
How to do it
- Sit on the edge of a chair with your hands gripping the sides of the seat for support.
- Lean back slightly and extend one leg out in front of you.
- Draw your knee toward your chest, contracting your abs at the top.
- Extend the leg back out and repeat on the same side for the desired reps before switching.
- Keep your core engaged throughout the movement.
Form cues
- Sit tall on the edge of the chair with your chest proud.
- Grip the sides of the seat firmly for stable support.
- Lean back slightly without rounding your lower back.
- Drive your knee toward your chest smoothly.
- Exhale as you pull your knee up and contract your abs.
Breathing: Exhale as you draw your knee to your chest to contract the abs, and inhale as you extend the leg back out.
Common mistakes
- Slouching the upper back, which reduces ab activation and strains the spine.
- Rushing through the reps using momentum instead of controlled muscle engagement.
- Holding your breath during the knee drive, which raises blood pressure and tires you out faster.
- Leaning back too far, which shifts the work entirely to the hip flexors and strains the lower back.
Muscles worked
Primary: abs. Secondary: hip flexors, lower back.
Suggested sets & reps
Get fitter
3 sets × 10–12 reps per side, rest 60 s
Lose weight
3 sets × 12–15 reps per side, rest 45 s
Build muscle
3 sets × 10–12 reps per side, rest 60 s
Easier, harder & alternatives
Make it easier
Make it harder
Take care if…
- If you feel lower back discomfort, reduce your range of motion or lean back less.
- Stop if you experience any sharp pain during the movement.
General educational guidance, not medical advice. Stop on sharp pain and check with a qualified professional if unsure.
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Start free →Frequently asked questions
What if I feel this more in my hip flexors than my abs?
That is very common. Try leaning back slightly less and focus actively on curling your ribcage toward your pelvis rather than just lifting your leg.
Do I need a special chair for this exercise?
Any sturdy, non-rolling chair works well. Avoid chairs with wheels or unstable folding chairs to ensure safety.
How many times a week can I do seated knee-to-chest crunches?
You can safely perform this movement 2 to 4 times a week as part of your core or full-body routine.