Exercise guide
Seated Frog Half To Full Sit Up
- Intermediate
- Compound
- Rep-based
- Waist
This hybrid core movement targets the entire abdominal wall and obliques by combining a partial crunch with a full range sit-up, while the frog-leg position minimizes hip flexor recruitment.
Reviewed by the Crucible Fit team · Updated June 2026
Muscles worked
Setup
- Sit on the end of a flat bench with your knees bent and feet pulled in so the soles are touching.
- Allow your knees to flare out to the sides in a frog position and lean back slightly to find your balance on your sit bones.
- Place your hands lightly behind your ears or cross them over your chest.
How to do it
- Exhale and crunch halfway up, focusing on rib-to-pelvis compression, then lower slightly without letting your back touch the bench.
- Immediately exhale again and perform a full sit-up, bringing your torso toward your thighs while keeping the knees wide.
- Inhale as you lower your torso back to the starting position using a slow, controlled 3-second tempo.
Form checklist
- Keep the knees flared wide throughout the entire set to deactivate the hip flexors.
- Maintain a slight 'C-curve' in the spine to ensure the abs are doing the work rather than the lower back.
- Keep your chin tucked slightly to avoid straining the neck.
- Avoid using momentum or swinging the arms to pull yourself up.
Pro tips
- Focus on 'peeling' your spine off the bench one vertebra at a time during the full sit-up phase to maximize muscle fiber recruitment.
- Squeeze the soles of your feet together hard to help stabilize the pelvis and increase lower abdominal engagement.
Make it harder
- Hold a light weight plate or medicine ball against your chest or extended overhead.
- Increase the time under tension by adding a 2-second pause at the top of both the half and full sit-up.
Frequently asked
- What muscles does the seated frog half to full sit up work?
- The seated frog half to full sit up primarily targets the abs and obliques, and also works the erector spinae as secondary muscles.
- What equipment do you need for the seated frog half to full sit up?
- The seated frog half to full sit up requires no equipment — just your body weight.
- Is the seated frog half to full sit up good for beginners?
- The seated frog half to full sit up is rated intermediate. Build a base with simpler variations first, then progress to it with light load and strict form.