Exercise guide
Atomic Sit Up
- Intermediate
- Compound
- Rep-based
- Waist
The Atomic Sit Up is a dynamic core exercise that combines a traditional sit-up with a knee tuck to target the entire rectus abdominis, hip flexors, and quadriceps. It is highly effective for building explosive core power and improving total-body coordination.
Reviewed by the Crucible team · Updated June 2026
Muscles worked
Setup
- Lie flat on your back on a mat with your legs fully extended and feet together.
- Reach your arms overhead, resting them on the floor behind you.
- Press your lower back into the mat to engage your deep core before starting.
How to do it
- In one explosive motion, exhale and sit up while simultaneously pulling your knees toward your chest.
- Reach your arms forward past your knees or tuck them toward your shins at the peak of the movement.
- Inhale as you slowly reverse the motion, extending your legs and arms back to the starting position.
- Maintain a controlled 1-0-1-0 tempo, avoiding the use of excessive momentum from the arms.
Form checklist
- Keep your feet and shoulder blades slightly off the floor between reps to maintain constant tension.
- Ensure your upper body and lower body meet in the middle at the same time.
- Avoid arching your lower back as you extend your legs back to the starting position.
- Focus on pulling your ribs toward your pelvis during the concentric phase.
Pro tips
- To maximize muscle engagement, pause for a split second at the top of the movement to emphasize the peak contraction.
- Think about 'hollowing' your stomach as you sit up to ensure the deep transverse abdominis is firing.
Make it harder
- Hold a light medicine ball or weight plate in your hands throughout the entire range of motion.
- Slow down the eccentric (lowering) phase to a 3-second count to increase time under tension.
Frequently asked
- What muscles does the atomic sit up work?
- The atomic sit up primarily targets the abs, and also works the hip flexors as secondary muscles.
- What equipment do you need for the atomic sit up?
- The atomic sit up requires no equipment — just your body weight.
- Is the atomic sit up good for beginners?
- The atomic sit up is rated intermediate. Build a base with simpler variations first, then progress to it with light load and strict form.