Exercise guide
Straight Leg Opposite Sit Up
- Intermediate
- Compound
- Rep-based
- Core
This exercise targets the rectus abdominis and obliques by combining trunk flexion with rotation, while simultaneously engaging the hip flexors and quadriceps to lift the legs. It is highly effective for developing functional core strength and midsection definition.
Reviewed by the Crucible Fit team · Updated June 2026
Muscles worked
Setup
- Lie flat on your back on a mat with your legs fully extended and feet together.
- Extend your arms straight overhead, resting them on the floor.
- Engage your core by pressing your lower back firmly into the mat to eliminate any arch.
How to do it
- Exhale as you simultaneously lift your right leg and your entire upper body off the floor in a folding motion.
- Reach your left hand toward your right foot, rotating your torso so your shoulder moves toward the opposite hip.
- Inhale as you lower your torso and leg back to the starting position with a slow, controlled tempo.
- Repeat the movement on the opposite side, alternating between right and left for the duration of the set.
Form checklist
- Keep the moving leg as straight as possible throughout the entire range of motion.
- Avoid using momentum or swinging your arms to 'throw' yourself upward.
- Ensure your shoulder blades fully clear the floor at the peak of the movement.
- Keep your neck neutral by tucking your chin slightly rather than pulling on your head.
Pro tips
- Focus on the 'mind-muscle connection' by imagining your belly button is the hinge point where your upper and lower body meet.
- Exhale forcefully at the top of the movement to achieve a deeper contraction in the transverse abdominis and obliques.
Make it harder
- Maintain a 'hollow body' position by keeping your heels and shoulder blades hovering 2 inches off the floor between every rep.
- Hold a light dumbbell or medicine ball with both hands to increase the resistance during the trunk flexion and rotation.
Frequently asked
- What muscles does the straight leg opposite sit up work?
- The straight leg opposite sit up primarily targets the abs and obliques, and also works the hip flexors and quadriceps as secondary muscles.
- What equipment do you need for the straight leg opposite sit up?
- The straight leg opposite sit up requires no equipment — just your body weight.
- Is the straight leg opposite sit up good for beginners?
- The straight leg opposite sit up is rated intermediate. Build a base with simpler variations first, then progress to it with light load and strict form.