Flexion Leg Sit Up (straight Arm)
intermediate strength exercise · body weight · targets abs
- Body part
- waist
- Primary target
- abs
- Equipment
- body weight
- Difficulty
- intermediate
The flexion leg sit-up with straight arm is a sit-up variation performed with the arms extended overhead rather than crossed at the chest or behind the head. The extended arm position increases the lever arm of the upper body, dramatically increasing the difficulty of each rep compared to standard sit-ups. This variation is significantly harder than typical sit-ups due to the extended arm lever. Most trainees who can do 20-30 standard sit-ups can only manage 10-15 of the straight-arm variation. The increased difficulty comes from physics — the further the load is from the pivot point (hips), the more force the abs must produce. Where this earns its place is as a progression from standard sit-ups for trainees who've outgrown them. The increased difficulty drives more meaningful adaptation per rep. Programmed 2-3 times per week as part of core training, the straight-arm sit-up complements planks and rotational work for comprehensive ab development.
Why train the Flexion Leg Sit Up (straight Arm)?
- Increases sit-up difficulty through extended arm lever.
- Drives more meaningful ab adaptation per rep than standard sit-ups.
- Useful as progression for trainees who've outgrown standard sit-ups.
- Engages shoulders and upper back through sustained arm-overhead position.
- Pairs naturally with planks for compound core work.
- Costs nothing and requires no equipment.
How to do the Flexion Leg Sit Up (straight Arm): step by step
- 1Lie flat on your back with your legs extended and arms straight above your head.
- 2Engaging your abs, lift your upper body off the ground while simultaneously lifting your legs towards your chest.
- 3Reach your hands towards your toes as you lift your upper body and legs.
- 4Pause for a moment at the top, then slowly lower your upper body and legs back down to the starting position.
- 5Repeat for the desired number of repetitions.
Muscles worked
Primary
abs
Secondary
hip flexors, quadriceps
Common mistakes to avoid
Letting arms drop forward
Arms must stay extended overhead throughout the rep. Dropping reduces the lever and the difficulty.
Anchoring feet
Feet free; anchored feet recruit hip flexors.
Bouncing through reps
Slow controlled motion produces ab engagement.
Insufficient prerequisites
Master 20+ standard sit-ups before attempting straight-arm version.
Cutting range
Full range required for the lever to matter.
Easier and harder variations
Easier
Cross arms at chest (standard sit-up). Or perform with feet bent and feet flat without straight arms.
Harder
Hold a weight overhead (small plate or kettlebell). Or slow tempo. Or add a 1-2 second pause at the top.
Alternative exercises
Standard sit-up
Easier version with arms crossed at chest. Use as foundation.
Hollow body hold
Isometric core work in similar position.
V-up
Combined upper-and-lower body lift. More demanding.
How to program the Flexion Leg Sit Up (straight Arm) into your training
Sets and reps: 3 sets of 8-15 reps. Frequency: 2-3 times per week. In core sessions: as primary front-ab work after foundational planks.
Recovery and frequency
Recovery within 24-48 hours. Watch for lower-back discomfort.
Frequently asked questions
How many reps?
8-15 per set. Significantly fewer than standard sit-ups due to increased difficulty.
How often?
2-3 times per week.
Why is this harder?
Extended arm lever multiplies the force the abs must produce.
Should beginners do this?
No — master standard sit-ups (20+ reps) first.
Will this build abs?
Yes — meaningful ab development with adequate volume and consistent training.
Should I add weight?
Eventually — hold a small weight overhead for advanced loading.
Useful tools for this exercise
Build a workout with the Flexion Leg Sit Up (straight Arm)
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