Straight Leg Sit-Up

Body Part: Waist

Muscle: Abs

Equipment: Other

Straight Leg Sit-Up is a floor-based core exercise built around a long lever: your legs stay straight while your torso curls up from the mat. That longer body position makes the movement more demanding than a standard crunch, so it is useful for training trunk flexion, midline control, and the ability to keep the ribs and pelvis organized while the body moves through a full sit-up pattern.

The main work comes from the abs, especially the rectus abdominis, with the obliques helping keep the torso from twisting and the hip flexors contributing as you rise. Because the legs remain straight, the hips and hamstrings also influence how smooth the rep feels. If the low back takes over or the movement turns into a swing, the set stops feeling like a Straight Leg Sit-Up and starts turning into momentum.

The setup matters more than it looks. Lie flat on a mat with the legs extended, feet relaxed on the floor, and the arms reaching overhead so the body starts long and balanced. Before each rep, lightly brace the midsection, keep the chin slightly tucked, and make sure the lower back is settled before you begin curling up. That first position should feel organized, not loose or stretched out of control.

To perform the rep, exhale as you lift the head, shoulders, and ribcage off the floor, then continue curling the torso until you can reach toward the feet with control. Keep the legs long and avoid kicking or swinging them to help the ascent. At the top, sit tall enough that the abs are still doing the work, then lower back down slowly so each section of the spine returns to the mat instead of dropping all at once.

Straight Leg Sit-Up works well as a bodyweight core drill, part of an abdominal circuit, or a foundational movement before more advanced loaded core work. It also makes a good benchmark exercise because small changes in control, range, and tempo are easy to notice. If the movement feels too aggressive on the lower back, shorten the range or soften the knees slightly rather than forcing a sloppy full sit-up.

Use this exercise when you want a clear, simple test of trunk strength and control without equipment. Clean reps matter more than speed here, and the best sets are the ones where the torso rises smoothly, the legs stay quiet, and the return to the floor is just as controlled as the lift.

Instructions

• Lie on a mat with your legs straight, feet lightly on the floor, and your arms reaching overhead so your body starts long.
• Keep your heels relaxed, your knees extended, and your hands close to the floor behind you without letting your ribs flare.
• Tighten your midsection and press your lower back into the mat before the first rep begins.
• Exhale and curl your head, shoulders, and upper back off the floor, leading with your ribcage instead of throwing your arms forward.
• Continue the sit-up by reaching your hands toward your feet while keeping your legs long and quiet.
• Finish tall with your torso over your hips and your abs still doing the work, not your lower back.
• Inhale and lower yourself one section at a time until your shoulder blades touch down again.
• Return your arms overhead, reset your brace, and repeat for the planned reps.

Tips & Tricks

• Keep the legs dead still; if they start swinging, the hip flexors are stealing the rep from the abs.
• Think about curling the ribcage toward the pelvis instead of simply reaching your hands forward.
• A slow, smooth descent makes the Straight Leg Sit-Up much harder on the abs than a quick drop.
• If your lower back arches hard off the mat at the start, shorten the range before trying to sit all the way up.
• Keep the chin slightly tucked so the neck does not lead the movement.
• Let the feet stay lightly planted instead of lifting them to chase more height.
• Use a smaller range if tight hamstrings pull on the pelvis and make the rep jerky.
• Stop the set when you need to kick, jerk, or snap the torso upright to finish the rep.

Frequently Asked Questions

What muscles does Straight Leg Sit-Up work most?

The main target is the abs, especially the rectus abdominis, with the obliques and hip flexors helping during the lift.

Is Straight Leg Sit-Up good for beginners?

Yes, but most beginners should start with a short range and slow tempo. If the full sit-up feels too hard on the lower back, bend the knees slightly or switch to a shorter floor curl.

Should my feet stay on the floor during Straight Leg Sit-Up?

Yes, keep the heels lightly planted and the legs long. If the feet fly up, the rep is usually turning into a hip-flexor swing instead of a controlled sit-up.

How far should I come up on Straight Leg Sit-Up?

Come up until your torso is tall and your abs are still controlling the movement. You do not need to snap straight upright if that only happens by jerking or pulling with momentum.

Why are the legs kept straight in Straight Leg Sit-Up?

The straight-leg position creates a longer lever and makes the trunk work harder to lift. It also makes control more important because the hips and hamstrings influence the whole rep.

What is the biggest mistake in Straight Leg Sit-Up?

The most common mistake is using momentum from the arms or hips to fling the torso up. A clean rep should look smooth on the way up and slow on the way down.

Can I add weight to Straight Leg Sit-Up?

You can, but only after bodyweight reps are clean. A light plate held at the chest is usually safer than loading the hands overhead, which can pull the lower back out of position.

What should I do if Straight Leg Sit-Up bothers my lower back?

Shorten the range, slow the lowering phase, or bend the knees a little. If pain continues, choose a different core drill instead of forcing the full sit-up.