Sit-Up

What is the Sit-Up?

The sit-up is a full-range bodyweight trunk-flexion movement: from lying flat you curl all the way up until your torso is upright, then lower back down. The longer range makes it a classic ab builder, though the hip flexors assist in the second half, so keeping the focus on curling the spine is what keeps the abs working.

Muscles worked

Primary: Abs

The rectus abdominis is the target, flexing the trunk to peel the spine off the floor and curl the ribcage toward the pelvis through a long range of motion.

Stabilizers

The transverse abdominis braces the trunk as you rise, controlling the curl rather than letting the movement collapse.

How to perform the Sit-Up

1. Lie on your back with knees bent and feet flat or anchored, hands crossed on the chest to avoid hauling on the neck.
2. Unlike a crunch, the sit-up carries the flexion through until the torso is upright, blending spinal flexion with hip flexion.
3. Begin by flexing the spine to peel the shoulders up, then continue folding at the hips to bring the chest toward the knees.
4. Lead with the ribcage curling toward the pelvis so the abs initiate before the hip flexors take over the upper portion.
5. Sit up until the torso is roughly vertical, keeping the movement smooth rather than jerking up with momentum.
6. Reverse under control, rolling the spine back down one segment at a time until the shoulder blades and then the head return to the floor.

Suggested working range: 15–20 reps. Default progression: double progression.

Mechanics

A full-range trunk-flexion isolation that travels much further than a crunch, from flat to fully upright. The abs do the initial curl off the floor; past the halfway point the hip flexors take over more of the work as the torso hinges up. Leading with a spinal curl rather than a straight-torso hinge keeps the emphasis on the abs.

Form cues

• •Curl up one vertebra at a time, leading with the ribs. Don’t jerk the whole torso up as a rigid plank hinging from the hips.
• •Lower under control all the way back down instead of dropping; the eccentric is where a lot of the ab work lives.
• •Keep your hands off your neck: cross them on the chest or reach toward the knees rather than yanking the head forward.

Common mistakes

• •Hooking the feet and yanking the torso up with the hip flexors before the abs even engage.
• •Pulling on the neck with the hands to haul the upper body off the floor.
• •Throwing the arms forward for momentum and bouncing up rather than curling the spine.
• •Dropping straight back down and slamming the shoulders instead of rolling the spine down under control.

Variations & alternatives

• •Crunch: the short-range version that trims the hip-flexor involvement and isolates the upper abs.
• •Bicycle crunch: a dynamic variation that alternates sides and brings the obliques into the curl.
• •Cable crunch: a loadable trunk-flexion option when you want to add resistance rather than range.

Crunch

Abs · Bodyweight

Cable Crunch

Abs · Cable

Hanging Leg Raise

Abs · Bodyweight

Machine Crunch

Abs · Machine

Decline Crunch

Abs · Bodyweight

Programming: sets, reps & when to use it

Program sit-ups for moderate-to-high reps, around 15–20 per set, using the full range as the training stimulus. If you feel it mostly in the front of your hips, shorten toward a crunch or slow the tempo so the abs lead the curl.

Frequently asked questions