The sit-up is a bodyweight core exercise performed supine with the knees bent that trains theabsand hip flexors by raising the whole torso from the floor to a seated position and lowering it. Unlike a crunch, which stops when the shoulder blades leave the mat, the sit-up continues through the second half of the range, where the hip flexors pull the pelvis toward the thighs and the abs keep the spine curled. That makes it a longer rep shared heavily by the hip flexors. It is a beginner exercise used late in a session or in fitness tests.
What Muscles Does the Sit-Up Work?
- Primary: Rectus abdominis (abs)
- Secondary: Iliopsoas and rectus femoris (hip flexors), external and internal obliques
- Tertiary: Tensor fasciae latae, deep neck flexors, serratus anterior
How Do You Set Up for the Sit-Up?
Lie on your back with your knees bent to about 90 degrees and your feet flat, hip width apart. Anchor your feet under a bench foot, or have a partner hold them, if you cannot keep them down. Cross your arms over your chest or place your fingertips at your temples. Tuck your chin slightly and pull your ribs toward your hips so your abs are tight before you move.
How Do You Perform the Sit-Up?
- Set your feet and brace, chin tucked and abs tight, with your lower back resting on the mat.
- Curl your shoulder blades off the mat, flexing your upper spine so the ribs move toward the hips.
- Continue up from the hips until your torso is upright and your chest is close to your thighs, with your feet still flat.
- Hold the top for one count, keeping the abs contracted so the spine stays gently curled rather than straight.
- Lower under control, uncurling from the hips first and then laying the spine back down one segment at a time.
- Rest your shoulder blades on the mat for a moment with your feet planted, then start the next rep.
What Are the Key Form Cues?
- Curl before you sit: the shoulder blades leave the mat before the hips fold, so the abs begin the rep rather than the hip flexors.
- Keep the spine rounded at the top: a tall, straight-backed finish hands the work entirely to the hip flexors.
- Press your heels lightly into the floor to feel the hamstrings help and the hip flexors relax.
- Exhale as you rise and keep your ribs down so the abs stay short through the whole climb.
- Lower slower than you rise; the descent is where the abs resist the pull of gravity on the torso.
What Are the Most Common Mistakes?
- Throwing the arms and head forward: the abs skip the hardest first inches and the neck takes the pull, so start every rep slowly with the arms still.
- Pulling with the hip flexors from the floor: the lower back arches off the mat and the lumbar spine flexes and extends under the torso's weight, which irritates the discs; curl the ribs down first.
- Letting the feet lift: the body rocks instead of sitting up, so anchor the feet or cross the arms.
- Dropping back to the mat: the eccentric is lost and the tailbone takes a hit, so lower for a 2 to 3 second count.
- Grinding out high reps with a flat back: the abs quit and the hip flexors and lower back finish the set, so stop when the shoulder blades no longer lead the rep.
What Are the Best Sit-Up Variations?
- Crunch: stops when the shoulder blades clear the mat, removing the hip flexor half for beginners.
- Anchored feet sit up: feet hooked under a support so more load can be added through the hands.
- Sit-up cross crunch: adds a twist at the top so one elbow reaches the opposite knee, loading the obliques.
- Decline sit-up on a bench: the head starts below the hips for a longer range under more load.
- Plate sit-up: a plate held on the chest or pressed overhead adds resistance to the same pattern.
How Do You Progress the Sit-Up?
- Add load by holding a 5 or 10 pound plate on the chest once 20 clean reps are easy with the arms crossed.
- Work 10 to 20 reps and add two reps per set each session until you reach 20.
- Start with 2 sets and add a third once the last reps still curl before they sit.
- Slow the descent to 3 seconds, or pause 2 seconds at the top, before adding a plate.
How Should You Program the Sit-Up?
Program the sit-up as a core finisher at the end of a session, after the main lifts, or as one station in a bodyweight circuit. Two to three sessions a week is enough. Do 2 to 3 sets of 10 to 20 reps with 30 to 60 seconds of rest, and pair it with a plank or a dead bug so the abs train anti-extension as well as flexion in the same block.