Straight Leg Sit-Up
- Primary muscleAbs
- EquipmentBodyweight
- DifficultyBeginner
- TypeCore · Core flexion
- Secondary muscles
- Hip Flexors
- Body part
- Core
- Position
- Lying
- Laterality
- Bilateral (both sides together)
- Category
- Strength
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Performing sit-ups with your legs extended flat instead of bent changes your pelvic starting position and lengthens the hip flexors, so the abs must initiate the curl before anything else can help. Press your lower back toward the floor as you begin each rep; if your feet fly up, the movement has turned into a hip-flexor pull.
How to do the Straight Leg Sit-Up
- Lie on your back with your legs straight and your arms crossed over your chest.
- Press your heels lightly into the floor and brace your abs.
- Curl your torso up until you are sitting upright.
- Lower your back to the floor slowly.
Tip: Reach the hands forward along the thighs and think of peeling the spine off the floor from the top down.
Muscles worked
Primary
Abs · Core
The abs curl the torso off the floor and then control it back down, and they do the most work in the first 30 degrees of the movement before the hip flexors take over.
Secondary
- Hip Flexors — The hip flexors pull you the rest of the way up once the abs have curled the ribs, and they will dominate if the feet are anchored and the range is rushed.
Common mistakes
- Yanking the neck — hands behind the head should support only; keep the elbows wide or cross the arms on the chest.
- Jerking up flat-backed — the spine should curl up one segment at a time starting from the head, not lift as a rigid board.
- Dropping back down — the lowering half is where the abs work hardest, so take two or three seconds to come down.
- Anchoring the feet — this lets the hip flexors do everything; if you must anchor, keep the knees bent and focus on curling the torso.
Where it fits in a workout
Sit-ups go at the end of a session with the other core work. Superset them with a back extension to balance the front and back of the trunk.
How many sets, how heavy and how hard: see what the ACSM position stands support.
Variations and alternatives
Similar exercises
Without bodyweight
When to talk to someone
- Chest discomfort, feeling faint or lightheaded, or trouble breathing during or after exercise can be signs of a heart attack. In the US, call 911 right away; elsewhere, call your local emergency number.
- Heart, metabolic or kidney disease, or symptoms like these when you are active: talk to your doctor before you start or step up training.
- Pregnant: ask your obstetric care provider which exercise suits you.
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More exercises
Sources
- ACSM position stand on exercise quantity and quality (Garber et al., 2011)
- ACSM preparticipation health screening (Riebe et al., 2015)
- ACOG Committee Opinion No. 804 on exercise in pregnancy (2020)
- CDC: About Heart Attack Symptoms, Risk, and Recovery (2024)
Sources checked on October 17, 2026. Full citations are in the exercise library.
Animation and exercise data: ExerciseDB, licensed to SetGrip. General information, not medical or coaching advice.