Sit-Up
What Is the Sit-Up?
Sit-Up is an isolation exercise that primarily targets the core and also engages the hip flexors. It is a beginner-level movement that needs no equipment, only enough floor space to lie down with your knees bent.
Each rep has two parts. The first is the same curl as a Crunch: the abdominals bend the spine and lift the head, shoulders and upper back until the shoulder blades clear the floor. A crunch stops there. A sit-up keeps rising to an upright seat, and that part of the rise is hip flexion, driven mainly by the hip flexors (the iliopsoas and the rectus femoris) while the abs hold the trunk curled. Leg position shifts the balance: in an EMG study of six healthy men, full sit-ups with bent, supported legs raised hip flexor activity, while the abdominals generally worked at the same level. Bending the knees does not take the hip flexors out of the movement.
The sit-up is one of the oldest fitness-test exercises. One-minute sit-up tests are still common in police academy entry tests, many of them built on Cooper Institute norms. The US Army, which tested two minutes of sit-ups for decades, now uses a plank in its fitness test. In a gym program, sit-ups usually come at the end of a session as core accessory work or as a station in a circuit.
Sit-Ups suit anyone who wants to train trunk and hip flexion together or needs to pass a sit-up test. Arm position sets the difficulty: reaching the arms forward is the easiest version, crossing them over the chest is harder, and hands behind the head is the hardest of the three because it keeps the weight of the arms farthest from the hips. If a full rep is not there yet, build the curl with the Crunch and trunk control with the Dead Bug. Once bodyweight reps are easy, hold a weight plate against your chest or move on to the V-Up.
Muscles Worked
- Rectus Abdominis
- Primary
- External Oblique
- Medium
- Rectus Femoris
- Medium
- Sartorius
- Low
- Sternocleidomastoid
- Minimal
Instructions
- Lie on your back on a mat with your knees bent and your feet flat on the floor, about hip-width apart. Nothing holds your feet down.
- Place your hands behind your head with your fingers lightly interlaced and your elbows out to the sides.
- Brace your abs and let your lower back rest close to the floor.
- Exhale and tuck your chin slightly, then curl your head, shoulders and upper back off the floor, bringing your ribs toward your pelvis.
- Once your shoulder blades are clear, keep the curl and continue rising by bending at the hips until your torso is upright over your hips. Press your heels into the floor so your feet stay down.
- Inhale and lower yourself under control, uncurling from the lower back up until your shoulders and head touch down lightly.
- Start the next rep without bouncing off the floor, and keep your hands supporting your head rather than pulling it.
Common Mistakes
Pulling on the head
Yanking the head forward with your hands strains the neck, so let the hands only support the head and keep a slight chin tuck.
Swinging up with momentum
Throwing the arms or jerking the torso off the floor lets momentum lift you instead of your abs, so rise at a steady pace.
Rising with a flat back
Hinging straight up from the hips without first curling the upper back hands most of the rep to the hip flexors, so peel your head, shoulders and upper back off the floor first.
Feet lifting off the floor
When your feet pop up as you rise, press your heels into the floor, slow down or switch to an easier arm position until you can keep them down.
Dropping back to the floor
Falling back from the top skips the lowering half of the rep, so uncurl slowly until your shoulders touch down.
Injuries
Sit-Up is a low risk exercise when performed with proper technique. The usual strain points are the neck, when the hands pull the head forward to start the rep, and the lower back, which the hip flexors can pull into an arch as the torso lifts, especially when the rep starts with a jerk instead of a curl. The front of the hips can also feel tight or sore after high-rep sets, since the hip flexors do much of the second half of every rep.
Let your hands only support the weight of your head, and start every rep by curling the head, shoulders and upper back off the floor before the hips take over. Rise and lower at a steady pace instead of bouncing off the floor, and add volume gradually, especially when practicing for a timed test.
If a full rep is not possible without jerking, reach the arms forward, have a partner hold your feet or hook them under a stable support, or practice only the lowering half from the top. The Crunch and Dead Bug train the abdominals with less hip flexor work. To progress, hold a weight plate against your chest or move on to the V-Up.
Stop the set if you feel sharp pain in the lower back, pain, tingling or numbness running down a leg, or neck pain that lingers after the set. People with current back pain, a disc problem, a hernia or recent abdominal surgery should check with a clinician first. Osteoporosis guidance advises modifying or avoiding repeated, end-range spinal flexion such as sit-ups.
- Primary Focus
- Core
- Equipment
- Body weight
- Modality
- Strength
- Difficulty
- Beginner
Alternative Exercises
Frequently Asked Questions
- Q: Are Sit-Ups better than crunches?
Neither is better overall, because they train different things. A crunch stops once the shoulder blades clear the floor, so the abdominals do nearly all the work, while a sit-up keeps rising to an upright seat and that extra range is hip flexion driven mainly by the hip flexors. Choose the Crunch to focus on the abs, and the Sit-Up when you also want hip flexor strength or are preparing for a sit-up test.
- Q: Should I anchor my feet during Sit-Ups?
It is optional. Holding the feet down lets the hip flexors pull harder, which makes the rep easier to finish while the abs still do the curl at the start, so it is a reasonable way to build up to free-feet reps.
- Q: Are Sit-Ups bad for your back?
For healthy people, the evidence does not show that sit-ups cause back injuries. In a 16-week trial with 1,141 US Army soldiers in training, companies that swapped sit-up training for core stabilization exercises had the same overall rate of musculoskeletal injuries as companies that kept it, though soldiers in the sit-up program who hurt their lower back spent more days on restricted duty (8.3 against 4.2 on average), a difference the authors called marginal. If you have current back pain, a disc problem or osteoporosis, choose other core exercises unless a clinician has cleared sit-ups for you.
- Q: I can't do a full Sit-Up yet. What should I do?
- Q: How many Sit-Ups should I do?
Most people do 2 to 4 sets of 10 to 20 controlled reps, two to four times a week. End the set when your feet start lifting or you have to swing up, and if you are training for a timed test, practice the test format itself as well.
- Q: Will Sit-Ups flatten my stomach?
Not on their own. Sit-Ups strengthen the abdominal muscles, but no exercise burns fat from one chosen area, and how visible your abs are depends on overall body fat, which changes with diet and total activity.