While many use the terms synonymously, situps and crunches are different exercises. The crunch and situp vary in execution, and while both exercises target the abdominal muscles, each exercise engages different synergists and stabilizers. Although both may help tone and define the abs, you can only achieve a flat tummy and strong abdominal definition by cutting fat and building lean muscle. This requires both strength-training and regular cardiovascular exercise in addition to an abdominal regimen.
To perform a situp, lie with your back flat on the ground, your knees bent and your feet secured under a bar or brace. Alternatively, enlist a partner to hold your feet. Keep your feet together and place your hands gently on the back or sides of your neck. With a slow and controlled motion, bring your chest up toward your knees until your torso is completely vertical, driving the motion with your hips. Return to the starting position and repeat. Placing your hands further up your neck or on your head increases the challenge.
The crunch essentially compacts the movement of the situp, requiring a smaller range of movement in order to focus on abdominal contraction. To execute a crunch, lie with your back flat on the ground and your lower legs elevated on a bench or simply bent at the knees with your feet flat on the ground. For either style, keep your feet together. Place your hands behind your head or cross your arms over your chest. Drive the motion from your abs -- not your back, neck, hips or head -- as you raise your upper torso as high as you can while your lower back remains on the mat. Return to the starting position and repeat.
Both situps and crunches target the rectus abdominis, and both exercises engage the obliques – muscles located on either side of the torso – as synergists, or muscles that help other muscles complete a movement. Obliques act as the only synergists for crunches, but situps also work hip and thigh muscles such as the iliopsoas, tensor fasciae latae, rectus femoris and sartorius. While the crunch does not employ any significant stabilizers – muscles that help the body maintain a specific posture – the situp engages the tibalis anterior of the shins.
In simple terms, the situp puts more focus on the hip flexor muscles than it does the abs, while the crunch puts exclusive focus on the abs and core “six pack” muscles. Because the hips flexors work in conjunction with the lumbar spine, situps may cause lower back pain. As such, institutions such as the American Council on Exercise have removed the situp from their exercise libraries, replacing the exercise with the crunch, also known as the bent-knee situp. Both exercises accommodate numerous variations, such as incline, decline, stability ball and weighted varieties.
- Mayo Clinic: Can Situps Flatten Your Stomach?
- ExRx.net: Situp
- ExRx.net: Crunch
- American Council on Exercise: Bent-Knee Situp/Crunches
- Mayo Clinic: Video: Abdominal Crunch
- Muscle and Strength: The Great Abs Mistake – Crunches and Situps and Still No Abs
- American Council on Exercise: Ask the Expert – “I Get Low Back Pain During Situps. Am I Doing Something Wrong or Should I Avoid Them?”
- Stockbyte/Stockbyte/Getty Images
- Sit-Up & Crunches for a Flatter Stomach
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- Straight-Leg Situps
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