The classic sit-up is performed with a partner holding your feet or with your feet anchored under a brace as you lift your torso all the way up toward your thighs. This variation may be common, but it isn't the best way to train your core. Anchored-feet sit-ups require more activation from your hip flexors than from your abdominal muscles to bend your torso, so you're not working the muscles that you hope.
Doing the move without anchoring your feet is more challenging, but possible. Even if you can't sit all the way up, know you're still getting significant training for the abs. A few tips will help you make the sit-up or crunch an effective exercise for you.
What's Wrong with the Anchor?
While the hip flexors, a group of muscles that connect the leg, pelvis and abdomen, activate significantly in any sit-up, they're over exaggerated when you anchor the feet. Holding the feet down provides resistance against which they can pull. Working the hip flexors to this extent has negative effects:
- It decreases activity of the abdomen, the muscle you want to work;
- It pulls on the muscles of the low spine, which causes lumbar stress and could harmfully impact the lumbar discs;
- It contributes to tight hip flexors, which leads to muscle imbalances such as inactive glutes.
Sit-Ups Without an Anchor
A sit-up without an anchor is safer and provides greater stimulation of your abs. But, it can also feel harder. To do the move:
Lie on your back on an exercise mat. Place your hands behind your head, lightly touching the back of your skull. Bend your knees and plant your feet about hip-distance apart.
Exhale and engage your abdominal muscles by pulling your belly button in toward your spine. Keep this engagement as you roll up as high as possible.
Inhale as you slowly roll back to the starting position to complete one sit-up, or crunch if you don't come all the way up.
Move slowly and deliberately, rather than at a pace set by a metronome, coach or music beat. The more you visualize and feel your abs contract as you rise, the more you're working these muscles.
Troubleshooting the Sit-up
Don't stress if you can't sit all the way up with an unanchored sit-up. You're actually doing more work for your abs with a partial sit-up or crunch. The abs activate most when you lift to between a 30- and 45-degree angle off the floor, notes Professor Len Kravitz, exercise scientist and researcher of the University of New Mexico. This is equivalent to getting your shoulder blades up off the floor, not sitting up completely.
The crunch with unsupported feet provides greater ab activation and less hip flexor involvement than a full sit-up that's supported — or unsupported — so it's superior.
Don't rock and roll or thrust your body to get all the way up in the sit-up. Creating this momentum doesn't increase activation of your abs during the exercise. Avoid kicking your feet or scrambling with your arms in an effort to rise into a full, unsupported sit-up.
Variations of the Sit-up
In addition to the sit-up or crunch, other exercises that flex your torso to strengthen and develop the rectus abdominis — the front, superficial ab muscle — may be safer and more effective. The American Council on Exercise did a study in 2014 and found several exercises that were more effective than the standard crunch: