The half crunch is a bodyweight floor exercise performed lying supine with the knees bent, lifting only the shoulder blades off the mat to train the upperabsin a short range. The name marks the range, not a different movement: you travel half the way a sit-up does and stop the moment the lower back would leave the floor. That keeps the hip flexors out of the rep and holds tension on the rectus abdominis the whole set. Coaches use it to teach the crunch range and as a high-rep finisher.
What Muscles Does the Half Crunch Work?
- Primary: Rectus abdominis (upper abs)
- Secondary: Internal and external obliques
- Tertiary: Transversus abdominis, neck flexors, serratus anterior
How Do You Set Up for the Half Crunch?
Lie on your back on a mat with your knees bent to about 90 degrees and your feet flat, hip width apart. Cross your arms over your chest or rest your fingertips lightly behind your ears with the elbows out to the sides. Press your lower back flat into the mat, tuck your chin so a fist would fit under it, and pull your ribs down toward your pelvis until the abs are already tight.
How Do You Perform the Half Crunch?
- Press your lower back into the mat with the knees bent and the feet flat.
- Exhale and curl your ribs toward your pelvis, peeling the head and then the shoulder blades off the floor.
- Stop as soon as the shoulder blades clear the mat, with the mid back and lower back still down.
- Hold the short top position for one count and press the ribs down harder.
- Lower over two counts, setting the shoulder blades down and then the head.
- Keep the abs tight and the chin tucked at the bottom, then start the next rep.
What Are the Key Form Cues?
- Stop at the shoulder blades: treat the point where your mid back leaves the mat as the ceiling of the rep, not a stage to pass.
- Exhale the ribs down: breathe out through the whole lift so the ribcage closes toward the hips instead of flaring.
- Keep the feet flat and quiet; heels lifting means the hips are pulling.
- Let the arms ride passively on the chest so they add no swing.
- Keep a gap under your chin from the first rep to the last.
What Are the Most Common Mistakes?
- Sitting all the way up: once the lower back leaves the mat the hip flexors take the rep and the range stops being a half crunch, so cut the lift short.
- Pulling the head forward with the hands: the neck flexes under the load the abs should carry, so keep the fingertips light and lift from the sternum.
- Letting the head and shoulders drop to the mat between reps: the abs go slack and each rep restarts from nothing, so hover at the bottom.
- Rushing the reps for a high count: momentum bounces the torso and the short range gives it nowhere to hide, so lower on a two-count.
- Anchoring the feet under something heavy: the legs pull you up and the abs only hold on, so keep the feet free.
What Are the Best Half Crunch Variations?
- Feet-up half crunch: calves resting on a bench tilts the pelvis and removes any hip flexor help.
- Dumbbell crunch: a dumbbell held on the chest loads the same short range.
- Half crunch with arms overhead: reaching the arms back lengthens the lever without extra weight.
- Oblique half crunch: the shoulder lifts toward the opposite hip so the obliques rotate the ribcage.
- Sit-up: the full rise to sitting, adding the hip flexors and a longer range.
How Do You Progress the Half Crunch?
- Hold a 5 to 10 pound plate on your chest once bodyweight sets hit the top of the rep range.
- Work from 15 reps up to 25 per set before adding load.
- Add a set per week from 2 up to 4 while the last set keeps the same range as the first.
- Hold the top for three seconds, or lower over three counts, before the next load jump.
How Should You Program the Half Crunch?
Place the half crunch at the end of a session as an isolation accessory, after squats, presses or any loaded trunk work. Train it two to four times a week for 2 to 4 sets of 15 to 25 reps with 30 to 45 seconds of rest. Pair it with a reverse crunch or a leg raise so the pelvis-up range gets matching work in the same block.