Crunch
The crunch is a floor exercise in which you lie on your back with your knees bent and curl your upper body up until your shoulder blades lift off the floor. It works the rectus abdominis (the "six-pack" muscle) with little help from the hip flexors, and is the most common bodyweight abdominal exercise.
Also called: Ab Crunch, Abdominal Crunch, Trunk Curl, Curl-Up · Equipment: bodyweight · Pattern: isolation
Step by step
- Lie on your back on a mat with your knees bent to about 90° and your feet flat on the floor, hip-width apart.
- Rest your fingertips lightly behind your ears with your elbows wide, or cross your arms over your chest.
- Leave a fist-sized gap between your chin and chest, and keep your neck in line with your upper back for the whole set.
- Breathe out and curl your ribcage towards your pelvis, lifting your head and shoulder blades off the floor.
- Curl until your shoulder blades clear the floor, with your low back staying in contact with the mat.
- Hold the top for a moment and squeeze your abs.
- Uncurl under control, taking about two seconds, until your shoulder blades touch the floor, then start the next rep.
- Curl your ribs towards your pelvis
- Shoulder blades off, low back stays down
- Breathe out hard as you curl
- Fist-sized gap between chin and chest
- Fingertips rest lightly behind your ears
- Two seconds back to the floor
In VALDA, these cues are one tap away on the exercise while you train.
What it trains
| Muscle | Role | Evidence |
|---|---|---|
| Rectus abdominis: upper | Prime mover | B |
| Rectus abdominis: lower | Secondary | C |
| Obliques (internal/external) | Secondary | C |
| Transverse abdominis | Stabiliser | C |
| Hip flexors | Stabiliser | C |
Evidence grades: A = strong research base · B = good · C = limited · D = coaching consensus.
What goes wrong, and the fix
Pulling on the head with the hands
Fix: Rest your fingertips lightly and lead the curl with your ribcage.
Sitting all the way up
Fix: Curl only until your shoulder blades clear the floor, low back down.
Swinging up and dropping back
Fix: Curl smoothly, then take about two seconds to uncurl to the floor.
Holding the breath
Fix: Breathe out steadily as you curl your ribs towards your pelvis.
Chin jammed onto the chest
Fix: Keep a fist-sized gap between chin and chest on every rep.
What the research says
Muscle growthGeneral fitnessEndurance
- Muscle activity — EMG studies rank several exercises above the floor crunch for abdominal activity, including bicycle crunches, captain's-chair knee raises, hanging knee raises and inclined reverse crunches. Several of these also bring in more hip-flexor work. EMG measures muscle activity, not growth.
- Load and effort — Research on other muscles finds growth is similar across a wide range of loads when sets are taken close to failure, and true failure adds only a small extra return. Many lifters add a plate or move to a cable crunch once bodyweight sets become very long.
- Volume — Research links more weekly sets for a muscle to more growth, with diminishing returns. Few studies have measured abdominal growth directly, so this is applied by analogy.
- Range of motion — A systematic review of range of motion and muscle growth found no studies of the trunk muscles, so there is no direct research on crunch range. Stability-ball and decline crunches are the usual ways to add range.
Swap it mid-workout
With VALDA Pro, FLEX offers alternatives like these when you swap an exercise mid-workout.
Log the crunch in VALDA, with these cues one tap away while you train and your history for it in one place.
General information about exercise technique, not medical advice. If you have an injury or a health condition, your healthcare provider is the right person to ask.