Crunch
Muscles worked : Abdominals (rectus abdominis)
How to do it
- Lie on your back, knees bent, feet flat on the floor.
- Place your hands lightly behind your ears or crossed on your chest, without pulling on the neck.
- Lift the shoulder blades off the floor as you exhale, contracting the abdominals.
- Lower under control until you brush the floor without releasing all your weight onto it.
Common mistakes
- Pulling on the head with the hands to get higher: loads the neck instead of the abdominals.
- Coming all the way up to sitting: that is no longer a crunch, and the effect on the abdominals drops.
- Holding your breath instead of exhaling through the contraction.
Where you should feel it
The upper abdominal wall, over a short range. Tension in the neck always means the hands are pulling on the head: they should only accompany it.
Range of motion
Lift the shoulder blades off the floor, nothing more. Continuing up to sitting shifts the work to the hip flexors — the short range is not a concession, it is the correct movement.
Tempo and breathing
Two seconds up as you exhale, two seconds down as you inhale, without fully releasing at the bottom so the tension stays.
What works, precisely
The rectus abdominis draws the sternum towards the pelvis: that is the movement’s driver. The obliques contribute to stabilisation. The psoas barely intervenes as long as the range stays short — which is exactly what distinguishes a crunch from a full sit-up.
Movement mechanics
Spinal flexion in the sagittal plane, over a deliberately limited range. The movement puts the lumbar spine through repeated flexion: that is why it complements, but never replaces, anti-extension work like the plank or the dead bug.
Benefits
- Recruits the rectus abdominis directly, which isometric core exercises do not.
- Short range and floor position make it one of the most accessible ways to resume abdominal work.
- Combines well with the plank and the dead bug, which train stabilisation rather than flexion.
Adapt and progress
- Easier : Cross the arms on the chest rather than behind the head, and reduce the range.
- Harder : Slow down, pause at the top, or extend the arms overhead.
- Move on when : When three sets of twenty go by with no pull on the neck.
Precautions
Repeated spinal flexion does not suit everyone. With any lumbar sensitivity, favour the dead bug and the plank, which produce abdominal work without flexing the spine.