Flat crunch: lie down facing upwards, knees bent, feet placed on the floor shoulder width apart, arms close to your torso (hands crossed on top of chest or close to your ears). Tense your abs and lift your shoulders off the floor and towards your stomach, rounding your upper body, then lower back down. A small range of motion is fine; do not use your arms to swing yourself up.

Decline crunch: with legs locked, perform a crunch on a declined bench, with hands placed as per a flat crunch, or holding a weight.

Reverse crunch: lie down on a bench facing upwards, knees lifted at 90 degrees, holding the bench with your hands and pulling for support. Keep your upper back against the bench and lift your legs towards your torso, starting with a lift at the hips, and then lower back down, maintaining a tight 90 degree angle in your legs. Do not swing your legs by bending at the hip (maintain a 90 degree gap between your upper thighs and front torso, don't let your knees collapse towards your chest).