Crunch of legs on a stability ball

Bring the ribs and pelvis closer with a short, controlled trunk flexion. Avoid pulling on the head or using momentum to finish the repetition. Keep the same range from repetition to repetition instead of speeding up as you fatigue. Breathe continuously and end the set before technique starts to break down.

Choose a resistance that lets you preserve technique from start to finish. You should feel most of the work in abdominals, shoulders, glutes and hip flexors and lower back; if you feel sharp pain, joint pinching or a clear loss of control, reduce the load or range and stop if symptoms persist. On unstable surfaces, master the position with light resistance first; stability should limit difficulty before load does.