Pain with swiss ball crunches

Why would anyone have lower back pain when they perform a crunch on a swiss ball?

Incorrect pelvic tilt. Try adjusting your position on the ball, that works for me.

Alternatively, if keep your hands behind your head, and are actually pulling your head forward, that can strain your back… As to the pelvic tilt, I find that moving forward on the ball (i.e. moving my hips closer to the floor) is more comfortable.

If it’s in the low back, he/she may be suffering from spinal compression as a result of the ball being to small. For crunches make sure the ball is big enough so that when sitting upright their thighs are parallel with the ground

I get lower back pain when I do swissball situps or crunches if I do them in the days following my back workouts, but if I do them the day before I never have any problems. Just something to check out on your own workouts, hope it helps.

A swiss ball allows a much greater ROM throughout the exercise. Remember, you start in about 15-20deg of vertebral extension before flexion (vs. a normal crunch where you start closer to neutral spine). This allows for greater muscle recruitment/effectiveness, but also more discomfort for those with muscle instabilities/lack of ROM in this area.
Because vertebral compression is increased, you are at a greater risk for injury if you don’t possess a certain degree of muscle strength and trunk stability. I think its a great exercise if done properly and by an experienced indiv.