Konrad et al. (2001) compared a number
of gymnastic exercises and found that the horizontal straight leg anchored
side bend displayed the highest external oblique muscle activity, followed by the
reverse curl up Escamilla et al. (2006) compared the power wheel roll out (power wheel in hands), jack
knife and knee - tuck (power wheel attached to feet), the ab sling bent - leg hanging leg raise, the flat and decline
reverse curl up, the anchored bent leg sit up, and bent leg curl up.