Due to the origin of the primary hip flexors (psoas) on the lumber vertebrae, full sit ups actually place stress in excess of several times body weight on the anterior surfaces, and encourage posterior disc herniation. the best solution is to stop doing full sit ups and replace them with planks & crunches- also learn to identify thoracic spinal flexion during a crunch, as opposed to hip flexion (if the lower back comes off of the floor, your hip flexors are involved, taking the work off of the rectus abdominis and placing compressive loading on the lumbar spine). The first link below is most applicable, with the others being relevant to specific training actions:





Edited by Ayotl (02/16/12 12:05 PM)
Edit Reason: grammar