Rehab programs for the back focus on strengthening the abdominals. But in an item in the previous issue, we read that scores for bent-knee sit-ups and in the sit-and-reach tests did not correlate with low back pain. A recent paper by Juker et al. (1998) helps resolve this issue. They found substantial electrical activity in the psoas major muscle in all sit-up exercises, while curl-ups had minimal effect on these hip flexors. Activity in the psoas increases compressive and shear forces on the joints in the lower back, which is not good for people with bad backs. Fit individuals should be able to handle them, though. The authors concluded that there is no single best exercise to train all the abdominal muscles. The safest exercises that maximize abdominal activation and minimize hip flexor activation are probably curl-ups, cross-curl-ups, and isometric side support.