After reading the reverse sit up blog, a few readers asked if the hanging leg raise was a good substitute exercise for strengthening the lower abdominal muscles –along with the hip flexors. Both of these muscles are strongly involved in hill running as well as in sprinting. The hanging leg raise is a good exercise, but it mainly targets the lower abdominals. The hip flexors are involved but only moderately, unless you do straight leg raises in which you have a long lever and great resistance. If you raise the knees with the legs bent there is much less resistance. However, raising the hips and legs as a unit creates substantial resistance against which the abdominal muscles must work. This variant strongly involves both the hip flexors and the abdominals, especially the lower section until the legs get to and beyond the level postion. The hip flexors are involved in the initial lift of the thighs and only for about 15 to 30° of motion before the abdominals actively kick in. The exact range of motion depends upon how tight your hamstring muscles are. This is why the hanging leg raise is not a great exercise for strengthening the hip flexors. Perhaps even more important is the fact that in running –regardless of distance — the hip flexors are strongly involved when the leg is behind the body, not directly underneath the body as it is in hanging leg raises. As a result, in this exercise you learn to drive the knees upward rather than forward. This creates more of a vertical component in your run rather than a horizontal component. Thus, strengthening the hip flexors in this manner may be great for hill running but it is not great for improving your running when on level ground. The abdominals are strongly involved when the hip flexors cease their active contractions in order to rotate the pelvis-legs unit, which is a moderate-heavy load for them, to the thigh level position. When done for many repetitions, you develop more muscular endurance than strength. The abdominal muscular endurance in this case is of limited value for improvement of long distance running. The reason for this is that there is little pelvic rotation in long-distance running and you rely more on the hip flexors to bring the leg forward. But the hanging leg raise does not provide the hip flexor strength needed to do this. In sprinting as brought out above, the hip flexor development is different in the hanging leg raise from what is needed in the run. The abdominal development however, is excellent. Thus if you want to do this exercise, keep in mind that it only benefits one aspect of the run. Be sure you do other exercises such as the knee drive with the Total Athlete System™ to improve your run even more. For more information on the role of the abdominals and hip flexors in running, see Explosive Running.