Abdominal Muscle Training

Abdominal muscle strengthening exercises are frequently recommended as part of back rehabilitation programs.(1,2) Stronger abdominal muscles, esp. the internal and external oblique and the transverse abdominus muscles, may help to support the spine and prevent low back problems via either increasing intra-abdominal pressure (3,4) or via increasing tension across the thoracolumbar fascia.(5,6)  But which exercise(s) are best?

While several previous studies have pointed to the bent knee curl (crunch) exercise as the most effective for activating the abdominal muscles, a recent study indicates that the double straight leg lowering (DSLL) exercise while controlling pelvic position is more effective.(7)  This exercise involves starting from a position with the hips bent at 90 degrees and performing a posterior pelvic tilt.  The knees may be flexed slightly to reduce tension on the hamstrings. Then the legs are slowly lowered, making sure that the back is pressed into the floor.  When this pelvic position can no longer be maintained, the exercise is stopped and the legs are brought back to the top for another repetition.  Such an exercise would be part of a continuum of pelvic tilt with knee and leg raise exercises normally included in a lumbar stabilization exercise program.

This study found that the DSLL exercise was more effective at activating the abdominal muscles than the curl exercise, esp. the external (EO) and internal oblique (IO) muscles.  The external oblique (EO) muscle, in particular, is involved in stabilizing the pelvis during the posterior pelvic tilt due to the orientation of some of its fibers in a posterior to anterior direction.  Thus, the DSLL is a more demanding exercise on the abdominal muscles and may be more effective in strengthening the abdominal wall than the crunch (curl) exercise.  Based on this research I would recommend that more focus should be placed on this and similar exercises (such as the posterior pelvic tilt and single leg raise) during a lumbar stabilization exercise program rather than on crunches.

It was also discovered that some subjects performed the DSLL with a pattern of muscle activation that involved primarily the EO and IO muscles, whereas other subjects performed the DSLL using relatively equal contributions from the rectus abdominus and the oblique muscles.  It is not clear what the significance of this finding is.  Could it be that those who use the first pattern of muscle activation are less likely to experience low back pain due to the greater activation of the trunk stabilizing function of the pull of the oblique abdominal muscles on the thoraco-lumbar fascia or on the increase in the intra-abdominal pressure?

It would be interesting to find out if the DSLL activated the transverse abdominus muscle more than the abdominal crunch exercise.  The transverse abdominus muscle is often considered to be one of the primary stabilizing muscles of the spine, though this muscle was not tested in this study..


1. Saal JA, Saal JS. Nonoperative treatment of herniated lumbar inter-vertebral disc with radiculopathy: An outcome study. Spine. 1989;14:431-7.
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3. Bartelink DL. The role of abdominal pressure in relieving pressure on the lumbar intervertebral discs. J Bone Joint Surg. (Br) 1957, 39B: 718-725.
4. Gracovetsky S, Farfan H, Lamy C. The mechanism of the lumbar spine. Spine. 1981; 6: 249-262.
5. Gracovetsky S, Farfan H, Helleur C. The abdominal mechanism. Spine. 1985; 10: 317-24.
6. Tesh KM, Shaw Dunn J, Evans JH. The abdominal muscles and vertebral stability. Spine. 1987; 12: 501-8.
7. Shields RK, Heiss DG. An electromyographic comparison of abdominal muscle synergies during curl and double straight leg lowering exercises with control of the pelvic position. Spine. 1997; 22: 1873-1879.