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
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
1. Saal JA, Saal JS. Nonoperative treatment of
herniated lumbar inter-vertebral disc with radiculopathy: An
outcome study. Spine. 1989;14:431-7.
2. Liebenson C, Hyman J, Gluck N, Murphy DR. Spinal stabilization. Top Clin Chiro 1996; 3(3): 60-74.
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.