Number Six, March 2002    -    SPORTS MEDICINE     &     USAPL SUSPENSION LIST 
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Dr. Michael Hartle
Medical Committee Chair
Trunk Stabilization Concepts and Exercises
by Michael A. Hartle, D.C., D.A.C.B.N., C.C.N., C.C.S.P., C.S.C.S., E.M.T.

Part Three of Six


Wohlfahrt D, Jull G, Richardson C. The relationship between dynamic and static function of abdominal muscles. Aust Physiother 1993; 39(1): 9-13.

This study looked at 38 subjects and divided them into 2 groups, those who were able to perform more than 51 abdominal crunch exercises and those who can perform fewer than 51. The subjects were soldiers for whom crunches were a part of their regular training regimen. They also analyzed the speed at which the subjects performed the exercises. The soldiers had been trained to perform crunches at a 1 repetition per 3 seconds cadence, and the researchers noticed that some would perform them slowly, each rep lasting the full three seconds, while others performed them quickly, the rep lasting only one second with 2 seconds rest in between. They measured spinal stabilization ability with a 4-cell pressure sensor that was placed under the lumbar spine of the study subjects to measure sagittal plane and rotational movements and with progressive exercises involving movements of the lower extremities while attempting to maintain stability of the lumbar spine.

The results showed that the greater number of reps the subjects were able to perform in the crunch test, the greater their spinal stabilization capacity. But the stability capacity was even more dependent on the speed at which the crunches were performed in training, i.e., those who performed their crunches faster exhibited poorer stabilization capacity and those who performed their crunches more slowly exhibited greater stabilization capacity. This finding is consistent with other studies by this and other groups that have shown that fast movements improve power at the expense of stability. When performing crunches quickly, the rectus abdominis dominates the movement. When they are performed slowly, the abdominal obliques and transverse (and, probably the multifidus) are utilized. This demonstrates that for stabilization training, it is important for movements to be performed slowly so that the appropriate muscles can be recruited in the pattern that maximizes the efficiency of the stabilizing system of the spine. (Murphy)

Hodges PW, Richardson CA. Contraction of the abdominal muscles associated with movement of the lower limb. Phys Ther 1997; 77:132-144.

In the first study the authors used fine wire and needle EMG to record the activity in the transverse abdominis, internal oblique, external oblique, multifidus, rectus abdominis, gluteus medius, tensor fascia lata (TFL), rectus femoris and gluteus maximus to assess the relative contraction latencies between the trunk stabilizers and the prime movers of the hip. They had 15 healthy subjects move their right hip into flexion, abduction and extension and recorded the activity.

With hip flexion, all the trunk muscles except the external oblique contracted to stabilize before the rectus femoris contracted to move the thigh. The transverse abdominis was the first muscle to contract in all subjects. With abduction, only the transverse abdominis and internal oblique contracted to stabilize before the TFL. With extension, the transverse abdominis, rectus abdominis and internal oblique contracted before the gluteus maximus. So the transverse abdominis was the only muscle that contracted proactively to act as a stabilizer of the trunk with all hip movements. The multifidus contracted proactively to stabilize with all movements except hip extension. (Murphy)

Hides JA, Richardson CA, Jull GA. Multifidis muscle recovery is not automatic after resolution of acute, first-episode low back pain. Spine 1996; 21(23):2763-2769.

Study number three looked at chronic low back pain patients and healthy controls and measured EMG activity in the erector spinae and multifidis when a 2 kg weight attached to a shoulder harness was dropped from 45 cm to create a sudden, unexpected flexion moment.

They found that the EMG activity of the multifidis that was seen as a response to a sudden, unexpected load was found to be delayed and smaller in magnitude in the chronic low back pain patients as compared to healthy controls. This suggests that these patients do not have good reaction time or recruitment in the multifidis and so they have to try to compensate for it with the muscles of the lower extremities. (Murphy)

These last two studies demonstrate that the transverse abdominis and multifidis are important in contracting to stabilize the spine prior to extremity movements. To be able to do this, they must be able to react very quickly. When sudden forces are acted upon the body, there is a very small time period in which these muscles must contract strongly to protect the area where they are located from injury.

The mutlifidus responds to injury by becoming inhibited and wasted. Once the injury resolves and the pain is gone, the multifidus wasting does not automatically resolve. This inhibition is demonstrated by the inability to react and contract quickly when a force or load is acted upon the body. Acute low back pain is usually perceived to be "self-limiting", however, the rate of recurrence in the first year is up to 80%. The multifidus, with the wasting and inhibition that can occur during acute injury, may be one of the major factors responsible for the high rate of recurrence.

Ng J, Richardson C. Reliability of electromyographic power spectral analysis of back muscle endurance in healthy subjects. Arch Phys Med Rehabil 1996;77:259-264.

Biering-Sorensen F. Physical measurements as risk indicators for low-back trouble over a one-year period. Spine 1984;9: 106-119.

Luoto S, Heliovaara M, Hurri H, Alaranta H. Static back endurance and the risk of low-back pain. Clin Biomech 10:6;323-324, 1995.

The above three studies reference an important muscle that one must not overlook in regards to the proper health and function of the spine: multifidus. This muscle, in some places the size of your pinky finger, contracts and helps stabilize the spine in concert with the contraction of the transverse abdominis (pulling your abdominals in). The multifidus is a primary intersegmental stabilizer of the spine. It has a short reaction time due to its location near the center of rotation of the vertebrae. It is the primary muscle active during static back extensor endurance testing (i.e., Sorensen's test), where poor endurance has been found to be able to predict first time onset of lower back pain (LBP) in healthy individuals and recurrence rates in those recovering from LBP.

Liebenson C (ed) Spinal Rehabilitation: A Manual of Active Care Procedures. Williams and Wilkins, Baltimore 1996.

Liebenson discusses what happens to the multifidus with low back pain (LBP). Type 2 fiber atrophy has been found in chronic LBP and disc patients. Moth eaten changes have been confirmed in type 1 fibers. Muscular atrophy has been found in acute LBP patients and was greatly improved with stabilization training. Again, confirming the above studies regarding the wasting of the mutlifidus and its role in LBP.

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Michael A. Hartle,
USA Powerlifting Executive Committee Board Member
Chairman, USA Powerlifting Sports Medicine Committee
Chairman, USA Powerlifting Drug Testing Committee

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