More Than a Cat Nap Needed to Recover after Prolonged Bending
People whose work or sport requires them to bend their lower backs forward a lot risk low back pain and injury. After periods of bending, the multifidus--the deep muscles that run along each side of the spine --may not adequately support the spine. Also, the other supportive tissues in the low back relax. When the multifidus muscles tire and other supportive tissues relax, the spine is left unprotected and prone to injury.

These tissues need a chance to recover after the spine is bent forward for long periods. But how much rest do they need in order to keep the spine safe? The purpose of this study was to describe the recovery in the spine after periods of bending. Specifically, the authors wanted to know how long it took for the muscles and other supportive tissues to recover. They also wanted to learn the extent of the recovery.

Seven cats were anesthetized and kept with their spines in a forward bent position for 20 minutes. They were then put in a normal resting position for seven hours. During the rest period, the cats were again bent forward in nine, six-second tests. The activity of the multifidus muscles was recorded. Low back tension was also measured.

Twenty minutes of bending resulted in considerable fatigue of the multifidus muscles. This was followed by erratic spasm within the muscles. The tension of the low back tissues also decreased. Some signs of back strain lasted after the 20 minutes were up.

Prolonged use may deactivate the multifidus muscles to the point that they can't give the spine the stability it needs. The normal level of supportive tension in the back is also reduced. This leaves the spine unprotected and prone to injury. In fact, the spasms observed in these models suggest that some damage had already occurred during the test period.

In addition, the tissues in the low back did not completely recover in the seven hours of rest. Tension reached a low of 32 percent after 20 minutes of bending. After seven hours of rest, the tension was only 79 percent, a total improvement of 47 percent. Most of the recovery happened within the first 10 minutes of rest. However, recovery was slow after that. Using this model, the authors suspect that 24 hours may be needed for the muscles and elastic tissues to recover fully--much more than a simple cat nap.

Clearly, long periods of forward bending threaten the stability of the spine and can cause strain and muscle spasm. Long periods of rest may be necessary to restore optimal back function after the spine has been kept in a forward-bent position.
McLean Jackson, BSc, et al. Multifidus EMG and Tension-Relaxation Recovery After Prolonged Static Lumbar Flexion. In Spine. April 1, 2001. Vol. 26. No. 7. Pp. 715-723.