Response of the Flexion–Relaxation Phenomenon Relative to the Lumbar Motion to Load and Speed

Study Design. Nonrandomized control trial. Objective. To determine if the variations of speed and loading conditions during trunk flexion–extension could influence the times of occurrence and disappearance of the electrical silence of the erector spinae muscles, the degrees of lumbar flexion at those instants, and the relative lumbar motion time. Summary of Background Data. It has been suggested that varying either the speed of movement or the load on the trunk during trunk flexion–extension movements may influence the flexion–relaxation phenomenon or the kinesiologic data. However, no study dealt with the simultaneous effect of the speed of movement on the spine rhythm and on the occurrence of the electrical silence of the erector spinae. Methods. A total of 22 pain-free volunteers performed a series of trunk flexion–extension movements varying the speed and load. The motion of the lumbar spine (°) and the integrated electromyography (&mgr;V) of erector spinae muscles were simultaneously recorded. Two measures were calculated: the percentage of the maximum lumbar spine flexion at the instants when changes of electrical activity represented the beginning and end of the electrical silence and the relative lumbar spine motion time during trunk flexion and extension movements. Results. The increase in speed of movement significantly increased the relative lumbar flexion time and significantly reduced the relative lumbar extension time (t = 2.49 and t = 2.25, P < 0.05); furthermore, it significantly delayed the appearance of the electrical silence in the range of flexion (t = 3.52, P < 0.01). There was no significant effect from a change in load. Conclusions. The relative spine motion time differed depending on the direction of movement, being longer during trunk flexion and shorter during extension. The increase in speed of movement produced greater differences in the relative time between trunk flexion and extension; furthermore, it delayed the appearance of the electrical silence of the erector spinae muscles in the range of flexion.

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