Compensatory behavior of the postural control system to flexion-relaxation phenomena.

SUMMARY: Laxity of the passive tissues of the spine during prolonged spinal flexion has been shown to disturb spinal stability. This study investigated the effects of short periods of static lumbar flexion and short rest periods on the flexion-relaxation angle for the erector spinae muscles in 36 healthy female college students. The surface electromyographic activity of the erector spinae muscles was measured in three states before the onset of creep, immediately after 7 min of static lumbar flexion, and after a 10 min rest. The results showed that 7 min of static lumbar flexion will produce relaxation of the erector spinae muscles that occurs at greater absolute lumbar and trunk angles, during the forward bending activity (P<0.05), while the corresponding relative angles did not change before and after creep. The results also indicate that postural compensations are dominant over the muscular compensations for load sharing in flexion-relaxation phenomena of asymptomatic healthy participants. This further highlights the importance of postural modulation in the control of movement and preservation of skeletal stability. CLINICAL RELEVANCE: Considering spinal posture in the upright condition, and its changes by phenomena such as creep, can reduce postural injuries by instructing subjects to approach a more vertical posture, after periods of bending, to compensate the stretching effects of the tissues and thus regaining the normal muscular activity pattern.