The effects of gravity inversion on exercise-induced spinal loading

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Abstract
Changes in stature reflect the creep behaviour of the intervertebral discs when loaded and unloaded. Running, weight-training and bounding are exercises which load the spine and cause a loss in stature. Gravity-facilitated traction (inversion) has been shown to unload the spine and increase stature. This study examined the use of a gravity-inverted posture for attenuating the shrinkage induced by a bounding exercise regimen. Eight male subjects, aged 20-26, performed the experimental protocol twice, at the same time of day (14.00 hours) with an alteration only to their 10 min pre-exercise behaviour. The first occasion involved standing and the second involved gravity inversion at an angle of 50 degrees to the vertical. Prior to testing, each subject stood for a period of 20 min. Measurements of stature were taken at the beginning of the experiment, before and after the pre-exercise treatments, after the exercise period and at 5 min intervals during a 20 min standing recovery. A stadiometer, accurate to within 0.5 mm, was used to record alterations in stature. The exercise regimen consisted of ten sets of five standing broad jumps with 15 s recovery between each set. Standing pre-exercise caused little change in stature, whereas, gravity inversion caused a mean increase in stature of 2.7 mm (p < 0.001). Exercise caused a mean shrinkage of 1.7 mm and 3.5 mm when it followed standing and gravity inversion, respectively (p < 0.05). These results suggest that the benefits gained by unloading the spine are short-lived.