Vagotonic effect of inversion therapy upon resting neuromuscular tension.

Inversion therapy has become a popular treatment for low back pain but little experimental evidence is available to suggest a physiological basis for such use. On the basis of earlier work showing a vagotonic influence of inversion upon the cardiovascular system, it was our purpose to test the hypothesis that such vagotonic effects are also operative in the nervous system and thus cause decreased electrical activation of the resting musculature. To test this hypothesis 12 healthy subjects, seven female, five male (age 19-37, M = 28.9 +/- 5.8 years) were selected from among 45 who were screened on the basis of having resting IEMG scores at least one S.E. above electrical silence. Each subject acted as his own control and visited the laboratory on four occasions of which two involved EMG testing pre and post inversion for two minutes and the other two were control before and after an equivalent period of rest. The mean reduction in neuromuscular tension after inversion was 28.3 percent compared with 7.1 percent after control. This difference was significant at P less than 0.04. A two minute period appears to be sufficient and the effect may persist for as much as two hours. Heart rate and blood pressures taken before and after inversion were not significantly different from controls.