Spinal Manipulative Therapy Effects in Autonomic Regulation and Exercise Performance in Recreational Healthy Athletes

STUDY DESIGN: A randomized, double blind, parallel groups, sham-controlled trial. OBJECTIVE: The aim of this study was to analyze the acute effects of spinal manipulative therapy (SMT) on performance and autonomic modulation. SUMMARY OF BACKGROUND DATA: The use of SMT is progressively spreading from the clinical to the sporting context owing to its purported ergogenic effects. However, its effects remain unclear. METHODS: Thirty-seven male recreational athletes (aged 37 ± 9 years) who had never received SMT were assigned to a sham (n = 19) or actual SMT group (n = 18). Study endpoints included autonomic modulation (heart rate variability), handgrip strength, jumping ability, and cycling performance [8-minute time trial (TT)]. Differences in custom effects between interventions were determined using magnitude-based inferences. RESULTS: A significant and very likely lower value of a marker of sympathetic modulation, the stress score, was observed in response to actual compared with sham SMT [P = 0.007; effect size (ES) = -0.97]. A trend toward a significant and likely lower sympathetic:parasympathetic ratio (P = 0.055; ES = -0.96) and a likely higher natural logarithm of the root-mean-square differences of successive heartbeat intervals [(LnRMSSD), P = 0.12; ES = 0.36] was also found with actual SMT. Moreover, a significantly lower mean power output was observed during the TT with actual compared with sham SMT (P = 0.035; ES = -0.28). Nonsignificant (P > 0.05) and unclear or likely trivial differences (ES < 0.2) were found for the rest of endpoints, including handgrip strength, heart rate during the TT, and jump loss thereafter. CONCLUSION: A single pre-exercise SMT session induced an acute shift toward parasympathetic dominance and slightly impaired performance in recreational healthy athletes. LEVEL OF EVIDENCE: 2.