Adaptations of the Autonomic Nervous System and Body Composition After 8 Weeks of Specific Training and Nutritional Re-education in Amateur Muay Thai Athletes: A Clinical Trial

Background: Considering that the autonomic nervous system plays an important role in cardiac autonomic modulation (CAM) and that low CAM is associated with cardiovascular mortality, it is essential to evaluate the effects of training to increase parasympathetic modulation in Muay Thai (MT) athletes. Therefore, the aim of this study was to evaluate the effects of an 8-week intervention based on strength training and nutritional counseling on performance, CAM, and nutritional status in amateur MT fighters. Methods: This is a longitudinal and interventional study in which 22 MT fighters underwent a strength training program and nutritional protocol. Before and after the intervention, they underwent the ten-second frequency speed of kick test (FSKT-10s), multiple frequency speed of kick test (FSKT-mult), bioimpedance analysis (BIA), and assessment of heart rate variability. Results: After the intervention, there was an increase in the number of kicks in both FSKT-10s and FSKT-mult (p = 0.0008 and p = 0.032, respectively). In BIA, there was a significant decrease in fat-free mass and a significant increase in basal metabolic rate (p = 0.031 and p = 0.020, respectively). After the intervention, significant increases were observed during the fight in the following variables that denote improvement in parasympathetic modulation: square root of the mean squared differences of successive RR intervals (p = 0.005); percentage of adjacent RR intervals with a difference in duration greater than 50 ms (p = 0.002); high frequency range (p < 0.0001); and standard deviation measuring the dispersion of points in the plot perpendicular to the line of identity (p = 0.004). Conclusions: In amateur MT athletes, an intervention with strength training and nutritional guidance is able to improve CAM through greater parasympathetic activation. Furthermore, there is an improvement in performance and body composition after the intervention.