The acute effect of respiratory muscle training on cortisol, testosterone, and testosterone-to-cortisol ratio in well-trained triathletes - exploratory study

The study investigated acute changes in cortisol (C) and testosterone (T) associated with a popular RMT method, voluntary isocapnic hyperpnoea (VIH), in well-trained triathletes. 19 athletes (7 females, 12 males) performed a VIH training session with pre- and post- serum C and T measurements. Repeated measures ANOVA was employed to analyze hormone changes during VIH, with additional time-sex interaction. Pearson correlation coefficient has been computed to identify the relationship between hormonal changes and age, anthropometric indices, respiratory muscle strength, and training experience. There was a statistically significant effect for C changes (F = 13.101, p = 0.002, η_p² = 0.421, ω² = 0.08). The C concentration was significantly lower after VIH (Mean Difference = -32.49 ± 39.13 nmol*L^-1). No significant effects for T, T/C ratio, and time-sex interactions were observed (p > 0.05). Amongst many, significant correlations between the percentage of body fat and changes in C (r=-0.464, p=0.045), body mass and changes in T (r=0.516, p=0.024), height and changes in T (r=0.509, p=0.026) were found. VIH significantly lowered C concentration. No significant effects for T, T/C ratio, and no between-sex differences were observed. Noteworthy individual variability was observed in all the monitored indices. Significant correlations were found between acute hormone changes associated with VIH and selected anthropometric indices. The study provides initial insight into VIH's role in athletes' hormonal balance to possibly guide exercise prescription, autoregulation, arousal state management, and recovery practices in athletes.