Using Heart Rate Variability and Respiratory Measures to Estimate Ventilatory Thresholds During Running in Adolescents

This study aims to determine the validity of the short-term scaling exponent of detrended fluctuation analysis (DFA-a1), respiration rate, and the ratio between respiration rate and the DFA-a1 (RRa1) in the estimation of the load associated with the first and second ventilatory thresholds (VT1, VT2) during running in a sample of adolescents. Twenty-two adolescents (11 males and 11 females) performed an incremental graded exercise test, monitored through the Polar H10 chest strap, synchronized with the Garmin Forerunner 965 equipped with the alphaHRV app. In the estimation of the load associated with the VT1, there was no significant HRV indices effect (F(2,36) = 1.528; p = 0.231), nor a HRV indices and sex interaction effect (F(2,36) = 0.319; p = 0.729). In the estimation of the VT2, there was a significant HRV indices effect (F(2,36) = 20.3; p ≤ 0.001). Specifically, DFA-a1 displayed a moderate overestimation of the speed associated with the VT2 (0.41 [0.14 to 0.68] km/h); meanwhile, the respiration rate (−0.56 [−1.03 to −0.09] km/h) and RRa1 (−0.87 [−1.38 to −0.36] km/h) displayed a small and large underestimation, respectively. No significant HRV indices and sex interaction effect was observed (F(2,36) = 1.626; p = 0.211). In conclusion, DFA-a1, respiration rate and RRa1 are valid HRV indices to estimate the load associated with the VT1. However, DFA-a1 displayed a moderate overestimation of the load associated with the VT2, while the respiration rate and RRa1 displayed a small and large underestimation, respectively.