Author(s): GRONWALD, T., KETELHUT, S., GÜRLICH, T., KOCK, H., HOOS, O., MÖHLE, M., Institution: MARTIN LUTHER UNIVERSITY HALLE-WITTENBERG, Country: GERMANY, Abstract-ID: 1901

INTRODUCTION:
This study investigated whether varying active recovery durations influence heart rate (HR) time series measures after repeated Wingate exercise and whether these responses differ between sexes.
METHODS:
Forty-eight well-trained adults (22 females; age: 37.7±13.9 years; body height: 1.74±0.09 m, body mass: 68.7±10.9 kg, body fat: 14.6±7.5%; VO2MAX: 48.4±9.3 ml/kg/min; training volume: 8.6±3.1 h/week; sport-specificity: triathlon, biking, mountain biking, running, swimming) participated in a randomized within-subject crossover design consisting of four laboratory sessions. Following baseline assessments, participants completed three experimental protocols with a one-week washout period. Each protocol consisted of a warm-up and 4x 30-second all-out cycling sprints (Wingate tests) interspersed with active recovery periods of 1, 3, or 10 min at standardized workloads, followed by a 15-min active cool-down (all at 70 W for females, 100 W for males). RR intervals were recorded during warm-up and during active recovery (including cool-down). HR, time-domain root mean square of successive differences of normal‐to-normal RR‐intervals (RMSSD) and non-linear exponent alpha 1 of detrended fluctuation analysis (DFAa1) were calculated from 2-min segments during recovery (3, 6, 9, 12, 15 minutes) and expressed as changes relative to warm-up values (Δ). Linear mixed-effects models assessed the effects of time, condition, and sex.
RESULTS:
Significant main effects of time were observed for all outcomes (p < 0.01). For ΔDFAa1, significant main effects of condition (F(2,444.6)=17.79, p<0.001) and sex (F(1,41.5)=8.77, p=0.005) were found, indicating less pronounced decreases in female athletes (β=0.233, SE=0.079). No significant interaction effects were detected, suggesting that this sex difference remained stable across experimental conditions and time points. HR showed significant main effects of condition (F(2,442.9)=22.25, p<0.001) and sex (F(1,40)=9.95, p=0.003), with female athletes exhibiting lower ΔHR values (β=-6.93 bpm, SE=2.200). Additionally, a significant interaction effect of sex and condition emerged (F(2,442.9)=8.78, p<0.001), indicating that sex differences varied depending on the experimental condition. ΔRMSSD showed a significant main effect of condition (F(2,438.8)=7.22, p<0.001), but no main effect of sex (F(1,41.8)=1.62, p=0.210). However, a significant interaction effect of sex and condition (F(2,438.8)=12.63, p<0.001) revealed divergent responses between sexes depending on recovery duration.
CONCLUSION:
The duration of active recovery significantly modulated autonomic recovery dynamics following repeated high-intensity exercise, with differential effects across HR time series metrics. Different indices reflect distinct physiological control mechanisms; consequently, sex-specific modulation may emerge selectively depending on whether measures capture overall HR responses, fractal dynamics, or vagally mediated variability.