Asymmetric Spread Analysis of Heart Rate Variability in XC Mountain Biking During a 20-Minute Autonomic Profile Test

Abstract

The heart is innervated by the autonomic nervous system (ANS), which plays a role in regulating the heart rate. Cross-country mountain biking (MTBXC) is a sport with high physiological demands, where the autonomic nervous system plays a significant role. The main objective of this study was to analyze the asymmetry of heart rate in Colombian National Team mountain bikers, sub-23 category, during a 20 min cardiovascular autonomic profile test.

Method: The cardiovascular autonomic profile was measured through heart rate variability during a 20 min test, divided into eight phases (supine, controlled ventilation at 10 cycles/min, controlled ventilation at 12 cycles/min, postural change, orthostasis, Ruffier test, 1 min recovery, and final recovery) in a group of n = 10 MTB cyclists from the National Sub-23 Team, including 5 males and 5 females.

Results: The results for the male athletes were as follows: age: 19 ± 1 years; VO2max: 67.5 mL/kg/min; max power: 355 W; HRmax: 204 bpm. The results for the female athletes were as follows: age: 19 ± 1 years; VOmax: 58.5 mL/kg/min; max power: 265 W; HRmax: 194 bpm. Both genders showed the expected autonomic behavior in each phase. Asymmetrical propagation of heart rate was observed, with a greater deceleration pattern after postural changes and effort and a symmetrical acceleration pattern in these two phases.

Discussion: Athletes exhibit increased vagal response compared to non-athletes. Mountain bikers show rapid heart rate reduction after exertion.

Conclusion: This study demonstrates how mountain bikers exhibit increased heart rate deceleration following sympathetic stimuli.

Keywords: asymmetry; autonomic nervous system; heart rate variability; mountain biking.

Figure 1

Asymmetric Spread Index of heart rate variability per phase. Note: A Kruskal–Wallis one-way ANOVA was used to compare ASI between genders across phases. A statistically significant difference was found only in Phase 5 (χ²(1) = 5.46, p = 0.019), indicating gender-related differences in asymmetric heart rate dynamics during this stage. The Asymmetric Spread Index (ASI) is unitless.

Figure 2

SD1, SD2, and SD1/SD2.

Figure 3

Index values per phase.

Figure 4

Indices by gender. Mean ± SD values of the Porta, Guzik, and Ehlers Indices across experimental phases, separated by gender (male and female). A two-way ANOVA revealed a significant main effect of the phase on the Porta Index (p < 0.001), but no significant effects of gender (p = 0.478) or the phase × gender interaction (p = 0.811). The Guzik Index showed a trend toward significance across all phases (p = 0.054), while the Ehlers Index showed no significant differences. Post hoc Tukey HSD tests for the Porta Index revealed that Phase 4 significantly differed from Phase 1 (p = 0.003) and Phase 8 (p = 0.008), and that Phase 7 was significantly lower than Phases 2 through 6 (all p < 0.001) and higher than Phase 8 (p = 0.027).