Relationship Between Heart Rate Variability Threshold And Ventilatory Threshold Across Exercise Modalities

Heart rate variability (HRV) is the variation between successive heartbeats and is influenced by exercise intensity. Ventilatory threshold (VT) marks the point during exercise where ventilation increases disproportionately to oxygen consumption. As exercise intensity rises, sympathetic activity increases, decreasing HRV and raising heart rate. The HRV metric detrended fluctuation analysis alpha 1 (DFA-α1) quantifies autonomic activity, and a value of 0.75 has been associated with VT and is used to determine the heart rate variability threshold (HRVT), offering a practical method for assessing exercise intensity. PURPOSE: The purpose of this research was to examine the relationship HRVT and VT across cycling and running. METHODS: Eight apparently healthy adults (5 men: 20 ± 1 yrs., 88.2 ± 7.4 kg, 187.7 ± 5.2 cm, 11.9 ± 1.1% body fat; 3 women: 20 ± 1 yrs., 60.3 ± 2.9 kg, 167.2 ± 5.4 cm, 23.3 ± 0.9% body fat) completed four maximal graded exercise tests (GXT), two on a treadmill and two on a cycle ergometer. Intensity gradually increased by approximately 5% via speed and/or grade every 2-minutes on the treadmill, and continuously increased at a rate of 25 Watts every minute while cycling. HR and expired gases were continuously collected via HR monitors and open-circuit spirometry. VT was estimated utilizing the v-slope method and HRVT was determined by DFA-α1 value of 0.75. A two-way repeated measures ANOVA with planned contrasts evaluated threshold estimates by exercise modality and across trials. RESULTS: A significant main effect of exercise modality was observed for peak oxygen consumption (V̇O2peak), HRmax, HR at VT, and DFA-α1 at VT (p < 0.001 respectively) (Table 1). CONCLUSIONS: Cycling elicited a lower V̇O2peak and HRmax compared to running, and the HRVT (DFA-α1 at 0.75) overestimated HR associated VT during cycling. Further investigation into the relationship between HRVT and VT is needed to refine DFA-α1 thresholds, as they may be exercise modality-specific. Table 1. - Descriptive statistics reported as mean ± SD of variables of interest during along with the Cohen’s d effect size showing the difference between the aggregate running and cycling trials. Variable Trial # Running Cycling Cohen’s d (95% CI) V̇O2peak (ml/kg/min)* 1 47.1 ± 2.9 36.9 ± 4.5 2.67 (3.62, 1.69) 2 48.3 ± 4.5 37.3 ± 4.2 HRmax (bpm)* 1 196 ± 9 182 ± 10 1.41 (0.42, 2.39) 2 196 ± 9 184 ± 7 HR at VT (bpm)* 1 158 ± 18 123 ± 18 1.56 (2.35, 0.75) 2 155 ± 18 133 ± 20 HR at HRVT (bpm) 1 158 ± 19 154 ± 24 0.24 (0.95, 0.49) 2 158 ± 17 153 ± 15 DFA-α1 at VT (au)* 1 0.90 ± 0.30 1.28 ± 0.13 -1.31 (-2.38, -0.23) 2 0.93 ± 0.35 1.21 ± 0.17 *, significant main effect for exercise mode; CI, confidence interval; DFA, detrending fluctuations analysis; HR, heart rate; HRVT, heart rate variability threshold; V̇O2peak, peak oxygen consumption; VT, ventilatory threshold measure by v-slope method