Correlation properties of heart rate variability to assess the first ventilatory threshold and fatigue in runners

Figures & data

Figure 1. Exemplary course of the excess CO₂ and DFA-a1 data during the double ramp of one 23-year-old female participant (VO_2peak of 49 ml∙kg⁻¹∙min⁻¹). The method of determining VT1 by excess CO₂ (blue dots) and HRVT at DFA-a1 value of 0.75 is shown. DFA-a1 (red dots) is displayed over time with areas of linear regression in grey dots. Abbreviations: CO₂, carbon dioxide; DFA-a1, alpha1 of detrended fluctuation analysis; HRVT, heart rate variability threshold; VT1, first ventilatory threshold.

Figure 2. Change in VO₂ and HR at gas exchange VT1 (a & c) and HRVT (b & d) for both ramps. Dots represent individual data points, box and whiskers depict the median and interquartile range, and distribution plots represent the distribution of the datapoints. Abbreviations: HR, heart rate; HRVT, heart rate variability threshold; VO₂, rate of oxygen uptake; VT1, first ventilatory threshold.

Figure 3. Bland-Altman plots depicting the agreement between VO₂ at gas exchange VT1 and HRVT during the first (a) and second (b) ramp, and HR at gas exchange VT1 and HRVT during the first (c) and second (d) ramp. Black dots represent individual data points, black dashed lines represent the 95% limits of agreement. Abbreviations: HRVT, heart rate variability threshold; VO₂, rate of oxygen uptake; VT1, first ventilatory threshold.

Table 1. Mean ± standard deviation difference and 95% limits of agreement between the gas exchange and HRVT during both ramps.

Outcome	Ramp 1 mean ± SD difference (95% LoA)	Ramp 2 mean ± SD difference (95% LoA)
VO2 at gas exchange VT1 vs VO2 at HRVT (ml∙kg^−1∙min^−1)	−0.5 ± 3.2 (−6.8 to 5.8)	−7.3 ± 5.5 (−18.1 to 3.5)
HR at gas exchange VT1 vs HR at HRVT (beats∙min^−1)	−0.9 ± 5.8 (−12.2 to 10.5)	−12.3 ± 9.3 (−30.4 to 5.9)
VO2 at gas exchange VT1 vs VO2 at HRVT (MAPE)	5.8 ± 5.0 (−4.1 to 15.6)	18.5 ± 12.8 (−6.6 to 43.7)
HR at gas exchange VT1 vs HR at HRVT (MAPE)	11.4 ± 9.7 (−7.5 to 30.3)	45.1 ± 42.8 (−38.7 to 12.9)

Abbreviations: HR, heart rate; HRVT, heart rate variability threshold; LoA, limits of agreement; MAPE, mean absolute percentage error; SD, standard deviation; VO₂, rate of oxygen uptake; VT1, first ventilatory threshold.

Data availability statement

All data used in analyses are provided as a supplementary file.