Table 3.

Association of VO₂ with the components of HRV determined in the stages of the different ETT.

	S1 β (95% CI)	p-value	S2 β (95% CI)	p-value	S3 β (95% CI)	P-value	S4 β (95% CI)	p-value	S5 β (95% CI)	p-value	REC β (95% CI)	p-value
T1
VLF	0.033 (− 0.071; 0.137)	0.524	0.094 (− 0.507; 0.695)	0.752	0.545 (− 1.453; 0.363)	0.230	3.939 (0.812; 7.066)	0.015*	− 3.355 (− 20.465; 13.754)	0.684	− 0.345 (− 1.123; 0.432)	0.372
LF	0.013 (0.001; 0.025)	0.032*	0.028 (− 0.003; 0.058)	0.073	0.139 (− 0.022; − 0.255)	0.021*	0.597 (− 2.491; 3.666)	0.698	1.548 (− 6.780; 9.875)	0.701	− 0.087 (− 0.816; 0.641)	0.808
HF	− 0.014 (− 0.053; 0.026)	0.481	− 0.017 (− 0.060; 0.026)	0.426	− 0.185 (− 0.528; 0.158)	0.281	0.424 (− 0.341; 1.189)	0.265	1.648 (0.144; 3.153)	0.033*	0.132 (− 0.118; 0.381)	0.290
T2
VLF	0.021 (− 0.041; 0.083)	0.497	0.168 (− 0.506; 0.171)	0.320	1.088 (− 0.360; 2.536)	0.135	0.469 (− 0.668; 1.607)	0.404	2.031 (− 6.786; 10.848)	0.610	− 0.244 (− 0.381; − 0.107)	0.001*
LF	0.012 (0.002; 0.021)	0.020*	0.056 (0.014; 0.098)	0.011*	0.264 (− 0.713; 0.186)	0.241	− 0.612 (− 1.693; 0.469)	0.255	− 1.110 (− 4.783; 2.563)	0.511	− 0.134 (− 0.331; 0.064)	0.178
HF	− 0.016 (− 0.048; 0.015)	0.293	− 0.051 (− 0.133; 0.032)	0.219	0.108 (− 0.070; 0.285)	0.227	0.471 (− 2.062; 3.004)	0.705	0.446 (− 1.039; 1.931)	0.518	0.010 (− 0.176; 0.158)	0.906

Values reported in calculated value of β (minimum value − maximum value). The value of β corresponds to how many ml kg⁻¹ min⁻¹ are added to VO₂ when a unit of the HRV variable is increased. The analysis was performed only including values from S1 to S5 because the number of subjects who participate of S6 and S7 were not sufficient to obtain statistically significant results.

VLF very low frequency component, HF: high frequency component, LF: low frequency component, L/H ratio between LF and HF, REC to recovery period of the test (3 min), S1 stage one, S2 stage two, S3 stage three, S4 stage four, S5 stage five, REC recovery time to ST with a 3-min duration.

*p < 0.05.