An investigation into the relationship between heart rate variability and the ventilatory threshold in healthy moderately trained males.

BACKGROUND: During incremental exercise, heart rate variability (HRV) has been shown to display distinct stabilization and inflection points, which have been used to indirectly detect the ventilatory threshold (VT).

METHODS: Ten moderately trained males (26·5 ± 5·9 years: VO2peak 48·7 ± 4·1 ml min-1  kg-1 ) performed an incremental test on a cycle ergometer until volitional exhaustion with both R-R intervals and respiratory indices recorded. HRV was quantified using both nonlinear (Poincare plot; short-term variability SD1) and spectral analysis of the R-R intervals (high-frequency component; HFp). The VT was identified using the V-slope method. The relationship between HRV parameters and the VT was assessed using both a paired t-test and Pearson's product correlation. In addition, Bland and Altman plots were used to quantify the mean difference along with a 95% confidence interval.

RESULTS: When expressed as the corresponding heart rate values, both the SD1 and the HFp stabilization points revealed a strong (r = 0·86 and 0·087, respectively) correlation with the VT. However, only for SD1 this relationship was different to the VT (t-test). The Bland-Altman plots supported these findings showing wide limits of agreement present for SD1 and the VT whilst the relationship between HFp and the VT revealed narrower limits.

CONCLUSION: There does not appear to be a relationship present between the VT and the SD1 stabilization point in moderately trained healthy males, whereas the HFp stabilization point revealed a strong relationship with the VT when expressed as heart rate.