Second Ventilatory Threshold Assessed by Heart Rate Variability in a Multiple Shuttle Run Test.

Many studies have focused on heart rate variability in association with ventilatory thresholds. The purpose of the current study was to consider the ECG-derived respiration and the high frequency product of heart rate variability as applicable methods to assess the second ventilatory threshold (VT). Fifteen healthy young soccer players participated in the study. Respiratory gases and ECGs were collected during an incremental laboratory test and in a multistage shuttle run test until exhaustion. VΤ was individually calculated using the deflection point of ventilatory equivalents. In addition, VT was assessed both by the deflection point of ECG-derived respiration and high frequency product. Results showed no statistically significant differences between VT, and the threshold as determined with high frequency product and ECG-derived respiration (F(2,28)=0.83, p=0.45, η=0.05). A significant intraclass correlation was observed for ECG-derived respiration (r=0.94) and high frequency product (r=0.95) with VT. Similarly, Bland Altman analysis showed a considerable agreement between VT vs. ECG-derived respiration (mean difference of -0.06 km·h, 95% CL: ±0.40) and VT vs. high frequency product (mean difference of 0.02 km·h, 95% CL: ±0.38). This study suggests that, high frequency product and ECG-derived respiration are indeed reliable heart rate variability indices determining VT in a field shuttle run test.