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 (VT₂). 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. VΤ₂ was individually calculated using the deflection point of ventilatory equivalents. In addition, VT₂ was assessed both by the deflection point of ECG-derived respiration and high frequency product. Results showed no statistically significant differences between VT₂, and the threshold as determined with high frequency product and ECG-derived respiration (F(2,28)=0.83, p=0.45, η²=0.05). A significant intraclass correlation was observed for ECG-derived respiration (r=0.94) and high frequency product (r=0.95) with VT₂. Similarly, Bland Altman analysis showed a considerable agreement between VT₂ vs. ECG-derived respiration (mean difference of -0.06 km·h^-1, 95% CL: ±0.40) and VT₂ vs. high frequency product (mean difference of 0.02 km·h^-1, 95% CL: ±0.38). This study suggests that, high frequency product and ECG-derived respiration are indeed reliable heart rate variability indices determining VT₂ in a field shuttle run test.