Determination of Lactate Thresholds in Maximal Running Test by Heart Rate Variability Data Set

Background: Heart rate variability (HRV) data set has been used to identify HRV thresholds during exercise. However, the relationship between HRV thresholds and the first (LT1) and second lactate threshold (LT2), has been poorly investigated during maximal running test. In this regard, HRV may act as a useful, less expensive and time consuming method to estimate physiological thresholds. Objectives: The aim of the present study was to verify the validity and reproducibility of the heart rate variability (HRV) method to determine first and second lactate thresholds during a maximal running test. Methods: Nineteen male runners (30.4 ± 4.1 years; body mass of 74.3 ± 8.5 kg; height of 176 ± 6.4 cm and body fat of 13.8 ± 4.6 %) performed two progressive maximal tests on a treadmill, with initial speed at 5 km.h-1 and 1 km.h-1 increments every 3 minutes, until exhaustion. Measures of HRV and blood lactate concentrations were obtained during the tests and physiological thresholds were identified as lactate thresholds by using fixed concentrations (2.0 and 3.5 mmol.L-1) and Dmax method, as well as HRV thresholds. Results: There were no differences between the first physiological thresholds identified as lactate (2.0 mmol.L-1 = 11.9 ± 2.9 km.h-1 and Dmax = 12.3 ± 1.5 km.h-1) or HRV threshold (11.6 ± 1.6 km.h-1). Accordingly, there were no differences between the second physiological thresholds identified as lactate threshold (3.5 mmol.L-1 = 14.2 ± 2.6 km.h-1) or HRV threshold (14.2 ± 2.0 km.h-1). Furthermore, HRV thresholds showed good agreement between test and retest. Conclusions: Physiological thresholds identified by using HVR data set provided reliable and practical estimation of LT1 and LT2 during a maximal running test.