Validation of Anaerobic Threshold Detection Based on the HR Kinetics

Abstract

Since the theorization of the anaerobic threshold (AT), several direct and indirect methods have been developed for its detection. Based on the pioneer work of Sietsema (1989) about the heart rate (HR) kinetics, it has been hypothesized that a slow component on the HR kinetics, superimposing the workload requisition, would appear during supra-AT exercises which would not be true for low intensities. PURPOSE: to detect the AT based on the HR kinetics during step workload and validate it through lactacidemy measurement. METHODS: Twenty six male soccer athletes (22±5yrs; 74±7Kg; 177±7cm) completed a progressive maximum treadmill test (Bruce protocol). The HR (Polar S610, Sweden) and the pulmonary gas exchange (VO2000, Aerosport, Brazil) were monitored continuously during all tests, and lactacidemy was measured at each stage. The real AT was characterized by the onset of blood lactate accumulation and, concerning the HR kinetics, was attributed to the point where the HR could not establish steady state, characterizing the slow component. The HR kinetics was analyzed for each workload according to: (1) the coefficients of a double-exponential model (EM) extracted through non linear regression; (2) the coefficient of variation (CV) of HR during the final minute; and (3) the difference between the maximal and minimal HR (AHR) during the last minute. The AT detected by the methods described above was compared through one-way ANOVA (α= 0.05). The HR methods were compared with AT using t-paired Student's Test its reliability was expressed by Bland and Altman method. RESULTS: Volunteers achieved a maximal oxygen uptake (VO2max) averaging 56.1 1±6.35ml.kg-1.min−1, attaining the AT at 71.5±9.9% of the VO2max. All HR-based methods were able to identify the HR slow component resulting, on average, in76.9±15.1,80.6±13.2and68.6±14.9%oftheVO2maxforEM, AHR and CV respectively. Although no significant differences have been found among them, the highest correlations with the AT were attained by EM (0.67% p < 0.05) and CV (0.58%p < 0.05), and further, except for AHR, EM (p=0.44) and CV (p=0.67) were not different from the real AT. CONCLUSION: The HR-based methods were well correlated to AT, presenting acceptable reliability and validity. Besides the large applicability of a HR-based method, the HR kinetics analysis could easily be used for determining the AT.