Evaluation of Anaerobic Thresholds Based on the Heart Rate Changes Recorded during Standard Exercise Tests

A method is described for an accurate extrapolation of heart rates (HR) recorded during exercise testing to their steady-state levels attainable at every load step. The method makes it possible to study individual correlations between the HR and load power, e.g., in short-term myocardial ischemia. The load ranges over which the HR changed linearly or nonlinearly with power were found on testing 36 angina pectoris patients with transient STdepressions. The 24-hour HR minima and the threshold HR magnitudes corresponding to the aerobic thresholds of specific myocardial loci were within linear ranges, whereas the maximum attainable HR magnitudes most frequently were within nonlinear ranges. This nonlinearity is likely to be due to the onset of anaerobic processes contributing to the total energy production in the body. Hence, the point of transition to nonlinear HR changes, experimentally detectable during exercise tests with ECG monitoring, determines the anaerobic threshold.