Inadequacy of first and second order models to characterize the heart rate response induced by dynamic exercise

Six normal subjects were submitted to dynamic exercise at workloads of 25, 50, 100 and 150 w for 4 min, intercalated by periods of rest, before and after an aerobic training period of 10 weeks. The heart rate response was fitted to 2 mathematical models, a 1st-order model and a 2nd-order model. The results indicate that these 2 models were not adequate to characterize the physiological response of heart rate induced by dynamic exercise.