Kinetics of heart rate increase with exercise in different athletes

The kinetics of heart rate (HR) increase in man at the beginning of muscular exercise follow a biexponential function whose fast and slow components seem to depend on neurogenic (0-2 min) and/or chemical stimuli (1-5 min of exercise). The feasibility of this model and the different roles played by the two components have been analyzed in endurance (EA) and sprinter (SA) athletes and in sedentary controls (SC) during bicycle exercise of different intensities at 0.15-0.90 of the maximal aerobic power, V̇(O2) max, range. It appears that: 1) in EA group, characterized by both high V̇(O2) max and fraction of slow twitch muscle fibers, the fast component alone is responsible for the HR increase up to a work load of about 0.6 V̇(O2) max. In SA and SC the corresponding value is 0.5 and 0.3 V̇(O2) max respectively; 2) the half-time values of the fast and slow exponential functions are in the range of 3-15 sec and, if any, of 35-100 sec respectively, independent of work intensity and athletic characteristics. The different training history seems therefore to affect differently the mode of the heart control elicited by muscular exercise.