The problem of evaluating the mobilization of body functioning during exercise combines two questions: first, the velocity of adaptation at onset of exercise, and second, to what extent the body function was mobilized. The aim of this study was to find out the peculiarities in mobilization of cardiovascular function during constant-load and all-out exercise tests in non-athletes and sportsmen: cohorts of sprinters, endurance and combat athletes. Every subject underwent a Roufier's test (30 squats per 45 seconds), a 30-second duration maximal vertical jump test, and a bicycle ergometry (graded stress). Indirect arterial blood pressure measurements were taken from the arm with a sphygmomanometer and standard-size arm cuff and various indices registered in 12-lead electrocardiogram (ECG) using a computerized ECG analysis system "Kaunas-load" were analyzed. The results obtained during the study showed that the change in ratio of JR/RR intervals of ECG allows assessing the dynamics of mobilization of cardiovascular system during the exercise tests or workouts. The greater mobilization of cardiovascular system when performing constant-load exercise tests is rather characteristic for non-athletes than sportsmen's cohorts. Constant-load exercise tests rather than all-out exercise tests are more suitable for assessments of individual peculiarities or differences between the cohorts. The individual peculiarities in velocity of adaptation of cardiovascular system at onset of exercise can be evaluated making use of the index of velocity of adaptation (V(Ad)), which represents the difference between the relative changes of JT and RR intervals of ECG. Velocity of adaptation at onset of exercise depends on the residual effects of training but not on the type of exercise test.