OBJECTIVES: It is long established that baroreflex control of cardiovascular system is modified during physical exercise. However, the effect of exercise intensity on baroreflex activity and time-dependence of the transient processes in baroreflex control are poorly understood. The aim of this study was to study the intensity-dependence and dynamic characteristics of baroreflex activity changes during exercise. For evaluation of baroreflex activity we used phase synchronization of blood pressure and heart rate. METHODS: 10 young healthy men performed a 15-minute bicycle exercise twice: with an intensity of 60% and 80% of anaerobic threshold (AT). The exercises were preceded by a 15-min rest period. To determine AT the volunteers performed bicycle ramp test before the experiment. Blood pressure and ECG were continuously recorded during the experiment, then phase synchronization index (PSI) was calculated off-line as described elsewhere (Borovik et al, 2014). The dynamics of baroreflex activity changes was studied for 8 subjects who performed the cycling exercise with sine-like intensity modulation (mean value 50% AT, amplitude 30% AT, frequency changed from 1 to 10 mHz), PSI were then calculated in successive 4-min episodes. RESULTS: Mean value of PSI in the frequency range of baroreflex waves (near 0.1 Hz) tended to be lower during light exercise (0.15±0.04) and was significantly reduced during heavy exercise (0.11±0.04) compared to PSI value at rest (0.19±0.07). The experiments with sine-like intensity pattern showed that PSI changes with alternating power are rather slow – PSI modulation disappeared at 2 mHz, whereas blood pressure and heart rate modulations were clearly seen at this frequency and higher. CONCLUSION: The phase synchronization of blood pressure and heart rate during exercise might be masked by modulating effect of the intensity-dependent muscle pressor reflex upon baroreflex activity. Exercise intensity-induced PSI changes develop slowly, during several tens of seconds. The work is performed according to the Plan for Fundamental research of SRC RF Institute of Biomedical Problems RAS and with partial financial support of the RFBR (N17-04-01943).