OBJECTIVE: We investigated the effect of autonomic nervous system activity on exaggerated systolic blood pressure (SBP) response to exercise in healthy subjects using heart rate variability (HRV) analysis. METHOD AND RESULTS: We studied 53 healthy volunteer subjects with exercise treadmill test according to the Bruce protocol. Time domain and frequency domain of HRV were measured for each 5-minute segment before (rest) and after exercise (recovery) and during the total exercise period. The mean change in SBP (delta SBP) was 39 +/- 18 mm Hg. The delta SBP above the value of mean (> or = 40 mm Hg) was defined as an exaggerated delta SBP. According to the delta SBP, subjects were classified into two groups. Group I consisted of 32 patients who showed a normal delta SBP, group II consisted of 21 patients who showed exaggerated delta SBP. There were no significant differences in baseline clinical characteristics and exercise duration between the two groups. There were no significant differences in the mean RR intervals, SDNN (standard deviation of all RR intervals), RMSSD (the square root of the mean of the sum of the squares of differences between adjacent RR intervals), and HF (high-frequency power, 0.15 to 0.40 Hz) at rest between the two groups. However, LF (low-frequency power, 0.04 to 0.15 Hz) and LF/HF ratio at rest were significantly higher at rest in group II than in group I. There were no significant differences in the mean RR intervals and HF at exercise between the groups. However, SDNN and RMSSD were significantly lower, LF and the LF/HF ratio were significantly higher at exercise in group II than in group I. No differences in these parameters were observed at recovery between the two groups. CONCLUSIONS: The sympathetic activity was higher at rest and during the total exercise period, parasympathetic activity was lower during the total exercise period in healthy subjects with exaggerated SBP response to exercise than in those with normal SBP response.