Recently double product (DP)has been considered as a useful index in context of sport science and cardiovascular health. DP or rate product ratio (RPR) equals Systolic Blood Pressure (SBP) multiplied by Resting Hear Rate (RHR). The aim of present study was to investigate the circadian rhythm variation of DP after1 (60 minutes) and 2 split exercise sessions (2×30 minutes) a day. Fourteen healthy males volunteered to participate in present study from University of Tabriz. Two groups of subjects in a crossover design were randomly distributed as group I (one session a day, twice a day) and vice versa for group II. Having completed the test (treadmill running with an intensity of 70 per cent of Maximum Heart Rate), RHR and SBP were measured every two hours for 24 hours. After one-week break, the procedure repeated for two groups vice versa and 24-hour measurement of RHR and SB.P was carried out. For analysis for data, repeated measure (ANOVA) was used. Each variables demonstrated a normal circadian rhythm. There were significant variations in circadian mean values for SBP (101.3±12.5 , 93.9±4.5 , P=0.009) and RHR (91.9±10.9 , 96.7±6.8 , P=0.03) in 1 and 2 split session of exercise a day respectively. There was not significant changes in circadian rhythm of DP (72.05±1.47 U and equaled 73.88±12.16 U) in 1 and 2 split session of exercise a day respectively although mean values from 20:00 to 08:00 in the morning were higher in 2 split sessions than 1 session. One aerobic exercise session compared to two split sessions a day with the same total time of exercise a day may not change circadian rhythm of double product within 24 hours following aerobic exercise. Split exercise sessions could be substituted for one session a day or the other way round without any extra overload on cardiac muscle. If the blood pressure is the main center of medical attention, split exercise sessions may be of value since the circadian rhythm of systolic blood pressure in this case is lower than 1 session a day.
