The response of hemorheological factors to intense physical exercise at different times of the day

  The purpose of this study was to investigate the effect of exercise at different times of day on hemorheological variables.

For this reason, fifteen healthy male subjects (Mean±SD: age, 24.7±2.3 years, weight, 65.2±7.3 kg, height, 171.1±10.2 cm) participated in the present study voluntarily. All subjects performed an aerobic exercise protocol on a cycle ergometer at intervals of 3 days and at four different times of day (08:00, 12:00, 16:00 and, 20:00). In each session, subjects performed the cycling protocol for 30 minutes at an intensity corresponding to 90% of HRmax after warming up. Heart rate and rate of perceived exertion were recorded during 30 minutes of exercise. In each trial, two venous blood samples (10 ml) were taken before and immediately after exercise. Blood samples were analyzed for hemorheological variables (blood viscosity, plasma viscosity, hematocrit, fibrinogen, albumin and, total protein).

statistical analysis of data revealed no significant effect of time of day on responses of blood viscosity (P=0.056), plasma viscosity at a shear rate of 12 (P=0.070), hematocrit (P=0.152), fibrinogen (P=0.078), erythrocyte sedimentation rate (P=0.461), heart rate (P=0.838) and mean arterial blood pressure (P=0.581). However, time of day significantly affected responses of plasma viscosity (P=0.045, shear rate of 60), total protein (P=0.014), and body temperature (P=0.035) to endurance exercise.

According to the findings of the present study, it could be concluded that except for plasma viscosity at the high shear rate, responses of hemorheological variables to exhaustive endurance exercise are not related to the time of day that exercise is performed.  Therefore, it seems that healthy people can probably exercise at different times of the day without worrying about their blood status.