time of 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.

The aim of this study was to investigate the effect of time of day (morning and evening) on the rate of fat oxidation and its changes trend in submaximal exercise in sedentary overweight girls. In this semi-experimental study, a practical approach was applied. 15 sedentary overweight female students (mean±SD age, height, weight, BMI and BF%: 23.3 ± 0.9 years, 162.6 ± 6.5 cm, 70.4 ± 4.5 kg, 26.6 ± 1.1 kg/m2 and 33.6 ± 2.2%) filled out a questionnaire and were randomly selected as the sample from eligible participants and divided into two groups: morning (n=7) and evening (n=8) with counterbalance method. The exercise protocol consisted of 60 min. of continuous running on a treadmill with %60 HRmax or about 56%VO2max performed in two sessions of 07:00 AM and 06:00 PM with a 7-day interval. VO2 and VCO2 were measured by gas analyzer system and the rate of fat oxidation per minute was calculated by Frayn stoichiometric equations. Paired t test and analysis of variance with repeated measures were used (P≤0.05). The results showed that the rate of fat oxidation and its changes trend in the evening was significantly higher than morning (P≤0.001). Finally, based on the results of this study, it appears that submaximal exercise in the evening has a higher effect on fat oxidation and helps weight loss.

To examine whether time of day significantly affects salivary IgA, cortisol, α-amylase and total protein levels before and after sub-maximal swimming. Fourteen female swimmers (age 13±1.33 years, weight 48±4.75 kg, Vo2max 45.92±3.96 ml/kg/min) volunteered to participate in the study. In a fully randomized, cross over design, each subject performed 10×200 m front crawl at 80% of their seasonal best time, with one minute rest between each 200 m, at 08:00 and 18:00 hours on two days aware. Timed, unstimulated saliva samples were collected before and after exercise. Saliva samples were analyzed by two-factor analysis of variance (ANOVA) with repeated measures. Statistical significance was accepted at p<0.05. Significant time of day effects (am and pm respectively) were observed in s-IgA, S-IgA, cortisol, and saliva flow rate, αamylase and total protein before exercise (P<0.05). The exercise protocol did not significantly affect s-IgA but, in comparison with values before exercise, caused significant alterations in cortisol, S-IgA, saliva flow rate, αamylase and total protein (P<0.05). There was no significant interaction effect of time of day by exercise on any salivary variables measured except αamylase. These results suggest a significant circadian variation in the variables measured before exercise, with showing a significant effect on their acute responses to exercise except s-IgA and a significant interaction effect of time of day by exercise on salivary αamylase.

Fat oxidation during exercise can be influenced by exercise intensity and duration, training status, diet and physical activity level. However, few studies have investigated the effect of time of day on the rate of fat oxidation during exercise. Thus the present study was designed to investigate the effect of time of day on indexes of fat oxidation in active young women. For this purpose, 14 healthy women (mean±SD age, BF%, weight, BMI and Vo2max: 21.6±1.6 years, 18.3± 4.6 %, 51.2± 3.3 kg, 22±1.7 kg/m2, 40.8±4.2 ml/kg.min) voluntarily participated in this study. The exercise test was performed in two separate sessions in the morning (7:00) and evening (19:00). There was a 7-day interval between the two tests. The protocol was an incremental exercise to exhaustion on a treadmill. The volunteers started exercising at a speed of 58.3 m/min and at a gradient of 1%. Then, the speed increased to 16.7 m/min every three minutes until 125 m/min. At this point, the gradient increased by 2% per three minutes until RER=1 was achieved. VO2 and VCO2 were measured throughout the exercise by an automated gas analysis system. The data were analyzed using independent t test (α=0.05). The findings of the present study showed that no significant difference in maximal fat oxidation between morning and evening exercises (morning: 0.39±0.13 vs. evening: 0.44±0.11, P>0.05). There was no significant difference in FAT Max between morning and evening (P>0.05). However, the mean intensity of maximal fat oxidation was higher in the evening. Finally, it can be concluded that probably time of day (morning and evening) does not have an effect on substrate oxidation during intensive exercise.