The aim of the present study was to examine the effects of time of day on stroke parameters and motor organization in front-crawl swimmers. In a randomized order, fourteen regional swimmers (age: 18.7 ± 1.6 years) performed maximal front crawls over 12.5m during two experimental sessions; the morning sessions were conducted between 07:00 and 09:00 h and the evening experiments were conducted between 17:00 and 19:00 h. Stroke parameters (swim velocity, stroke rate and stroke length), motor organization (arm stroke phases and arm coordination) were calculated from aerial and underwater side-view cameras. Arm coordination was quantified in terms of an index of coordination (Idc). Results showed that oral temperature was significantly higher in the evening 36.8 ± 0.2°C than in the morning 36.1 ± 0.2°C (p < 0.001), with a morning-evening differences of -0.7 ± 0.1°C. Performance was also higher in the evening (7.4 ± 0.6 s) than in the morning (8.0 ± 0.8 s) (p < 0.001), with a morning-evening differences of 0.55 ± 0.30 s. Likewise, values of swim velocity and stroke rate were higher in the evening than in the morning (p < 0.001) with morning-evening differences of -0.10 ± 0.04 m.s -1 and -3.99 ± 2.91 cycles.min -1 , respectively. Percentage IdC increased significantly (p < 0.01) between the morning (-5.1 ± 6.5%) and evening (-1.6 ± 7.0%). It is concluded that maximal swimming trials are performed better in the evening than the morning, and that this might be explained by better stroke parameters and motor organization at this time.
The aim of this study is to see whether Ramadan fasting has an effect on the diurnal variations in anaerobic power and swimming performance or not. Ten participants whose mean ± SE for age, height, body mass are 19.4 ± 1.4 years, 1.72 ± 0.1 m and 72.8 ± 6.6 kg, respectively. They are tested at 3 testing periods [i.e., one week before Ramadan (BR), the middle period of Ramadan (MPR), the end period of Ramadan (EPR)], tests are performed at 07:00 h and 17:00 h throughout every course. The test sessions were started with oral temperature and body mass measurements. Regularly doing first the Wingate test then a 25-m swim at maximal speed at each test session. During the three experimental periods, dietary intake was assessed. The result shows a significant diurnal variation of muscle power and fatigue throughout the Wingate test before Ramadan. Likewise, there is a daily rhythm in the stroke parameters and swimming performance in the mentioned period. These diurnal variations change during the month of Ramadan with a decrease in power output, swim performance, swim speed and stroke length in the evening, with no changes for the morning tests. Moreover, the diurnal variations of muscle fatigue during the three morning tests show no changes and remain the same. Whereas the three evening tests show a gradual increase towards tiredness. The results show that Ramadan may has a great effect on the circadian rhythm of muscle power and swimming performance. The time-of-day effects the anaerobic power variables during the normal days which disappear during Ramadan. Ramadan fasting effects performance in the evening; however, the morning performance tests are unchangeable during Ramadan. Additionally, Ramadan fasting has no adverse effect on energy intake, and percentages of macronutrient intake.
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