Diurnal variation in stroke parameters and motor organization in front-crawl swimmers

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 +/- 1.6years) performed maximal front crawls over 12.5m during two experimental sessions; the morning sessions were conducted between 07:00 and 09:00h and the evening experiments were conducted between 17:00 and 19:00h. Stroke parameters (swim velocity, stroke rate [SR], 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 degrees C than in the morning 36.1 +/- 0.2 degrees C (p<0.001), with a morning-evening difference of -0.7 +/- 0.1 degrees C. Performance was also higher in the evening (7.4 +/- 0.6s) than in the morning (8.0 +/- 0.8s) (p<0.001), with a morning-evening difference of 0.55 +/- 0.30s. Likewise, values of swim velocity and SR were higher in the evening than in the morning (p<0.001) with morning-evening differences of -0.10 +/- 0.04ms(-1) and -3.99 +/- 2.91 cyclesmin(-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.