Race analysis is a tool broadly applied to evaluate the swimmer performance and develop specific training plans. We aimed to analyse the race components differences between national and regional female swimmers taking part in 50m freestyle short course event and the relevance of individual emersion distances after the start and turn. Fifty-five national level performances (Spanish Short Course Nationals, December 2016) and 85 regionals (local competitions developed at our University swimming pool, season 2016/17) were compared, no swimmers repeated in both competitions. Each group had a mean age of 18.3 ± 2.5 years and 15.8 ± 2.6 years respectively. Each swimmer`s mean stroke rate (SR, cyc/min), stroke length (SL, m) and stroke index (SI, m2/s) were collected from 50Hz HD video, event time was obtained from official results (T50, s). The starting phase was obtained from the starting signal until swimmer`s head crossed the 10m (T10, s) and 15m (T15, s) mark. The turning phase commenced when the swimmer`s head passed through a distance of 5m out from the wall until swimmer`s head crossed the 35m reference (Turn15m, s). The emersion distance and time after the start ([D_Emers1, m], [T_Emers1, s]) or after the turn ([D_Emers2, m], [T_Emers2, s]) were measured. T-test for independent samples and Pearson correlation coefficient were applied. National female swimmers obtained significantly shorter times than regional: T10 (4.49 ± 0.20 vs 5.14 ± 0.44), T15 (7.17 ± 0.20 vs 8.41 ± 0.60), T15turn (8.15 ± 0.28 vs 9.56 ± 0.63), T50 (26.94 ± 0.62 vs 31.31 ± 2.05), longer SL (1.89 ± 0.12 vs 1.67 ± 0.15) and higher SI (3.31 ± 3.22 vs 2.51 ± 0.30). Whilst, SR was not different between groups (55.86 ± 3.67 vs 54.34 ± 5.03). National swimmers attained similar emersion times than regional [T_Emers1 (3.83 ± 0.70 vs 3.91 ± 0.68), T_Emers2 (2.30 ± 0.56 vs 2.22 ± 0.58)] and significantly longer emersion distances [D_Emers1 (8.99 ± 1.42 vs 8.08 ± 1.25), D_Emers2 (5.20 ± 1.01 vs 4.54 ± 0.90)]. High and significant correlation co-efficients were obtained, analysing each group separately, between 50m time and T10 (0.77 vs 0.87), T15 (0.85 vs 0.94), T15turn (0.90 vs 0.98). Low correlations were found between 50m race time and D_Emers1 (-0.14 vs -0.44), D_Emers2 (-0.02 vs -0.50), T_Emers1 (0.02 vs -0.10) and T_Emers2 (0.09 vs -0.22). Differences in performances between national and regional groups were explained by the absolute split times, SL, SI and emersion distances, while the SR and emersion times did no differentiate both groups. Additionally, individual emersion distances and times did not correlate with 50m time.
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