Repeated-sprint training can induce small to large improvements in power, speed, repeated-sprint ability and endurance, and may have relevance for training in team sports.

(YYIRTL1) performance. Internal (heart rate) and external (GPS-derived measures) training 34 loads were monitored throughout. Data were analysed using magnitude-based inferences. 35Results: Internal and external loads were higher in STR than CoD with large differences in 36 maximum velocity (28.7%; ±90% confidence limits 3.3%), moderate differences in mean heart 37 rates (7.0%; ±1.4%) and PlayerLoad™ (17.6%; ±8.6%), and small differences in peak heart 38 rates (3.0%; ±1.6%). Large improvements in 5-m (STR: 9.6%; ±7.0% and CoD: 9.4%; ±3.3%), 10-m (STR: 6.6%; ±4.6% and CoD: 6.7%; ±2.2%) and 20-m (STR: 3.6; ±4.0%

word count: 221 14 Text only word count: 3070 15 Number of tables: 3 16 Number of figures: 2 17 2 Abstract: 18 Change-of-direction ability is an important performance skill in football. Consequently, several 19 testing protocols are used to assess this component. This study assessed the test-retest reliability 20 of a modified 505 test (M505) and the change-of-direction deficit (CODD) in elite youth 21 football players. Data were collected from 110 players from the Under [u] 12-18 years age 22 groups (u18 n = 26, u16 n=26, u14 n=39, u12 n=19) within two English Premier League 23 Category 1 Football Academies. Players completed the M505 twice in 7-days, in addition to a 24 10-m sprint test to allow CODD to be calculated. Reliability was assessed with respect to 25 chronological and biological age (according to PHV status). Typical error (%), minimal 26 detectable change (MDC%) and intraclass correlation coefficients (ICC) were calculated. 27Typical errors in M505 were moderate to large (2.0 to 3.2%), while intraclass correlation 28 coefficients (ICC) ranged from low to high (r = 0.26 to r = 0.82). Typical errors in CODD were 29 moderate to large (7.1 to 12.0%), with ICC's ranging from low to high (r = 0.19 to 0.79). 30Minimal detectable changes were 5.5 to 8.9% in M505 and 17.7 to 33.3% in CODD. The 31 typical errors and minimal detectable changes observed here indicate that the M505 and CODD 32 tests have limited practical utility in the evaluation of change of direction ability in elite youth 33 football players. 34 35 36The 'Elite player performance plan' (EPPP), was introduced by the English Premier League 37 with the aim of increasing the number, and quality of home grown players graduating from 38 English football academies (EPPP guidelines, 2011). In this respect, standardised 'benchmark 39 performance testing' is completed nationwide, using a testing battery that includes a 'modified 40 505 test' (M505) to profile change-of-direction ability in elite youth players. Change-of-41 direction ability is an important component of performance in football, with high-speed 42 changes of direction occurring around key moments in match-play. Specifically, ~10% of goals 43 are preceded by a change-of-direction sprint, while it is possible that change-of-direction ability 44 is of greater importance in defensive situations (Faude et al. 2012). Consequently, several 45 change-of-direction tests have been developed, with versions of the '505 test' popular in 46 football, due to the simplicity of this test and isolated nature of the turn (Svensson and Drust, 47 2005). 48 It has been suggested that short-sprint performance and change-of-direction ability are related 49 in several currently used protocols, potentially skewing data interpretation (Sayers, 2015; 50 Gabbett et al. 2008). Specifically, changing direction is reported to account for only 31% of 51 total 505 time (Nimphius et al. 2013). This has led to the emergence of the change-of-direction 52 deficit (CODD), defined as 'the additional time that one direction...

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CitationTaylor, J., Weston, M. and Portas, M. (2013) The aim of our study was to investigate the effect of a short, practical two-phase warm-up on 52 repeated-sprint performance when compared to more traditional warm-up protocols that 53 contain stretching activities. Eleven sub-elite male soccer players completed a warm-up 54 protocol that commenced with 5-min jogging at ~65% of maximal heart rate, followed by 55 either no stretching, static stretching, or dynamic stretching, and then finishing with a task-56 specific, high-intensity activity. Using a cross-over design the three warm-up protocols were 57 performed in a counterbalanced order with at least 48 h between sessions. Repeated-sprint 58 performance was measured using a repeated-sprint test which consisted of 6 x 40 m maximal 59 sprints interspersed with 20 s recovery. There were trivial differences in mean sprint time 60(0.2%) and post-test blood lactate (3.1%) between the two-phase warm-up and the three-phase 61 warm-up that included dynamic stretching, whereas the short warm-up had a possibly 62 detrimental effect on fastest sprint time (0.7%). Fastest (-1.1%) and mean (-1.2%) sprint times 63 were quicker, and post-test blood lactates higher (13.2%) following the two-phase warm-up 64 when compared to the three-phase warm-up that included static stretching. When compared to 65 more traditional, three-phase warm-ups that include a bout of stretching, a short, practical 66 two-phase warm-up is an effective means of preparing for subsequent repeated-sprint activity.