Repeated-sprint training in soccer: should we use straight-line and shuttle sprints interchangeably?

Repeated-sprint training (RST) has the potential to be an effective multi-component training method for the physical development of team-sports players. Improvements in speed, power and aerobic fitness have previously been reported following RST. However, it is possible that the specific protocol used, modulates training responses and subsequent adaptations. Therefore, the aim of this study was to compare the effects of straight-line (STR) and shuttle (SHU) repeated-sprint training (RST) on soccer-specific fitness. Two semi-professional soccer teams completed straight-line (n = 13; age 25 ± 4 years) or shuttle (n = 12; age 26 ± 6 years) RST twice per week for 4-weeks during the soccer pre-season. Heart rates and differential ratings of perceived exertion (dRPE) were recorded throughout to assess internal training loads. Fitness measures included 10- and 20-m sprints, countermovement jump (CMJ), standing-long jump (SLJ), left and right change-of-direction ability (CODL, CODR), and Yo-Yo intermittent recovery test level 1 (YYIRTL1). Ethics approval from the Teesside university IRB was obtained before the study was commenced. STR had large beneficial effects on 10 (−4.7%; ±90% Confidence limits – 2.0%) and 20-m (−3.6%; ±1.3%) sprints, a moderate beneficial effect on YYIRTL1 (17.4%; ±12.9%) and small beneficial effects on CMJ (3.4%; ±1.6%), SLJ (1.8% ±0.9%). For SHU, a moderate beneficial effect on YYIRTL1 (19.8%; ±9.0%), and small beneficial effects on CMJ (2.5%; ±1.5%) and SLJ (2.2%; ±2.8%) were observed, while moderate and small harmful effects for 10-m (2.6%; ±2.4%) and 20-m (2.4%; ±1.6%) sprints were observed, respectively. When compared to SHU, large beneficial effects for 10-m (8.0%; ±3.4%) and 20-m sprints (6.2%; ±2.3%) and also for CODL (10.9%; ±12.7%) and CODR (11.3%; ±8.3%) were observed in STR. Trivial between groups effects were reported for YYIRTL1. Higher training loads were observed in SHU with the magnitude of effects ranging from small (in peak heart rate) to large (in dRPE). Our results suggest that straight-line RST is more effective than short shuttle RST (<10-m) in developing soccerspecific fitness, specifically short-sprint performance. Furthermore, straight-line RST induces higher central and peripheral training loads, which should be accounted for when using this mode of RST.