Training & Testing 573 Small K et al. Soccer Fatigue, Sprinting and Hamstring … Int J Sports Med 2009; 30: 573–578 accepted after revision January 26, 2009 Bibliography DOI 10.1055/s-0029-1202822 Published online: May 19, 2009 Int J Sports Med 2009; 30: 573–578 © Georg Thieme Verlag KG Stuttgart · New York ISSN 0172-4622 Correspondence Dr. K. Small, PhD Department of Sport, Health & Exercise Science University of Hull Loten Building Hull United Kingdom HU6 7RX Tel.: + 14/824/651 08 Fax: + 44/148/246 64 04 k.small@hull.ac.uk Key words ● ▶ kinematics ● ▶ muscle strain ● ▶ match-play ● ▶ re-warm-up Soccer Fatigue, Sprinting and Hamstring Injury Risk the stance phase when the muscle shortens forcefully to extend the hip during take-off, potentially inducing a concentric contraction injury [13]. Fatigue during soccer match-play has been asso- ciated with decreased eccentric hamstring strength [7, 19]. This may be related with increased hamstring injury risk; with nearly half of all hamstring injuries observed to occur during the final 15 min of each half [26]. Therefore, it could be hypothesised that fatigue during the lat- ter stages of soccer match-play may cause increased predisposition to hamstring strain injury by negatively altering the biomechanics of sprinting in relation to muscle flexibility, muscu- lar strength, or body mechanics. Experimental research has reported a significant decrease in eccentric hamstring strength during simulated soccer match-play [7]. Therefore, if the hamstrings have insufficient strength to deceler- ate the limb during the latter part of the swing phase, eccentric overload could cause tearing in the musculo-tendinous unit [6]. Research has suggested that if the hamstring muscles lack flex- Introduction & Recently there has been an increased preponder- ance of hamstring muscle strain injuries in high- level soccer players, accounting for 12–16 % of total injuries [26]. Such injuries are considered to have one of the highest rates of injury re-occurrence of any muscle injury [14]. However, biomechanical analysis of hamstring function is difficult consid- ering their anatomical complexity and ability to influence movement over multiple joints [3]. Consequently, identification of injury risk factors and development of effective injury prevention strategies becomes more challenging [3]. Sprinting is the primary mechanism for ham- string strains; responsible for 57 % of all ham- string injuries [26]. The hamstrings are biarthrodial muscles and undergo lengthening over two joints simultaneously during the latter part of the swing phase of the gait cycle [22] and strains may be most likely to occur at this point whilst working eccentrically to decelerate the limb and control knee extension [26]. Alterna- tively, injury may occur during the latter part of Authors K. Small 1 , L. R. McNaughton 1 , M. Greig 2 , M. Lohkamp 2 , R. Lovell 1 Affiliations 1 Department of Sport, Health & Exercise Science, University of Hull, Hull, United Kingdom 2 Department of Sport and Physical Activity, Edge Hill University, Ormskirk, United Kingdom Abstract & The aim of this study was to investigate the effect of a multi-directional soccer-specific fatigue protocol on sprinting kinematics in relation to hamstring injury risk. Nine semi-professional soccer players (Mean ± SD: Age: 21.3 ± 2.9 year; Height 185.0 ± 8.7 cm; Body Mass 81.6 ± 6.7 kg) completed the SAFT 90 ; a multi-directional, inter- mittent 90 min exercise protocol representa- tive of soccer match-play. The 10m sprint times and three-dimensional kinematic data were recorded using a high-speed motion capture system (Qualisys Track Manager ® ) every 15 min during the SAFT 90 . A significant time dependent increase was observed in sprint time during the SAFT 90 (P < 0.01) with a corresponding significant decrease in stride length (P < 0.01). Analysis of the kinematic sprint data revealed significantly reduced combined maximal hip flexion and knee extension angle, indicating reduced ham- string length, between pre-exercise and half- time (P < 0.01) and pre-exercise and full-time (P < 0.05). These findings revealed that the SAFT 90 produced time dependent impairments in sprinting performance and kinematics of tech- nique which may result from shorter hamstring muscle length. Alterations in sprinting technique may have implications for the increased predis- position to hamstring strain injury during the latter stages of soccer match-play.