INTRODUCTION Hamstring muscle strain-type injuries are common in sports that involve sprinting,1 acceleration, deceleration, rapid change in direction and jumping.2 3 Occurring in both recreational and professional sports, these injuries can result in substantial time lost from sport and commonly recur.4 5 In the Australian Football League (AFL), hamstring muscle strain-type injuries have displayed a high incidence rate, with a 10 year mean of 6.1 new injuries per club each year and a 23% average recurrence rate.6 A recurrence rate of 17% has been reported in elite soccer players7 with hamstring injuries also recorded as the most common injury accounting for 12% of all injuries and resulting in an average of four missed games per injury.8 The high incidence of hamstring muscle straintype injuries and potential associated costs has resulted in a substantial amount of research into the factors related to such injuries. Two recent systematic reviews have been completed in an attempt to collate the evidence around risk factors for hamstring injuries.9 10 Both reviews identifi ed hamstring muscle weakness and thigh muscle imbalance, muscle fl exibility, previous hamstring injury, other previous injury and age as potential risk factors; however, these reviews concluded that single variables were inconsistently identifi ed as associated factors. Both reviews provided a qualitative synthesis of the literature and included risk factor studies as well as intervention studies, where a potential risk factor was modifi ed with a training programme. The inclusion of intervention studies may potentially complicate risk factor analyses, as such studies assume that the factor being modifi ed is associated with the injury and that the factor can be modifi ed by the treatment programme. The aim of the current review was to assemble all available knowledge and data to identify the intrinsic and extrinsic risk factors associated with hamstring muscle strain-type injuries in sport.