Multiple risk factors for HSMS have been identified. Perhaps the strongest modifiable risk factor associated with HSMS is an imbalance between quadriceps and hamstring strength, specifically the eccentric hamstrings and concentric quadriceps strength ratio. The rationale is that sufficient eccentric capacity of the hamstring muscles is necessary to offset the concentric quadriceps contraction during the terminal swing phase of running. Not surprisingly, prevention programs that emphasize eccentric hamstring strengthening have been effective in reduction of HSMS injury rates.Prospective studies have demonstrated mixed results regarding the relationship between hamstring flexibility and hamstring injury, and the effectiveness of a flexibility program for reduction of the incidence of HSMS remains controversial. Stretching duration, frequency, timing of stretching relative to sports activities and the type of stretch being performed have been suggested as important factors in the effectiveness of a flexibility program at reducing injury occurrence. In addition, reduced hip flexor and quadriceps flexibility has been identified as a risk factor for HSMS. Further investigation is necessary to determine if a flexibility program that addresses both anterior and posterior thigh musculature reduces injury risk. The role of neuromuscular (NM) deficits as a risk factor in HSMS injuries is unclear. Inclusion of NM exercises in a six week training period improved lower extremity control and movement discrimination, which has been suggested to contribute to HSMS injury prevention. However, the impact of a NM injury prevention program on HSMS rates has not been established.