BACKGROUND & OBJECTIVE
Hamstring muscle strains are one of the most common injuries sustained by field athletes who routinely sprint at near maximal speeds. The high rate of injury and recurrence result in significant time and financial losses for both athletes and their clubs/teams. Although tremendous efforts have been made to prevent injury and improve rehabilitation, injury incidence and recurrence rate have remained relatively unchanged in 3 decades. The purpose of this study was to examine the relationship of hamstring flexibility with actual peak hamstring muscle strains during sprinting. In the context of this study and review, muscle strain is defined as the ratio of muscle length deformation to resting muscle length.
Twenty college students (10 males, 10 females) with sprint training experience who regularly participate in sports volunteered for the study. All participants denied any history of hamstring or lower extremity injury. Three variables were assessed on each participant: a passive straight leg raise test to determine flexibility bilaterally, a sprint test with kinematic data collected via retroreflective anatomical body markers, and an isokinetic strength test to determine optimal hamstring lengths bilaterally. The motion was captured from the 20 to 25m split during the sprint trial. Optimal hamstring muscle length was calculated as the range of motion at which maximal force was produced. Instantaneous hamstring muscle lengths during gait cycle were measured via retroreflective markers at origin and insertion points of the muscle. Muscle strain was calculated from instantaneous muscle lengths and optimal muscle lengths.
The results of the study are consistent with previous research on hamstring injury. Muscular strain is most likely to occur during the late swing phase and subsequent eccentric lengthening of the hamstring group. This study also showed a potential for