Background Hamstring strain injuries (HSIs) are a common and recurrent complaint in sport, with most insults occurring during high-speed overground running.

Objective To determine, during high-speed overground running, the spatial patterns of hamstring muscle voluntary activation (VA) in limbs with and without a history of HSI.

Design Retrospective cross-sectional study.

Setting Elite and sub-elite level track and field (T&F).

Participants Five healthy, elite (n=4) and sub-elite (n=1) level T&F athletes, with a history of unilateral HSI were recruited (average time of 6.5±3.9 months post-injury; average age 20±1.8 years; stature 182.1±6.5 cm and mass 78.3±4.8 kg).

Assessment of risk factors Functional MRI was performed on participants thighs before and after 3 sets of 6, 40m sprints (30s rest between reps; 1 min rest between sets). T2 relaxation times of all hamstring muscles (biceps femoris long (BFlh) and short head (BFsh); semitendinosus (ST); semimembranosus (SM)), were measured at rest and immediately after the running protocol.

Main outcome measurements The percentage change in T2 relaxation time for each hamstring muscle, in both the previously injured and contralateral uninjured limbs.

Results For the spatial analysis of uninjured limbs, no significant differences were observed in the percentage increase in T2 relaxation for any muscles (BFlh vs ST, P=.07; BFlh vs BFsh, P=.66; BFlh vs SM, P=.08; BFsh vs ST, P=.08; BFsh vs SM, P=.54; SM vs ST, P=.57). However, previously injured hamstring muscles displayed significantly smaller increases in T2 relaxation time compared with homonymous muscles in the uninjured contralateral limb (mean difference=–8.1%, 95% CI=-16.5 to -0.3%, P=.02).

Conclusions These preliminary findings indicate that the hamstrings of uninjured limbs are activated somewhat uniformly during high-speed overground running however, following an HSI, VA is chronically reduced in the previously injured muscle.