Background Eccentric strength training can reduce hamstring strain injuries (HSIs), although a persistent neuromuscular inhibition after injury may reduce the trainability of this muscle group.
Objective To test the a priori hypothesis that previous HSI results in a reduced increase in eccentric strength during pre-season training in elite AFL players.
Design Case controlled observational study. Players with unilateral HSI, confirmed by MRI within the previous 12 months were compared with players who had no HSI.
Setting 5 elite Australian football teams from the AFL.
Participants 103 players were recruited, 28 of whom had sustained unilateral HSI in the previous 12 months. Others were free of lower limb injuries that may have influenced knee flexor strength.
Risk factor assessment The categorical independent variable was the existence of HSI in the 12 months prior to the study (yes or no).
Main outcome measurements Eccentric knee flexor strength gain in the preseason training period. Eccentric strength was measured as knee flexion forces at the ankles during the performance of the Nordic hamstring exercise.
Results ANCOVA on changes in strength indicated that players with recent HSI made less progress in eccentric hamstring strength (–30 N; CI=-57 to –4 N; P=.0266) than those without HSI. This muted strength gain was observed in both the previously injured (13±61 N) and uninjured limbs (10±64 N) of players who had sustained unilateral injury.
Conclusions Players with recent unilateral HSI exhibited reduced eccentric knee flexor strength gains in both limbs. The mechanism for this is unknown. Additional research should focus on both the reason for this diminished progress and on how to improve eccentric strength in footballers who have suffered hamstring strains.