Four weeks of Nordic hamstring exercise reduce muscle injury risk factors in young adults
The Nordic hamstring exercise (NHE) is a field-based exercise designed for knee-flexor eccentric strengthening, aimed at muscle strains prevention. However, possible effects of NHE programmes on other hamstring injury risk factors remain unclear. The purpose of this study was to investigate the effects of a NHE training programme on multiple hamstring injury risk factors. Twenty physically active young adults were allocated into two equal sized groups: control group (CG) and training group (TG). The TG was engaged in a 4-week NHE programme, twice a week, 3 sets of 6-10 repetitions; while CG received no exercise intervention. The knee flexor and extensor strength was assessed through isokinetic dynamometry, the biceps femoris long head muscle architecture through ultrasound images, and the hamstring flexibility through sit-and-reach test. The results showed that CG subjects had no significant change in any outcome. TG presented higher percent changes than CG for hamstring isometric peak torque (9%; effect size=0.27), eccentric peak torque (13%; effect size=0.60), eccentric work (18%; effect size=0.86), and functional hamstring-to-quadriceps torque ratio (13%; effect size=0.80). The NHE programme led also to increased fascicle length (22%; effect size=2.77) and reduced pennation angle (-17%; effect size=1.27) in biceps femoris long head of the TG, without significant changes on muscle thickness. In conclusion, a short-term NHE training programme (4 weeks; 8 training sessions) counteracts multiple hamstring injury risk factors in physically active young adults.