Background Eccentric hamstring strength exercise has been adopted in lower extremity injury prevention programs extensively, but the study of its effect on knee flexor strength is limited.

Objective The objective of this study was to examine the effects of eccentric hamstring strength exercise on knee flexor strength using three different measuring methods, and to compare the effects between men and women.

Design Prospective cohort study.

Setting The evaluation was performed in a rehabilitation laboratory.

Participants 18 healthy volunteers (10 men, 8 women) participated in this study.

Intervention All subjects were asked to perform eccentric hamstring strength exercise (the so-called Nordic hamstring exercise) 3 days a week for 6 weeks.

Main outcome measurements Concentric, eccentric and isometric knee flexor strengths were measured before and after the training periods using the Biodex dynamometer. Concentric and eccentric peak torques at 60 deg/sec, and isometric peak torque with 90° of knee flexion for 5 s, were measured. These were compared before and after intervention. The rate of increase was calculated and compared between men and women.

Results The eccentric torque measurements for men after intervention were significantly higher than before intervention (p<0.05), while there was no significant difference in women. No significant differences between before and after intervention were shown for concentric and isometric torques in both sexes. The rate of increase for men (20.0%) was significantly higher than that for women (8.8%) in eccentric torque (p<0.05), while no significant differences were observed between men and women in concentric and isometric torque.

Conclusion It seems that the effect of the eccentric hamstrings strength exercise in women was lower than in men. Therefore, careful attention should be paid in instructing the exercise to women.