PURPOSE: To investigate the effect on hip-flexion strength of a 6-week hip-flexor training programme using elastic bands as resistance. We hypothesized that the training group, compared to a control group, would increase their hip-flexion strength more.

METHODS: Thirty-three healthy subjects (45 % females), 24(5) years of age, were included in a randomized controlled trial and allocated to heavy strength training of the hip-flexor muscles or to control (no strength training). Strength training of the hip-flexors (dominant leg) was performed three times 10 min per week for 6 weeks. The strength training group progressed from 15 repetition maximum (RM) (week 1) to 8 RM (week 6). Isometric hip-flexion strength (primary outcome) was measured by a blinded assessor using a reliable test procedure.

RESULTS: In the strength training group, the isometric hip-flexion strength of the trained leg increased by 17 %, (p < 0.001). The between-group difference in hip-flexion strength change in the trained leg (dominant leg, training group) versus the non-trained leg (dominant leg, control group) was significantly different from baseline to follow-up, corresponding to a mean change of 0.34 (95 % CI 0.17-0.52) Nm/kg, in favour of the strength training group (p < 0.001).

CONCLUSION: Simple hip-flexor strength training using elastic bands as external loading, for only 6 weeks, substantially improves hip-flexor muscle strength. This simple exercise programme seems promising for future prevention and treatment of acute and longstanding hip-flexor injuries, such as acute rectus femoris injuries and longstanding iliopsoas-related pain and impingement.

LEVEL OF EVIDENCE: I.