Objectives To profile professional rugby union players using longitudinal hip, groin and hamstring strength measures and identify characteristics associated with non-contact lower limb injury and reinjury. Design Prospective cohort study. Methods 248 players were involved in the study. Over 24 months, injury surveillance data was collected, and a battery of strength tests were conducted at the start of each pre-season and mid-season. The strength tests included: Nordic hamstring exercise (Nordic); hip abduction and adduction at 60° (ABD60, ADD60); and 90° of hip flexion (ABD90 and ADD90). Results Strength profiles are presented. For the 55 players who featured at the first and last test of the study; Nordic, ADD90 and ABD90 increased in the forwards only (P=0.002 to 0.01). Strength changes at the end of the study were correlated with measures obtained at the start (r=-0.38 to -0.49), and amongst the test battery measures (r=0.42 to r=0.68). Hamstring, and hip/groin made up 43% of lower limb non-contact injuries. Those who sustained a hip/groin injury had greater odds (OR=4.0, P=0.0016) of also suffering a hamstring injury. For injured players, only ABD60 reduced post-injury (P=0.0021). Players who reinjured were characterised by lower pre-injury ADD90; and either higher pre-injury Nordic or an ADD90 that did not improve post-index injury. Pre-season strength profiles remained unchanged for uninjured players. Conclusions Strength changes were observed overtime, and post-injury. Players who were weaker from the outset improved whilst those who were stronger struggled to maintain strength. Changes from pre-season to in-season are important since most prospective injury studies only measure strength during pre-season. Strong knee flexor strength alone may not protect from reinjury, and further investigations are required to further support the observations that adductor strength is a protective factor in lower limb non-contact reinjury in rugby union players. Practical implications 1. Maintenance of pre-season strength throughout mid-season was a characteristic of players who remained non-contact lower limb injury-free during the study period and should be a focus of training programmes in men's professional rugby union. 2. Reinjury was characterised by players with either i) poor adductor strength and strong knee flexor strength, or, ii) poor adductor strength with poor knee flexor strength and little change in adductor strength post injury. This study underscores the potentially important role of adductor muscle strength in the rehabilitation of noncontact lower limb injuries and reinjury prevention. 3. Future studies should consider the impact of adductor strengthening programmes on noncontact lower limb injury prevalence in men's professional rugby union.
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