The association between size and symmetry of the lumbar multifidus muscle, and injuries in adolescent rugby union players.

OBJECTIVES:This study aimed to investigate the association between size and symmetry of the lumbar multifidus muscle, and season injuries in adolescent rugby union players. DESIGN:Prospective longitudinal cohort study. SETTING:Pre-season assessment of the size (cross-sectional area) of the lumbar multifidus (L2-5) muscles using ultrasound imaging. PARTICIPANTS:Seventy-one adolescent rugby union players (aged 15-18 years). MAIN OUTCOME MEASURES:"Time-loss" injuries were recorded during the season and divided into four injury regions (head and neck, upper limb, trunk and lower limb). RESULTS:Thirty-nine injuries were recorded during the season. Players who sustained an upper limb injury during the season had smaller lumbar multifidus muscles at the L5 vertebral level (effect size = 0.7, p = 0.03) and asymmetry in muscle size at the L2 (p = 0.05) and L5 (p = 0.04) in the pre-season. There was no association between size of the lumbar multifidus muscle and other injuries (p > 0.05). CONCLUSION:Lumbar multifidus muscle size and symmetry may impact lumbopelvic control which may increase the risk of sustaining an upper limb injury during rugby union. Future research should aim to identify whether lumbar multifidus muscle size is a modifiable risk factor for rugby union injuries to guide future intervention programs.