1 Department of Health, Kinesiology and Applied Physiology, Concordia University, Montreal, QE, Canada.
2 PERFORM Centre, Concordia University, Montreal, QE, Canada.
3 Department of Electrical & Computer Engineering, Concordia University, Montreal, QE, Canada.
4 Department of Diagnostic Radiology, McGill University Health Center, Montreal, QE, Canada.
5 Centre de Recherche Interdisciplinaire en Réadaptation, Montreal, QE, Canada.

Context: A smaller lumbar multifidus (LM) muscle was reported to be a strong predictor of lower limb injury in professional Australian Football League players. However, despite the high prevalence of low back pain (LBP) and lower limb injury in rugby players, their LM characteristics have yet to be explored.

Objective: To (1) examine LM characteristics in male and female university rugby players and their possible associations with LBP and lower limb injury and (2) investigate the relationship between LM characteristics and body composition in this group of athletes.

Design: Cross-sectional study.

Setting: University research center.

Patients or other participants: Thirty-four university rugby players (20 women, 14 men).

Main outcome measure(s): Ultrasound measurements of LM cross-sectional area (CSA), thickness, and percentage change in thickness during contraction were obtained bilaterally, at the L5-S1 level, in prone and standing positions. Body composition measures were obtained using dual-energy X-ray absorptiometry. Self-reported questionnaires were used to obtain LBP and lower limb injury history.

Results: Players who reported LBP in the previous 3 months showed a smaller percentage change in thickness during contraction in the standing position (F = 5.21, P = .03). The LM CSA side-to-side asymmetry (right versus left) was greater in players who reported having a lower limb injury in the previous 12-months (F = 4.98, P = .03). The LM CSA was significantly associated with body composition measurements. A greater percentage change in thickness during contraction was significantly associated with a lower percentage of body fat. The LM echo intensity was strongly associated with the total percentage of body fat and was significantly greater in women.

Conclusions: The influence of body composition on LM morphology in athletes cannot be ignored and warrants further investigation. Our findings also provide preliminary evidence of an association between LM morphology, LBP, and lower limb injury in university rugby players.