Introduction: Low back pain (LBP) is more prevalent in athletes compared to the general population. Previous studies in athletes with LBP have reported a decrease in lumbar multifidus (LM) cross-sectional area (CSA) and increase in side-to-side CSA asymmetry. Similar change in LM morphology were also associated lower limb injury (LLI) in athletes. However, previous studies mostly investigated small samples in a single sport at a time. Therefore, the primary aim of this study was to examine LM morphology and function across a general sample of male and female university level varsity athletes. A secondary aim was to investigate if LM morphology and function were predictors of LBP and LLI.

Methods: A total of 134 university varsity athletes (50 female, 84 male) from hockey, rugby, soccer, and football were included in this study. A self-reported questionnaire was used to acquire player demographics information and history of LBP and lower limb injury in the previous 3 months and 12 months, respectively. Ultrasound images of LM at L5 were obtained bilaterally, and measurements of interest included: CSA, echo-intensity (EI) and thickness at rest and contracted, and % thickness change (from rest to contracted) in both prone and standing positions. DEXA was used to assess body composition. Paired t-tests were used to examine difference in LM measurements between the right and left side, and independent t-tests were used to compare LM measurements between sex. Univariate and multivariate logistic regression analyses were performed to assess if LM characteristics were predictors of LBP and LLI. Sex and players’ body composition measurements were tested as possible covariates.

Results: Males had significantly larger LM CSA and thickness at rest and contracted in both prone and standing positions (all p<0.001). Females had significantly higher EI than males (p<0.001). The left LM CSA was significantly larger in both males and females in prone and standing (all p<0.05). Similarly, LM thickness at rest and contracted was significantly larger on the left side both in males (p<0.001) and females (p<0.05) in prone, while contracted in standing was significant for males only (p<0.05). There was no significant difference in the % change in thickness between or within males and females in prone or standing. Increased weight (OR= 1.03 [1.01, 1.06], p=0.007) and years played at the university level (OR=1.32 [1.02, 1.71], p=0.03) were associated with a 3% and 32% increased odds of having LBP in the previous 3 months, respectively. Increased LM CSA asymmetry (OR=1.14 [1.01, 1.28], p=0.03) in prone and type of sport (OR=1.44 [1.04, 1.96], p=0.02) were associated with 14% and 44% increased odds of having a LLI in the previous 12 months, with football having the strongest association.

Conclusion: The results provide novel insights regarding LM morphology and function in a large sample of male and female university-level athletes. Significant differences in LM morphology in prone and standing were observed between male and female athletes. While LM characteristics were not predictors of LBP history in the previous 3-months, increased LM CSA asymmetry was a significant predictor of LLI.