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Background: The lumbar multifidus muscle (LMM) plays a critical role to stabilize the spine. While low back pain (LBP) is a common complaint in soccer players, few studies have examined LMM characteristics in this athletic population and their possible associations with LBP and lower limb injury. Therefore, the purpose of this study was to 1) investigate LMM characteristics in university soccer players and their potential association with LBP and lower limb injury; 2) examine the relationship between LMM characteristics and body composition measurements; and 3) examine seasonal changes in LMM characteristics. Methods: LMM ultrasound assessments were acquired in 27 soccer players (12 females, 15 males) from Concordia University during the preseason and assessments were repeated in 18 players at the end of the season. LMM crosssectional area (CSA), echo-intensity and thickness at rest and during contraction (e.g. function) were assessed bilaterally in prone and standing positions, at the L5-S1 spinal level. A self-reported questionnaire was used to assess the history of LBP and lower limb injury. Dual-energy x-ray absorptiometry (DEXA) was used to acquire body composition measurements. Results: Side-to-side asymmetry of the LMM was significantly greater in males (p = 0.02). LMM thickness when contracted in the prone position (p = 0.04) and LMM CSA in standing (p = 0.02) were also significantly greater on the left side in male players. The LMM % thickness change during contraction in the prone position was significantly greater in players who reported having LBP in the previous 3-months (p < 0.001). LMM CSA (r = − 0.41, p = 0.01) and echo-intensity (r = 0.69, p < 0.001) were positively correlated to total % body fat. There was a small decrease in LMM thickness at rest in the prone position over the course of the season (p = 0.03). Conclusions: The greater LMM contraction in players with LBP may be a maladaptive strategy to splint and project the spine. LMM morphology measurements were correlated to body composition. The results provide new insights with regards to LMM morphology and activation in soccer players and their associations with injury and body composition measurements.

Purpose The primary objective of this study was to examine and compare lumbar multifidus (LM) muscle size, asymmetry, and function in university football players with and without low back pain (LBP). A secondary objective was to examine the relationship between LM characteristics and body composition in football players. Methods Ultrasound assessments of the LM muscle were performed in 41 university football players during the preseason. LM muscle cross-sectional area, echo intensity (e.g., indicator of fatty infiltration and connective tissue), thickness at rest, and thickness during submaximal contraction (e.g., contralateral arm lift) measurements in prone and standing positions were obtained bilaterally at the L5–S1 level. Body composition measures were acquired using dual-energy x-ray absorptiometry. A self-administered questionnaire was used to obtain LBP history data. Results The LM muscle thickness at rest in prone and in standing was significantly smaller in football players who reported the presence of LBP in the previous 3 months. The LM cross-sectional area in prone was significantly and positively correlated with weight, height, lean body mass, total fat mass, and total percent body fat. LM echo intensity was strongly correlated with total percent body fat and total fat mass and negatively correlated with the percent thickness change during contraction. Conclusion The results of this study provide novel information on LM muscle morphology and activation in football players in prone and standing and suggest that players with LBP in the previous 3 months had smaller LM muscle thickness. LM morphology was strongly correlated with body composition measurements.