Increased Stiffness Is Evidenced in the Deep But Not Superficial Lumbar Multifidus Muscle in Professional Athletes With Chronic Low Back Pain

Objectives: Elevated lumbar multifidus stiffness has been observed in populations with chronic low back pain (LBP). However, the modulation of deep (DLM) and superficial (SLM) lumbar multifidus stiffness, considering their distinct structural characteristics and functions, remains unaddressed, especially in athletes. This study aimed to compare differences in DLM and SLM stiffness in professional athletes from different sports with and without chronic LBP. Design: Cross-sectional study. Setting: This study was conducted at a provincial sports training center. Participants: Ninety-nine professional athletes (age: 18-27 years) from weightlifting, badminton, and track and field teams were recruited. Thirty-eight had chronic bilateral LBP. Interventions: Not applicable. Main Outcome Measures: Ultrasound shear wave elastography measured Young's modulus (stiffness indicator) of DLM and SLM at the L4/5 facet joint level. Two-way analysis of variance examined the effects of chronic LBP and sport type on DLM and SLM stiffness while considering proper confounders. Significance was set at P<.05. Results: Athletes with chronic LBP demonstrated significantly higher DLM stiffness on the dominant (by 17.73%, mean difference [MD]=2.52 kPa, P=.001) and nondominant sides (by 13.54%, MD=1.83 kPa, P=.046) compared with pain-free counterparts. SLM stiffness varied significantly among the 3 athlete groups. Post-hoc analyses revealed greater SLM stiffness on the nondominant side in weightlifters than in badminton players (by 51.76%, MD=8.97 kPa, P=.010) or track and field athletes (by 72.01%, MD=11.01 kPa, P=.008). Conclusions: Chronic LBP and sport type significantly impact multifidus muscle stiffness, suggesting the need for targeted clinical assessments and reconditioning strategies focusing on DLM for chronic LBP and SLM for athletes in trunk extension-intensive sports.