INCREASE IN MUSCLE STIFFNESS IS EVIDENCED AT THE DEEP BUT NOT SUPERFICIAL MUTLIFIDUS MUSCLE IN ATHLETES WITH LOW BACK PAIN

Background and purpose:
Chronic low back pain (CLBP) is a common musculoskeletal
problem in athletes. Lumbar multifidus (LM) dysfunction is
thought to be one of the potential causes of CLBP and has
been extensively studied by examining muscle activity or
morphometry. Our study aimed to investigate the potential
alterations in the mechanical property of LM in elite athletes
with CLBP.
Methods:
A total of 104 (age: 18 to 27 years; 52 females) elite athletes
in weightlifting, badminton, and track & field teams were
recruited. Forty-three of them had CLBP for more than 3
months, ultrasound shear wave elastography was used to
measure muscle shear modulus (as an index of stiffness) of
the deep and superficial layers of LM at the L5 level. Threeway ANCOVA was used to compare LM stiffness between athletes with and without CLBP among different sports and different genders.
Results:
With age and body mass index as covariates, CLBP and sport is a significant factor influencing deep LM (F=4.42, p=0.04) and superficial LM stiffness (F=4.00, p=0.02), respectively. Further analysis indicated that athletes with CLBP showed 12% higher stiffness at deep LM than pain-free individuals (MD=1.68kPa, 95%CI=0.18-3.17); weightlifters had significant higher superficial LM stiffness
than athletes of badminton (MD=3.48kPa, 95%CI=0.93-
6.02) and track & field (MD=5.02kPa, 95%CI=2.34-7.69).
Conclusion:
Differential increase in stiffness of deep LM but not superficial LM may imply CLBP-related selective reduction in contractile tissues of deep LM, which may compromise lumbar stability. Physical requirements from different sports may also affect the mechanical property of superficial LM.