Relationships between muscle electrical activity and the control of inter-vertebral motion during a forward bending task.

Abstract

Muscle strengthening exercises are commonly used in primary care for the treatment of chronic, non-specific low back pain (CNSLBP) as it has been theorised that increased muscle activity contributes to the stabilisation of intervertebral motion segments during bending and other spinal movements, however this has never been demonstrated in vivo. This study used contemporaneous quantitative fluoroscopy (QF) and surface electromyography (sEMG) to investigate relationships between continuous intervertebral motion variables and muscle electrical activity in the lumbar multifidus (LMU), lumbar and thoracic erector spinae (LES and TES) during standardised lumbar flexion and return in 18 healthy male human subjects. Our results demonstrated that intervertebral angular Motion Share Variability (MSV) and motion segment laxity were significantly (p<0.05) negatively correlated (Spearman) with, and weakly dependent (Kendall’s tau) on muscle electrical activity throughout the participant bend for both locally and globally acting muscle groups. MSV and laxity were also strongly correlated with each other for L2-3 laxity. The former suggests a damping mechanism reducing irregular displacements during bending and an action of spinal stabilisation by muscles at segmental levels and the latter a synergy between laxity at L2-3 and MSV. While this has previously been theorised, it has never been shown in vivo at the intervertebral level. These assessments may be considered for use in validation studies of exercise programs for CNSLBP, however further replication is required.