Back-to-Back, a proof of concept study investigating the role of back muscle characteristics to tailor exercise therapy for recurrent non-specific low back pain: study protocol and preliminary analysis of proprioceptive postural control results

Abstract

Background and aim Non-specific low back pain (NSLBP) is the main cause of disability worldwide and current treatments have limited effects. Alterations in macroscopic, microscopic, electrophysiological and hemodynamic lumbar muscle characteristics and proprioceptive postural control (PPC) are found in people with NSLBP and directing treatment based on shared underlying mechanisms (phenotypes), could improve its effects. Therefore, this study aims to determine the most discriminating lumbar muscle characteristics between patients with NSLBP and healthy controls, investigate their interrelatedness and relationship with PPC and delineate NSLBP phenotypes based on them. Additionally, to investigate whether proprioceptive exercises have a greater effect on specific NSLBP phenotypes.

Methods Lumbar multifidus and erector spinae muscle characteristics will be evaluated and compared in 53 people with recurrent NSLBP and 47 healthy controls. For PPC, the COP displacements in response to vibration to the ankle and back muscles are measured on a force plate, while standing on stable and unstable surface with vision occluded. Proprioceptive dominance is evaluated by the Relative Proprioceptive Weighting (RPW) ratio, with lower RPW values indicating more lumbar proprioceptive reliance. Muscle volume is investigated with 3D freehand ultrasound, and muscle activation and oxygenation with electromyography and near-infrared spectroscopy, respectively. The 53 people with NSLBP also receive a 16-week intervention focusing on improving their ability to sense and discriminate low back position, muscle activation and lumbar movement. These proprioceptive exercises are integrated into the patients’ daily lives and comprise a high-load lifting exercise. Their effects are evaluated at 8 weeks, 16 weeks and 16 weeks after the end of the intervention.

Results Recruitment is ongoing, currently five people with recurrent NSLBP are enrolled and analysed descriptively. Preliminary results on PPC include increased lumbar proprioceptive reliance after eight (Pre: 0.69 ± 0.04; Post: 0.46 ± 0.30 stable and Pre: 0.58 ± 0.13; Post: 0.44 ± 0.31 unstable) and 16 weeks (Post: 0.40 ± 0.30 stable and Post: 0.34 ± 0.16 unstable) and increased COP displacement in response to lumbar vibration on stable (Pre: 0.018 ± 0.011; Post: 0.020 ±0.012) and unstable (Pre: 0.015 ± 0.013; Post: 0.021 ± 0.009) after 16 weeks of intervention.

Conclusion Preliminary results show increased lumbar proprioceptive use and a switch in dominant reliance from ankle to lumbar proprioception in response to this proprioceptive intervention, translating to improved PPC. Further effects on the different lumbar muscle characteristics and their correlation with PPC will be investigated. Phenotypes of people with NSLBP will be delineated and the effects of this intervention on them will be examined. Results may improve patient-tailored exercise therapy for people with NSLBP.