Movement, posture and low back pain. How do they relate? A replicated single-case design in 12 people with persistent, disabling low back pain

Background Movement and posture are commonly believed to relate to non-specific low back pain (NSLBP). While people with NSLBP appear to move and posture themselves differently from those without NSLBP, changes in movement and posture infrequently relate to improvements in NSLBP when analysed at a group-level. Additionally, little is known about how movement or posture change when clinical outcome improves. Methods Within-person relationships were investigated using a replicated, repeated measures, single-case design in 12 people with persistent, disabling NSLBP. Individually relevant movement and posture were captured using wearable sensors on up to 20 occasions over a 22-week period (5-week baseline, 12-week physiotherapy-led intervention, 5-week follow-up), while pain and activity limitation were collected concomitantly. A series of cross-correlation analyses estimated the presence, strength, and direction of relationships. Results Many participants (n = 10/12) had strong (e.g.r = 0.91,p = <0.001) relationships between changes in movement or posture and changes in pain and activity limitation, while some showed no strong association. Where relationships were observed, clinical improvement predominantly (93% or 57/61 relationships) related to increased spinal movement range and velocity during forward bending and lifting, reduced lumbar muscle EMG activity at maximum voluntary flexion, and increased posterior-pelvic-tilt during sitting and standing. Conclusion Within-person changes to individually relevant movement and posture appear to often relate to clinical outcome, but not always. When changes were related, movement and posture appear to return towards being 'less protective', however causal directions remain unknown. Important activities, movements, and postural parameters varied across the participants, highlighting the potential importance of individualized management. Significance Changes to individually relevant movement and posture appear to often relate to clinical outcome, but not always. Patient-specific activities, and movement or postural parameters that related to improved pain and activity limitation, varied across the 12 participants, highlighting the potential importance of individualised management. Where clinical improvements were related to changes in movement or posture, participants consistently returned towards being 'less protective' (increased range and speed of movement, increased posterior-pelvic-tilt during sitting and standing). Mechanisms and generalizability remain unclear.