Neuromuscular and biomechanical adaptations associated with chronic low back pain
AuthorPranata, Adrian Christer
Document TypePhD thesis
Access StatusOpen Access
© 2016 Dr. Adrian Christer Pranata
Neuromuscular adaptations are a hallmark presentation of chronic low back pain (CLBP). People with CLBP have demonstrated trunk muscle co-contraction, trunk muscle weakness and decreased lumbar range of motion (ROM). The relationship between traditional neuromuscular assessments (e.g., lumbar ROM or trunk muscle strength) and self-reported disability is low. Arguably, the measurement of trunk ROM and trunk muscle strength are non-specific and cannot adequately explain the variances in disability in CLBP. Perhaps novel assessments assessing different domains of neuromuscular adaptations can better explain variances in self-reported disability in people with CLBP. Novel assessment of knee muscle force control demonstrated an impairment in the quadriceps ability to produce an accurate force in anterior cruciate ligament reconstructed (ACLR) population compared to healthy cohort. The assessment of muscle force control has not been performed in the CLBP cohort. Similarly, the assessment of inter-joint coordination using relative phase angle analysis was originally developed to identify safe lifting technique in manual workers but has not been performed in CLBP cohort. Therefore the aims of this thesis were i) to compare CLBP and healthy participants on novel trunk muscle force control assessment, ii) to compare CLBP and healthy participants on the assessment of lifting inter-joint coordination and iii) to investigate the relationship between self-reported disability and the aforementioned novel neuromuscular assessments in people with CLBP. To address these aims, four cross-sectional studies were conducted. Forty three participants with CLBP (mean Oswestry Disability Index (ODI) = 22.1 ± 13.2, mean pain Numerical Rating Scale (NRS) = 3.6 ± 1.9) and 29 matched healthy control participants were recruited. Inter-session reliability were assessed on 17 CLBP participants and 16 healthy participants. Study 1 compared and described the participant characteristics with respect to pain and self-reported disability quantified using NRS and ODI respectively. The findings demonstrated that people with CLBP reported significantly higher level of pain and disability than healthy participants. Incidentally, CLBP participants were nine years older than healthy people. Study 2 compared lumbar extensor maximal voluntary isometric contraction (MVIC) and lumbar extensor muscle force control in people with CLBP and healthy people using a novel force matching protocol adapted from studies in the quadriceps. The assessment protocol utilised a force target varied between 20%-50% MVIC (i.e., increasing and decreasing force output). No significant differences in lumbar extensor MVIC were evident between the groups. CLBP group demonstrated increased force matching error compared to healthy people, suggestive of impairment in lumbar extensor muscle force control. People with CLBP demonstrated more error when increasing force production compared to when decreasing force production. Study 3 compared kinematic and vertical ground reaction force assessment during a lifting task in people with and without CLBP. Participants with CLBP were characterised based on their disability phenotype (i.e., higher and lower disability). In addition to the measurement of trunk and lower limb ROM and angular velocity, trunk and lower limb joint coordination was assessed using relative phase angle analysis. There was no significant difference in trunk and lower limb ROM and angular velocity between all groups. Both groups demonstrated similar lifting trunk and lower limb joint coordination pattern and vertical ground reaction force pattern. However, people with CLBP took longer to lift a light load compared to healthy controls. Study 4 investigated the relationship between the assessments outlined in Studies 2 and 3 and ODI. There was no significant correlation between lumbar extensor MVIC, trunk and lower limb ROM and angular velocity during lifting and ODI. One unit increase in error when decreasing force production was associated with 47% increase in ODI. Similarly, one second increase in coordinated movement duration between the thorax and lumbar spine was associated with 47% increase in ODI. The amount of error when decreasing force output and duration of coordinated movement between the thorax and lumbar spine explained 27% of ODI variance. The findings of this thesis suggest that the assessment of lumbar extensor muscle force control and inter-joint coordination during lifting explain a significant portion of self-reported disability; thus, these measures are valid for CLBP patients. Future research is required to investigate whether improvement in the novel neuromuscular variables are associated with a decrease in self-reported disability.
Keywordschronic low back pain; low back pain; motor control; muscle force control; joint coordination; lifting; biomechanics; disability
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