Exploring the Relationship Between Dynamic Stability and Coordination Variability of the Lumbar Spine Using Neuromuscular Fatigue and Movement Training

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Larson, Dennis John
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University of Guelph

In an unchallenged, rested state, the neuromuscular system typically integrates all proprioceptive information to effectively control and coordinate spine and pelvis motion to avoid injury and pain. However, if the neuromuscular system is impaired (i.e., fatigued) or challenged (i.e., learning a new lifting strategy), small neuromuscular control errors or disruptions may cause spine instability or changes in movement coordination that could increase the potential for developing spine musculoskeletal injuries or pain. Therefore, the aim of this dissertation was to challenge the neuromuscular system with trunk extensor neuromuscular fatigue and lift technique (re)training to further understand how the neuromuscular system controls and coordinates lumbar spine motion during complex dynamic tasks. Experiment 1 investigated whether a measure of lumbar spine local dynamic stability in an unchallenged, rested state could provide insight into an individual’s dynamic stability in a challenged, fatigued state during a repetitive flexion/extension task. Overall, the hypothesis was not confirmed, and further analysis revealed three distinct responses in which participants either stabilized, destabilized, or had no change in dynamic stability when fatigued. Experiment 2 further explored whether the heterogeneous dynamic stability responses from Experiment 1 were related to distinct individual differences in thorax-pelvis coordination variability. As hypothesized, a relationship between dynamic stability and coordination variability was observed such that increased dynamic stability was associated with increased coordination variability, while decreased dynamic stability was associated with decreased coordination variability. Experiment 3 assessed how neuromuscular fatigue and lift technique (re)training involving tactile and performance feedback influenced lumbar spine dynamic stability and coordination variability during repetitive lifting. Both unfatigued and fatigued groups demonstrated reduced lumbar spine flexion, greater dynamic stability, and increased thorax-pelvis coordination variability, supporting the observed relationship from Experiment 2. Overall, performing lift (re)training while experiencing trunk extensor muscle fatigue only marginally influenced learning a modified lifting technique. These combined findings highlight the heterogeneous nature of lumbar spine movement behaviours within a healthy population, how tactile and performance feedback can be used to (re)train lifting strategies, and the existence of a relationship between lumbar spine local dynamic stability and thorax-pelvis coordination variability during repetitive movements.

Local dynamic stability, Coordination variability, Neuromuscular fatigue, Lumbar spine, Lift (re)training
Larson, D.J., Pinto, B.L., & Brown, S.H.M. (2018). Differential effects of muscle fatigue on dynamic spine stability: Implications for injury risk. Journal of Electromyography and Kinesiology 43: 209-216. doi: 10.1016/j.jelekin.2018.11.001.
Larson, D.J., & Brown, S.H.M. (2022). Influence of back muscle fatigue on dynamic lumbar spine stability and coordination variability of the thorax-pelvis during repetitive flexion-extension movements. Journal of Biomechanics 133: 110959. doi: 10.1016/j.jbiomech.2022.110959.