Abstract
Human motor function emerges from the interaction between the neuromuscular and the musculoskeletal systems. Despite the knowledge of the mechanisms underlying neural and mechanical functions, there is no relevant understanding of the neuro-mechanical interplay in the neuro-musculo-skeletal system. This currently represents the major challenge to the understanding of human movement. We address this challenge by proposing a paradigm for investigating spinal motor neuron contribution to skeletal joint mechanical function in the intact human in vivo. We employ multi-muscle spatial sampling and deconvolution of high-density fiber electrical activity to decode accurate α-motor neuron discharges across five lumbosacral segments in the human spinal cord. We use complete α-motor neuron discharge series to drive forward subject-specific models of the musculoskeletal system in open-loop with no corrective feedback. We perform validation tests where mechanical moments are estimated with no knowledge of reference data over unseen conditions. This enables accurate blinded estimation of ankle function purely from motor neuron information. Remarkably, this enables observing causal associations between spinal motor neuron activity and joint moment control. We provide a new class of neural data-driven musculoskeletal modeling formulations for bridging between movement neural and mechanical levels in vivo with implications for understanding motor physiology, pathology, and recovery.
Highlights
Motor function emerges from the neuro-mechanical interplay taking place in the composite neuro-musculo-skeletal system[2,9]
We propose a novel technique for probing the mechanical forces elicited by the activity of spinal motor neuron pools displaced across five lumbosacral segments of the human spinal cord
Results showed that our proposed paradigm enabled revealing direct associations between modulations in spinal motor neuron activity and joint moment control (Figs 5 and 8)
Summary
Motor function emerges from the neuro-mechanical interplay taking place in the composite neuro-musculo-skeletal system[2,9]. The breakthrough with respect to current theoretical models (not driven by neural signals) is that our proposed approach enables decoding subject-specific motor neuron strategies across any condition (i.e. task, pathology, training) from muscle fiber electrical activity, with no direct need for creating numerical models of spinal neuronal networks. This is done in a purely open-loop way, i.e. with no closed-loop corrective mechanism that compensates for moment prediction errors. This opens new avenues for understanding neuro-mechanical causalities in human movement and the alterations caused by impairment[33], with potentials for establishing novel treatments
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