Transcranial magnetic stimulation and electrical stimulation techniques used to measure the excitability of distinct neuronal populations that influence motor output in people with persistent musculoskeletal conditions: A scoping review and narrative synthesis of evidence

Functional impairments are evident in persistent musculoskeletal (MSK) conditions, and linked to altered excitability of neuronal elements contributing to motor output. In MSK conditions, transcranial magnetic stimulation (TMS) or electrical stimulation (ES) techniques have been used to investigate intracortical, corticospinal, spinal and neuromuscular excitability, which influence the efficacy of descending volley transmission to produce movement. This review compiled studies using TMS or ES to investigate neuronal excitability in persistent MSK conditions, to identify techniques used, and to synthesis evidence for neural deficits. We used narrative synthesis to summarise individual study findings. We included 60 studies; 52/60 used at least one TMS technique, and more frequently measured corticospinal tract excitability (48/52). 15/60 studies used at least one ES technique, and more frequently measured neuromuscular excitability (15/15). In tendinopathy, excitability was assessed for a range of distinct neurones; no study measured neuromuscular excitability in low back pain, osteoarthritis or shoulder pain, nor spinal or intracortical excitability in shoulder pain. This review identified a range of TMS and ES techniques used to assess excitability of neural elements. It provides insight for specific deficits contributing to functional impairments in certain persistent MSK conditions, while highlighting evidence gaps hindering the ability to draw meaningful inferences.