Corticospinal excitability is facilitated during coordinative action observation and motor imagery of adapted single-leg sit-to-stand movements in young healthy adults

Combined action observation and motor imagery (AOMI) facilitates corticospinal excitability (CSE). This study used single-pulse transcranial magnetic stimulation (TMS) to explore changes in CSE for coordinative AOMI of a single-leg sit-to-stand (SL-STS) movement. Twenty-one healthy adults completed two testing sessions, where they engaged with baseline (BL), action observation (AO), and motor imagery (MI) control conditions, and three experimental conditions where they observed a slow-paced SL-STS while simultaneously imagining a slow- (AOMI _HICO ), medium- (AOMI _MOCO ), or fast-paced (AOMI _LOCO ) SL-STS, with imagery guided through audio sonification. A TMS pulse was delivered to the right leg representation of the left primary motor cortex at three stimulation timepoints aligned with peak EMG activity of the knee extensor muscle group for the slow- , medium- , and fast-paced SL-STS during each condition. Motor evoked potential (MEP) amplitudes were recorded from the KE muscle group as a marker of CSE for all stimulation timepoints and conditions. A main effect for experimental condition was reported for all three stimulation timepoints. MEP amplitudes were significantly greater for AOMI _HICO at T1 and T3, and AOMI _MOCO and AOMI _LOCO at all stimulation timepoints, when compared with control conditions. The findings provide empirical support for the propositions of the Dual-Action Simulation Hypothesis and Visual Guidance Hypothesis accounts for coordinative AOMI. This study builds on existing neurophysiological support for the use of coordinative AOMI as an alternative method for movement (re)learning. Longitudinal research incorporating neurophysiological and behavioral measures is warranted to explore the efficacy of coordinative AOMI for this purpose.