Acute and chronic effects of local muscle vibration training inducing illusions on wrist strength and neurophysiological measures

Local muscle vibrations (LMV) acutely and chronically influence the sensorimotor system, but their effects depend on application conditions. The mechanisms underlying repeated LMV exposure remain debated. This study examined the chronic effects of LMV under illusion-inducing conditions on the upper limb. Nineteen healthy participants underwent 9 LMV sessions (80 Hz, 20 min) over 11 days targeting the right wrist flexors. Illusions were assessed using subjective scales and EEG (alpha band desynchronization). Neurophysiological parameters (spinal, corticospinal excitabilities, and intracortical inhibition) and grip strength were evaluated before and after a control session (20-min rest) and an LMV session, as well as after 9 LMV sessions and 5 days post-protocol. Participants consistently experienced illusions throughout the protocol, with stronger perceptions in the first 15 minutes. Yet, subjective and objective measures were found independent. Acute LMV significantly reduced the H-reflex (-45%) but did not alter strength or other neurophysiological measures. More, repeated LMV exposure induced no chronic changes in strength or neural excitabilities/inhibition. While confirming acute LMV effects under illusion conditions, this study found no evidence of chronic adaptations. It also suggests that subjective and objective (EEG-based) illusion measures reflect distinct neurophysiological mechanisms.