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

Local muscle vibrations (LMV) acutely and chronically affect the sensorimotor system, but their effects vary depending on application conditions. The mechanisms behind repeated LMV exposure are still debated. This study investigated the chronic effects of LMV under illusion-inducing conditions on the upper limb. Nineteen healthy participants completed 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 during the first 15 min. However, subjective and objective measures were found to be independent. Acute LMV significantly reduced the H-reflex (-52.3% [-69.7 ; -21.0]) but did not affect strength or other neurophysiological measures. Additionally, repeated LMV exposure induced no chronic changes in strength or neural excitabilities and 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.