Effects of water immersion on short- and long-latency afferent inhibition, short-interval intracortical inhibition, and intracortical facilitation.

Objective: The aim of the present study was to investigate the effect of water immersion (WI) on short- and long-latency afferent inhibition (SAI and LAI), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF).

Methods: Motor evoked potentials (MEPs) were measured from the first dorsal interosseous (FDI) muscle of fifteen healthy males before, during, and after a 15-min WI at 30°C up to the axilla. Both SAI and LAI were evaluated by measuring MEPs in response to transcranial magnetic stimulation (TMS) of the left motor cortex following electrical stimulation of the right median nerve (fixed at about three times the sensory threshold) at interstimulus intervals (ISIs) of 20 ms to assess SAI and 200 ms to assess LAI. The paired-pulse TMS paradigm was used to measure SICI and ICF.

Results: Both SAI and LAI were reduced during WI, while SICI and ICF were not significantly different before, during, and after WI.

Conclusions: WI decreased SAI and LAI by modulating the processing of afferent inputs.

Significance: Changes in somatosensory processing and sensorimotor integration may contribute to the therapeutic benefits of WI for chronic pain or movement disorders.