Target-Speed-Dependent Effects of Water Immersion on Wrist Speed Modulation and Somatosensory Processing

Water immersion alters both movement-related mechanical demands and somatosensory inputs, but whether its effects on motor control depend on target speed and long-term motor experience in water remains unclear. Eighteen competitive swimmers and 15 non-swimmers performed a wrist flexion speed-modulation task under land and water conditions. After adapting to 50% of maximal wrist flexion speed, participants modulated movement speed to 10%, 30%, 50%, 70%, and 90% of maximum. Single-pulse somatosensory evoked potentials and paired-pulse inhibition at interstimulus intervals of 30 and 100 ms (PPI30 and PPI100) were recorded before and after motor adaptation. Movement error was greater in water at the 10% and 30% targets, and the Water–Land difference decreased linearly as target speed increased. N20–P25 amplitude was reduced in water, indicating attenuation of the initial somatosensory-evoked response in the primary somatosensory cortex (S1). After motor adaptation in water, swimmers showed higher PPI30 and lower PPI100 values than non-swimmers, indicating that group differences in paired-pulse processing depended on interstimulus interval. Lower PPI100 values were associated with greater stabilization of the practiced 50% reference speed, whereas no significant associations were found at other target speeds. These findings indicate that water immersion affects wrist speed modulation in a target-speed-dependent manner and attenuates resting S1 responsiveness. In addition, paired-pulse somatosensory processing after motor adaptation in water differed according to long-term competitive swimming experience, whereas its behavioral association was specific to immediate stabilization of the practiced reference speed.