Hydration status does not have a significant effect on soleus motoneuron pool excitability

The purpose of this study was to examine the effect of hydration status on the soleus Hoffmann reflex (H-reflex): muscle response ratio in nine healthy subjects. Soleus H-reflex, urine specific gravity (USG), and body weight (BW) were collected prior to and following a 12-hr fluid restriction protocol and compared to euhydrated measures. Individual repeated measure ANOVAs compared H-reflex, USG, and BW across conditions. A main effect for hydration status was observed between the hypohydration and euhydration condition (p < .01). H-reflex and BW demonstrated no change from baseline across conditions. Although hypohydration creates deficits in muscle function, it does not appear to be the result of decreased central activation.