Hypohydration and muscular fatigue of the thumb alter median nerve somatosensory evoked potentials.

The mechanisms by which dehydration impairs endurance performance remain unresolved but may involve alterations in afferent neural processing. The purpose of this study was to determine the effect of hypohydration on somatosensory evoked potentials (SEPs) at rest and during recovery from fatiguing exercise. Fourteen volunteers (12 men, 2 women) performed repetitive isometric thumb contractions (50% maximal voluntary contractions (MVC) and 100% MVC in a 5:1 ratio, each contraction separated by 5 s of rest) until exhaustion when euhydrated (EU) and when hypohydrated by 4% body mass (HY). SEPs were obtained from the median nerve. The results indicated that HY did not produce statistical differences in time to exhaustion (EU=754 (SD 255); HY=714 (SD 318) s; p=0.66) or rate of muscle fatigue. However, HY was associated with greater subjective feelings of fatigue and loss of vigor after exhaustive exercise (p<0.01). HY affected N20 latency with an interaction effect of hydration by fatigue state (EU-Rest: 18.5 (SD 1.6) ms; EU-Fatigue: 19.0 (SD 1.6) ms; HY-Rest: 18.3 (SD 1.3) ms; HY-Fatigue: 18.4 (SD 1.5) ms; p=0.034), but N20 and N20-P22 amplitude responses were similar between HY and EU trials. We concluded that moderate water deficits appear to alter afferent signal processing within the cerebral cortex.