The mechanism(s) by which dehydration (both intra- and extracellular) impairs performance are still poorly described. A loss of volume results in increased occurrence of orthostatic intolerance, including dizziness, fatigue, headaches and related symptoms with upright posture. Any of these symptoms can contribute to decreased performance in maneuvers performed in the upright posture, which includes many military tasks. Thus, loss of volume challenges the cardiovascular and blood pressure responses to systemic whole body endurance exercise, while osmolality is the stimulus for intracellular dehydration that may impair local muscle force production by impairing contractile function, neural signaling, or both. In this study, we will compare how both types of dehydration affect MSNA and CAC.