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. The results of this study will provide mechanistic insight for how dehydration (intra- or extracellular) impairs systemic whole body and local small muscle performance in vivo. This Basic Science study seeks to understand how volume and osmolality impact MSNA and CAC as a basis for improving potential countermeasures, such as a more optimally formulated rehydration beverage. Therefore, this study directly complements Task Area T10 (Hot Weather Operations and Hydration: Injury and Performance Optimization) and impacts virtually all 14 Military Operational Medicine Research Program Drivers.
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Water and electrolyte retention
Timeframe: 180 minutes