Assessment of the Efficacy of Military Training Fluid Intake Guidance in a Variety of Conditions

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Fluid intake during military training is prescribed based on the interactions among environmental conditions, uniform configurations and work rates. The efficacy of this guidance has not been empirically assessed for work bouts lasting >4 hours. PURPOSE: To determine the acceptability of the fluid intake guidance, sweat losses were measured in a variety of conditions and modern uniform/body armor configurations and were then compared to prescribed fluid intakes for each condition (clothing, environment, workload, duration). METHODS: Whole body sweat losses of 141 soldiers were measured over a variety of environmental conditions (White-Black flag), uniform configurations (including Battle Dress Uniform and body armor), exercise intensities (easy, moderate, heavy), and work durations (2,4, and 8 hr). Using the prescribed fluid intake guidance for each condition, the differences between the prescribed fluid intake and the total observed sweat loss were calculated. Differences were then expressed as a percent loss or gain of body weight using the following equation: [% body water flux= ((drinking volume- sweating volume)/body weight) x 100]. Values within a threshold of ±2% body water flux (BWF) were deemed acceptable. This threshold was considered the starting point for performance and health concerns. To simulate a worst-case scenario, it was assumed no urine was produced throughout testing. RESULTS: During short work durations (2 and 4hr), 0 of 75 Soldiers exceeded the +2% BWF. During longer work durations (8hr), 50 of 66 Soldiers exceeded the +2% BWF. In all conditions, 50 of 141 Soldiers (35%) exceeded the +2% BWF. In no condition did a Soldier exceed the -2% BWF. CONCLUSION: Current fluid intake guidance appears to be sufficient (no over- or under-drinking ±2% BWF) during work durations lasting ≤4 hours. However, for conditions beyond published guidance (>4hr), recommended drinking rates over-prescribe water needs in worst-case scenarios where no urine was produced. It is recommended that military fluid intake guidance be re-evaluated to include longer work durations of 8 hours. The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government.