Validation of a Personal Fluid Loss Monitor


Health Promotion and Physical Education

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Dehydration raises heat injury risk and reduces performance [2,5,6]. The purpose was to validate the Hydra-Alert Jr (Acumen). The Hydra-Alert was tested in two exercise/clothing conditions. Participants wore it while wearing exercise clothing and exercising at a self-selected intensity (n = 8). Others wore the Hydra-Alert while wearing a ballistic-vest and performing an industrial- protocol (n = 8). For each condition, the Hydra-Alert was tested on two occasions (T1 and T2). The Hydra-Alert was tested against nude weight loss for both conditions. The Hydra-Alert had low test-retest reliability for both conditions (average absolute value of the error between Hydra-Alert outputs of T1 and T2 = 0.08 ± 0.08 percentage points). With exercise-clothing, the Hydra-Alert evidenced low-moderate correlations between percent nude weight loss and Hydra-Alert output at 20min (r=0.59-T1, p=0.13; r=0.12-T2, p=0.78), at 40min (r=0.93-T1, p=0.001; r=0.63-T2, p=0.10), and at ∼2% weight loss (r = 0.21-T1 and T2, p 0.61 and 0.62, respectively). The correlation at 40 min during T1 fell during T2 suggesting the Hydra-Alert was inconsistent. When wearing a ballistic-vest, the Hydra-Alert had poor validity (T1: r=-0.29 [p=0.48] for weight loss vs. monitor; T2: r=0.11 [p=0.80]). At the higher levels of dehydration (∼2%), the Hydra-Alert error was so high as to render its readings of little value. In some cases, the Hydra-Alert could lead to a false level of security if dehydrated. Therefore, the Hydra-Alert is of little use for those who want to measure their fluid loss while exercising in the heat.

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