Validation of a Personal Fluid Loss Monitor
Health Promotion and Physical Education
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.
Wickwire, P. J., Bishop, P. A., Green, J. M., Richardson, M. T., Lomax, R. G., Casaru, C., . . . Curtner-Smith, M. (2008). Validation of a personal fluid loss monitor. International Journal of Sports Medicine, 29(2), 139-144.