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RENAL STRESS AND PLASMA VOLUME RESPONSES TO WORK IN THE HEAT FOLLOWING DIFFERENT HYDRATION REGIMENS

Abstract

Rachel A. Backes1, Whitley C. Atkins1, Samantha L. Thomas1, Colin E. Glenny1, Brendon P. McDermott1, FACSM1 University of Arkansas, Fayetteville, Arkansas

Current workplace safety organizations recommend that workers predicted to incur heavy sweat losses should consume a ‘sport drink’ during work. These sugar-sweetened beverages (SSB) often include moderate concentrations of fructose, which can increase renal stress and lead to acute kidney injury (AKI). PURPOSE: Investigate the effect of beverage type (SSB versus placebo) on renal stress and plasma volume changes (DPV) in response to simulating industrial work in the heat. METHODS: Twenty healthy, male participants (24 ±2y, 179 ±6cm, 24.7 ±9.0% body fat) completed two randomized, matched trials of simulated industrial work in the heat (30oC, 55% RH).The simulated work protocol included treadmill walking, 30-lb weighted box carrying, 3-lb weight carrying over steps, loosening and tightening nuts on bolts, and lunges with rotations. They completed two 45min work bouts, each followed by a 15min rest. Equal amounts of SSB or placebo were provided during rest breaks and within 2-hr of completing work protocol. Serum sodium, hemoglobin, and hematocrit levels were measured at baseline, pre-and post-work, and 16-hr post-work. Urinary kidney injury molecule-1 (uKIM-1) was measured pre-and post-work, 3-hrand 16-hr post-work. Total urine volume was measured for the 16-hr following work. DPV was calculated using the Dill & Costill equation. RESULTS: Serum [Na+] was elevated post-work compared to baseline and 16-hr post-work (p=.006), but was not different between trials (p=.612). Hemoglobin levels showed no significant difference between trials (p=.650). Sixteen-hr post-exercise hemoglobin was significantly lower than pre-work (p=.019). Hematocrit was not different between trials (p=.637) or over time (p=.172). uKIM-1demonstrated significant elevation at post-work and 16-hr post-work compared to baseline (p£.028) and 3-hr post-work (p£.009), but did not differ between trials (p=.126). Total urine volume in 16-hr post-work was not different between trials (p=.277). There was no significant difference between trials (p=.098), or time points (p=.118) for DPV. CONCLUSION: These findings indicate that beverage type (SSB versus placebo) did not affect plasma volume or renal stress biomarkers following simulated industrial work in the heat.

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