Cory L. ButtsƗ1, Aaron R. CaldwellƗ1, Samantha A. MohlerƗ1, Matthew S. Ganioǂ1, FACSM, Nicholas P. Greeneǂ1, Stavros A. Kavourasǂ1, FACSM, Brendon P. McDermottǂ1, FACSM; 1University of Arkansas, Fayetteville, AR

Dehydration, exertional hyperthermia, and muscle damage commonly occur in athletic, military, and occupational settings, yet, their combined effects on biomarkers of acute kidney injury are not well understood. PURPOSE: Investigate the combination of dehydration, muscle damage, and exercise in the heat on biomarkers of renal stress. METHODS: Six male participants (age 24±5 y, ht 1.79±0.05 m, body mass 74.9±6.3 kg, body fat 14.5±4.1%) completed two trials, one euhydrated (EU; fluid replacement ≤2% body mass loss) and one hypohydrated (HY; fluid restriction 24-h prior to and throughout exercise), separated by ~28 days. Trials consisted of muscle damaging unilateral eccentric knee flexion, 60 minutes of treadmill running (~60% VO2max) in the heat (33 °C, 54% RH), and 30 minutes of passive recovery. Participants were provided a rehydration protocol in both trials and returned 24-h later for a follow-up visit. Data were analyzed using two-way repeated measures analysis of variance with Bonferroni corrected post-hoc tests. RESULTS: Urine osmolality when HY was greater pre- (HY 1045±102, EU 612±142 mOsm/kg; P <0.01) and post-trial (HY 1007±105, EU 503±205 mOsm/kg; P <0.01), but not 24-h post (HY 543±310, EU 545±404 mOsm/kg; P = 0.98). Serum osmolality was also different pre-trial (HY 301±5, EU 290±5 mOsm/kg; P = 0.02), but was similar 24-h post (HY 295±4, EU 293±3 mOsm/kg; P = 0.25). Isometric strength was reduced in both conditions immediately (mean Δ = -33.6±27.9 N·m, P = 0.03) after eccentric exercise. Rectal temperature increased to a greater degree when HY (2.11±0.60 °C) compared to EU (1.65±0.44 °C; P = 0.01). Plasma neutrophil gelatinase-associated lipocalin (NGAL) increased independent of condition (pre- 59.9±7.3, post-exercise 77.6±12.0 ng/mL, P <0.01), but was not different between trials (P = 0.84). However, percent changes from baseline in plasma NGAL were greater when HY (19.1±7.5%) compared to EU (6.1±11.2%), regardless of time (P < 0.01). CONCLUSION: Exercise in the heat with muscle damage increased renal strain when HY and resulted in greater changes in plasma NGAL, a biomarker of acute kidney injury. These preliminary findings suggest that improper fluid consumption prior to and during exercise may augment renal stress, yet the long-term consequences of these detriments require further investigation.

Supported by funding from Central States ACSM Student Grant Award

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