Date of Graduation

8-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Kinesiology (PhD)

Degree Level

Graduate

Department

Health, Human Performance and Recreation

Advisor/Mentor

Brendon McDermott

Committee Member

Matthew Ganio

Second Committee Member

Stavros Kavouras

Third Committee Member

Nicholas Greene

Fourth Committee Member

Ronna Turner

Keywords

Acute Kidney Injury, Dehydration, Hyperthermia

Abstract

Purpose: The purpose was to identify the combined influence of dehydration, muscle damage, and exertional hyperthermia on biological markers of acute kidney injury and renal function. We also investigated the effects of performing muscle damaging exercise during mild hypohydration on muscle damage biomarkers and muscular strength recovery. Methods: Eighteen recreationally-active males (age 24 ± 5 y, body fat 17.3 ± 6.2%) completed a familiarization visit and two experimental trials separated by ≥28 days. The two experimental conditions consisted of either euhydration (EU; maintaining hydration, -1.2 ± 0.8%) or hypohydration (HY; restricting fluid consumption for 24 hours prior to and during the trial, -4.4 ± 1.9%). Participants completed a unilateral eccentric knee flexion muscle damaging protocol, 60-minute treadmill exercise in the heat, 30-minute passive recovery, and a rehydrated 24-h follow-up visit, respectively. Results: Strength was reduced across time independent of trial for isometric strength at 70° (P<0.001), isometric strength at 90° (P=0.001), and isokinetic strength at 60°·sec-1 (P=0.001). Serum creatine kinase increased regardless of trial (P<0.001), with the 24-h follow-up greater (grand mean; 58.7 ± 25.1 U/L) than at baseline (grand mean; 35.7 ± 23.1 U/L, P<0.001) and post-exercise (grand mean; 51.6 ± 23.2 U/L, P=0.009). Percent change in plasma neutrophil gelatinous associated lipocalin was greater in the HY trial post-exercise (EU 28.0 ± 15.2%, HY 41.8 ± 17.5%, P<0.001), but not at 24-h follow-up (P=0.39). Serum creatinine was increased in the HY trial regardless of time (EU 0.97 ± 0.14, HY 1.04 ± 0.15, mg/dL, P=0.025). Urine NGAL and urine creatinine were also elevated in the HY trial pre-exercise and post-exercise (all, P<0.05) but were returned to EU levels by 24-h follow-up (all, P>0.05). Conclusions: We demonstrated no significant impact of hydration status when performing muscle damaging exercise, followed by exercise in the heat, on indices of muscle damage recovery. Exercise in the heat with muscle damage increased physiological and renal strain when HY, but the rehydration protocol ameliorated differences between trials by the 24-h follow-up. These findings highlight the importance of proper fluid intake following exercise to mitigate renal stress.

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