Year of Award

2016

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Health and Human Performance (Exercise Science Option)

Department or School/College

Department of Health and Human Performance

Committee Chair

Charles Dumke

Commitee Members

Brent Ruby, Carl Seielstad

Keywords

Heat Acclimation, Dehydration, Heat Stress, Aerobic Performance, Plasma Volume

Publisher

University of Montana

Subject Categories

Sports Sciences

Abstract

Heat acclimation promotes adaptations to attenuate physiological and perceptual strain associated with heat stress, and may be enhanced by promoting dehydration during acclimation. Purpose: To determine i) the effect of fluid delivery during acclimation by inducing dehydration (DEH=0.5 mL / kg / 15 min) vs. euhydration (EUH=2.0 mL / kg / 15min) following three heat acclimation bouts on heat stress factors, and ii) to determine if fluid delivery (EUH vs. DEH) affects aerobic performance in the heat. Methods: Thirteen aerobically fit males completed 90-minute heat stress test (HST) in hot conditions (40°C, 30% RH) walking at 50% VO2 max prior to and following three-days of EUH and DEH acclimation trials. Acclimation trials were in the same environment and intensity as HST, and separated by one day. Participants wore standard Wildland Firefighter (WLFF) Nomex: shirt, pants, and a cotton T-shirt. Following each HST, aerobic performance was assessed by a graded ramp protocol increasing grade 1% until 15%, and then increased 1.6km*h-1 every minute until volitional exhaustion. Peak core temperature (TC), skin temperature (Tsk), heart rate (HR), rating of perceived exertion (RPE), physiological strain index (PSI), aerobic performance, and sweat rate were collected following HST. Skin blood flow (SBF) was measured via laser doppler flowmetry at 30, 60, and 90 minutes during exercise, and a five-minute recovery period. All data was analyzed by a two-way analysis of variance (ANOVA) 2 (Trt) x 2 (Time). RESULTS: Acclimation significantly decreased peak Tc (DEH= 39.5°C± 0.10 to 39.0± 0.12, EUH=39.5°C± 0.12 to 38.9± 0.12, psk, (DEH=37.8°C± 0.19 to 37.6± 0.12, EUH=37.9°C± 0.20 to 37.5± 0.10, p=0.005), peak HR (DEH=178.1 b/min ± 3.33 to 164.1± 4.43, EUH= 179.3 b/min± 3.38 to 167.4 ± 3.72 p-1± 0.06 to 1.9 L*h-1 ± 0.09) compared to EUH (1.6 L/h± 0.06 to 1.8 L/h± 0.08) (TrtXTime: p=0.015), and blood plasma percentage increased in the DEH group as a main effect for Time (DEH= 7.1% ± 1.84, EUH= 4.1% ± 2.46, p=0.002). CONCLUSION: Short-term heat acclimation effectively attenuates heat stress, and improves aerobic performance in the heat. Fluid delivery strategies during acclimation do not affect thermal strain or performance, but may increase sweat capacity and plasma volume to additionally protect from heat stress.

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© Copyright 2016 Michael W. Schleh