Date of Completion

8-11-2015

Embargo Period

8-11-2015

Keywords

thermoregulation, bout, subsequent exercise, heat illness

Major Advisor

Douglas J Casa

Associate Advisor

Lawrence E Armstrong

Associate Advisor

Carl M Maresh

Associate Advisor

Elaine C Lee

Associate Advisor

Jeffrey M Anderson

Field of Study

Kinesiology

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Introduction: Best practice recommendations suggest five days of short term heat acclimation (STHA) prior to multi-bout exercise days to reduce risk of exertional heat illnesses. It is unknown if five days of STHA is sufficient to mitigate thermal strain and protect against EHI. Purpose: To determine lasting physiological effects of exercise in heat on subsequent exercise before and after STHA. Methods: Eighteen men (age: 22 ± 3 y, height: 180.0 ± 6.0 cm, weight: 74.24 ± 7.42 kg, body fat: 9.4 ± 4.1%, maximal oxygen consumption: 54.6 ± 5.1 ml·kg-1·min-1) performed two intermittent treadmill exercise sessions two hours apart, followed by one session the following day (40°C, 40% relative humidity). Three additional days of STHA consisted of 90 minutes of exercise in the same environment. Subjects again completed a double exercise session followed by a single session the following day. Heart rate (HR), rectal temperature (Tre), and perceptual scales were assessed throughout exercise. Environmental symptoms and blood variables were assessed Pre- and Post-exercise. Results: Before STHA, resting HR and Tre were lower before Bout 1 (80 ± 12 bpm, 36.79 ± 0.44°C) compared to Bout 2 (103 ± 17 bpm, p < 0.001; 37.06 ± 0.50°C, p = 0.038) but were similar to Day 2 (81 ± 13 bpm, p = 0.728; 36.80 ± 0.32°C, p = 0.924), respectively. Exercising HR and Tre were similar between Bouts 1 and 2 despite a shorter exercise duration during Bout 2 (93 ± 27 min) than Bout 1 (120 ± 0 min, p < 0.001). Rate of Tre rise was greater during Bout 2 (0.031 ± 0.011°C·min-1) than Bout 1 (0.023 ± 0.004°C·min-1, p = 0.011). The STHA protocol induced a partially acclimated state, indicated by decreased exercising Tre, HR, thermal sensation, and perceived exertion (p < 0.05). Both Pre- and Post-STHA, many participants were unable to complete the full exercise protocol due to elevated Tre, environmental symptoms, and fatigue. Conclusion: Multi-bout exercise on the first of two sequential days led to a higher resting level of fatigue and premature cessation of exercise during the second bout of exercise both Pre- and Post-STHA.

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