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Heat Exposure and Hypohydration Exacerbate Physiological Strain During Load Carrying

Adams, Elizabeth L.1,2; Casa, Douglas J.1; Huggins, Robert A.1; DeMartini-Nolan, Julie K.3; Stearns, Rebecca L.1; Kennedy, Rachel M.4; Bosworth, Megan M.5; DiStefano, Lindsay J.1; Armstrong, Lawrence E.1; Maresh, Carl M.6

The Journal of Strength & Conditioning Research: March 2019 - Volume 33 - Issue 3 - p 727–735
doi: 10.1519/JSC.0000000000001831
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Adams, EL, Casa, DJ, Huggins, RA, DeMartini-Nolan, JK, Stearns, RL, Kennedy, RM, Bosworth, MM, DiStefano, LJ, Armstrong, LE, and Maresh, CM. Heat exposure and hypohydration exacerbate physiological strain during load carrying. J Strength Cond Res 33(3): 727–735, 2019—Heat exposure and hypohydration induce physiological and psychological strain during exercise; however, it is unknown if the separate effects of heat exposure and hypohydration are synergistic when co-occurring during loaded exercise. This study compared separate and combined effects of heat exposure and hypohydration on physiological strain, mood state, and visual vigilance during loaded exercise. Twelve men (mean ± SD; age, 20 ± 2 years; body mass, 74.0 ± 8.2 kg; maximal oxygen uptake, 57.0 ± 6.0 ml·kg−1·min−1) completed 4 trials under the following conditions: euhydrated temperate (EUT), hypohydrated temperate (HYT), euhydrated hot (EUH), and hypohydrated hot (HYH). Exercise was 90 minutes of treadmill walking (∼50% V[Combining Dot Above]O2max, 5% grade) while carrying a 45-lb rucksack. Profile of Mood States and the Scanning Visual Vigilance Test were completed before and after exercise. The separate effects of heat exposure (EUH) and hypohydration (HYT) on post-exercise rectal temperature (Tre) were similar (38.25 ± 0.63°C vs. 38.22 ± 0.29°C, respectively, p > 0.05), whereas in combination (HYH), post-exercise Tre was far greater (39.32 ± 0.43°C). Increase in Tre per 1% body mass loss (BML) for HYH (vs. EUH) was greater than HYT (vs. EUT) (0.32 vs. 0.04°C, respectively, p = 0.02); heart rate increase per 1% BML for HYH (vs. EUH) was 7 b·min−1 compared with HYT (vs. EUT) at 3 b·min−1 (p = 0.30). Hypohydrated hot induced greater mood disturbance (post-exercise ‐ pre-exercise) (35 ± 21 units) compared with other conditions (EUT = 3 ± 9 units; HYT = 3 ± 16 units; EUH = 16 ± 26 units; p < 0.001). No differences occurred in visual vigilance (p > 0.05). Independently, heat exposure and hypohydration induced similar physiological strain during loaded exercise; when combined, heat exposure with hypohydration, synergistically exacerbated physiological strain and mood disturbance.

1Human Performance Laboratory, Korey Stringer Institute, Department of Kinesiology, University of Connecticut, Storrs, Connecticut;

2Department of Nutritional Sciences, The Pennsylvania State University, University Park, Pennsylvania;

3Department of Athletic Training, College of Health Professions, Sacred Heart University, Fairfield, Connecticut;

4Department of Sports Medicine, Lehigh University, Bethlehem, Pennsylvania;

5Department of Athletics, University of Hartford, West Hartford, Connecticut; and

6Department of Human Sciences, The Ohio State University, Columbus, Ohio

Address correspondence to Douglas J. Casa, douglas.casa@uconn.edu.

Copyright © 2019 by the National Strength & Conditioning Association.