Resumen de Heat Exposure and Hypohydration Exacerbate Physiological Strain During Load Carrying
Elizabeth L. Adams, Douglas J. Casa, Robert A. Huggins, Julie K. DeMartini, Rebecca L. Stearns, Rachel M. Kennedy, Megan M. Bosworth, Lindsay J. DiStefano, Lawrence E. Armstrong, Carl M. Maresh
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[middle dot]kg-1[middle dot]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[degrees]C vs. 38.22 +/- 0.29[degrees]C, respectively, p > 0.05), whereas in combination (HYH), post-exercise Tre was far greater (39.32 +/- 0.43[degrees]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[degrees]C, respectively, p = 0.02); heart rate increase per 1% BML for HYH (vs. EUH) was 7 b[middle dot]min-1 compared with HYT (vs. EUT) at 3 b[middle dot]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.
