Abstract des Autors

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]O 2 max, 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 (T re) were similar (38.25 ± 0.63°C vs. 38.22 ± 0.29°C, respectively, p > 0.05), whereas in combination (HYH), post-exercise T re was far greater (39.32 ± 0.43°C). Increase in T re 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.