Training in a Hot Environment Fails to Elicit Changes in the Blood Oxidative Stress Response

Abstract

Environmental temperature can impact exercise-induced blood oxidative stress; however, the effects of heat acclimation on this response have not been fully elucidated. The purpose of the study was to investigate the effects of hot (33°C) and room temperature (20°C) environments on post-exercise blood oxidative stress responses following 15 temperature acclimation sessions. Untrained participants (n = 38, 26 ± 7 years, VO_2peak = 38.0 ± 7.2 years) completed 15 temperature acclimation sessions of a cycling bout at an intensity perceived as "hard" in either a hot (33°C) or room temperature (20°C) environment. Pre and post acclimation exercise tolerance trials were conducted, which involved cycling at 50% W_peak for one hour. Blood sampling occurred before exercise, immediately after, two hours, and four hours after the exercise tolerance trials. Blood samples were analyzed for oxidative stress markers including lipid hydroperoxides, 8-isoprostanes, protein carbonyls, 3-nitrotyrosine, ferric-reducing ability of plasma, and Trolox-equivalent antioxidant capacity. Exercise-dependent increases were observed in lipid hydroperoxides, Trolox-equivalent antioxidant capacity, and ferric-reducing ability of plasma (p < 0.001). Considering exercise-induced elevations in markers of blood oxidative stress, there were no differences observed between environmental temperatures before or after the acclimation training period.

Keywords: free radicals; heat physiology; hyperthermic exercise; recovery; redox balance.

Figure 1

Experimental Design. Participants completed a pre- and post-acclimation trial separated by 15 exercise training sessions. Pre- and post-acclimation trials involved an identical 60-min bout of cycle ergometry at 50% of W_peak. The experimental conditions included the following environmental conditions: Hot (33ºC, 40% Relative Humidity) and Room Temperature (20ºC, 40% Relative Humidity).

Figure 2

(A) Plasma lipid hydroperoxides. Lipid hydroperoxides are expressed as lipid hydroperoxide equivalents (µM) for exercise in a room temperature environment during the pre-acclimation trial (shaded bars), a hot environment during the pre-acclimation trial (black bars), a room temperature environment during the post-acclimation trial (dashed bars), and a hot environment during the post-acclimation trial (white bars). (B) Plasma 8-Isoprostanes. 8-Isoprostane values are expressed in standard comparison to 8-Isoprostanes protein content (pg/mL). * Significantly different from pre-exercise values. # Significantly different from the pre-acclimation trial. Means are expressed ± SEM.

Figure 3

(A) Protein Carbonyl values are expressed in standard comparison to protein carbonyl equivalents (nmol/mg protein) for exercise in a room temperature environment during the pre-acclimation trial (shaded bars), a hot environment during the pre-acclimation trial (black bars), a room temperature environment during the post-acclimation trial (dashed bars), and a hot environment during the post-acclimation trial (white bars). (B) Plasma Nitrotyrosine. Nitrotyrosine values are expressed in standard comparison to nitrotyrosine protein content (ug/mL). # Significantly different from the pre-acclimation trial. † Significantly different between environmental temperatures. Means are expressed ± SEM.

Figure 4

(A) Trolox Equivalent Antioxidant Capacity. Trolox Equivalent Antioxidant Capacity values are expressed as Trolox equivalent antioxidant capacity equivalents (umol/L) for exercise in a room temperature environment during the pre-acclimation trial (shaded bars), a hot environment during the pre-acclimation trial (black bars), a room temperature environment during the post-acclimation trial (dashed bars), and a hot environment during the post-acclimation trial (white bars). (B) Ferric-reducing Ability of Plasma. Ferric-reducing Ability of Plasma values are expressed as ascorbate equivalents (µmol/L). * Significantly different from pre-exercise values. Means are expressed ± SEM.