The Effect of Prolonged Exercise in the Heat and Subsequent Submaximal Exercise on Markers of Oxidative Stress

Abstract

PURPOSE: To investigate the effect of a 3 hr exercise protocol performed in the heat followed by sub-max exercise at varying temperatures with and without fluid replacement on oxidative stress. METHODS: Thirty-two males (age; 22 ± 4 yrs, height; 1.80 ± 0.05 m, weight; 85.4 ± 10.8 kg)were divided into four cohorts (n=8) and tested in one environment (TEMP; 10, 20, 30, 40°C) while eu- and dehydrated (EUH, DEH). DEH was induced via 3 hr of intermittent exercise (< 30% VO2peak) in 50°C. In the EUH trials, fluid lost was replaced with a 0.05% NaCl-water solution (3.7 ± 0.6 liters). Volunteers recovered for 90 min (22°C), sat in their assigned TEMP for ∼30 min and then performed 30-min of cycling at 50% VO2peak (SUBMAX). Blood was drawn prior to 50°C heat exposure (PRE), after ∼30 min rest in TEMP (REST), and immediately following (SUBMAX). Plasma was stored and later assayed for lipid hydroperoxide (LOOH) and protein carbonyl (PC) concentrations. RESULTS: Subjects were euhydrated prior to each test (USG < 1.020, Posm <290 mOsm·kg-1) but lost -4% body mass in DEH trials. There was a significant main effect of exercise in the heat for both LOOH (p=0.003; EUH-PRE = 23.4±2.8; EUH-REST = 27.9±2.5; DEH-PRE = 23.4±2.3, DEH-REST = 25.9±2.7μM) and PC (p=0.009; EUH-PRE = 0.148±0.19, EUH-REST = 0.160±0.012; DEH-PRE = 0.148± 0.014, DEH-REST= 0.194±0.019 nmol/mg). There was no effect of TEMP on change in LOOH or PC following SUBMAX therefore data were collapsed across TEMP. Paired T-tests revealed no effect (p = 0.922) of EUH-SUBMAX on LOOH, however DEH-SUBMAX resulted in a significant increase in LOOH from REST (p = 0.034). There was no significant difference in PC between REST and SUBMAX in either EUH or DEH. CONCLUSIONS: In both EUH and DEH trials, prolonged intermittent exercise (3 hr) in 50°C increased two markers of oxidative stress. Despite environmental temp, subsequent submax exercise resulted in a further increase in LOOH when dehydrated. The opinions or assertions contained herein should not to be construed as official or reflecting the views of the Army or the DoD.