Changes in Inflammatory and Anti-inflammatory Cytokines During 10d of Exercise Heat Acclimation and 28h of Sleep Loss

Exercise, heat exposure and sleep loss represent separate, distinct threats to the body\u27s dynamic equilibrium, known as homeostasis. In the unfit, mild exercise increases core temperature, and induces oxidative, hormonal and mechanical stresses, which may be magnified when coincident with heat exposure or sleep loss. Students, soldiers, recreational athletes and busy professionals may experience these stressors in combination; information on immune consequences to these moderate stressors in combination is scarce. Methods: Eleven males (mean ±SD: age 20 ± 1y; height 183.7 ± 8.4cm; weight, 81.7 ± 12.2kg; percent body fat, 10.1 ± 2.9%; V˙O2max, 53.2 ± 8.8 ml·kg -1·min-1) walked for 90min at 93.6 m·min -1 (5.6 km·h-1), 5% grade in the heat 33 ± 1°C, 40 ± 9% RH on 10 consecutive days followed by 28h sleep loss and an 11th walking session. Rectal temperature (Tre) and heartrate (HR) were measured every 10min during exercise. Venous blood was collected immediately prior to and immediately following exercise on days 1, 4, 7, 10 and 11. Two-way (day x time) repeated measures ANOVA, alpha 0.05 were used for analysis. Results: Exercise heat acclimation (EHA) was confirmed by changes in Tre and HR: D1 90min Tre \u3e D4, D7 and D10 (p\u3c0.005); 90min HR D1 \u3e D4, D7 and D10 (p\u3c0.05); Hemoglobin (Hb) D1 \u3e D7 and D11 (p = 0.017, 95% CI 0.132 - 1.487; p = 0.003, 95% CI 0.411 - 1.861 respectively) and Hematocrit (Hct) D1 \u3e D11 (p = 0.009, 95% CI -4.733 – -0.650) suggesting a plasma volume increase during EHA. We analyzed 4 cytokines (IL-8, IL-10, TNFα, IFNγ). There were no significant differences among cytokines within or between days. Cortisol was significantly greater post-exercise (P \u3c 0.001, 95%CI 317.37 - 395.89). Conclusions: Our results suggest moderate exercise and mild heat stress do not perturb the balance of inflammatory and anti-inflammatory cytokines in untrained, healthy individuals during a 10d EHA protocol. Heat acclimated individuals tolerated 28h of sleep loss without apparent effect to these markers of immune response.^ Key Words: Inflammatory response, perturbation, immune stressors