11Prospective application of serum cytokines, lipopolysaccharide, and heat shock proteins 12 requires reliable measurement of these biomarkers of exercise-induced heat stress in hot 13 conditions. To accomplish this, both short-term (seven day) reliability (at rest, n=12) and the 14 acute responsiveness of each biomarker to exercise in the heat (pre and post 60 min cycling, 15 34.5 o C and 70% RH, n=20) were evaluated. Venous blood was analysed for the serum 16 concentration of C-reactive protein (CRP), interleukin (IL)-6, heat shock protein 72 17 (eHSP72), immunoglobulin M (IgM) and lipopolysaccharide (LPS). Test-retest reliability 18 was determined as the coefficient of variation (CV). Biomarkers with the least short-term 19 within-subject variation were IL-6 (19%, ± 20%; CV, ± 95% confidence limits) and LPS 20 (23%, ± 13%). Greater variability was observed for IgM, eHSP72 and CRP (CV range 28-21 38%). IL-6 exhibited the largest increase in response to acute exercise (95%, ± 11%, p = 22 <0.001) and although CRP had a modest CV (12%, ± 7%) it increased substantially post-23 exercise (p = 0.02, ES; 0.78). In contrast, eHSP72 and LPS exhibited trivial changes post-24exercise. It appears the mean change of common inflammatory markers after exercise in the 25 heat is not always discernible from short-term (weekly) variation. 26
KeywordsLipopolysaccharide, heat shock proteins, inflammatory cytokines, heat 27 tolerance. 28