The Impact of a 24-hour Continuous Running Competition Conducted in a Thermoneutral Environment on Circulatory Endotoxin Concentration and Cytokine Profile


Modest rises in circulatory endotoxin concentration and increased pro-inflammatory cytokine responses have previously been observed during exertional-heat stress. How these immune variables respond to physical exertion without heat stress but inclusion of other stressors (e.g. sleep deprivation and severe energy deficit) during ultra-marathon competition is unknown. This observational study aimed to determine circulatory endotoxin concentration and cytokine responses to a continuous 24-hours ultra-marathon competition (total distance range: 122-207km; average intensity: 7.2METs) conducted in thermoneutral ambient conditions. Body mass, tympanic temperature and venous blood samples were taken from ultra-endurance runners (UER, N=25) and control non-runners (CON, N=20) before and immediately after competition. Aliquots of plasma were used to determine plasma osmolality by freezepoint osmometry, endotoxin by LAL chromogenic endpoint assay, CRP and cytokine profile by ELISA. Total energy expenditure was determined by triaxial accelerometer; while total food and fluid intake was established through direct dietary monitoring technique and analysed on dietary analysis software. Gastrointestinal symptoms were monitored throughout the ultra-marathon. Data was analysed using ANOVA with post hoc Tukeys, and verification by non-parametric equivalents were appropriate. Significance was accepted as p<0.05. Total energy expenditure and intake in UER was 13080±2587kcal and 4708±2568kcal, respectively (p<0.001 vs. CON). Individual body mass loss ranged between -2.4% to 4.4%. Overall mean pre- and post-competition plasma osmolality in UER was 285±11mOsmol/kg and 287±10mOsmol/kg, respectively. Tympanic temperature was within normal range in all UER before and after competition. 24-hours of continuous competition resulted in 43% average rise (p=0.021) in plasma endotoxin concentration, which was evident in 68% of all UER (p=0.005 vs. CON). A 31.8-fold average increase in plasma CRP concentration was observed immediately after competition in UER (p<0.001), with no change in CON. IL-6 (32-fold, p<0.000), TNFα (34%, p=0.015), IL-10 (4.2-fold, p<0.001) and IL-8 (3.2-fold, p<0.001) plasma concentrations were raised following competition in UER. Pre-competition cytokine profile did not differ between UER and CON; however IL-6, TNFα, IL-1β, IL-12p70, IL-10 and IL-8 plasma concentrations were higher in UER than CON immediately after competition (p<0.05). Incidences of gastrointestinal distress were reported by 65% of UER, but no associations with blood parameters measured were identified. 24-hours of ultra-marathon competition in thermoneutral ambient conditions resulted in a disturbed pro-inflammatory immune profile, which may have been exacerbated by the substantial rise in circulatory endotoxin concentration. In addition, the accompanying acute period of sleep deprivation and severe energy deficit may have also contributed to the perturbed responses observed following competition.

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