Salivary and plasma concentrations of inflammatory cytokines at rest and following high-intensity interval exercise were compared in adolescent swimmers (21 male and 22 female, aged 13-17 years) to validate a non-invasive method of assessing inflammation in youth. Following provision of morning, fasted, resting blood and saliva samples, swimmers performed an intense swimming trial consisting of a maximal 200m swim, plus a high intensity interval swimming protocol (5x100m, 5x50m and 5x25m; 1:1 work-to-rest ratio), followed by post-exercise blood and saliva samples (~15 min). Salivary and plasma concentrations of interleukin-6 (IL-6), interleukin 10 (IL-10), and tumor necrosis factor alpha (TNF-α) were similar in males and females across time. Resting concentrations of IL-10 were significantly lower while IL-6 and TNF-α were significantly higher in saliva compared with plasma. IL-6 did not show a significant time effect or interaction, so although its relative decrease from pre- to post-swimming was higher in saliva than in plasma this difference was not significant (-21% vs. -3%, respectively; p = 0.06). There was a significant time-by-media interaction for IL-10, which increased from pre- to post-swimming in plasma, but this response was attenuated in saliva (51% vs. 29%; p = 0.02). TNF-α showed a significant time-by-media interaction, reflecting a decrease from pre- to post-swimming only in saliva (-27%, p = 0.01). Intraclass correlation coefficients revealed no agreement between salivary and plasma cytokine levels, and low Pearson correlations revealed no association between these measures either at rest or in response to intense swimming. In conclusion, although the overall direction of the post-exercise response was similar between saliva and plasma, the magnitude of the response was consistently different in saliva compared with plasma, which combined with the different resting concentrations and the absence of correlation between measures, suggest that salivary cytokine measures are not representative of blood levels in young athletes
