Salivary Hormone Critical Difference And Biological Variation In A Professional American Football Season

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Although a large body of research has investigated various hormonal and immunological responses to exercise, few studies have assessed the biological significance of those responses utilizing critical difference values (CDV) and biological variation (BV) in the context of monitoring biomarkers in professional athletes. PURPOSE: To assess salivary hormone changes over a professional American football season and determine if individual monitoring of these biomarkers is valuable. METHODS: Professional American football players (n=24) were recruited to provide weekly saliva samples over the course of a seven week season. Saliva samples were collected between 0600 and 0800 hours following an overnight fast and a mouth rinse with distilled water. Eight samples (two baseline and six weekly samples) were collected per player and analyzed for salivary testosterone (T), cortisol (C), uric acid (sUA), and immunoglobulin A concentration (SIgA). Player data were included for analysis if they provided samples at ≥70% of all collection time points (n=17). Data were analyzed using parametric statistics after confirmation of normality by Shapiro-Wilk and Reed’s Criterion tests. The within-subject biological variation, CDV, and index of individuality (II) were calculated in accordance with the methods of Frasier and Harris. Lastly, relative percent change from baseline for each weekly collection was assessed using repeated measures one-way ANOVA. RESULTS: The CDV for salivary T, C, sUA, and SIgA were 27.5%, 61.3%, 48.0%, and 59.2%; while BV was 10.8%, 26.1%, 20.5%, and 25% respectively. II was calculated as 0.93, 0.52, 0.59, and 0.65 (arbitrary units) for T, C, sUA, and SIgA, respectively. All hormones exhibited significant differences between players (p<0.001), however were not significantly different between weeks (P>0.05). CONCLUSION: These data suggest that individual players experience week-to-week variation in salivary hormone response over a professional American football season, however team-wide fluctuations are minimal. Furthermore, the relatively low II values may imply that these salivary biomarkers are useful in terms of monitoring meaningful individual changes across a season.