Circadian effects on the acute responses of salivary cortisol and IgA in well trained swimmers

Objective: To examine whether time of day significantly affects salivary cortisol and IgA levels before and after submaximal swimming. Methods: Fourteen male competitive swimmers (mean (SD) age 18 (3.2) years) volunteered to participate in the study. In a fully randomised, cross over design, each subject performed 5 x 400 m front crawl at 85 (1.2)% of their seasonal best time (277 (16) seconds), with one minute rest between each 400 m, at 0600 and 1800 hours on two separate days. Timed, unstimulated saliva samples were collected before and after exercise. Saliva samples were analysed for cortisol and IgA by radioimmunoassay and single radial immunodiffusion respectively. Results: Significant time of day effects (am and pm respectively) were observed in IgA concentration (0.396 (0.179) v 0.322 (0.105) mg/ml, p < 0.05), IgA secretary rate (0.109 (0.081) v 0.144 (0.083) mg/min, p < 0.01), and saliva flow rate (0.31 (0.23) v 0.46 (0.22) ml/min, p < 0.001) before exercise (all values mean (SD)). Differences in cortisol levels before exercise (1.09 (0.56) v 0.67 (0.94) mu g/dl) approached significance (p = 0.059). The exercise protocol did not significantly affect IgA concentration and secretary rate (p > 0.05) but, in comparison with values before exercise, caused significant alterations in cortisol (p < 0.01) and saliva flow rate (p < 0.01). There was no significant interaction effect of time of day by exercise on any salivary variables measured (p > 0.05). However, most of the values of the salivary variables before exercise were significantly inversely related to their exercise induced response (p < 0.05). Conclusion: These results suggest a significant circadian variation in the variables measured before exercise, without showing a significant effect on their acute responses to exercise.