The effects of soccer-specific intermittent exercise on salivary IgA responses
Exercise has been demonstrated to influence susceptibility to upper respiratory tract infections (URTI) because various aspects of immune function including mucosal immunity are temporarily changed after exercise. Lower concentrations of salivary 19A (s-IgA) as a predominant immunoglobulin and component of saliva or a chronic deficiency in s-IgA have been associated with an increased frequency of URTI episodes. Previous studies of aerobic exercise have incorporated the performance of running or cycling. Responses of s-19A to intermittent exercise patterns as they occur in soccer remain to be resolved. A laboratory based soccerspecific intermittent exercise protocol was used within this thesis to mimic the physiological stress associated with soccer, characterised by highintensity activity as noted during soccer play. The aims of this thesis were to determine the s-IgA responses to a bout or repeated bouts of soccerspecific intermittent exercise and investigate the effects of carbohydrate ingestion on s-IgA when such exercise is performed in increased ambient temperature. Laboratory based soccer-specific intermittent exercise and continuous exercise at the same moderate exercise intensity evoked insufficient stimulation of the hypothalamic-pituitary-adrenal axis to modify s-IgA responses. Changes in s-19A and cortisol did not differ between exercise types during or immediately following exercise, or 6 h, 24 h and 48 h afterwards. Physiological responses to intermittent exercise also conforming to the activity pattern of soccer match-play were similar to those for continuous exercise at the same average work-rate, despite the higher perceived exertion during intermittent exercise. Two bouts of soccer-specific intermittent exercise 48 h apart that were designed to provide a repeatable physiological stress comparable to strenuous soccer training induced s-19A responses that were similar following both bouts of exercise. Performing the second bout of exercise did not significantly suppress s-IgA concentration after 48 h recovery although a small progressive reduction in s-19A was observed. Performance of a second soccer-specific exercise bout in one day with a 2.25 h rest in between bouts elicited an increase in heart rate and perceived exertion, compared with a single session at the same time of day, but did not appear to suppress s-IgA outcomes. There was also no difference between responses of s-IgA concentration and secretion rate or salivary cortisol at the different times of day. Soccer can be played under hot environmental conditions and it is thought that addition of carbohydrate to fluids may prevent adverse changes in mucosal immune responses. Carbohydrate supplementation before and at regular intervals whilst performing soccer-specific intermittent exercise at 30°C, did not influence s-IgA responses or salivary cortisol when compared to placebo. In view of the failure of these experimental interventions to discern effects on s-IgA responses, a meta-analysis of the literature was conducted. The meta-analysis revealed an overall elevation in s-IgA concentration post acute exercise and following chronic exercise. In contrast, in term of s-IgA secretion rate, an overall significant decline after both acute and chronic exercise was a consistent finding. In conclusion, one exercise bout or repeated soccer-specific intermittent exercise in the present experiments did not induce compromises in s-IgA responses. There was no adverse effect upon s-IgA responses to intermittent exercise performance under conditions of heat stress with or without carbohydrate treatment. Although, 32 percent of studies included in the meta-analysis have indicated similar results, the disparity with overall findings may arise from differences in the exercise protocols used and/or bias for s-IgA changes in published studies.