Abstract
High-intensity training is associated with reduced secretion of salivary secretory immunoglobulin A (SIgA) and an increased risk of upper respiratory tract infections. Conditioning to attenuate this decline in SIgA is therefore important. Daytime napping is a conditioning strategy, which can be implemented by athletes and can benefit their endocrine and autonomic nervous systems; however, its effect on salivary SIgA secretion, an indicator of immune function, remains unexamined. We examined the effect of a power nap on SIgA secretion during a summer training camp. Fourteen male university rugby players were randomly assigned to a napping (n = 7) or a control group (n = 7). The intervention lasted 3 days, with measurements spanning 4 days. The napping group took a post-lunch nap of up to 30 min, while controls remained awake during the same period. Saliva was collected each morning upon awakening, before breakfast. The SIgA secretion rate decreased significantly from before the camp to the first measurement day in all participants. A linear mixed-effects model showed a significant time × group interaction (p = 0.016). In the napping group, the SIgA secretion rate increased from the first measurement day to two days later (mean difference 10.59 μg/min, 95% confidence interval 3.00–18.17) and remained higher than that in controls on the final morning (14.5 vs. 7.4 μg/min). Saliva flow rate and salivary cortisol showed no significant group differences. Thus, short napping during a training camp may attenuate the decline in salivary SIgA secretion and serve as a practical conditioning strategy.
