Changes In Awakening Cortisol Response During Long-term Training In Long-distance Runners: A Case Study

Awakening cortisol response (ACR) is a non-invasive salivary index defined as the change in cortisol concentration which increases in 30 minutes immediately after awakening. The ACR shows a close association with ACTH-induced cortisol secretion. Although previous study reported that the ACR changed after short-term training camp, it is yet to be known about continuous ACR changes during long-term training along with training load. PURPOSE: The aim of this study was to examine continuous changes of ACR in long-distance (ekiden) runners during strenuous long-term training periods. METHODS: To compare the effect of training load on ACR, we chose two ekiden runners who engaged different training load, which is, elite runner (ER) and recreational runner (RR). Runners were subjected to collect saliva sampling for ACR every week for 10 to 15 times. First saliva sample was collected immediately after awakening, and further samplings in 15 and 30 minutes. Measurement for heart rate variability (HRV) was also performed for 5 minutes between samplings in 15 and 30 minutes. Spectral analysis was used to calculate spectral power in the high-frequency (HF) band (0.15-0.40Hz) which represents parasympathetic autonomic activity. These two runners provided us with information of their running distance of each running menu and answers for an eight-item questionnaire on fatigue (Total Fatigue Score, TFS). RESULTS: The average weekly running distance of ER and RR were 175.1±23.5 and 79.8±16.9 km, respectively. The peak increase of salivary cortisol concentrations in both athletes were observed at 30 minutes after their awakenings on all sampling days (ER, 0.16±0.11 to 0.45±0.18 ug/dl; RR, 0.41±0.11 to 0.73±0.10 ug/dl). The percentage of ACR increase was 404.6±219.8 % in ER, 192.2±48.9 % in RR. Basal and peak cortisol level increased according to the increases of weekly running distance and TFS, in contrast to the decrease in HF at the same time point. CONCLUSIONS: These findings suggest that the ACR is one of the available indices which reflect runner’s fatigue along with their training. It is also important to consider individual variations and accurate sampling time after awakening in terms of salivary cortisol testing. Supported by Grant in Aid for Young Scientist B.