Background: Overtraining syndrome, caused by prolonged excessive stress, results in reduced performance and cortisol responsiveness in athletes. It is necessary to collect saliva samples sequentially within circadian rhythm for assessing exercise stress by measuring cortisol concentrations, and automated cortisol measurements using electrochemiluminescence immunoassay (ECLIA) may be useful for measuring a large number of saliva samples. In this study, we evaluated the appropriate use of cortisol-based exercise stress assessment within the circadian rhythm, which may diagnose and prevent overtraining syndrome in athletes. Methods: We collected saliva and sera from 54 healthy participants and analyzed the correlation between salivary cortisol concentrations measured by ECLIA and enzyme-linked immunosorbent assay (ELISA) or serum cortisol analysis. We also collected saliva continuously from 12 female long-distance runners on 2 consecutive days involving different intensities and types of exercise early in the morning and in the afternoon and measured salivary cortisol concentrations using ECLIA. Each exercise intensity of runners was measured by running velocities, Borg Scale score, and rate of change in the pulse rate by exercise.

There are conflicting reports regarding the efficacy of cortisol as a stress marker in altitude training due to the influence of the circadian rhythm. This study aimed to verify whether the automated measurement of salivary cortisol concentration via sequential sampling could detect the differences in exercise stress between two altitudes. We enrolled 12 elite female long-distance runners living near sea level. For the first higher-altitude camp, the runners lived at 1800 m and trained at 1700 m for 7 days. For the second lower-altitude camp, they lived at 1550 m and trained at 1300 m for 7 days. Their saliva was sequentially collected on the last 2 days during each camp which involved different intensity exercises in the morning and afternoon. The salivary cortisol concentrations were measured using electrochemiluminescence immunoassay. Before dinner, the basal salivary cortisol concentrations were significantly higher in the higher-altitude camp. The rate of change in the salivary cortisol concentration during the morning exercise was significantly higher in the higher-altitude camp than in lower-altitude camp (p = 0.028) despite the same exercise programs and intensities. Salivary cortisol level measurements during the athletes' circadian rhythms could detect the differences in acclimatization and exercise stress between two altitudes.

<b><i>Objective:</i></b> Given the association between diabetes suppression and inhibition of diet-induced elevation in glucose and insulin, we investigated the effects of adding glucomannan to rice gruel on pre- and postprandial glucose and insulin concentrations. <b><i>Methods:</i></b> A total of 25 Japanese subjects without a history of diabetes or gastrointestinal disease (all males; aged 37–60 years; body mass index 20.4–31.6) participated in this study. Subjects received a 75-g oral glucose tolerance test (75gOGTT) and rice gruel containing 0, 0.4, or 0.8% of glucomannan. Blood samples were then obtained at preload and at 30, 60, and 120 min after receiving 75 g of glucose or rice gruel with or without glucomannan. <b><i>Results:</i></b> After the 75gOGTT, 8 subjects had normal glucose tolerance (NGT), whereas 17 showed a borderline pattern. Moreover, our data showed that greater amounts of glucomannan promoted lesser 30-min postload plasma glucose and insulin levels, with differences being larger in the borderline group than in the NGT group. <b><i>Conclusions:</i></b> Glucomannan dose-dependently inhibited the rice gruel-induced increase in 30-min postprandial plasma glucose and insulin levels. Furthermore, greater inhibitory effects on glucose and insulin elevation were observed in the borderline group than in the NGT group.