Differences in stress response between two altitudes assessed by salivary cortisol levels within circadian rhythms in long-distance runners

Abstract

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.

Assessment of exercise-induced stress via automated measurement of salivary cortisol concentrations and the testosterone-to-cortisol ratio

“…After 4 weeks, saliva samples were collected sequentially from the participants in the morning and evening for two consecutive days, during which they performed exercises of different types and intensities. This took place during a training period su ciently removed from races and followed the same procedure as described in previous studies [9,10]. Then, we divided the participants into high-and low-intensity exercise groups, which were de ned with and without interval training, respectively, in the evening on day 1.…”

“…To load faster running within a short time period, interval training was only included in the high-intensity exercise program. The participants were provided su cient drinking water during training sessions to prevent dehydration [9,10]. On the two training days, saliva samples were collected at eight time points: upon waking (5:00 am), before morning exercise (5:30 am), after morning exercise (7:00 am), before breakfast (7:30 am), before lunch (12:00 pm), before evening exercise (16:00 pm), after evening exercise (18:30 pm), and before dinner (19:00 pm).…”

“…On the two training days, saliva samples were collected at eight time points: upon waking (5:00 am), before morning exercise (5:30 am), after morning exercise (7:00 am), before breakfast (7:30 am), before lunch (12:00 pm), before evening exercise (16:00 pm), after evening exercise (18:30 pm), and before dinner (19:00 pm). This followed the same schedule as described in previous studies [9,10].…”

“…The resting pulse rate at wakeup time and the maximum pulse rates during each exercise session were assessed by using the wearable devices. The distance and duration of running during each exercise session were recorded, and the running velocity was calculated as the distance divided by the duration (m/min) following the procedure described in previous studies [9,10]. The 6-20 Borg scale [13] was used to rate the perceived exertion after exercise.…”

“…This requires sequential sampling during days of exercise and the e cient measurement of a large number of samples. Our previous study showed that sequential saliva sampling and automated electrochemiluminescence immunoassay (ECLIA)-based salivary cortisol assessments can be used to detect the circadian rhythm and compare stresses induced by endurance exercises of different intensities among female long-distance runners at the same time on different days [9,10].…”