Effects of Aerobic Physical Exercise Performed Under Hypoxic Conditions on Melatonin

Abstract

Melatonin is a hormone which controls sleep, inflammation, and oxidative stress. Aerobic physical exercise can influence melatonin in normoxia. However, there is controversy about the effects of exercise on the melatonin level in hypoxia, which is characterized by impaired sleep. PURPOSE: This work evaluated the effects of aerobic physical exercise on melatonin under hypoxic conditions. METHODS: Forty healthy men were randomized into 4 groups: Normoxia (N) - (22.1 ± 3.1 y, 69.1 ± 1.1 kg); Hypoxia (H) - (23.2 ± 2.1 y, 67.2 ± 4.1 kg); Exercise under Normoxia (EN) - (26.1 ± 3.2 y, 71.1 ± 3.2 kg); and Exercise under Hypoxia (EH) - (24.1 ± 3.1 y, 72.3 ± 2.1 kg). The observation period for all groups was 36 hrs, beginning with a first night devoid of any intervention.The normobaric hypoxia condition was conducted in a room equipped for altitude simulation that can reach up to 4,500 m (normobaric chamber, CAT - Colorado Altitude Training ™ / 12 CAT-Air Unit, USA). Aerobic exercise was performed by the EN and EH groups on a treadmill at 50% of VO2.peak for 60 minutes. Venous blood samples for the melatonin measurement were obtained on the 1st and 2nd days at 7:30 AM as well as on the1st and 2nd nights at 10:30 PM. Data are reported as mean ± standard deviation. A repeated measures and one-way analysis of variance (ANOVA) followed by the Tukey’s post hoc test were used to detect significant differences between groups. The accepted significance level was p ≤ 0.05. RESULTS: On the 2nd night, melatonin was higher in the H group compared to the N group (48.3 ± 2.2 vs. 26.1 ± 1.1, p< 0.05); low in the N group compared to the EH group (26.1 ± 1.1 vs. ± 59.2 ± 2.1, p< 0.05); low in the H group compared to the EH group (48.3 ± 2.2 vs. ± 59.2 ± 2.1, p< 0.05); and low in the EN group compared to the EH group (37.2 ± 1.0 vs. ± 59.2 ± 2.1, p< 0.05). On the 2nd day, melatonin was higher in the H group compared to the N group (39.1 ± 3.1 vs. 28.1 ± 2.1, p< 0.05); low in the N group compared to the EH group (28.1 ± 2.1 vs. 46.2 ± 2.0, p< 0.05); and high in the EH group compared to the H group (46.2 ± 2.0 vs. ± 39.1 ± 3.1, p< 0.05). CONCLUSIONS: Hypoxia acutely increases melatonin. Diurnal remission of the nocturnal increase in melatonin seems to be delayed by hypoxia and to an even greater extent if acting together with exercise.