Hot environments decrease exercise capacity and elevate multiple neurotransmitters

AIMS:This study aimed to test the hypothesis that different neurotransmitters and hormones are presented at exercise fatigue in hot temperatures with differing relative humidities (RH). MAIN METHODS:Eight trained male athletes performed a graded maximum oxygen consumption (VO2max) test in five different environmental conditions, namely, 21°C/20% RH (Normal), 33°C/20% RH (Hot 20%), 33°C/40% RH (Hot 40%), 33°C/60% RH (Hot 60%), and 33°C/80% RH (Hot 80%). Blood samples were taken pre- and post-exercise and analyzed for noradrenaline (NA), adrenaline (ADR), dopamine (DA), serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), and prolactin (PRL). Weight and oral and skin temperatures were recorded pre- and post-exercise. Heart rate was continuously monitored throughout the exercise. KEY FINDINGS:Hot 20%, Hot 40%, and Hot 80% had lower VO2max levels compared with Normal (P<0.05). The data pooled from all five conditions indicated that the NA (P<0.0001), PRL (P<0.0001), 5-HT (P=0.002), 5-HIAA (P=0.029), and DA (P=0.016) levels were affected by exercise. Accordingly, NA level was significantly associated with performance time. However, ADR did not show any significant effect between pre- and post-exercise (P=0.187). SIGNIFICANCE:The maximal aerobic capacity was impaired in high temperature and most humidity conditions. NA was strongly associated with exercise time, which suggested that exercise duration and intensity had an important influence on NA neurotransmitter level irrespective of the environmental conditions.