When air quality negatively affects mental health during exercise: practitioners in gyms with high CO2 concentrations are more likely to present a negative mood

Purpose: This study aimed to verify the association of CO2 concentration and mood in people performing exercise in gyms. Methods: A total of 327 exercise practitioners (149 men and 178 women) were evaluated, with a mean age of 35.1 years, exercising at 3 gyms ventilated with either split-system or central system air conditioners. The air quality was assessed by determining the CO2 concentration level, as measured by a non-dispersive infrared sensor, positioned centrally in the weight room, at a height that corresponds to the breathing zone, measuring continuously from 7:00 a.m. to 11:00 p.m. CO2 measurements were conducted for 1 week in each gym. Mood states were evaluated using the Brunel Mood Scale. Results: The recommended value for indoor CO2 level according to the national guideline of Brazil (1000 ppm) was exceeded for 79.6% of the time. The highest mean CO2 concentration (p < 0.01) and the maximum value were measured in gym 1, which was ventilated with a split system. Exercise practitioners in gyms with CO2 concentrations below this value showed higher vigor than those in gyms above 1000 ppm (p = 0.02). Binary logistic regression revealed that exercise practitioners in gyms with high CO2 concentrations (above 2146 ppm) were 2.26 times more likely to present a negative mood disturbance (p = 0.01) than those in gyms with up to 1115 ppm. Conclusion: We concluded that there was an association of CO2 concentration and mood in people performing exercise in gyms. Increasing the natural ventilation through opening doors and windows is suggested as practical implication.