NASM Group Fitness Instructor Practice Exam 2025 – Complete Preparation Guide

Exercise should generally be avoided in environments where the Air Quality Index (AQI) exceeds a level of 150 because this indicates that air quality is classified as "unhealthy." At AQI levels above 150, everyone may begin to experience health effects, particularly those who are sensitive to air pollution, such as individuals with respiratory conditions, the elderly, and children. Engaging in physical activity in such conditions can lead to increased exposure to pollutants, which can exacerbate respiratory issues, decrease lung function, and overall negatively impact health.

In environments with an AQI of 100 or lower, the air quality is considered "good," and exercise can typically be performed without significant health concerns. An AQI of 200 or 300 signifies that air quality is very unhealthy or hazardous, respectively, warranting that even healthy individuals should avoid outdoor activities. Thus, exercising when the AQI exceeds 150 is particularly risky, prompting the recommendation to avoid outdoor exercise for safety reasons.