“For healthy people, wearing masks during exercise has not been shown to be harmful. However, individuals affected by lung disease, such as asthma or COPD, or heart disease, should be evaluated by a healthcare provider before attempting exercise with any mask,” the CDC added.
Article source: https://www.huffpost.com/entry/cdc-stricter-gym-precautions-covid-19-outbreaks_n_6037f55ac5b6371109dabf7e