"Cardiorespiratory endurance, also called aerobic endurance, is the ability of the heart, blood vessels, and lungs to work together to deliver oxygen to body tissues, deliver nutrients, and remove waste products. Cardiorespiratory endurance exercises involve large muscle groups in prolonged, dynamic movement, such as running and swimming. Aerobic physical activity should preferably be spread throughout the week, and activity performed on at least 3 days a week produces health benefits. Both moderate- and vigorous-intensity aerobic activity should be performed in episodes of at least 10 minutes. Adults can do moderate-intensity or vigorous-intensity aerobic activities, or a combination of both. A general rule of thumb is that 2 minutes of moderate-intensity activity counts the same as 1 minute of vigorous-intensity activity. A person doing moderate-intensity aerobic activity can talk, but not sing, while a person doing vigorous-intensity activity cannot say more than a few words without pausing for a breath."