Cardiorespiratory fitness refers to how well the heart and lungs supply oxygen to the body’s muscles and organs during physical exertion. Good cardiorespiratory fitness has been shown to lower risks for obesity, diabetes, hypertension, cardiovascular disease, poor mental health, and more.
Study participants included 339 teens, ages 13 and 14, who took part for two years in school-based exercise programs that focused on running, with wrist-worn trackers calculating the intensity of their workouts.
The researchers found that the teens maximized their cardiorespiratory fitness at 20 minutes of vigorous running. Exercising longer did not improve their fitness. Current guidelines call for youths to do at least 60 minutes a day of moderate to vigorous physical activity to maximize their fitness, but health and fitness experts have said many teens find the daily time commitment difficult to maintain.
Just one-fourth of youths are physically active for an hour a day, according to the Centers for Disease Control and Prevention. The researchers say their findings show that, when exercising vigorously rather than moderately (running, for instance, instead of brisk walking), longer stints of physical activity are not needed to improve cardiorespiratory fitness. They note, however, that only cardiorespiratory fitness was assessed, and that other aspects of teens’ health may benefit from physical activity at a lower intensity.