Obesity is a major health problem in this country. It should be no surprise that exercise can help prevent weight gain. But based on a study of more than 85,000 healthy Norwegians followed for more than 20 years, Norwegian researchers determined that a specific measurement – physical activity equivalent to 100 PAI a week – can counteract excessive weight gain. PAI stands for Personal Activity Intelligence, and it measures all physical activity, not just exercise, that causes your heart rate to increase above a certain level. The PAI Health app, available for free on both iPhone and Android platforms, uses data from your Apple Watch, FitBit and other devices to calculate a weekly score based on your personal profile and variations in heart rate over the period. Even if you have a healthy weight, getting 100 PAI each week has been shown to help you live longer and decrease your risk for cardiovascular disease.