Recently, using the HUNT study data, the Cardiac Exercise Research Group devised a simple metric termed Personal Activity Intelligence (PAI) which, using individual heart rate patterns of the body, estimates the optimal threshold of physical activity required for a specific objective: to decrease risk of premature death in an individual from the general population. The idea is to keep the weekly PAI score above 100. Since PAI is a personalized reflection of the body's response to physical activity based on heart rate, PAI score of 100 is specific to an individual. For example, a 100 PAI for a fit person is not the same as 100 PAI for an unfit person. PAI can be accumulated over a course of one week using physical activity of personal preference (i.e. walking, swimming, dancing, playing with grandchildren etc.) and allows for days with no activity as long as they are followed up by days of higher activity. However, the optimal amount and intensity (i.e. the number of PAI) of physical activity that would help for weight gain prevention still remains to be determined.