Your PAI score is based on your past 7 days of heart rate data and your personal bio-data (age, weight, etc.), so it’s personalized for your body. Your heart rate is the most important input, so the more intense your workout (i.e. the higher your heart rate), the faster you'll earn PAI points.
After 7 days, your exercise activities expire, so you may see your score reduce on some days. You will need to earn PAI (i.e. exercise) regularly in order to maintain your PAI score. Also keep in mind that your first 7 days earn PAI points faster because your activities haven’t yet started to expire!
PAI is designed to strengthen your heart over time, so PAI points become harder to earn as you maintain a high PAI score. Just as when you start lifting weights you will eventually increase the weight or number of repetitions, PAI gets more difficult over time, too. If you fall behind by not earning any PAI points for several days, your PAI score will adapt by making things a little easier on you. And if you know you can't exercise on some days, you can 'bank' your PAI points by exercising harder on the days that suit you.
As you continue to earn PAI points, your score takes into account other factors like past PAI scores, so it’s not as straightforward as simply adding your PAI score each day. While the exact formula is a secret, you can trust that the algorithm was created from analyzing 25 years of health data on 45,000 people, it has been scientifically validated, and matches the American Heart Association's 2018 Physical Activity Guidelines
PAI is meant to help improve your cardiorespiratory fitness (your heart’s health). Maintaining 100 PAI will give you 100% of the benefits in reducing your risk of cardiovascular disease, but even reaching just 50 PAI still gives you 60% of the associated health benefits!
Also note that you can only earn a maximum of 75 PAI in a single day, so plan to exercise more than once a week!