Miss a day or two of working out? No problem. You don't need to exercise every day to reach 100 PAI. Daily goals can be demotivating as life gets busy, and everyone needs a rest day every now and then.
Your PAI score is based on your elevated heart rates over the past 7-days. If you do low-intensity exercise (only slightly elevating your heart rate, e.g. yoga), you will find it takes much more time to reach 100 PAI than if you do high-intensity exercise (your heart beating much faster, e.g. running). You can decide what you prefer and choose days that suit you to get there.
You can only earn up to 75 PAI in a single day.