Fitbit charge 5 + premium connects the dots between your activity . sleep . and stress so you can make the best decisions for your body . mind . and health. It all starts with your six-month Fitbit premium membership and daily readiness . a score based on activity . sleep . and heart rate variability (HRV) that helps you optimize your workout routine. Your score comes with personalized activity recommendations low means go easy and recover light yoga . and deep breathing while a high score gives you the green light to go all out.