• Sometimes customizing is necessary because of an injury or the inability to do, for a short or long period, the kind of exercise you formerly did. When you're used to customizing for fun, doing it under duress won't seem like such an imposition. Either way, experiment until you find activities that make you happy as well as healthy. Choose your exercise using the same criteria you'd apply to choosing a date--that is, attractive to you and able to hold your interest for an hour.