In providing guidance to my patients about exercise, I used to be very general in my instructions: 20 to 30 minutes, at least 2 or 3 times a week, of whatever activity you like most (eg, walking, playing tennis, or swimming). My thought, to the extent I thought about it at all, was that if they liked the activity they engaged in, they would be more likely to persist in it. Similarly, if a patient told me that she swam 3 times a week, I was more than satisfied. It would not have occurred to me to say: swimming is great, but because it is not weightbearing, it is not good protection against osteoporosis. Although any form of exercise is better than a sedentary lifestyle, additional research in the field can guide prescriptions for exercise regimens as specific as our prescriptions for hypertension medications or human immunodeficiency virus antiretroviral therapy. They should consider not only patient preference but also the differential benefits of different forms of exercise.