For most healthy adults, the Department of Health and Human Services recommends at least 150 minutes of moderate aerobic activity or 75 minutes of vigorous aerobic activity a week, or a combination of moderate and vigorous activity. Moderate aerobic exercise includes activities such as brisk walking or swimming. Vigorous aerobic exercise includes activities such as running or aerobic dancing. The guidelines suggest that you spread out this exercise during the course of a week. The guidelines also recommend that you do strength training exercises for all major muscle groups at least twice a week.