Moderator: I know people who go to the gym six days a week and some who swear by those 20-minute fitness places a couple of times a week. For general fitness, just how much time is right for the average adult, if there is such a thing?
Weil: Like most things in science and medicine, there's never always one simple answer. There are two primary guidelines for physical activity in the United States. The first is from the American College of Sports Medicine. They recommend 20 to 60 minutes of moderate to vigorous aerobic exercise at 60% to 85% of your maximum heart rate.
If you don't take your heart rate, simply ask yourself how hard does the work feel? If you feel out of breath and sweaty, that's what counts, and as a result your aerobic fitness and your stamina and your endurance and your energy and your general health will improve.
In addition, the American College of Sports Medicine recommends two days per week of weight lifting. Now, that's new for them to recommend, and it's important that they have recommended it because it speaks to how important building muscle and strength is. The ACSM recommends two days per week lifting, eight to 10 exercises for all the major muscle groups, and you lift 8 to 12 repetitions. The major muscle groups are your chest, back, shoulders, arms, abdominal muscles, and legs.
So the complete guideline from the ACSM is three to five days per week for 20 to 60 minutes of aerobic conditioning, and two days of weight lifting.
That's more formal exercise, but then the Surgeon General has a different guideline: Accumulate 30 minutes of moderate intensity physical activity on five or more days of the week. There are two key words/phrases in the Surgeon General's recommendation. Number one is accumulate, which means you can do 10 minutes in the morning, 10 minutes later on in the afternoon, and 10 minutes in the evening, or you could do two bouts of 15 minutes, or one bout of 30. The second key is moderate intensity, which means that you feel warm and slightly out of breath when you're doing the activity.