What's So Great About Cardio?

Gauging Workout Intensity

How can you tell if you're exercising enough to get your heart fit?

One method is to measure your target heart rate, or the rate at which your heart should be beating in the middle of your exercise routine. To calculate your target heart rate, first find your maximum heart rate by subtracting your age from 220. Then take 70 to 85 percent of the maximum heart rate to get your target heart rate. For example, if you are 40 years old, your target heart rate would be 220-40 = 180, times 0.70 to .85, or 126 to 175.

To measure your heart rate, take your pulse five minutes into your exercise routine. Place your fingers on the radial artery at the center of your wrist and count the beats for ten seconds. Based on your age, the number of beats per ten seconds should be:

At age 20: 23 to 28 beats At age 30: 22 to 27 beats At age 40: 21 to 26 beats At age 50: 20 to 24 beats At age 60: 18 to 23 beats

If you're not a numbers person, the Borg Perceived Exertion Scale, a scale from six to 20 that measures the intensity of a workout, is another option. "Perceived exertion" means how hard you think your body is working during an activity based on the sensations you experience during the activity, such as an increased breathing rate, increased sweating, and muscle fatigue.

Though it's a subjective measurement -- you're the one evaluating it -- experts agree that your perception of physical exertion is actually a good estimate of your heart rate during the activity. Once you become more aware of how your body responds to different activity levels, you can change the intensity by increasing or decreasing your movement.

The Borg Scale is easy to use. Use the number ranges below to describe the intensity of your physical activity based on how your body responds:

6-12: Ranges from no exertion to very light and light exertion. A person exercising at the midpoint of this range of intensity would be moving at what's normal for her -- walking at her regular pace, for example.

13-17: Ranges from somewhat hard, to hard and very hard exertion. A person exercising at the lower end of this range might find the activity hard exertion-wise, but feel comfortable enough to continue. The upper range would be described as "strenuous" exertion.

19-20: Ranges from extremely hard to maximal exertion. A person exercising at this intensity is exercising extremely strenuously -- possibly at intensity stronger than they've ever experienced before.

Another good gauge of intensity is the "talk test." You should exercise at a level where you feel as if you're working hard, but still be able to have a conversation," Dr. Goldberg says. As you become more experienced with exercise, you'll gain a better sense of how much you're exerting yourself.

According to the AHA, exercising for 30 to 60 minutes at 50 to 80 percent of your maximum capacity on most days of the week will help you exceed a moderate level of cardiac fitness.