Scottsdale, Arizona - When you work out, are you working hard or hardly working? Exercising at the correct intensity can help you get the most out of your physical activity - making sure you're not overdoing or even underdoing it. Here's a look at what exercise intensity means and how to make it work for you.

Choosing your exercise intensity

How do you know how hard you should be exercising? For most healthy adults, the Department of Health and Human Services recommends these exercise guidelines:

• Aerobic activity. Get at least 150 minutes a week of moderate aerobic activity — such as brisk walking, swimming or mowing the lawn — or 75 minutes a week of vigorous aerobic activity — such as running or aerobic dancing. You can also do a combination of moderate and vigorous activity, preferably spread throughout the course of a week.
• Strength training. Do strength training exercises at least twice a week. Consider free weights, weight machines or activities that use your own body weight — such as rock climbing or heavy gardening. The amount of time for each session is up to you.

To reap the most health benefits from exercise, your exercise intensity must generally be at a moderate or vigorous level. For weight loss, the more intense your exercise, or the longer you exercise, the more calories you burn.

However, balance is important. Overdoing it can increase your risk of soreness, injury and burnout. If you're new to regular exercise and physical activity, you may need to start out at a light intensity and gradually build up to a moderate or vigorous intensity.

So think about your reasons for exercising. Do you want to improve your fitness, lose weight, train for a competition or do a combination of these? Your answer will help determine the appropriate level of exercise intensity. Be realistic and don't push yourself too hard, too fast. Fitness is a lifetime project, not a sprint. Of course, if you have any medical conditions or you're not sure what your exercise intensity should be, talk to your doctor.

Understanding exercise intensity

When you're doing aerobic activity, such as walking or biking, exercise intensity correlates with how hard the activity feels to you. Exercise intensity also is reflected in your breathing and heart rate, whether you're sweating, and how tired your muscles feel.

There are two basic ways to measure exercise intensity:

• How you feel. Exercise intensity is a subjective measure of how hard physical activity feels to you while you're doing it — your perceived exertion. Your perceived level of exertion may be different from what someone else feels doing the same exercise. For example, what feels to you like a hard run can feel like an easy workout to someone who's more fit.
• Your heart rate. Your heart rate offers a more objective look at exercise intensity. In general, the higher your heart rate during physical activity, the higher the exercise intensity.

Studies show that your perceived exertion correlates well with your heart rate. So if you think you're working hard, your heart rate is likely elevated.

You can use either way of gauging exercise intensity. If you like technology and care about the numbers, a heart rate monitor might be a useful device for you. If you feel you're in tune with your body and your level of exertion, you likely will do fine without a monitor.

Gauging intensity by how you feel

Here are some clues to help you judge your exercise intensity.

Moderate exercise intensity

Moderate activity feels somewhat hard. Here are clues that your exercise intensity is at a moderate level:

• Your breathing quickens, but you're not out of breath.
• You develop a light sweat after about 10 minutes of activity.
• You can carry on a conversation, but you can't sing.

Vigorous exercise intensity

Vigorous activity feels challenging. Here are clues that your exercise intensity is at a vigorous level:

• Your breathing is deep and rapid.
• You develop a sweat after a few minutes of activity.
• You can't say more than a few words without pausing for breath.'

Overexerting yourself

Beware of pushing yourself too hard too often. If you're short of breath, in pain or can't work out as long as you'd planned, your exercise intensity is probably higher than your fitness level allows. Back off a bit and build intensity gradually.

Gauging intensity using your heart rate

Another way to gauge your exercise intensity is to see how hard your heart is beating during physical activity. To use this method, you first have to figure out your maximum heart rate - the upper limit of what your cardiovascular system can handle during physical activity.

The basic way to calculate your maximum heart rate is to subtract your age from 220. For example, if you're 45 years old, subtract 45 from 220 to get a maximum heart rate of 175. This is the maximum number of times your heart should beat per minute while you're exercising.

Once you know your maximum heart rate, you can calculate your desired target heart rate zone — the level at which your heart is being exercised and conditioned but not overworked.

Here's how heart rate matches up with exercise intensity levels:

• Moderate exercise intensity: 50 to 70 percent of your maximum heart rate
• Vigorous exercise intensity: 70 to 85 percent of your maximum heart rate

If you're not fit or you're just beginning an exercise program, aim for the lower end of your target zone (50 percent). Then, gradually build up the intensity. If you're healthy and want a vigorous intensity, opt for the higher end of the zone.

How to determine your target zone

To determine your desired target heart rate zone, use an online calculator. Or, here's a simple way to do the math yourself. If you're aiming for a target heart rate of 70 to 85 percent, which is in the vigorous range, you would calculate it like this:

• Subtract your age from 220 to get your maximum heart rate.
• Multiple that number by 0.7 (70 percent) to determine the lower end of your target heart rate zone.
• Multiply your maximum heart rate by 0.85 (85 percent) to determine the upper end of your target heart rate zone.

For example, say your age is 45 and you want to figure out your target heart rate zone for vigorous intensity exercise. Subtract 45 from 220 to get 175 — this is your maximum heart rate. To get the lower end of your target zone, multiply 175 by 0.7 to get 123. To get the higher end, multiply 175 by 0.85 to get 149. So your target heart rate zone for vigorous exercise intensity is 123 to 149 beats per minute.

How to tell if you're in the zone

So how do you know if you're in your target heart rate zone? Use these steps to check your heart rate during exercise:

• Stop momentarily.
• Take your pulse for 15 seconds. To check your pulse over your carotid artery, place your index and third fingers on your neck to the side of your windpipe. To check your pulse at your wrist, place two fingers between the bone and the tendon over your radial artery — which is located on the thumb side of your wrist.
• Multiply this number by 4 to calculate your beats per minute.

Here's an example: You stop exercising and take your pulse for 15 seconds, getting 33 beats. Multiply 33 by 4, to get 132.  If you're 45 years old, this puts you in the middle of your target heart rate zone for vigorous exercise, since that zone is 123 to 149 beats per minute. If you're under or over your target heart rate zone, adjust your exercise intensity.

Target heart rate tips

It's important to note that maximum heart rate is just a guide. You may have a higher or lower maximum heart rate, sometimes by as much as 15 to 20 beats per minute. If you want a more definitive range, consider discussing your target heart rate zone with an exercise physiologist or a personal trainer.

Generally only elite athletes are concerned about this level of precision. They may also use slightly different calculations that take into account gender differences in target heart rate zones. These differences are so small that most casual athletes don't need separate calculations for men and women.

Also note that several types of medications can lower your maximum heart rate and, therefore, lower your target heart rate zone. Ask your doctor if you need to use a lower target heart rate zone because of any medications you take or medical conditions you have.

Interestingly, research has shown that interval training, which includes short bouts (60 to 90 seconds) of higher intensity exercise interspersed throughout your workout, is well tolerated, even by those with certain cardiac conditions. This type of training is also very effective at increasing your cardiovascular fitness.

Reap the rewards of exercise intensity

You'll get the most from your workouts if you're exercising at the proper exercise intensity for your health and fitness goals. If you're not feeling any exertion or your heart rate is too low, pick up the pace. If you're worried that you're pushing yourself too hard or your heart rate is too high, back off a bit.