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There is more than one way to gauge the intensity of your workout.
updated 1/22/2008 8:41:27 AM ET 2008-01-22T13:41:27

Is it OK to exercise beyond your target heart rate? Should you work out in the "fat-burning zone" to lose more weight? Smart Fitness answers your workout queries.

Have an exercise question? To e-mail us, click here. We’ll post select answers in future columns.

Q:  I push myself hard when I'm jogging and it feels great both during the exercise and after. But I often exceed my target heart rate while working out. Is that OK?

A: Certainly people can and sometimes do push themselves too far during exercise, particularly if they are out of shape, engage in grueling endurance activities or over-exert themselves in scorching temperatures.

But you say you're feeling great at the intensity you're working at. So what gives? It's possible that your target heart rate (THR) calculation is considerably off the mark.

The traditional formula for calculating maximum heart rate — the fastest your heart can pump — is 220 minus your age. Trainers often suggest that people doing moderate-intensity activity work out at a THR of 50 percent to 70 percent of their maximum heart rate, while those doing high-intensity activity work at 70 percent to 85 percent of their max. Pushing harder is generally considered inadvisable, and shouldn't actually feel good since your heart can't go full speed ahead for very long.

The problem, though, is that this formula gives averages that aren't precise for everyone, says exercise physiologist Michael Bracko, a spokesperson for the American College of Sports Medicine and director of the Institute for Hockey Research in Calgary, Alberta, Canada.

"The standard '220 minus age' is not accurate," he says. "It produces numbers that are very low."

He says the following, more complicated formula is better:

• 220 - Age = Theoretical Max Heart Rate
• Theoretical Max Heart Rate - Resting Heart Rate = Range
• Range x .5 + Resting Heart Rate = 50 percent intensity
Range x .6 + Resting Heart Rate = 60 percent intensity
Range x .7 + Resting Heart Rate = 70 percent intensity
Range x .8 + Resting Heart Rate = 80 percent intensity

Though not perfect, either, these calculations will result in THRs that are higher — and more realistic — than the traditional formula, says Bracko.

Still, most people really don't need to crunch a lot of numbers to stay fit, experts say.

"Having a target heart rate and monitoring the exercising heart rate is most important in the early stages of a cardio training program so as not to train too hard," Bracko says. "As a person continues to train, they can use a rating of perceived exertion because they will know how hard they are training by how their body feels."

The Borg Rating of Perceived Exertion, for example, is a subjective test in which you rate how hard you're working out on a scale of 6 (no exertion at all) to 20 (maximal exertion). Ideally, according to this scale, most people should be somewhere in the middle, around 12 to 14.

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Another test is even simpler. It's the talk test: If you can sing during exercise, it's too easy. If you can talk, it's just right. And if you can't talk (or sing), it's too hard.

Ultimately, which approach you use is up to your personal preference and your goals, says Bracko. If you're training for a sporting event, you may be acutely interested in your heart rate, tracking every beat to gauge your progress. But if you jog mainly to stay healthy, the talk test may do just fine.

"I'm an advocate of making exercise as easy as possible to help with compliance," says Bracko. "Therefore, I don't like to have people do math while they exercise."

Q: I am wondering what the difference is between the fat-burning and cardio heart rates on the machines at the gym? If you are trying to lose weight, does it matter which mode you are using?

A: There's a popular misconception that to lose weight it's better to work out at a lower intensity — in the so-called fat-burning zone, which is usually somewhere around 50 percent to 60 percent of your maximum heart rate — than at a higher intensity. So some cardio machine monitors tell users whether they're working out in the fat-burning zone or in a more intense zone for training the heart.

But you don't have to trade off one for the other, says Dr. Jeffrey Tanji, associate medical director of sports medicine at the University of California at Davis.

"I would consider the 'fat burning zone' to be a myth," he says. "All exercise and for that matter, all movement, burns a combination of carbohydrates and fat."

Depending on how hard we work and our individual metabolisms, he says, some people burn more carbs or fat than others during a workout. And generally speaking, we all tend to burn proportionately more carbs and less fat as exercise intensity increases. But ultimately, what matters most for weight loss is how many calories we burn in total — not where they're coming from.

If you work out hard, you'll burn more calories minute for minute than if you cruise along at a more comfortable pace. Of course, you could work out at that more comfortable pace for a longer period of time and burn just as many calories overall.

The key is to find a type of exercise and an intensity that you like — and then to stick with it.

Q: It's so cumbersome to monitor heart rate in order to stay in the fat-burning zone. If I run 3 miles, how much greater is the benefit if I stay in the zone?

A: As discussed above, you don't need to worry about staying in the fat-burning zone. You won't lose any more weight by staying in the zone, and it'll take you longer to finish your workout.

If you like tracking your heart rate and your performance though, as many runners do, you could invest in a heart rate monitor that you strap on. It's easier than trying to accurately calculate your beats per minute by taking your pulse.

Otherwise, just get out there and hit your stride.