Q:

What's the best way to find my maximum heart rate? I've heard the "220 minus your age" formula is inaccurate.

A: Yes, the formula that involves subtracting your age from 220 is "very old school and has no scientific background," says ultra-endurance athlete Sally Edwards, author of several books about heart-rate training, including The Heart Rate Guide Book to Heart Zone Training (Heart Zone Publishing, 1999). This formula has remained popular over the years because it's simple, but it assumes that your maximum heart rate will decrease by about one beat per year, which isn't true for everyone. "Everyone's max heart rate is hugely different, regardless of age or fitness," Edwards says. "The only way to know it is to test it."

The most precise tests are done in a lab. While you're running on a treadmill or pedaling a stationary bike, the tester will gradually crank up the intensity every 15 seconds and within a few minutes you'll reach your maximum heart rate. A more practical, less grueling approach is to test yourself using a "submax" method; you'll increase your intensity to a certain below-maximum level, then use various formulas to extrapolate what your maximum would be. A submax test isn't as precise as a max test, Edwards says, "but you can get a pretty accurate idea, within five beats." She recommends taking two or three different submax tests and averaging the results.

One example of a submax test is the step test. Step up and down on an 8-to 10-inch step for three minutes without pausing between steps, then take your average heart rate (HR) for one minute (see last question on next page for information on heart-rate monitors that can determine this) and add the appropriate estimate factor for your fitness level using the formula that follows. To ensure consistency, keep both the step height and the cadence the same each time you test yourself.

Avg. HR last min. + Estimate factor = Estimate max HR

Estimate Factor:

Poor shape = 55; Average shape = 65; Excellent shape = 75; Competitor = 80

You'll find several other submax tests at heartzones.com. Once you've estimated your maximum heart rate, you can base your exercise program on different percentages of this maximum. The American College of Sports Medicine recommends working out in your "target zone" -- from 55 percent to 90 percent of your maximum heart rate -- to burn the most calories and gain aerobic fitness without risking overexertion or injury. Exercising near the 90 percent range will result in higher calorie burn, but it's tough to maintain this level for long periods. Interval training, or alternating between the top, middle and lower ends of your target zone, is one way to gradually train your body to tolerate the higher intensity of the 90 percent range.