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Maximize your time. Workout Smart!

For years, keeping fit has meant hitting your target heart rate zone. Unfortunately, the formula is only an estimate based on your theoretical maximal heart rate. Your true maximal heart rate may be as much as 15 beats per minute higher or lower. Consequently, you may be exercising at an intensity that is either too easy or too strenuous, and potentially dangerous to your health.

“You should never rely solely on the numbers,” says Patrick Hagerman, EdD, Clinical Assistant Professor of Exercise and Sport Science at the University of Tulsa in Oklahoma. Factors that may affect your maximal heart rate include certain drugs, such as beta-blockers, and eating too few carbohydrates. Other factors: stress, heat, dehydration, and the type of exercise itself.

It can get complicated and unrealistic to factor in these things just before a jog. Fortunately, there’s an easier way; it’s called rating of perceived exertion. You rate the intensity using a scale of 0 to 10. A zero equates to sitting on the couch eating potato chips. A 10 is an all-out, gasping-for-air, praying-for-deliverance sprint.

“You have to listen to your whole body and rate the totality of the sensations,” explains Robert Robergs, PhD, Director of the Exercise Physiology Laboratories at the University of New Mexico in Albuquerque. If a walk feels somewhat hard and a light sweat is dotting your brow, give it a 4. For an optimal workout, stay between 4 and 6. At the 6 level, says Hagerman, you should be “somewhat out of breath. A lot of physical discomfort is a sign you’re overdoing it, no matter what your heart rate monitor says. Ease off a bit.