Times-Picayune (New Orleans, LA)
August 22, 2001 Wednesday

Research shows heart-rate maximum has significant variations

 Jack Curry Jr.

Exercisers who peg the intensity of their workouts to a formula based on how fast a human heart can beat may be doing a lot more or a lot less exercise than they think.

The most common formula for determining maximal heart rate -- a person's age subtracted from 220 -- yields an average age-predicted maximal heart rate, not a personal heart-rate maximum, a qualification many dedicated health buffs overlook when computing their training session target heart rates.

"The typical error in a heart-rate-max formula is between 5 to 11 percent," said Mark Loftin, a professor in the department of Health and Human Performance at UNO.

The true maximal heart rate of an exerciser may be 200 beats per minute, but within this statistical range it could be overestimated or underestimated by the formula by as much as 22 beats per minute -- a range of between 178 and 222 beats per minute.

Other physiologists feel the range in heart-rate maximums among individuals in a particular age group is even wider. A Cleveland cardiologist said 40 percent of his cardiac patients hit heart rates of more than 100 percent above their age predicted maximum during treadmill tests.

Exercisers who want an accurate, maximal heart rate must work for the knowledge. Motivated, dedicated athletes, willing to endure the physical stress, achieve maximal heart rates just before stopping from exhaustion, the end result of performing standard tests to measure maximum cardiovascular fitness. For everyone else, the formula serves as a convenient and less painful shortcut.

Yet, even when a person's true maximal heart rate is known, environmental factors can make the use of heart rate to measure effort an iffy process.

"So many factors can drive up heart rate. Heat and humidity are phenomenal stresses for the body and can drive a heart rate that may be 140 to 150 beats per minute to over 170 beats per minute," said Loftin, a marathon runner.

Exercisers wear inexpensive heart-rate monitors the size of wrist watches to get immediate, beat-by-beat feedback on how they are doing, allowing them to adjust their pace on the fly. They mix brief intervals of intense exercise at 85 to 90 percent of heart-rate maximum to increase capacity for exercise with longer times at lower intensity to boost endurance.

The ability to rate exercise intensity is important, but except for the serious athlete, it does not require any special monitoring devices, Loftin said.

Casual exercisers can improve their cardiovascular health using something as simple as the "talk test" to keep exercise beneficial, fun and safe. If the effort is too strenuous to maintain a conversation, slow down, Loftin said.

"I tend to like the perceived exertion charts, where exercisers rate how strenuous the exercise feels based on personal feedback such as how heavy the breathing is and if there is fatigue," Loftin said.

The charts, which rate exercise effort from very, very easy (6) to very, very hard (20), focus on what exercisers should be most in tune with already -- their bodies.

"One of the most important things we can do to monitor exercise is to listen to our bodies. We tend to ignore what is really happening to us, and when we do, we get into trouble," Loftin said.

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