Race cars often don't have a speedometer. What they do have is a tachometer that shows how fast the engine is revving.
A heart rate monitor is a tachometer for the human body -- it tells a user how quickly the heart is beating during exercise. Sports- and fitness-related use of the device has mushroomed since its invention in 1977, but many people don't know how to use one effectively. For starters, simple formulas to determine heart rate training zones aren't reliable. A monitor should be used not just to achieve a target, but as a regulator to avoid overtraining. The devices, although generally accurate, can sometimes generate false readings that cause unnecessary worry. And for the easily obsessed, focusing too much on numbers can turn a fun bike ride into a laboratory experiment.
Most monitors have a chest strap sensor that picks up and transmits electrical impulses from the heart to a receiver, worn on the wrist or handlebars of a bike. The receiver converts signals from the strap to a digital display of beats per minute. Strapless models are also available. Basic monitors cost less than $100 and display heart rate and time. Fancier models record heart rates during a workout and can set alarms for high and low heart rate zone limits. Other models integrate bike computer functions, such as speed and distance, or use GPS satellite signals to determine speed, distance, location and altitude in addition to recording heart rate.
"A heart rate monitor allows an individual to make any activity into a healthful and beneficial exercise, such as walking the dog or even cleaning your house, because you can modulate your effort to achieve the exercise effect," says Jose Maresma-Fois, an exercise physiologist with heart rate monitor manufacturer Polar Electro.
The health benefits of exercise aren't gained without enough intensity. The American College of Sports Medicine and the American Heart Assn. suggest that healthy individuals under 65 do moderately intense cardio exercise 30 minutes a day, five days a week or vigorously intense cardio 20 minutes a day, three days a week, in addition to strength training and stretching.
Determining what is "moderately intense" or "vigorously intense" is the rub. That's where heart rate monitors and training zones come in.
Finding a training zone
Most gyms have one on the wall -- a multihued chart that shows a single heart rate training zone based on age. The zones are derived from a commonly used formula to estimate a person's maximum heart rate: 220 minus age. That rate is genetically fixed for a given activity and declines about one beat per year with age (eventually reaching zero).
But experts say these charts are oversimplified and that for many people they are simply wrong.
"There are plenty of exceptions to that rule, both above and below," says cardiologist and cyclist Dr. John Ellis of Thousand Oaks. "It's a very general guideline, and your results may vary."
A person's maximum heart rate can differ by as many as 30 beats per minute from what the formula produces. Maximum heart rate also varies by activity. So to make heart rate monitors useful, exercisers first need to determine their maximum heart rate for each activity. Runners can establish their actual maximum heart rate during stress tests in which a doctor monitors heart rhythms at increasing exercise levels on a treadmill until the heart rate stops increasing. There is also a do-it-yourself method.
Joe Friel, a coach and author of 10 books about training for endurance athletes, says the truly motivated can determine their maximum heart rate by doing a series of intense intervals while cycling or running. This is like a stress test, except there are no doctors, nurses or crash cart handy if there are problems. After warming up, performing a series of three all-out uphill efforts of two minutes each with 30-second rests will usually peg the heart rate.
For the weekend athlete, a heart rate monitor can be as much a governor as a goad to keep from overexercising.
"Weekenders often overtrain," says Maresma-Fois. "Too many people think they have to train till they puke. It's in vogue right now to do high-intensity work to burn calories. That's fine, but too many people go out and injure themselves."
Cyclist Steve Gottschalk, 54, rides in the San Fernando Valley and Ventura County wearing a heart rate monitor. "I'm not a young chicken anymore," he says. "I pay attention to my heart rate. If I get above a certain level, I back off."
Endurance athletes and coaches use heart rate monitors that record training sessions to fine-tune training programs.
Frequency, duration and intensity are the three basic exercise variables, says Friel. The first two variables can be tracked with a calendar and a watch, but measuring intensity without a device is difficult. Because heart rate responds to stress on the body, measuring and recording heart rate during workouts allow coaches such as Friel to prescribe quantifiable dosages of exercise.
The dosages are expressed as time in a specific heart rate zone. Many coaches, rather than use a single heart rate zone for exercise, will break down heart rates into four or five zones from easy to maximal effort. These zones are determined as a percentage of a person's measured maximum heart rate or lactate threshold (the point where the body produces more lactic acid than it can process).
Exercises to increase VO2 max, the ability of the body to use oxygen, could include a warm-up in zone 1 (less than 60% of max heart rate), then a series of short efforts in zone 4 (70% to 80% of max), then a cool-down in zone 1. A workout to increase lactate threshold that improves a cyclist's ability to climb hills might include a series of longer efforts in zone 3 (70% to 80% of max).
All of these carefully scripted workouts are possible with heart rate monitors, which makers advertise as "EKG accurate." That's not exactly true, although most are precise enough for training purposes. Tests for The Times of six different models in a cardiology laboratory showed that, though none of the monitors precisely tracked the EKG-measured heart rates, differences were usually only a few beats per second.
"Accuracy in a heart rate monitor is nice to have," says Friel, "but what you want is reliability." The reading should be consistent from day to day. "Like a bathroom scale, what you want to know is that the heart rate is changing, not the device."
Most users of heart rate monitors have experienced situations where the indicated rate spikes to nearly twice its real value. Interference from power lines, cellphone towers or other monitors can all cause false readings. That cost cyclist Gottschalk, of the west San Fernando Valley, an unnecessary night in a hospital.
The model he uses records heart rate readings, which Gottschalk downloads onto his computer after a ride. He noticed after one ride that his rate had spiked to a level he'd never seen before. He didn't think anything of it until a subsequent ride showed a heart rate of 241 beats per minute for 30 seconds -- at least 50 beats higher than his normal maximum.
"My anxiety kicked in," says Gottschalk. He saw his doctor, who did an EKG, which was normal, and sent him to a hospital for blood work. At the hospital he was kept overnight for observation. In the morning he had another stress test and an echocardiogram. All the tests were negative.
Gottschalk's monitor has a built-in GPS that when downloaded shows his route on a map. He found that both abnormal readings came within 100 yards of each other. When Gottschalk visited that spot, he saw a new cellphone tower.
There doesn't seem to be a simple answer to this problem, other than stopping and taking a pulse manually to compare to the reading on the heart rate monitor, and avoiding running under power lines.
Does worry about false readings or constantly looking at a digital readout take away from the fun of a run or a ride? Possibly.
"I'm a slave to my monitor," says bicycle racer Eddie Morris of Newbury Park. "You spend your whole workout staring at your heart rate monitor."
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Your heart (rate) on your sleeve
Most of these traditional style heart-rate monitors were remarkably accurate when tested against a laboratory EKG machine.
-- Bill Becher
In the zone
Polar F6: Basic model designed for recreational exercisers, calculates "Own Zone" training zones; coded transmission.
Likes: Accurate in lab tests against an EKG; simple to operate; personal exercise zones can be calculated without an intense interval session or set manually.
Dislikes: Entire transmitter must be replaced when the built-in battery is exhausted.
Price: $119.95. (800) 227-1314; www.polarusa.com.
Polar RS 800: All the bells and whistles for serious exercise geeks; coded transmission and optional GPS and stride sensors
Likes: Comfortable, soft chest strap; data display can be customized; measures recovery state; works with the included training analysis software.
Dislikes: Separate GPS sensor must be worn for speed and distance; no mapping capability.
Price: $499.95. (800) 227-1314; www.polarusa.com.
GPS on the wrist
Garmin Forerunner 305: Advanced unit for people who love data and want to know where they've been.
Likes: Large, customizable displays, coded transmission, GPS integrated in the wrist unit; workout routes can be mapped using Google Earth.
Dislikes: Bulky; users are going to have to read the manual.
Price: $323.06. (800) 800-1020; www.garmin.com.
Suunto T1: New base model has coded transmission; can display current, average and maximum heart rate and calories burned.
Likes: Classy looks; easy to use; additional analog display of heart rate and zones; buttons can be locked.
Dislikes: Not compatible with company's speed and distance pods; display can be hard to read.
Price: $99. www.suunto.com.
Suunto T4: Adds more memory logs, computes "training effect" and is compatible with accessories that measure speed and distance.
Likes: Same stylish look as T1 but with more features.
Dislikes: Can be hard to read.
Price: $199. www.suunto.com.
Light and easy
Timex Zone Trainer: The company's more-than-basic model includes zones, averages, recovery timer and calories burned.
Likes: Small, light unit; easy.
Dislikes: Some readings of up to five beats per minute above or below the EKG; lowest transmitter range of units tested.
Price: $90. (800) 448-4639; www.timex.com.
Bill Becher can be reached at email@example.com.