Measuring Progress : Health: There are no industry standards to ensure that exercise machines provide accurate readings. Experts warn some monitors can err by as much as 20%.
So, you went to the gym, hopped on the stair-climbing machine and worked to near exhaustion. And, the machine’s monitor rewarded you with news you had burned off 400 calories.
It can’t hurt, you think, to treat yourself to that tempting, 282-calorie piece of apple pie.
Don’t be so sure, say some exercise physiologists and equipment manufacturers.
In reality, the 400 calories may have been only 250. Or 300. Or 500.
The electronic monitors--feedback devices that tell exercisers such things as heart rate, miles pedaled or calories burned--are often imprecise or inaccurate, experts say.
“There are no accuracy standards set for machines. There are ones that are really accurate and ones that aren’t accurate,” says Jim Erwin, an exercise physiologist at the Centinela Hospital Fitness Institute in Inglewood. Moreover, some monitors are intended only to give approximate readouts.
Americans have responded to the new generation of sophisticated exercise equipment in a big way. Participation in stair-climbing has increased by more than 500% since 1987 with about 1.8 million regular participants in 1990, according to a recent poll by the Sporting Goods Manufacturers Assn.
Treadmill use has increased by 300% over three years with about 2 million regular participants in 1990. Cycling and walking are also high on the list of favorite recreational pursuits.
But without industry standards to ensure that equipment monitors provide accurate readings, how do exercisers know if the feedback they are getting is right?
“I don’t know how the consumer would know,” says Jeff Zwiefel, an exercise physiologist with the Exercise for Life Institute, an information bureau sponsored by NordicTrack. “I would base it on the quality of the product and the brand name of the product.”
Says Michael Hoffman, of Life Fitness Inc., the Irvine-based maker of the Lifecycle Aerobic Trainer and other machines: “There is no ‘Federal Trade Commission’ for exercise products. It’s a self-policing industry at this point. The standards are a result of the integrity of the manufacturers and the increasing sophistication of the buyers of the product.”
Exercise experts, however, offer several tips to guide consumers. Feedback devices that give distance, speed, repetitions or time are usually technically uncomplicated and accurate, Zwiefel says. But some devices that give heart rates and calories burned have a larger margin for error.
For example, according to Zwiefel, consumers should ask themselves these questions: Does the equipment require you to enter weight, height, age and sex before beginning to exercise? If not--or if it only demands one parameter, such as weight--you could be getting a very inaccurate reading.
“A lot of people have an interest in seeing their caloric expenditure. But it’s usually a rough estimate,” Zwiefel says.
If the machine doesn’t allow the user to input any parameters, such as weight and sex, it is probably pre-set to calculate calories lost during the exercise by an average-sized person of about 150 pounds. If you weigh 110 or 220, you will get a very rough estimate.
But even if you can input height, weight, sex and age, the readout will be approximate. The machines do not compute muscle mass or individual metabolism, both of which affect calorie expenditure.
“I personally go to a gym and use a stair-climber and cycle and I’m not losing the amount of weight those devices tell me I’m burning,” says John Bergeron, chairman of Precise International, a manufacturer of exercise feedback devices.
“It’s a plus-or-minus 20% (accuracy) range for calorie expenditure. That’s a pretty wide range. So it’s more of an indication. People burn calories so differently. You burn more calories if you have more muscle than someone else, but you can be the same exact height and weight.”
Erwin verifies studies show caloric feedback devices are accurate to within about plus or minus 20%.
Heart-rate readings can also vary tremendously depending on the equipment, studies show. While some machines use heart-rate monitors, other have pulse meters.
The most expensive type of heart monitor is an electronic device that straps to the chest with electrodes. This device, used by cardiac rehab patients, measures the heart’s electrical impulses and is highly accurate, says Bergeron.
But pulse monitors--which include devices that clip to the earlobe or are strapped around a fingertip--rely on optical technology.
“This device uses an infrared (device) that senses changes in coloration of the skin,” Bergeron says. “When the heart beats, it pushes a flow of blood. The device measures the relative change in color. The problem with that device is it can move around and give false readings. Pulse meters are inherently inaccurate.”
While pulse devices may be fairly accurate for light to moderate workouts, they are particularly inaccurate for heavy exercise--such as those raising the heart rate to more than 140 beats per minute, says physiologist Erwin.
Product reputation and cost may not be good indicators of accuracy. A recent U.S. News & World Report study of 16 heart-rate monitors showed that price and accuracy were not necessarily related. The findings ranged from one completely accurate device to another off by 11 beats per minute.
Hoffman, of Life Fitness Inc., says the exercise-machine industry has become increasingly concerned about the accuracy of monitoring devices:
“People have less and less time to exercise these days. When they go into a club they want to get maximum results in the least amount of time. They need ways to verify what they’ve accomplished other than just how they feel.”
Inaccurate readouts also can throw off calorie-counting dieters.
“They see a readout that says ‘I’ve expended 325 calories.’ Based on that, people regulate their diets,” Hoffman says. “What if someone eats according to that readout and that readout is wrong?”
Even worse, inaccurate readouts could cause injury or other harm, although industry spokesmen say they know of no instances in which exercisers have been seriously injured because of an inaccurate monitoring device. Heart patients and pregnant women are among those whom physicians instruct to closely monitor heart rates during exercise.
“In some cases inaccurate devices can be harmful, especially if someone has a blood pressure problem or heart problem,” says Erwin. “If that pulse meter is off and they don’t know they are above (the given reading), they could be having serious ischemia (loss of oxygen) in the heart.”
So why even use the feedback devices?
Just ask any exerciser how exciting it is to pedal a stationary bike for 45 minutes while staring at a blank wall.
“People want to know where they’re at,” says physiologist Zwiefel. “It increases compliance and retention and allows them to work toward a goal. It allows them to compete with themselves and with other people. People need something to take their minds off what they’re doing.”
Joe Sanders agrees.
“Working out in a closed room is pretty boring,” says the 43-year-old Whittier man. “For me, to be able to get through the workout, I set up these little challenges for myself. The monitoring devices do function as a motivational factor. If I didn’t keep a log of what I was doing every day, I think I’d lose interest.”
Still, Sanders is among those often frustrated by what the feedback devices tell him. He climbs on a stationary exercise bike, sets the intensity level a little higher than the previous day and starts pedaling. But, he says, “No matter how hard I work I seem to end up with the same number of miles pedaled and the same amount of calories burned.”
He doesn’t seem to fare much better on the treadmill. The electronic readout that tells him how many calories he has burned always looks a little low, he complains, adding sheepishly: “I’m sure that’s a bias a lot of people have.”
Zwiefel says that while manufacturers are looking for even more bells and whistles, “the general public is going to become much more demanding of accuracy. People will demand that these devices be user-friendly and durable.”
To prove their products’ accuracy, some manufacturers have begun to submit their devices for independent testing. According to Hoffman, the test abstracts are then submitted to the American College of Sports Medicine where they are reviewed by exercise experts and accepted or rejected.
“That’s like getting a Good Housekeeping seal of approval,” says Hoffman.
In the absence of widespread clinical testing of exercise machines, however, experts suggest consumers gauge their workouts the old-fashioned way: If you work up a sweat, push harder than you did the day before (without feeling pain) and end up feeling a good sort of tired, you probably achieved a terrific workout.
Says Zwiefel: “There is nothing better than simple perceived exertion--the feeling of working hard.”
