Is Your Bike Lying to You?

Here's how to tell if it's telling you the whole truth about your performance.


After a killer indoor-cycling class, you might climb off the bike, feeling incredibly virtuous after the computer informs you that you’ve just torched 650 calories in less than an hour. Woo-hoo! But wait—is it telling you the truth? Maybe not, according to researchers, because a variety of hidden factors can affect the accuracy of the computer feedback from exercise machines.

The good news is, stationary cycles tend to be more reliable in this respect than most cardio machines are.

In an experiment done for Good Morning America in 2010, researchers from the University of California San Francisco’s Human Performance Center compared the accuracy of the calorie-burn estimates on various cardio machines: As it turned out, stationary bikes were the most accurate of all, but even they overestimated the calorie expenditure by 7 percent. The elliptical machine was the worst offender, overestimating calories burned by 42 percent. The treadmill and the stair climber came in with overestimates of 13 and 12 percent, respectively.

Here’s the deal: With any cardio machine, including stationary bikes, if you’re not asked to enter your body weight, that’s a tip-off that the calorie-burning calculations are probably based on a reference weight, which may be quite different from your weight. Even if the machine does request that you enter your weight, it won’t account for differences in body composition; this is significant because someone “with a greater percentage of lean muscle mass will burn more calories at a given intensity” in a given time period, according to the American Council on Exercise.

(That’s because pound for pound muscle burns more calories than body fat does.)

The machine also won’t account for individual differences in fitness level—beginners will burn calories at a faster rate because the work load will be harder for them—or age or gender. Nor can the calculator account for your cycling position, which could affect the rate at which you burn calories.

If you’re doing a heavy standing climb, for example, you’ll burn more calories than if you were to pedal against the same resistance at the same pace while seated. The reason: In a standing position, you’ll be supporting your own weight, which cranks up the challenge and burns more calories as a result. Then again, if you’re leaning heavily on the handlebars while you pedal, you’ll be offloading some of your weight, which can reduce your calorie-burning rate.

There also can be considerable differences from one bike to another in terms of how they’re calibrated. Even on the same models, the resistance might be set more tightly on some bikes than on others. Plus, wear and tear to the cycle, which the computer software can’t factor in, can skew the calorie-burning calculations, as well as the watts, RPMs, and distance reports.

The bottom line: Don’t take the computer feedback at face value. Ultimately, the only way to really get truly personalized calorie-burning feedback is to use a heart-rate monitor, which factors in your weight, age, and other personal details along with changes in your heart rate to figure out how many calories you’re burning.

But even if the computers on indoor cycles aren’t 100 percent accurate, they can provide some value. You can use them as a rough gauge for how many calories you’re burning in any given workout (and perhaps boost their accuracy by subtracting 7 percent) or you can compare how hard you’re working from day to day, especially if you’re riding the same bike. Seeing those impressive numbers, workout after workout can inspire you to keep riding hard!

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