I’ve always wondered how accurate heart rate monitors could possibly be at measuring calorie burn. I even wonder sometimes how accurate they are at measuring heart rate, but in that regard they tend to be pretty reliable. A study this month in the Journal of Strength and Conditioning Research compared calorie burn as estimated by a heart rate monitor to standard lab test measurements.
Heart rate monitors determine calorie burn by performing a calculation based on heart rate. This measurement is actually pretty accurate, for the most part. Up to a point, there is a close linear relationship between heart rate and energy expenditure. As heart rate climbs, energy expenditure also increases by a steady amount. This is true until hyperventilation takes place to remove acid buildup in the cells and blood.
Dr. Lloyd, the researcher in charge of this study, was curious about how arm action affects the accuracy of heart rate monitor measurements. A lot of arm involvement yields a higher heart rate per calorie burned, but heart rate monitors are calibrated for leg exercise with minimal arm involvement. Heart rate also increases with upper body work because of increased parasympathetic output. This effect increases even more if the arms are overhead, probably because the heart needs to work harder to pump blood against gravity than it does down to the legs.
In this study, Dr. Lloyd used a simple design. She compared a step routine using the arms and legs to the same routine using just the legs. She measured calorie expenditure using both a Polar F6 heart rate monitor and indirect calorimetry, which is the standard lab test for measuring calorie burn through oxygen consumption.
The results were a little funky. There was an increase in heart rate relative to energy expenditure when using the arms, which we knew would happen. Although the heart rate monitor did report increased calorie burn using the arms a little bit more than it should have, the increase wasn’t statistically significant. The weird part is that the monitor overestimated the calorie burn on both kinds of step routine, with and without the arms. It did so by nearly two calories per minute, which is a pretty big swing and a miss. So, while the heart rate monitor was indeed off in its prediction of calories, it wasn’t inaccurate in the way the researchers expected.
It’s unfortunate that people might not be getting the workout they think they are with the Polar F6, but to be honest, I don’t think it’s all that bad that the heart rate monitor overestimated the calorie burn. As long it’s the only monitor you use, you will get consistent readings with it. That said, it’s good to know you’ll need to push a little bit harder with a Polar F6 to get the exercise level you’re looking for. Just keep that in mind when using it.
Although the accuracy of heart rate monitors may get thrown off a small amount by a lot of arm work, if you’re still doing leg-intensive cardio, it should be accurate enough to get the job done. That is, as long as your heart rate monitor is accurate to begin with.
References:
1. Lisa Lloyd, “Is the Polar F6 Heart Rate Monitor Less Accurate During Aerobic Bench Stepping Because of Arm Movements?” Journal of Strength and Conditioning Research, DOI: 10.1519/JSC.0000000000000382
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