Heart Rate Monitor Inaccuracy

BY Hal Higdon

Hal Higdon suggests a number of reasons why a heart rate monitor might suddenly offer false numbers.

Have a question about running? You’re in the right place. Every Tuesday, world-renowned coach, author and athlete Hal Higdon posts and answers athlete questions here. You can submit your question by joining the discussions on Hal Higdon’s Virtual Training Bulletin Boards.


While running on the treadmill, sometimes my heart rate monitor appears to be inaccurate towards the end of the run. For instance, the other day I was running at a pace to keep my heart rate between 125 and 130 beats per minute. Toward the end of the run, my heart rate started to climb past 130, and I had to slow the treadmill down from 6.8 mph to 6.2 mph to stay in my target zone. All of the sudden, my heart rate jumped up to 147, and i had to drastically lower the speed to 4.0 mph. I have been able to run outside at a much higher pace for double the distance, and my heart rate stays consistent. Why is there such a difference on the treadmill?


There might be any number of reasons why a monitor might suddenly offer false numbers. There could be electronic disturbances indoors that interfere with accuracy (although this happens outdoors as well.) Perhaps it is the extra sweating in a warm, indoor environment causing the variations? There is also the possibility that once you hit the wall–indoors or out–you really hit the wall, and your heart rate takes a sudden jump. Not sure if this is true, but I throw it out as one explanation.

Apart from what your Magic Monitor tells you, what does your body tell you? Ignoring the numbers on the dial, does it feel like your heart rate suddenly increased? If so, there is a simple test: Jump off the treadmill, put finger to wrist and check your pulse rate the old-fashioned way.

But a warning: If your heart rate skyrockets for any reason, it might be a signal of hidden heart disease. If you have not had a recent physical, and if you are up in age, this might be the time do get a check-up to ward off bad things from happening.

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About Hal Higdon

Hal Higdon is a Contributing Editor for ‘Runner’s World‘ and author of 34 books, including the best-selling ‘Marathon: The Ultimate Training Guide’. He ran eight times in the Olympic Trials and won four world masters championships. Higdon estimates that over a quarter of a million runners have finished marathons using his training programs, and he also offers additional interactive programs at all distances through TrainingPeaks. Hal uses TrainingPeaks to power his interactive marathon and half marathon training plans — check out more of Hal Higdon’s training plans on his website.