Strange Heart Rate Data

By Marilyn Trout | 02/07/12
Strange Heart Rate Data

David Lendrum, “DSC_2894” July 17, 2006 via Flickr, Creative Commons Attribution.

We’ve teamed up with Marilyn Trout, certified USA Cycling Elite Coach to answer Voler Newsletter List members’ training questions. You can view her coach profile at Send your cycling inquiries to Marilyn, and for a limited time, if yours is selected to be answered in our Training column, Voler will send you a $20 gift certificate that can be used towards any purchase from the Voler Store at To submit your inquiry, e-mail her at, and type “Voler Training Question” in the subject line of the e-mail.

The following tip is a reprint of an August 2009 question submitted by Voler E-Mail List member Jerry Murr.

Strange Heart Rate Data

Hi Marilyn,

I am a 44 y/o cyclist that trains with Heart Rate... I have been doing so for about 8 years and have a pretty good idea when I'm pushing hard and when I'm not. My Lactate Threshold HR is ~175 and I saw a max HR of 194 back on May 30th in a Road Race.

Spent an hour on the spin bike yesterday to do some fast pedal drills and an hour and a half the day before that to do some 2 minute power intervals (stuck inside at work)... Today during my warm up I was heading out to do some Hill intervals and just felt like I was cruising along (RPE of maybe 3 or 4), when I glanced at my Heart Rate monitor it was at least 20 BPM higher than I expected; and it did that throughout my ride. I haven't seen a Max HR over 181 since May 30th! Today I saw 202!!! I saw some similar anomalies this past spring after Hockey season and getting back on the bike but I can't understand what the cause of this would be this time of year???? I got a clean bill of health last year from the doc and a Heart Scan, have no symptoms of any kind just some strange HR data?

Thank you,


Certainly, there could be an inerrant number that comes across your heart rate monitor due to some external electrical interference, such as power lines, however, let's consider a physiological scenario. My initial response would be centered around hydration. What was the weather like? Were you well hydrated going into the ride? What was your resting heart rate that morning?

"The weather was hot and sunny, 85-90 degrees, I chose not to do the hill intervals because my HR was so high during warm up. I thought that I was at least "normally" hydrated, I didn't check my resting HR but felt normal pre ride which usually means resting rate around 40. My only thought was that maybe I wasn't hydrated properly."

Our heart can be quite fickle and an unreliable training tool at times. Unlike a power meter that quantitatively measures your muscular performance undaunted by hydration, air temperature, core temperature, stress, anxiety, fatigue, or illness, your heart rate monitor gives a cardiovascular view of your body's response to the work being done. At times during racing, you are better off not knowing your heart rate because of all the factors that can stimulate it to pump faster. Is a heart rate monitor useful? You bet…but it's just one piece of the training puzzle.

When the heart rate rises due to these aforementioned factors, it is referred to as cardiac drift and it is not abnormal for a cyclist to experience a drift up to as much as 20 beats. In your situation, possibly not being hydrated going into the ride and certainly weather conditions which contribute to lowering body fluids even more, the blood plasma volume is decreased which lowers blood pressure. The body tries to maintain a stable blood pressure and somehow has to balance things between blood chemistry changes and the working muscles. To get the job done, the heart has to speed up. Cardiac drift can occur with a 2% loss of body fluids, however, this can be prevented if you are well hydrated going into a hot weather ride and every 10 to 15 during the exercise.

I commend you for your training wisdom in not pushing through the hill intervals under the given circumstances. As Joel Friel aptly states, "Cyclists who train smart always beat athletes who train hard."

Keep listening to your body,

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