The Tell-Tale Heart Rate Monitor

As a person ages, the maximum rate at which his or her heart is able to beat declines. According to 2013 study, “An inexorable decline in maximum heart rate (mHR) progressively limits human aerobic capacity with advancing age.” It’s all downhill from the time a person hits her mid-thirties, “Peak endurance performance is maintained until ∼35 years of age, followed by modest decreases until 50–60 years of age, with progressively steeper declines thereafter.” If I live that long, in 2024 I’ll turn sixty, and my running pace will begin to slow significantly. Even now, in my attempt to keep up with younger runners, I feel the disadvantage of my relatively elderly blood pump. The difference between mine’s maximum ability to beat and theirs is approximately equal to the difference in our ages. And that isn’t the only problem for older athletes, “Among the three main physiological determinants of endurance exercise performance…a progressive reduction in [maximal oxygen uptake, or VO2Max] appears to be the primary mechanism associated with declines in endurance performance with age.” Sadly, “Declines in endurance exercise performance and its physiological determinants with ageing appear to be mediated in large part by a reduction in the intensity (velocity) and volume of the exercise that can be performed during training sessions,” so as I get older, I won’t be able to run as fast, as far or as long as I could have when I was younger…sigh.

My wrist type and chest strap type heart rate monitors.

The American Heart Association (AHA) recommends use of the formula 220-age to determine a person’s predicted maximum heart rate in beats per minute (bpm); however, results of Age-Predicted Maximal Heart Rate in Healthy Subjects: The HUNT Fitness Study, suggest 211-(0.64)age as more accurate. Both yield the same value for a 25-year-old, but for 56-year-old me, The HUNT Fitness Study formula predicts that my highest heart rate is 175 bpm, 11 bpm more than the AHA formula’s prediction of 164 bpm.

Recently, I’ve been considering heart rate training in hopes of improving my running performance, so on the first Saturday in May, when I went for a 13.1 mile run in the Anacortes Community Forest Lands (ACFL), I wore a heart rate monitor. My sister JoDee, friend (and birthday girl) Nina, and I set out from the Heart Lake parking lot with hydration packs, cell phones and a marked map. The forecast called for light rain with temperatures in the mid-fifties as we departed for damp, pine-needle covered trails lined with wildflowers.

Whistle Lake Half Marathon Course

After a mile warmup along the flattish trails west northeast of Heart Lake, we returned to the parking lot, crossed Heart Lake Road to the Whistle Lake side, and began our ascent towards Little Round Top. With 500 feet of climb, it was the toughest mile of the course. Two steps past the peak, JoDee twisted her ankle. We stopped, walked, and talked about our options. She wanted to continue, so we made our way to the five mile point: Whistle Lake parking lot. By then, she felt a sharp pain in her ankle at every footfall. Two miles later, she decided to drop out and return home, which meant another three miles of running discomfort. Nina and I continued along the planned route, completing four hilly miles south and east of Whistle Lake before returning to the top of Trail 22 where we’d separated from my sister. By mile eleven, I was tired and anxious as I thought about the ascent to the Viewpoint, but after a pep talk and a quick stop to catch my breath and calm my mind, I joined Nina at the top. We welcomed the final 15 minute descent along rolling hills that led us back to the Heart Lake parking lot. After 13.3 miles and nearly 3,200 feet of climb, we social-distance hugged and headed home. Reuniting with JoDee at the house, I found her following the RICE Method for her badly swollen ankle, glad to have cut the run a few miles short.

The biggest surprise of the day was the output from my heart rate monitor, which indicated that during the warmup along the easiest part of the course, my heart rate exceeded its predicted maximum of 175 bpm by 31 bpm, reaching 206 bpm! Not only that, it beat above its predicted maximum rate for about 20 minutes, dipping back down as I approached the summit of the highest hill we climbed. I concluded that either the data was wrong, or my heart and I were in big trouble. My father had died suddenly and unexpectedly of congestive heart failure when he was only six years older than I am now, which made the data more disconcerting. And according to the CDC, heart disease is the second leading cause of death in the US for women 45-64 years old.

Whistle Lake Half Marathon heart rate, distance and elevation data.

During my next run, I wore both a wrist type and chest strap type heart rate monitor. David Roche of Trail Runner Magazine, explains the difference, “Most wrist-based heart-rate monitors rely on…using light to measure blood flow…Light refracted off the blood flowing beneath the surface of your skin is fed into algorithms that use it to spit out a heart-rate number.¶Chest straps, meanwhile, use sensors on the strap to record signals from the heart beat…A good chest strap will be close to 100% accurate…many wrist monitors are not as accurate.” The heart rate data from the two different Garmin-brand monitors matched exactly, which both surprised and scared me. Within the first mile, my heart rate exceeded its predicted value. I walked. Ran slowly. Walked again. Finally, my heart rate seemed to settle down to somewhere in the vicinity of 150 bpm, a good number. Googling the possibilities afterwards (cardiac drift?) simply scared me more. The next day I observed the notification “sensor detected” on my wrist monitor. Wait. What? Both watches were using the same chest strap data. I replaced the strap battery, disconnected it from the wrist monitor, and washed it (for the first time). Although the data between the two devices continued to differ significantly, after troubleshooting, the chest strap monitor ‘s heart rate readings were reasonable, and matched my perceived exertion and carotid pulse.

Chest Strap vs. Wrist Type Heart Rate During the Same Run

In the weeks since freaking out from heart rate data that seemed too bad to be true, I no longer believe that I’m likely to die from a sudden cardiac event any time soon. I still believe that technology is good. But skepticism is better.

2 thoughts on “The Tell-Tale Heart Rate Monitor

  1. I’m so glad your ticker is okay! I’ve heard the wrist monitors are not so good, and yet I rely on mine all the time. Good to be reminded of the possible inaccuracies by a trusted person’s real life experience. Thanks for sharing! And congratulations on another half under you belt…er…chest strap!

    • Aww…thank you for kind words and ongoing support. It’s funny how easy it is to fall into the data-believing trap. Once I realized that the wrist strap really wasn’t that accurate (although it does provide some useful information), I was able to leave that watch at home and just enjoy heart-rate-data-free running again.

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