A few months ago, “Kevin” posted a concern about his training in the 80/20 discussion forum. He explained that lately his heart rate had seemed rather high relative to his pace, and the VO2max estimates he got from his watch had dipped slightly. A newer runner, Kevin was becoming discouraged and beginning to doubt the 80/20 method’s effectiveness. In my reply, I asked Kevin how he actually felt while running, and whether he would be noticing anything amiss if he ran without his watch.
“Now that you ask,” he answered, “I think I feel fine while running, maybe even good, but when my pace is right and my heart rate seems high, I feel down about it and frustrated during my run and also after.” Just as I had suspected, Kevin’s supposed fitness crisis was in fact an entirely emotional phenomenon triggered by information that had a variety of possible explanations, all of them more plausible than the one he’d assumed in defiance of how he was actually feeling and performing.
The story of Kevin’s illusory fitness crisis is an example of what I call a measurement problem, or a fake problem created by measuring. If you’ve ever had the Check Engine light come on in your vehicle and taken it in for service only to discover that the problem was with the Check Engine light, not the engine itself, you know what a measurement problem is.
The physicists reading this article know all about measurement problems. Indeed, in physics there is something known as the measurement problem, which has to do with how wave functions behave when observed. Simply put, wave functions behave differently when observed than they are believed to behave in the absence of observation. This problem is famously exemplified in the thought experiment known as Schrödinger’s cat. In it, a hypothetical observer opens a box with a cat inside and discovers that the cat is either alive or dead, but until the box is opened the cat is both alive and dead.
This paradox sounds crazy if you’re not familiar with quantum physics, but a good many physicists believe that wave functions really do exist in an indeterminate state until they are forced essentially to “choose” a definite state upon being observed. What is certain is that, as German physicist Werner Heisenberg articulated in his eponymous Uncertainty Principle, you cannot measure any system from the outside, hence to measure something is to change it. An amusing example from the realm of physical exercise is the discovery that male subjects in exercise science studies give lower perceived effort ratings when the researcher collecting the data is female. Ah, men. We’re hopeless!
Most of the measurement problems I see in endurance sports are caused by heart rate monitors—or rather by athletes’ failure to recognize the flaws and limitations of these devices. All too often athletes treat their heart rate monitors like the voice of God, when in fact they’re more like the voice of a bossy backseat driver with macular degeneration, giving you too much information, much of it unreliable. The most common example of a heart rate measurement problem relates to cardiac lag, or the delayed response of the heart muscle to changes in exertion. I’ve lost count of the number of athletes who have told me that, no matter how fast they go, they “can’t get into Zone 5” during a 30-second Zone 5 interval. It’s all I can do sometimes not to ask these folks, “Did it not cross your mind that if you’re running literally as hard as you possibly can, then you’re probably not in Zone 2, or that if your pace is consistent and your heart rate is changing, it’s probably your pace that’s telling you the truth about your intensity, not your heart rate?” But that would be mean.
Heart rate doesn’t have a monopoly on measurement problems in endurance sports, though. I’ve heard a number of athletes express genuine worry that they’re losing fitness, despite feeling fantastic and crushing their workouts, because their Chronic Training Load (CTL) score on TrainingPeaks has declined. CTL is a mathematical construct—an abstract measurement of fitness, not fitness itself—yet many athletes put more trust in it than they do in the evidence of their own senses. To me this makes about as much sense as skipping dinner despite a rumbling stomach because your glucose monitor says you’re not hungry.
In all seriousness, I am equal parts fascinated and horrified to look on helplessly as growing numbers of athletes increasingly accept technological measurements as more real than the physical things they measure. An athlete who is running as fast as he can but believes he’s running at low intensity because his heart rate monitor says so is an athlete who believes his heart rate measurements are more real than his own body. Likewise, an athlete who is crushing workouts and feeling great yet believes she is losing fitness because her CTL says so is an athlete who believes that this technologically mediated variable is more real than her lived experience.
The next time one of the fitness devices or apps you use signals a potential problem, do me a favor. Ask yourself the same question I asked Kevin: If you weren’t using that particular technology and were judging your training the way all athletes did before this tsunami of gadgetry came along, would you still see a problem? If not, then there is no problem.