Everything changed when the stethoscope was invented. Credit Rene Laennec, the 18th-Century French physician and flautist who invented this revolutionary device. Laennec liked to carve his own flutes out of wood, and it was these musical instruments that gave him the inspiration for the medical instrument that has become a symbol of the entire medical profession.

Calling the stethoscope revolutionary is not hyperbolic, for it enabled doctors for the first time to assess the internal health of individuals without reference to how they felt. No longer did patients need to experience pain or some other interoceptive sign that something was wrong with them for physicians to know (or believe) something was wrong with them. Many more technologies that did essentially the same thing in different ways followed, so that in historical hindsight the stethoscope marks the beginning of a modern pivot toward diagnosis-centered medicine, where clinicians place a high priority on identifying health conditions by type, which allows for the best (or most accepted) treatment for each type to be applied.

This cartesian paradigm, where patient subjectivity is regarded as worthless and objective diagnostics are treated as the word of God, has wrought unfortunate consequences, defying Hippocrates’ exhortation to “do no harm.” Yet the consequences are not limited to the medical domain. The dualistic mindset that privileges measurement over qualia has overtaken the entire collective consciousness, not excluding the minds of athletes, coaches, and sports scientists. This is problematic, because feelings and perceptions are and will always be the most reliable source of actionable information for those invested in athletic performance.

Take running shoes, for example. For decades, footwear manufacturers tried to design shoes that improved efficiency and reduced injury risk in individual runners by matching anatomical and biomechanical characteristics such as arch height against design features such as medial posting. Ignored in all this analysis and measurement was how the shoes actually felt on the runner’s foot, an act of scientific arrogance that has been rewarded with well-deserved embarrassment, as research has consistently shown that the traditional paradigm for matching shoes with runners neither improves efficiency nor reduces injury risk, while simply allowing runners to select shoes based on comfort does.

Even more consequential is the failure to properly value athletes’ subjective response to training. Objective training metrics can be useful, because whenever subjective and objective measures disagree on how hard a workout is or how close to the limit an athlete is, the athlete’s perceptions are always right. That’s because endurance performance is ultimately limited by perception. Athletes quit when they feel they cannot continue, regardless of what the measurements say.

The latest evidence that subjective assessments of training are more dependable than objective measurements comes from a study conducted by researchers at Ghent University and published in the International Journal of Sport Physiology and Performance. The subjects were eleven male recreational cyclists, each of whom completed five separate 3 KM time trials, one to establish a baseline and the other four to assess the effect of prior training on performance, as they were done immediately following completion of a workout.

The researchers calculated the training load of the four workouts using seven different methods, six of them objective (including four measures of training impulse, using heart rate data as an import, and two measures of training stress, using power data as an output) and one subjective (rate of perceived exertion). The degree to which time trial performance declined from baseline was used as a standard representing how stressful the preceding workout was in reality vs. theoretically. This allowed the researchers to assess how accurate each method of calculating training load (TL) was in estimating the actual impact of the workout on the athlete.

Can you guess which method was most accurate? Bingo! “TL using the rating of perceived exertion was the only metric showing a response that was consistent with the acute performance decrements found for the different training sessions,” the study’s authors concluded.” In other words, simply asking the athlete how hard they felt the workout was resulted in not just the most accurate indication of how hard the workout really was but the only accurate indication of how hard the workout was.

As technology continues to penetrate all reaches of endurance sports, more and more athletes are getting hopelessly caught up in the diagnostic mindset that regards feelings, emotions, and perceptions as noise and objective data as infallible signal. It’s an unfortunate situation, but one that presents a tremendous opportunity to athletes capable of thinking for themselves instead of passively absorbing the prevailing mindset. The surest path to reaching your full potential as an endurance athlete is to monitor only the most essential data, and not too closely, while giving most of your attention to qualia and factoring them more heavily into your training decisions than you do the modern equivalents of stethoscope readings.