Is Your GPS Watch Gaslighting You About How Hard That Run Was?

Do you ever finish a "recovery jog" feeling like you just survived an interval workout, only to glance down and see a completely unremarkable number on your watch? Or the opposite: you grind through a hard session, check your training load score afterward, and it barely registers?

You're not imagining it. A study published this year in Sports Medicine - Open, out of the University of Twente in the Netherlands, put that mismatch to the test. The results are a good reminder that no single number tells the whole story of how hard you actually worked.

What they actually did

Researchers took 12 experienced recreational runners (already averaging about 39 km, or roughly 24 miles, a week) through three very different sessions: a 45-minute easy endurance run, a 5K at a hard but sustainable effort, and a session of five 1,000m repeats. Each run was measured three ways at once: a heart rate monitor, a motion sensor (the same kind of tech inside a lot of running watches) estimating the actual mechanical force moving through the body with every stride, and a simple post-run questionnaire asking how hard the session felt (what researchers call session RPE, or rate of perceived exertion).

The question was simple. If these three ways of measuring "how hard was that" agree with each other, you can trust whichever one is easiest to track and if they don't agree, that's worth knowing too.

Outcome: your gut turned out to be the most reliable narrator

Here's the part that stood out: the runners' own sense of effort clearly told the three sessions apart, rating the easy run as noticeably easier than either the intervals or the 5K effort. The heart-rate-based load number and the force-based mechanical load number, on the other hand, didn't reliably separate the sessions from each other at all. And when the researchers compared the three metrics head to head, the relationships ranged from weak to just moderate at best. A watch-based load score and a mechanical load estimate often weren't telling the same story, let alone matching how the run actually felt.

In plain terms: your watch, your heart rate, and your own perceived effort can each be describing a different piece of the puzzle. None of them is wrong exactly, they're just measuring different things (how your heart is working, how much force is going through your joints and tissues, and how your brain and body are interpreting the whole effort).

Why this matters if you're training for something, or coming back from an injury

This is a small study, twelve runners across three sessions each, so it's more of a "pay attention to this" finding than a "throw out your watch" finding. But it lines up with something we see constantly, both on the coaching side and in the clinic: runners who fixate on a single number, whether that's mileage, a load score, or a color on an app, and miss what their body is actually telling them along the way.

If you're building back up after an injury, or trying to figure out why a "moderate" week your watch rated as easy left you feeling wrecked, this is your permission slip to treat how you feel as the more valuable data, not just a feeling to push through. A good training plan, whether that's a coaching program or a rehab plan built around your specific tissue, should be checking in with more than one number: what the watch says, what your heart rate says, and what you say.

The honest caveats

This was one small observational study looking at experienced runners doing three specific session types over a short window, not a large trial. It doesn't tell us exactly which combination of metrics best predicts injury risk. That part is still being worked out. But the core finding, that these load metrics don't automatically agree with each other, is worth knowing before you let any single number override how your body actually feels.

Ready to build a plan that listens to more than your watch?

Whether you're chasing a new PR or working your way back from an injury, we build training and rehab plans around the whole picture, not just what a device says. Schedule a free 15-minute discovery visit with our running coach Andy or running specialist physical therapist Dr. Emily Hill and let's talk about what your body's actually telling you.

Source: Scheltinga BL, Buurke JH, Kok JN, Reenalda J. "Do Training Load Metrics Agree? A Comparison of Session Rate of Perceived Exertion, Physiological and Biomechanical Load in Outdoor Running." Sports Medicine - Open, 2026;12:18. DOI: 10.1186/s40798-025-00969-9. Open access, University of Twente.