Why Your Running Watch Thinks You’re Getting Slower (Even When You’re Getting Fitter)

The Lead Story - Upcoming 5K & 10K Races - Upcoming Half and Full Marathons - TEAM Ageless Runner Leaderboard

If you’ve been running for any length of time, there’s a good chance you’ve experienced this frustrating scenario. You head out for what feels like a fantastic run. Your pace feels comfortable, your breathing is controlled, and your legs still have plenty left in them when you finish. You come home feeling confident that your training is heading in the right direction, only to glance at your running watch and discover that it has a very different opinion.

Your VO₂ Max has dropped. Your training status says “Unproductive.” Your race predictions have become slower. Somehow, despite feeling fitter than you did a few weeks ago, your watch has decided you’re moving in the opposite direction.

For many runners over 40, this can be surprisingly discouraging. We already know that maintaining fitness becomes more challenging with age, so it’s easy to assume the watch must be confirming what we secretly fear—that we’re simply slowing down. Fortunately, that’s usually not what’s happening at all.

The reality is that your running watch isn’t actually measuring your fitness. Instead, it’s making an educated estimate based on a collection of data points that often tell only part of the story. Modern GPS watches are incredibly sophisticated pieces of technology, but even the most advanced models can’t directly measure how fit you are. They collect information such as your pace, heart rate, elevation, cadence, sleep patterns and training history, and then use mathematical models to estimate what those numbers probably mean.

That distinction is important because estimates are only as good as the information they’re based on. When the conditions surrounding a run change, those estimates can become surprisingly misleading.

Take VO₂ Max, for example. It’s one of the most popular metrics displayed on modern running watches, yet very few runners understand what it actually represents. In laboratory settings, VO₂ Max is measured by having an athlete run on a treadmill while wearing a specialized mask that analyzes every breath. The equipment measures exactly how much oxygen the body consumes during progressively harder exercise until maximum effort is reached.

Clearly, your watch can’t perform that test from your wrist.

Instead, it estimates your VO₂ Max by comparing your pace with your heart rate, while also taking into account factors such as your age, weight and recent training history. If you’re running a certain pace with a relatively low heart rate, the watch assumes you’ve become more efficient and therefore fitter. If your heart rate is higher than expected for that same pace, it assumes your fitness has declined.

Most of the time, that’s a perfectly reasonable assumption. The problem is that there are dozens of other factors that can elevate your heart rate without having anything to do with your fitness.

Consider two runs on the exact same route. During the first run, the temperature is cool, you’ve had a full night’s sleep, you’re well hydrated and you’ve had a relatively stress-free day. Everything lines up perfectly, and your heart rate stays comfortably low throughout the run.

A week later, you run the identical route at the same pace, but the weather is hot and humid, you slept poorly the night before, and work has been particularly stressful. Your heart rate is now ten beats per minute higher than it was on the previous run.

Your watch sees the elevated heart rate and assumes you’re less fit than you were a week ago. In reality, your body is simply working harder to cope with the environmental conditions.

Heat is probably the biggest culprit. As temperatures rise, your cardiovascular system has to work much harder because blood is diverted toward the skin to help cool your body. Since less blood is immediately available to your working muscles, your heart compensates by beating faster to deliver the oxygen they need. This phenomenon, known as cardiovascular drift, is completely normal and happens to runners of every ability level.

Sleep has a similar effect. Even a single poor night’s sleep can elevate your resting heart rate, increase perceived effort and reduce your body’s ability to recover from exercise. Emotional stress, dehydration, caffeine, illness and even altitude can produce similar changes. None of these factors mean you’ve suddenly become less fit—they simply mean your body is dealing with more than just the run itself.

As we get older, recovery also becomes much more individual. Two runners of the same age and ability can complete exactly the same workout and recover at completely different rates. One runner may feel fresh enough to run again the following day, while the other may need an extra day or two before feeling fully recovered.

Most watch algorithms are built around averages, which means they sometimes struggle to accurately interpret the recovery patterns of experienced runners over 40.

Another misconception is the belief that fitness improves in a straight line. We naturally expect every week of training to produce slightly better results than the week before, but that’s simply not how the human body adapts. There are weeks when you feel fantastic, weeks when you feel flat, and weeks when every run seems harder than it should. During periods of heavy training, your performance may even decline slightly before rebounding to a higher level once you’ve fully recovered.

Your watch only sees today’s numbers. It doesn’t know that your body is in the middle of adapting to weeks of consistent training.

Heart rate itself is far more variable than most runners realize. Wrist-based optical sensors have become remarkably accurate, but they still rely on light passing through your skin to estimate blood flow. Skin temperature, sweat, arm movement and even how tightly you’re wearing the watch can influence the readings.

Then there are the runs your watch simply wasn’t designed to understand. An easy recovery run with friends, a relaxed trail run, or a leisurely holiday run may all appear inefficient when viewed purely as data. Yet these are often some of the most valuable runs you’ll complete all year because they build endurance, improve recovery, reduce stress and remind you why you enjoy running in the first place.

Not every run is supposed to impress an algorithm.

Perhaps the biggest mistake many runners make is allowing their watch to become the judge of their progress. Modern watches provide an incredible amount of useful information, but it’s easy to become fixated on small daily fluctuations that have very little long-term meaning.

The runners who continue performing well into their fifties and sixties rarely obsess over daily metrics. Instead, they pay attention to broader trends. Are they able to train consistently? Are they recovering well? Are injuries becoming less frequent? Are easy runs becoming more comfortable? Can they complete workouts today that would have felt impossible six months ago?

Ironically, some runners become significantly fitter without their watch ever showing dramatic improvements. They may have developed better durability, become more resistant to injury, improved their pacing or built the consistency needed to string together months of uninterrupted training. None of those improvements necessarily produce dramatic changes in estimated VO₂ Max, but they’ll almost certainly make a difference when race day arrives.

I wear a running watch on every run because I genuinely appreciate the information it provides. It helps me pace workouts, track mileage and identify long-term trends that would otherwise be impossible to notice. Modern GPS watches are extraordinary training tools, and they’re more capable today than they were even a few years ago. But I’ve also learned that they’re exactly that—tools. They’re not coaches, they’re not judges, and they’re certainly not the final authority on how fit you are.

The next time your watch tells you you’re getting slower, resist the temptation to accept its verdict without question. Think about how you’ve been sleeping, how hot it was, how stressful your week has been and how your body actually felt during the run. More often than not, you’ll discover that the numbers on your wrist are simply reflecting the circumstances of that particular day rather than your true level of fitness.

Running fitness is built over months and years of consistent training, sensible recovery and staying healthy enough to keep showing up. No algorithm, no matter how sophisticated, can fully capture all of that. Sometimes the best indicator that you’re getting fitter isn’t the number on your watch at all. It’s the simple fact that you’re still looking forward to tomorrow’s run.

Run strong, Ageless Runner

This newsletter is for general informational and educational purposes only and is not medical, health, or fitness advice. The information here is based on publicly available research and my personal experience as a runner, and may not be appropriate for your individual circumstances. Always consult your physician or a qualified healthcare provider before beginning any new exercise or strength training program, particularly if you have pre-existing health conditions or injuries. Never disregard professional medical advice or delay seeking it because of something you read here. Any reliance you place on this information is strictly at your own risk.

USA/Canada/UK & Europe/Rest of World

August 1–2

• Sunshine Coast Marathon Festival 5K & 10K (Queensland, Australia)
https://www.sunshinecoastmarathon.com.au

• Sydney Striders 10K Series (Sydney, Australia)
https://www.sydneystriders.org.au

• SPAR Women’s Challenge 5K & 10K (Pretoria, South Africa)
https://runningcalendar.co.za

August 8–9

• Sarawak Marathon 10K (Kuching, Malaysia)
https://sarawakmarathon.com

• Whyalla Running Festival 5K & 10K (South Australia)
https://www.runningcalendar.com.au

• Totalsports Women’s Race 5K & 10K (Cape Town, South Africa)
https://runningcalendar.co.za

August 15–16

• Shepparton Running Festival 5K & 10K (Victoria, Australia)
https://www.runningcalendar.com.au

• Blacktown Mayoral Fun Run 5K (Sydney, Australia)
https://www.runningcalendar.com.au

• Themba Kasi 5K & 10K (George, South Africa)
https://runningcalendar.co.za

August 22–23

• MAWA Kings Park 5K & 10K (Perth, Australia)
https://www.runguides.com/australia/runs/5k/all

• Yarra River Running Festival 5K & 10K (Melbourne, Australia)
https://www.runguides.com/australia/runs/5k/all

• Nelson Mandela Bay Challenge 5K & 10K (Gqeberha, South Africa)
https://runningcalendar.co.za

August 29–30

• Kilometres 4 Kids 5K & 10K (Brisbane, Australia)
https://www.runguides.com/australia/runs/5k/all

• Coffs Harbour Running Festival 5K & 10K (New South Wales, Australia)
https://www.runguides.com/australia/runs/5k/all

• Dreamworld Fun Run 5K (Gold Coast, Australia)
https://www.runguides.com/australia/runs/5k/all

USA/Canada/UK & Europe/Rest of World

August 1–2

• Sunshine Coast Marathon & Half Marathon (Queensland, Australia)
https://www.sunshinecoastmarathon.com.au

• Surabaya Marathon & Half Marathon (Indonesia)
https://runsea.run

• LIVE!42K Brasília Marathon & Half Marathon (Brasília, Brazil)
https://live42k.com

August 8–9

• Dili International Marathon & Half Marathon (Timor-Leste)
https://runsea.run

• Sarawak Marathon & Half Marathon (Kuching, Malaysia)
https://runsea.run

August 15–16

• Cairns Marathon & Half Marathon (Queensland, Australia)
https://www.cairnsmarathon.com.au

• Nelson Mandela Marathon & Half Marathon (Pietermaritzburg, South Africa)
https://www.nmm.co.za

• Rio de Janeiro Half Marathon (Brazil)
https://www.yescom.com.br

August 22–23

• Maybank Marathon & Half Marathon (Bali, Indonesia)
https://maybankmarathon.com

• Da Nang International Marathon & Half Marathon (Vietnam)
https://www.danangmarathon.com

• Langkawi International Marathon & Half Marathon (Malaysia)
https://www.langkawimarathon.com

August 29–30

• Sydney Marathon (Sydney, Australia)
https://www.sydneymarathon.com

• Mexico City Marathon (Mexico City, Mexico)
https://maraton.cdmx.gob.mx

• Huế Amazing Marathon & Half Marathon (Vietnam)
https://runsea.run

• Bohol International Marathon & Half Marathon (Philippines)
https://runsea.run

If you would like to join TEAM Ageless Runner Click Here to link to our Strava Page

This article is for general informational purposes only and isn’t medical advice. Ageless Runner isn’t a substitute for a doctor or physical therapist. Check with a qualified healthcare professional before starting or changing any exercise program, especially if you have a health condition or injury. Exercise carries inherent risk — if you feel pain, dizziness, or discomfort, stop and seek medical attention. See our full Disclaimer for details.

Read our Disclaimer | Privacy Policy | Terms and Conditions