Somewhere between buying your first pair of proper running shoes and your third or fourth month of consistent training, most runners ask the same question about the watch on their wrist: is this thing actually telling me the truth? It's a fair question. These devices promise a lot — heart rate, calories burned, sleep stages, recovery scores, race predictions — and it's worth knowing which of those numbers you can trust, which ones are closer to educated guesses, and which ones are genuinely useful even when they're not perfectly accurate.

Heart rate is the strongest metric, but it has real limits

Of everything a wearable tracks, heart rate is generally the most reliable, and it's not particularly close. Most consumer devices use a technology called photoplethysmography, which shines light into your wrist and measures blood flow through the skin to estimate your pulse. In steady, controlled conditions — sitting, walking, a consistent easy run — this works reasonably well. Research comparing wrist-worn devices against medical-grade ECG monitors has generally found solid correlation for resting and steady-state heart rate, with accuracy varying noticeably by brand, and premium devices tending to outperform budget ones by a meaningful margin.

Where it gets shakier is during hard efforts. Fast arm movement, sweat, tighter-than-usual grip on the strap, and rapidly changing heart rate during intervals or sprint finishes all interfere with the optical sensor's ability to get a clean reading. Several studies have found heart rate can be underestimated by a noticeable margin during intense effort, sometimes by more beats per minute than most runners would guess. The practical takeaway: trust your wearable's heart rate for easy runs and general trends over time, but if you're doing serious interval work or heart rate zone training where precision actually matters, a chest strap monitor, which reads electrical activity directly rather than optical blood flow, will give you a more dependable number.

Step counting and distance are decent, not perfect

GPS-based distance tracking on running watches has genuinely gotten quite good. Studies testing GPS sport watches against measured race distances have found errors typically in the low single digits, often under two or three percent, particularly in open areas with a clear view of the sky. That's accurate enough for real training decisions. Where distance tracking gets less reliable is in dense urban environments or under heavy tree cover, both of which can interfere with satellite signal and push errors higher, sometimes underestimating distance by several percent in the worst conditions. If you're running the same route through Accra's more built-up areas, don't be surprised if your watch's distance reading drifts slightly from run to run even on an identical route — that's the environment, not a broken device.

Step counting, ironically, tends to be less reliable than distance tracking despite being the simpler-sounding metric. Wearables count steps by detecting wrist motion, which means they can misread other arm movements as steps or miss steps when your arm isn't swinging naturally, such as when you're pushing a stroller or carrying something. It's a useful general indicator of daily activity level, but it shouldn't be treated as an exact count.

Calorie burn is the weakest number on your wrist

If there's one metric worth taking with real skepticism, it's calories burned. Estimating energy expenditure requires the device to combine your heart rate, movement, and some assumptions about your body composition and fitness level into a formula, and every one of those inputs carries its own margin of error before they're even combined. Research comparing wearable calorie estimates against lab-measured energy expenditure has consistently found this to be the least accurate metric these devices produce, often meaningfully off in either direction depending on the brand and the type of activity. This matters most if you're using your watch's calorie count to make decisions about how much to eat — treat that number as a rough estimate for tracking trends over weeks, not a figure precise enough to build a diet around.

Sleep tracking is useful for patterns, not diagnosis

Modern wearables estimate sleep stages, light, deep, and REM, by combining movement data with heart rate and sometimes blood oxygen readings. Compared against the gold standard, which is a clinical sleep study measuring actual brain activity, wearables get the broad picture reasonably right, particularly for detecting when you're asleep versus awake, but they're noticeably less precise at distinguishing between specific sleep stages. Different brands also handle this differently, and accuracy varies meaningfully across devices. The honest use case here is pattern recognition. If your watch consistently shows shorter deep sleep on weeks you're running high mileage, or better sleep quality following consistent early runs, that trend is worth paying attention to, even if the exact number of minutes in deep sleep on any given night isn't something to take literally.

Race time predictions are surprisingly solid

This is one area where wearables have quietly gotten impressive. Newer GPS watches that predict finish times for 5K, 10K, and half marathon distances based on your training data have shown strong accuracy in recent research, with predicted and actual race times correlating closely across large groups of recreational runners. If your watch is telling you a realistic 10K time based on your recent training, it's worth taking that estimate seriously as a pacing guide rather than dismissing it as marketing fluff.

So, do they work?

The honest answer is that wearables work well for what they're actually good at, and less well for what they merely claim to do. Heart rate trends, distance in open areas, and race time predictions are metrics you can genuinely build training decisions around. Calorie counts, exact step totals, and precise sleep staging are better treated as rough indicators than hard numbers. None of that makes the device useless — it makes it a tool with a specific set of strengths, and the runners who get the most out of theirs are the ones who know which numbers to trust completely and which ones to treat as a general direction rather than a fact.

The device on your wrist was never going to replace listening to your own body. It's there to back up what you already feel, with numbers accurate enough to be useful and honest enough limitations to keep in mind.

Train smart, track what matters, and gear up for the miles in between. Shop Run Go Run →

Wearable Health Monitors: Do They Actually Work?

Comments (0)

Join The Circuit.