Heart rate monitoring: what wearables measure and why it
Heart rate monitoring has evolved from a clinical tool into a cornerstone of personal health tracking. Resting heart rate is a key biomarker of cardiovascular health and mortality [1], and wrist-worn fitness monitors have made it widely accessible [2]. However, accurate monitoring during intense exercise remains challenging due to motion artifacts [3]. Recent advances in contactless vital sign monitoring using radar offer a promising path toward continuous, unobtrusive health tracking, even under realistic body motion [4], and smartphones may soon enable passive heart rate tracking [5]. Historically, heart rate monitoring has been critical in obstetrics for assessing fetal status during labor [6][7][8][9] and in sports for optimizing training [10][11]. As technology progresses, heart rate monitoring is becoming more accurate, convenient, and integrated into everyday life.
Practical Playbook
Use heart rate zones to set training intensity
Zones aren't just marketing fluff. Zone 2 builds aerobic base; zone 4 pushes your lactate threshold. Most amateurs live in zone 3, which is nowhere. Pick the right zone for your goal. A 5K runner needs more zone 4 than a marathoner. Your watch can show you the zone, now actually use it.
When should you trust your watch's heart rate reading?
Optical HR sensors are good but not infallible. Cold weather, sweat, or a loose band can make readings spike or drop. If your watch shows 180 bpm on a recovery jog, stop and check your pulse manually. Trust the trend, not the instant number. For interval work, a chest strap is still the gold standard.
Calibrate your max heart rate for better accuracy
The 220-minus-age formula is barely better than guessing. I've seen 60-year-olds with a max of 170 and 30-year-olds stuck at 180. Do a hard 3-minute hill effort or a 400m repeat. Take the highest number you see. Use that to recalculate your zones. It changes everything.
Combine heart rate with perceived effort for smart loading
HR doesn't know if you slept poorly or had a stressful day. When your watch says zone 2 but your legs feel heavy, drop the weight or shorten the session. No algorithm replaces that conversation with yourself. Use HR as a guide, not a dictator. I've ignored HR on PR days and never regretted it.
Common Mistakes
- Mistake
- Gazing at the instantaneous HR number and ignoring its trajectory across minutes or days.
- Why
- Heart rate is noisy. Caffeine, posture, or a deep breath can spike it for 10 seconds. The trend over time tells you far more about recovery or effort than any single reading.
- Fix
- Open the trend chart in your wearable app. Look at 15-minute rolling averages, not the live number. A 5 bpm drift over a hour means something; a 15 bpm blip for 10 seconds probably doesn't.
- Mistake
- Plugging '220 minus age' into every conversation as if it's your personal max heart rate.
- Why
- That formula has a standard deviation of ~12 bpm. Half the population is off by more than that. Using it to set training zones will leave you either coasting or buried.
- Fix
- Do a field test: a 3-minute hard effort after a warm-up, then check the highest number you held for 20 seconds. That number is yours, not the formula's.
- Mistake
- Ignoring your resting heart rate (RHR) because it's 'boring' compared to workout spikes.
- Why
- RHR is the canary in the coal mine for overtraining, poor sleep, or illness. A sustained 5 bpm jump above your normal baseline is a stronger signal than any workout metric.
- Fix
- Check your RHR first thing, before coffee, 3 mornings in a row to get a baseline. If it's up 5% for 2 days straight, back off your training load by half.
- Mistake
- Relying on a single metric – heart rate – to judge workout quality, tossing out how you felt and how the weights moved.
- Why
- HR can be elevated by stress, heat, or hydration status, even when you're strong. Conversely, it can be lower than normal after high caffeine tolerance. The number alone can't tell you if your form is solid or your muscles are actually fatigued.
- Fix
- Rate your perceived exertion (RPE) on a 1-10 scale for at least one set per exercise. If RPE and HR disagree (e.g., HR says 8, you feel 4), trust yourself and push a little harder next set.
Frequently asked questions
From the Dorsi blog
Why Your Apple Watch Can't See Your Heart During a Deadlift
Two validation studies show Apple Watch HR lags during deadlifts and pull-ups by 5-15 seconds. It's not a bug—it's wrist-PPG physics. Here's what to use instead
Your Apple Watch HRV Number Is Wrong — Here's the 60-Second Fix
The HRV in your Health app is a misleading average of inconsistent daily readings. Learn the 60-second Breathe-app protocol that gives you a real training signa
Higher HRV Isn't Always Better. The Number Lies More Than You Think.
The instinct to chase a bigger HRV number is the cleanest way to misread your own body. What HRV actually is, why higher isn't a goal, and how to read it like Marco Altini does.
Sources we drew from
- 1
Liao S et al. · 2026 · Nature
Resting heart rate (RHR) is a key biomarker of cardiovascular health and mortality<sup>1-3</sup>, but passively tracking it longitudinally generally requires a wearable device, limiting its availability.
- 2Accuracy of Wrist-Worn Heart Rate MonitorsPeer-reviewed
Robert Wang et al. · 2016 · JAMA Cardiology
Wrist-worn fitness and heart rate (HR) monitors are popular.
- 3
Zhilin Zhang et al. · 2014 · IEEE Transactions on Biomedical Engineering
Heart rate monitoring using wrist-type photoplethysmographic signals during subjects' intensive exercise is a difficult problem, since the signals are contaminated by extremely strong motion artifacts caused by subjects' hand movements.
- 4Motion-resilient and rapid contactless heart rate monitoring by overcoming dual physical barriersPeer-reviewed
Bao Z et al. · 2026 · PPR
<title>Abstract</title> <p>Contactless vital sign monitoring using radar offers a promising path toward continuous, unobtrusive health tracking, but rapid and reliable heart rate estimation under realistic body motion remains challenging.
- 5
Lim GB · 2026 · Nature reviews. Cardiology
Heart rate monitoring during everyday use of smartphones.
- 6
2009 · Obstetrics and Gynecology
Obstetrics & Gynecology: July 2009 - Volume 114 - Issue 1 - p 192-202 doi: 10.1097/AOG.0b013e3181aef106
- 7
Dermot MacDonald et al. · 1985 · American Journal of Obstetrics and Gynecology
The Dublin randomized controlled trial of intrapartum fetal heart rate monitoring
- 8History of Fetal Heart Rate MonitoringPeer-reviewed
Kristina Wulf · 1985 · Unknown
History of Fetal Heart Rate Monitoring
- 9Fetal Heart Rate MonitoringPeer-reviewed
Paul Lyons MD · 2007 · Humana Press eBooks
Electronic fetal heart rate monitoring is a widely utilized means of assessment of fetal status during labor.
- 10Heart Rate MonitoringPeer-reviewed
Juul Achten & Asker E. Jeukendrup · 2003 · Sports Medicine
Heart Rate Monitoring
- 11The Heart Rate Monitor BookPeer-reviewed
Sally Edwards · 1994 · Medicine & Science in Sports & Exercise
THE HEART RATE MONITOR BOOK is for anyone who wants to learn about the use of one of the most important pieces of exercise equipment today.
Just show up. Dorsi handles the rest.
- HRV-driven readiness — today's plan adapts to how recovered you actually are.
- Adapts every session — no decision fatigue, no second-guessing your numbers.
- Apple Watch native — log a set with your wrist, not your phone.