# Heart rate monitoring: what wearables measure and why it > Updated: 2026-07-21 · Source: https://dorsi.ai/topics/heart-rate-monitoring Heart rate monitoring has evolved from a clinical tool into a cornerstone of personal health tracking. Resting heart rate is a key biomarker of… Heart rate monitoring tracks your pulse in real time: how fast your heart beats during rest, activity, and recovery. But raw numbers mean little without context. I use your HR data to spot when your nervous system is taxed or ready to push harder. A resting heart rate that climbs three days in a row? That's a signal to lower intensity. The page below breaks down the key metrics you actually need to watch. 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. ## 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. ## FAQ ### What is a good heart rate by age? There's no single 'good' number by age alone. The old 220-minus-age formula? Off by a lot for most people. A better marker is your resting heart rate. If you're 30 and resting in the low 60s, that's solid. For max heart rate during hard effort, a lab test beats any chart. But honestly? Watch how you feel, not just the display. ### What is the best way to monitor your heart rate? Chest strap for accuracy, but nobody wears one all day. The Apple Watch optical sensor is close enough for most training decisions, Dorsi uses it. The key is consistency: same spot on your wrist, snug fit, no arm hair interference. Phone cameras? Fine for a spot check, terrible for trends. Pick one device and stick with it. ### What is a red flag heart rate? Resting above 100 bpm when you're not sick or stressed. Sudden spikes during easy effort that don't drop after a minute. Or a max that drops way below your normal, that can signal fatigue or something worse. If your watch keeps nagging you about an irregular rhythm or high resting rate, don't ignore it. See a doctor. ### Can my phone detect my heart rate? Sort of. Most modern phones use the camera and flash to measure pulse through your fingertip. It works for a single reading, about as accurate as a cheap pulse oximeter. But continuous monitoring? No. Your phone can't track overnight HRV or detect trends. That's where a dedicated wearable matters. Use the phone in a pinch, but don't rely on it.