Albert Arnó — WritingAlbert Arnó is a physician and the founder of onmedic, a Barcelona health-technology studio working in eHealth since 2000. Notes on building measurement software for the body.https://albertarno.net/enReading Apple Health without fooling yourselfhttps://albertarno.net/writing/reading-apple-health-honestly/https://albertarno.net/writing/reading-apple-health-honestly/Apple Health holds dozens of metrics from several devices, recorded at wildly different qualities. The skill is knowing which ones were measured and which were inferred.Mon, 07 Sep 2026 00:00:00 GMTSleep stages from a wrist: what the device is really doinghttps://albertarno.net/writing/sleep-stages-from-a-wrist/https://albertarno.net/writing/sleep-stages-from-a-wrist/Your watch reports deep, core and REM in minutes. A sleep lab needs electrodes on your scalp to do that. Here is what the wrist is actually inferring, and which parts of it you can trust.Mon, 07 Sep 2026 00:00:00 GMTTraining load does not add up across sportshttps://albertarno.net/writing/training-load-across-sports/https://albertarno.net/writing/training-load-across-sports/Triathletes have been summing swim, bike and run load for years. The arithmetic is tidy and the physiology does not support it. What a multisport load number can and cannot mean.Mon, 07 Sep 2026 00:00:00 GMTCritical swim speed: the only pool test worth repeatinghttps://albertarno.net/writing/critical-swim-speed/https://albertarno.net/writing/critical-swim-speed/Two time trials, one subtraction, and a threshold pace that actually holds up. Why CSS beats heart rate and perceived effort in the water.Mon, 07 Sep 2026 00:00:00 GMTThe gait metric your phone already recordshttps://albertarno.net/writing/walking-asymmetry/https://albertarno.net/writing/walking-asymmetry/Walking asymmetry has been sitting in Apple Health for years, measured continuously, read by almost nobody. It is one of the few consumer metrics with real clinical grounding.Mon, 07 Sep 2026 00:00:00 GMTWhat a wrist can and cannot tell you about VO₂maxhttps://albertarno.net/writing/vo2max-from-a-wrist/https://albertarno.net/writing/vo2max-from-a-wrist/Your watch reports a VO₂max to one decimal place. It has never measured your oxygen consumption. Here is what the number actually is, and the one thing it is genuinely good for.Mon, 07 Sep 2026 00:00:00 GMTW′ balance, or what a match actually costshttps://albertarno.net/writing/w-prime-balance/https://albertarno.net/writing/w-prime-balance/Cyclists have said 'burning matches' for decades. W′ balance turns the metaphor into kilojoules you can watch drain and refill during a ride.Mon, 07 Sep 2026 00:00:00 GMTWhat I learned deleting 93% of my own websitehttps://albertarno.net/writing/deleting-most-of-my-website/https://albertarno.net/writing/deleting-most-of-my-website/AnalyticsZone had 15,004 URLs across eleven hostnames and almost no readers. Cutting it to about 1,100 pages on one host was the most useful thing I did all year.Sun, 06 Sep 2026 00:00:00 GMTRestarting this blog, seven years laterhttps://albertarno.net/writing/restarting-this-blog/https://albertarno.net/writing/restarting-this-blog/This site published 194 posts between 2012 and 2019, and I wrote none of them. Here is what it actually was, why it stopped, and what it is now.Sun, 06 Sep 2026 00:00:00 GMTThe maths runs on your phone, and that costs me thingshttps://albertarno.net/writing/the-maths-runs-on-your-phone/https://albertarno.net/writing/the-maths-runs-on-your-phone/Computing sports metrics on the device instead of the server is easy to say in a privacy policy and harder to live with. What it actually forecloses.Sun, 06 Sep 2026 00:00:00 GMT