You wake up, check your wearable, and get a number. But how useful are those readiness scores or the underlying data that feeds those “secret” algorithms? They aim to quantify how prepared you are to take on a heavy training load, but there is a reason these rating systems are the source of so many memes.
We get asked about this constantly. Garmin Body Battery (or the infamous and usually negative workout productivity ratings), Apple’s new sleep score, OURA has their own rating system, and WHOOP has their recovery percentage. Those are just the most popular. Athletes treat these numbers like the end-all, be-all. I say whoa Nelly!
THE TECH IS BETTER AT SOME THINGS THAN OTHERS
Plain old heart rate is pretty solid these days. A 2025 study out of the Air Force Research Laboratory tested top wearables — Garmin, Oura, Polar, WHOOP — against a hospital-grade ECG. Most devices measured resting heart rate accurately. Good news there. Once you start moving, that’s where the readings can get spotty in the short term with the sensors moving around.
HRV is where things get messy. That same study found Garmin’s HRV readings only reached “poor” agreement with the real thing, with average errors above 10%. WHOOP did better. Even the best device in the study, Oura, still carried some error. And HRV is the raw ingredient your watch uses to cook up that readiness score. Garbage in, garbage out.
Sleep tracking has similar problems. Researchers compared 11 popular sleep trackers against polysomnography, the sleep lab test doctors actually trust. The best trackers only matched the lab’s sleep-stage calls about 69% of the time. Some barely beat a coin flip. Most wearables also tend to overestimate how much real sleep you got.
WHY THIS MATTERS FOR TRAINING
Even when the raw numbers are close, the “score” itself is a black box. Companies don’t publish exactly how they turn HRV and sleep data into one readiness percentage. So when your watch says you’re 62% recovered, you have no idea what’s driving that number, or how much weight it’s putting on one rough night versus yesterday’s hard ride.
None of this means the technology is useless. Trends matter more than any single day’s number, like investing in the stock market; when in doubt, zoom out. If your HRV has been drifting down all week and you’re waking up tired, and your resting heart rate has been increasing in that same time period, that’s really good information, even if the exact daily score bounces around. Treat it as one data point. Not the decision maker.
WHAT I TELL MY ATHLETES
Don’t skip a key session because a ring told you to. Don’t force a hard day just because your watch flashed green, either. Your body still talks to you. Soreness, mood, motivation, how your legs feel on the first few strides out the door. That’s data too, and it’s been reliable a lot longer than any algorithm. I can’t tell you the number of times I’ve had a great session when my Oura ring told me I was cooked.
Use your wearable to spot patterns over weeks, not to make daily decisions. If something feels off and the score agrees, that’s useful confirmation; go ahead and back off. If something feels great and the score disagrees, trust yourself and get after it.
All wearables are just tools. It’s not a coach, and it’s definitely not the boss of you. Keep it in its lane, and keep listening to the athlete wearing it!
Dale Sanford is the co-founder of BPC Performance, Inc. and has been coaching individuals and athletes all over the world since 2009. You can catch up with Dale @bpcperformance on IG, or listen to the Coaches on Couches Podcast. If you’d like to start your health or sports performance journey with BPC, visit Buildpeakcompete.com.
