Do I Move or Recover? What to Do With Your Readiness Score

With up to half (46-60%) of U.S. adults using some kind of wearable fitness tracker or smartwatch, we have more personal data than ever to estimate our health (Nagappan et al., 2026). These metrics include a range: ideal exercise intensity, steps, heart rate, sleep quality, recovery, overall stress level, and readiness scores (Nagappan et al., 2026). You may have noticed your device of choice is now providing you with a detailed report, telling you exactly how much energy you should expend for the day. While there is no denying these wearables provide valuable data, we inevitably reach the question of how much value we should place in these reports. Should I skip my workout for today if my readiness score is low? If my readiness score is low but I feel great, should I exercise anyway?

How are these devices collecting data?

First, we must understand what metrics these devices are actually using to inform their reporting. Most (not all) devices will have a traditional HR (heart rate) measurement taken constantly or intermittently throughout the day (depending on the brand) typically using a technique called photoplethysmography (receptors using light absorption to measure blood flow). HR measurements tend to be among the most reliable compared to other biometric data. As described by Van Oost et al. (2025), wearables including Whoop, Garmin, and Fitbit proved to be valuable and accurate tools when compared to a 12-lead ECG (electrocardiogram) in low- to moderate intensity, but began to lose their efficacy during transition states or high-intensity bouts.

Among the more common measurements are accelerometers, pedometers, and/or step counters, using a combination of geospatial data (GPS location) and rhythm and pattern recognition to estimate the number of steps taken throughout the day. While these can be reliable enough, due to the variability in the real world of a phone’s step counter kept in a pocket vs. a ring or watch step counter kept on a swinging and mobile hand, it can be easy to both under- or overestimate by 5-30% (Höchsmann et al. 2020; Pan et al. 2024). That said, along with HR, pedometers are still considered to be one of the more accurate biometric tools available. This technology is also often used in sleep products like Whoop or Oura Rings as a way to track how much you move or wake up throughout the night.

Are these devices actually tracking your sleep?

Well, sort of. You may get a report detailing the exact time spent in each sleep stage, but these reports or scores are built as an “educated guess,” from body measurements including your HR and HRV (heart rate variability), time spent motionless, and, depending on the brand, blood oxygen saturation and body temperature. While these measurements can provide valuable insight into your sleep hygiene (try looking at your resting HR after a night of consuming alcohol compared to an average night), we should be careful not to place too much value in our sleep and/or readiness scores, considering the only way to “know” stages of sleep, for example, would be to measure brain waves using an EEG (electroencephalogram). As explored by Liang and Martell (2018), wearables targeting sleep are reasonably accurate at measuring onset and total sleep time, but were challenged when attempting to estimate time spent in specific sleep stages (light, deep, REM), consistently overestimating light sleep and underestimating deep sleep. That said, these measurements should not be disregarded and can still be used to track long-term adaptation and progress.

If sleep isn’t directly being measured, how much value should we be placing in a readiness score?

Ultimately, it comes down to recognizing that these devices can be useful tools but are by no means necessary to live a healthy life, and reports should be taken with a grain of salt. With each company comes a unique algorithm to determine a readiness score, but withholding how the score is determined decreases the value we can associate with it. Oura, for example, shares that their sleep score is built from 7 contributors, including total sleep, time spent in deep sleep, and efficiency, to name a few. Each of these contributors is calculated by a proprietary algorithm, in itself exposing some opportunity for error. Finally, a readiness score or stress score is calculated once again using a “secret” algorithm. This does not mean these companies are hiding something or purposefully hijacking your scores. Simply, we cannot effectively validate or replicate the results if these formulas are not transparent. All this to say that going for that jog with a mediocre readiness score may be better in the long run than waiting for the perfect amount of rest. Conversely, taking a day off from strength training after a long week is totally acceptable, even if your readiness score indicates you should exercise.

Final thoughts

Just because these devices are not perfectly accurate does not mean they have no value. Tracking long-term changes in HR, time spent motionless during sleep, or even changes in estimated VO2max (a common measurement to estimate cardiovascular efficiency) can be incredibly helpful, even if exact values are hard to validate. It is also worth mentioning that it is the nature of scientific discovery to slowly improve over time, and wearables are constantly improving in accuracy and user experience. It is not unlikely that quite soon we will have wearable devices as accurate for sleep measurement as an EEG, or as accurate for HR as an ECG. For now, being mindful of your own internal cues goes a long way, and learn to take readiness/sleep scores as guidance, not gospel.