Garmin, Oura, Whoop and Apple readiness scores face the same evidence gap

Most of us probably give that morning readiness score more credit than we realise. A fresh look at the evidence suggests wearable brands still have not shown that following its advice actually improves your health, recovery or performance.

That matters more now because these scores are popping up everywhere. Garmin, Oura, Whoop and Fitbit already have their own versions, and Apple has now joined them with Readiness on the Apple Watch Series 12 and Ultra 4.

The basic idea sounds sensible enough. Your wearable looks at HRV, resting heart rate, sleep and recent activity, then boils everything down to a number telling you whether to push harder, take it easy or have a rest.

The final score is the weak link

Topol was not questioning whether wearables can measure heart rate, sleep or HRV. He wanted to know whether the final readiness score can actually tell someone what to do next.

If Apple says “Recover” or Garmin reports low Training Readiness, does ignoring that advice lead to a worse workout, slower recovery or a greater risk of injury? Topol could find almost no published research testing those recommendations against real outcomes.

A 2025 review of 14 wearable health scores reached a similar conclusion. Most scores used HRV, resting heart rate, sleep and activity, but few manufacturers had published evidence validating the final number produced from that data.

The strongest example Topol found was a Whoop study involving 389 professional golfers. Players performed around half a stroke better when their Recovery score was 10 points higher, but the study had no control group and could only show an association.

That is the missing piece. Wearables can detect changes in the body, but companies have not yet shown that their scores consistently turn those changes into the right advice.

Your wearable may not be measuring HRV in the clinical sense

The HRV figure used by most readiness scores does not come from an ECG. Watches and smart rings use an optical sensor to track the timing of pulse waves at the skin, producing a closely related measurement called pulse-rate variability.

That distinction does not make the reading useless. Optical measurements can match ECG-derived HRV reasonably well while someone rests or sleeps, but the agreement becomes less reliable when movement, sensor fit, circulation or certain health conditions affect the pulse signal.

The research connecting low HRV with poorer health outcomes mainly uses ECG measurements. We cannot automatically apply those findings to short-term changes recorded by a consumer wearable.

HRV is also affected by exercise, alcohol, illness, stress, sleep and many other factors. A lower reading may show that something has changed, but it cannot tell the wearable what caused that change.

Useful signal or daily instruction

None of this means you should ignore readiness scores. A falling score can draw attention to a combination of poor sleep, higher resting heart rate and lower HRV, particularly when the pattern continues for several days.

The problem is the precision implied by the final number. An Oura score of 80 does not have the same meaning as 80 from another platform, and neither score follows a recognised clinical standard.

Readiness scores therefore make the most sense as personal trend indicators. Several unusual days from the same device deserve more attention than one low score after a poor night, late meal or unusually hard workout.

The sensors may have detected a genuine change in your body. The part that remains uncertain is whether the wearable knows exactly what you should do about it.