Can You Trust Wearables in Strain and Recovery Scores?

By Jiri Kaloc

Smart wearables have proven to be quite accurate in several useful metrics such as heart rate variability or resting heart rate. However, most of them offer other metrics that are derived from proprietary algorithms. Strain and Recovery are good examples of that. A new study puts these to the test. Let’s see what the researchers found.

A new study looked at WHOOP

Researchers from Penn State University set up a 6-week experiment where they looked at physiological and psychological measures that indicate an athlete’s stress and recovery states and compared them against the information shown by WHOOP’s wearable strap in the accompanying app. They evaluated metrics like HRV, RHR, and WHOOP’s proprietary Strain and Recovery.

They recruited an NCAA Division 1 Swim team, which included male and female Olympic Trials qualifiers, All-Americans and national team members from different countries. They designated a 6-week “Overload” period in the swimmers’ training. This was on purpose because the researchers knew this type of training would predictably lead to increased stress, which would serve as a good scenario to test how well the wearables capture this.


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HRV was accurate, Strain and Recovery were not

The study revealed that HRV shown by WHOOP was significantly correlated with sport-specific stress and total stress. This shows that the wearable was accurate since HRV is known to lower with increased stress and the swimmers were experiencing increased stress during their overload period. However, Strain and Recovery showed no relationship with any of the metabolic lab measurements or the recovery-stress questionnaire.

Should you ignore these types of metrics?

With the popularity of wearables increasing, manufacturers are trying to one-up each other by providing more and more new metrics to their users. That’s why it’s important to keep in mind that there are two very different types of metrics.

  • Things that can be directly measured. This would be the number of steps, heart rate, heart rate variability, temperature, etc.
  • Things that can be estimated based on proprietary algorithms. This would be stress levels, readiness, strain, recovery, body battery, sleep quality, etc.

The first type of metric is something that can be verified by science and compared to the gold standard. This new study confirms what we know from other research, wearables can measure these things quite accurately.

The second type of metric is much harder to verify by science because there’s not a clear number that can be measured. Plus, every wearable manufacturer keeps their algorithm secret. So, it’s more of an educated guess when your watch tells you that your sleep quality is bad or how strained you are.

But this doesn’t mean that these metrics are useless. They can provide value, especially when looking at trends over time. But this study serves as a warning that you shouldn’t make training decisions solely based on these metrics. Always look at them in the context of measurable data and your subjective feelings of stress and recovery.