Whoop & Oura measure and base recommendations on Heart Rate Variability, which is promising but currently of minimal or zero use for athletes. The measurements are way too dependent on variables which can't be controlled. HRV measurements are not even remotely repeatable IME, with values changing by 50+% from one minute to the next.
Many who use such devices swear by them, but the more experienced athletes I've known who are NOT sponsored by them (including myself) find that the recommendations are often way off. They will tell you to train hard when you're obviously tired more than your own self analysis would.
If you need to, spend the money on a training plan and follow it. Listen to your body, eat right, and don't rely on technology to show the way.
https://www.uphillathlete.com/why-we...g-on-hrv-apps/
"UPDATE—May 28, 2019: Eric Carter, a member of the US National Skimo Team and a PhD candidate in physiology, recently sent us this study on HRV. Over five years, the study used 57 national-level Nordic skiers and compared their training loads with HRV readings. Their conclusion? “[We saw] no causal relationship between training load/intensity and HRV fatigue patterns.”"