I am using a pixel 3 with fitbit premium. My cardio load is set to improve fitness. Last week I exceeded the recommended cardio load and it told me I was in danger of overtraining. This week I have exceeded every day however fitbit says I am only maintaining fitness. This is not helpful guidance. Also when I meet the recommended parameter for cardio load, it will give me a target to "get me back on track." If I am doing what is recommended, why I am not "on track." Come on guys, this is paid feature, right? You can do better, this is design thinking 101. Just imagine that you are the user getting these confusing messages.
Also it is difficult to assess cardio load when doing a work out. I have found that sometimes I have have zone minutes and 1.3 times desired cardio load. Other times they are close to the same. Cardio load should be more transparent to be useful. What is the formula of zone minutes to a unit of cardio load? Then you could plan a work out to reliably meet or exceed your cardio load.
