@brunoh The starting fitness level is put in manually based on the ammount of training per week. Eg. 1-3 hours per week is FL 6, 9-11 hours is FL 8 and more then 15 hours per week is FL10. It is a 0-10 scale with 0.5 increments. When using a training program like Firstbeat Athlete this application also weighs the duration of sessions and the intensity and changes the Fitness Level when needed.The fitness level is used to calculatie Peak Training Effect using EPOC. When you have FL 5 you need a much lower EPOC to get to a PTE of for instance 4.0 compared to the situation you have a FL of 8.5. The fitter you are, harder/longer you have to work in order to get a wanted Training Effect. As I am using my watch to pace my sessions, it needs to be set on the right Fitness level. When I ride 40km on my bike and want to reach a PTE of 3.0 I have to get to an EPOC of 64 in FL 7.5. So I have to “yield” 1.6 units op EPOC per km. During my training I can see what distance I traveled and what the EPOC is and I know whether I am on track or have to change the intensity. When my FL is 9.5, I have to get to an EPOC of 80 and need to “earn” 2 units of EPOC per km.