It is required to know the most important principles that must be taken into account when designing a training program for a professional athlete.
One principle is to validate the trainings effectiveness empirically. For that you need valid performance measures and a statistical model. A useful class of statistical models for trainings is parametric learning curves (https://schmettow.github.io/New_Stats/LCM.html).
Nour El Islem Dehamnia ....Nour, train the individual. Everyone is different. Our physical response to training is different. Our response to supplements, medication and injury is different. We also evolve and change physically, emotionally and psychologically. And each generation has new ideas for training and “normal” expectations of achievement. Our cultures influence our ability and ideas training. And as we exchange cultural norms we further change.