You use Condition packs to top up the players condition once they train on Highest Intensity.

For Example, I train my MC, Very near scout level, I bought him as an 18 year old for 580k, hardly contested and now he is nearing Scout-level so I buy Rest packs with tokens and I set his intensity to High and the rest of the team to Rest and use all three (Cardio, Stretching and Practise match) and once thats done I use Rest packs to get his condition to 100% again, keep repeating the process until I get to my desired skill level.