GM's have the option of buying more trainers, or doctors.
If you have more trainers it costs more money, but then you can train two different things in a certain week. This will help to train more stats, but will cost more money to the team.
Also, if a player gets injured, you have to assign a doctor to them, so if you have 2 or more doctors, you can have 2 or more people being cared for. (Players still heal if injured, just faster if doctor focuses on them.)
And then last, there are "Rookie Teams." The player must be 20 or younger to play on the team. They can play in normal league games, but it is easier for them to play on your "Rookie Team" because they can train, but there isn't any problem if you lose. You could have a tournament for the Rookie Team against the other Rookie Teams in your country, but there is no prize, or the prize is small.