The way that I understand it, when your player gets hurt, the medical affects the extent of the injury (time - how long he's out) and the ratings loss due to the injury. Hence the medical staff sending the email when a player gets hurt.
The other way I understood it was that training, in addition to the year over year gains/losses to arm, power, durability, velocity, etc., also is used when a player returns from injury. Hence the email from the training staff regarding recovery.
I could be wrong.