This is the wiki page for the cvar
The command allows modifying the amount of boost you start with in custom training.
To change the amount of boost you start with each shot in custom training, open the console and type
Replace 80 with desired boost %. -1 for infinite boost (default behaviour).
sv_training_limitboost (50, 80)
will give you a random amount of boost between 50 and 80 on every shot.