The necessary, and sometimes obsessive, method of bettering your Pokemon, namely leveling them up with the potential of their evolution.
Pokemon training is essential for any trainer that wishes to defeat another trainer in battle. Some trainers find it necessary to train their Pokemon to the maximum level of 100 where their Pokemon (usually) destroy any other Pokemon they see, unless the opposing Pokemon is also level 100. Several aids in Pokemon training have been developed (i.e. Macho Brace) or discovered (i.e.
Pokerus).
Pokemon training never seems to fatigue the Pokemon themselves (with the exception of their expected and regular decrease in HP and PP that can be instantly restored at a
Pokemon Center), but rather
fatigues the trainer/player. Obsessive training could result in, and not limited to: extreme drowsiness, missing of meals, constipation, late nights, frustration, irritability, and increased risk of illness.