Rank 9 (GDI)
All affected infantry units heal automatically
Medical training is an upgrade that grants all infantry units of the Defense Class increased health and the ability to heal over time while garrisoned or in vehicles.
GDI has a long history on the high value of human life, from the beginning of its days with field medics to the Armories of the Third Tiberium War. With Zone Armor now the armor of GDI infantry (which is difficult for medics to get taken off in a timely manner), GDI, with some additional research into Zone Armor technology, began allowing (and highly encouraging) commanders to retrofit Zone armor with systems akin to the previous generation's Power Packs, allowing GDI infantry to take cover in a building and recover from their wounds and patch up the armor without aid from a GDI medic either at the Crawler, or help from an Engineer, thus decreasing GDI casualties and saving more lives... or killing more enemies. Whichever works for the Commander in question.
Nod, on the other hand, has rarely deployed medics to the field, so the sudden U-Turn in outfitting their infantry forces with self-heal capabilities (when in cover in say, a civilian building) is a surprise to many commanders, Nod and GDI. They're probably outfitted with it due to the extra cost of cybernetics which most Nod infantry are now outfitted with, as these retrofits allow for patching up the cybernetics and healing the flesh.