Some wounded soldiers during ground combat can have 1 or 2 hp over their max hp.
When this happens, healing this soldier with an (advanced in my case) medpack, he will gain 1 or 2 TU (1 for 1hp over max, 2 for 2hp over max) for the healers. Healing doesnt cost anything. Looks like the med pack want to bring the soldier to max hp, but he is already over it
I didnt test how far I can go with it, but at one time I went to 200TU.