Irony being, that's what causes issues
That's called walking, running is a changing of support under oneself.
Calf problems tend to stem from either forcing yourself up onto tip toes, or actively pushing off with the foot.
By the fact you're asking for the best foot strike, I'm gathering you saw that people should run on the balls of their feet and tried to actively force it - and you found out why you shouldn't. Get technique right and it happens naturally.