I guess it would depend on country, but what kind of medical exemptions were in place for people conscripted during WWII? I can't imagine people being sent to the front line if they weren't combat effective. Was there a line drawn to determine who was healthy enough?
In the United States, it was fairly easy to be disqualified. Irregular heart beat, asthma, that sort of thing would disqualify you. Flat feet too, I've heard a few times.