Its probably something particular only to France: I've joined the Paris 20km run (almost a half marathon) on 15th October, and to do the actual run, I will need to present a certificate from the doctor saying that I should be fit to do it. So I took some time off this morning to visit the friendly neighbourhood doctor, and for 10mins, I got my blood pressure checked, and some readings of my heart beats through the stethoscope... and I got my certification to run! Its in the form of a letter from the doctor with your name and the statement that he has no reason to believe that you can't compete. Personally I dont see how this will help compared to no certificate. The only thing they will weed out are those people who are so weak they can't walk anyway. Anyway, I have the certificate, and hope to get a medal come October.
By the way, the quick examination cost me 40 Euros!!!!