my friend finished the New York City Marathon in her record time (2*the time she needs to run 13 miles) but she never ran the full distance in her training, only 13 miles. As a matter of fact she did so well in the Marathon that I was left there in the cold Nov air holding her favorite snack waiting for her to arrive but in reality she was already so far ahead by the time I arrived at the spot we picked beforehand. I remember that she was very careful about picking her running shoes (weight and quality to reduce the chance to get blisters etc.), socks and clothings.