I had a distinct advantage in that race. In 1969 the total number of entrants was far lower and not many Africans were involved. It was just beautiful and warm when we started, but there was a wind off the water right in your face as you got closer to Boston and the temperature rapidly cooled and it began to drizzle. You have it well figured though, that downhill is what is death on your legs and in my case, my knees. At the 18 mile mark i remember thinking to myself, it just cannot be this easy. Then slow death started-first the knees and then my thighs. I tried to run the race moving as little of my upper body as possible to conserve( a la Abebe Bikila, my idol from the 1960 and 1964 Olympics)-but my arms and head were all over the place as the last 8 miles unfolded. I had run lots of 10,000 meter races to prepare and was in the best shape of my life. The good news-I finished and had a very respectable time finishing less than 45 minutes behind the winner (a Japanese runner who set a course record at the time) and just barely breaking 3 hours. The bad news-I was physically sick for months after having become far too dehydrated during the race. Was glad i did it but would never have wanted to try it again choosing far easier races for the few other times I ran. BTW I am just under 6' tall and ran that race at 137 pounds. I had figured that every 5 pounds extra would be like running with 2 bricks in my pockets.