Halfway up Heartbreak Hill, something gives. My hamstrings, which have been grumbling with increasing regularity for the last three miles, tighten up altogether. I stop, limp to the side of the road and try to stretch some flexibility back into the fatigue-stiffened muscle. A fellow runner pats me on the back and offers some words of support and encouragement before continuing his own ascent to the summit.
This gesture recalls the moment when this previously anonymous incline earned its famous name. During the 1936 Boston Marathon, defending champion John A Kelley overtook Ellison 'Tarzan' Brown on this same stretch of road. As he passed, he gave his rival a consolatory pat on the shoulder. But this simply stoked Brown's competitive spirit - he chased Kelley down and went on to win the race, in doing so, said the Boston Globe, "breaking Kelley's heart".
Remembering this, I console myself that there are certainly worse places to grind to a halt. Maybe I can even take a strange kind of pride in pulling up at a spot that has crushed the dreams of far better runners than me.
But the fact remains: my attempt to record a personal best at the 2011 Boston Marathon, the world's oldest annual 26.2-miler, has come undone five miles from the finish. Had two years of anticipation, four months of training, 3,000 miles of travel and a missed kiss from the future first female President of the USA really come to this?
Making the cut
My road to Boston started in April 2009, when I ran a personal best of 3:13:28 in my second London Marathon. On the day I was just delighted to have posted a good time. It was only afterwards that I realised that these five digits possessed a quasi-religious significance - they meant I had earned a coveted Boston Qualifier (BQ).
A large part of Boston's mystique stems from the fact that it is the only major mass marathon that has qualifying standards. There's a BQ for all ages - if you can't hit yours, you're not getting in. Boston is therefore the only race in which even getting to the starting line is itself an achievement. This has turned it into recreational running's holy grail, with just an estimated 10 per cent of runners being fast enough to qualify. I signed up straight away.
A unique race
I 've previously run both the London and New York marathons three times each. These races are big - but Boston during marathon weekend has a special, race-focused aura all of its own.
The race takes place every third Monday in April on Patriot's Day, a state holiday in Massachusetts that marks the anniversary of the start of the American Revolution. Taxi drivers offer helpful tips on pre-race fuelling (bananas) and getting a restaurant reservation in North End, the city's 'Little Italy' on Marathon Eve, proves impossible.
I have researched the course as thoroughly as I can. But this has increased my trepidation rather than quelled it. One finisher described it as "14 miles of fun, eight miles of sweat and four miles of hell". Most of the first half of the race is downhill.
The sting, however, comes between miles 17 and 21 - a series of three hills that culminate in the aforementioned Heartbreak Hill at 20.5 miles, perfectly positioned for when the glycogen stores are starting to run dry. From there on, it's mostly downhill to the finish in Boston city centre. Four-time champion Bill Rodgers said "Boston is a course you need to do many times before you get the hang of it." For me, it's one shot or bust.
The course drops like a rollercoaster in the first half-mile. It's congested, so I try to avoid danger by not going out too fast. Running even splits throughout is unlikely, so my strategy involves making hay while the sun shines: running a faster first half to bank between two and three minutes for later, when the going gets tough.
While I'm still alert I take time to look up and appreciate the beautiful surroundings of Massachusetts in spring: an abundance of woodland, blossoming trees and pretty wooden houses. At around the 10K mark I cross a set of railway tracks. It's said that here, in the 1907 race, several members of the leading pack got separated from the eventual winner by a slow-moving freight train. As reasons for not having a great race go, it certainly beats cramp.
On the next page: Find out if Andy scooped a new PB or if Heartbreak Hill claimed another marathon victim.