The Ugly Side of Half Marathons
I've raced two half marathons in the last twelve months, and had two very different experiences. At the Great Eastern Run, I rattled out nine consecutive eight-minute miles, then experienced the bodily equivalent of that light on your dashboard that means you'll soon be driving a hire car. In the second race (Bath Half) I ran the same sort of pace overall, but managed to hold on to things for the whole race. This graph shows my average speed as the miles progressed - can you see when I called the RAC?
Getting your endurance training and race pacing licked is an essential skill, and getting it wrong can ruin your day. Running well doesn't just involve running fast - it's about learning how to run consistently and finish strongly - and that's something we can all work on, no matter what speed we're capable of. Watch any televised running, and you'll see the splits of the leading athletes pop up as they glide along - they're remarkably consistent. When Paula Radcliffe set her record marathon time, her fastest mile was 4:57, and the slowest was 5:18. And when Patrick Makau set the men's record, his fastest and slowest 5k splits were just 39 seconds apart.
There are thousands of half marathon performances in the Fetch database, and some interesting trends that we can all attempt to overcome.
Let's warm up by looking at the variation between the fastest and slowest mile of our runners - see the first graph on the right. The fastest group (the fastest thousand runners) typically squeeze all their half marathon mile splits within a 39 second margin. The slowest thousand runners typically show a variation of 89 seconds between fastest and slowest mile. Improving consistency is one sign of good training, but it also comes from a good race strategy.
How does it work? Do the faster runners start more conservatively? Do slower runners blow it all in the first mile and then spend the next 12 paying the price? The next graph shows how each of our groups handle pace in each quarter of the race. It seems that even the fastest group can't resist the urge to go off quickly, typically 1.62% faster than the pace they achieve overall, but it's our slowest group that find it hardest to curb their enthusiasm, running the first three miles nearly 3% faster than overall race pace. In the second quarter, reality bites all round; and in the third quarter, the emphasis switches to holding on. By the last three miles of the race, all groups are struggling to hold on to the initial pace. But whilst our fastest group are 1.25% slower than their overall pace, our slowest group are swearing like wounded pirates, paying back the loan at a stiff 2.5%.
Lots of us are driven by the urge to beat our best times, and it's hard not to let adrenaline take early control on the big day. I wondered if it was something that comes with experience, but even amongst runners with five, ten and even twenty half marathons in the locker, 80% of people run the first three miles faster than they run the rest of the race.
So it's pretty difficult to keep yourself under control early on, and every likelihood that you'll slow down as the race goes on. Getting the balance right is the key to a PB and a smile at the end.
The first table on the right illustrates how your PB dreams are linked to how far ahead of the game you are throughout the race. For example, if you get to six miles, and your overall pace 4% faster than your PB pace, you've got an 80% chance of holding on for a PB - but if you're only matching PB pace, you've only got a 23% chance.
It's tempting to run your finger along the rows and draw the assumption that if you go bananas in the first three miles, you've got a great chance of getting a PB. If you need me to point out the flaw in that thinking, then you may as well go the whole hog and run the whole race in a pair of cut-off jeans and some flip-flops. These figures are based on an analysis of runners who are (for the most part) training sensibly. Without adequate long run training and preparation to handle race pace, you're in for a lot of pain.
Overall though, building up a buffer at the start of the race does increase your chances of getting a PB. Too much, and you can spend the rest of the race managing a drastic slowdown, feeling dreadful, and being eyed eagerly by the folks from St Johns. But those who take a conservative approach to undercutting their PB pace end up slowing down as a half marathon wears on, and what might feel like a comfortable-if-small PB in the first six miles can gradually slip away.
The final table shows how your race outcome is linked to your progress at various points in the race. For example, if you're running at exactly PB pace when you've completed six miles, the bad news is that you're likely to miss out on a PB by about 1.8%. However, if you're just 2% faster than PB pace at the six mile mark, you're on target to take a princely 0.3% off your best time!
I will end with the usual cover-all caveat - if everyone was the same, we wouldn't need averages - and that's all these are. But take a second look at your race pacing, and you might find the key to your next PB.
*EDIT* I'd like to make it clear for anyone reading, that I really don't advocate going out like a nutter, then trying to hold on. The fastest group in my study were most conservative when setting their early pace, and consequently, they stayed in control towards the end of the race. Rave safe kids.
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