A prevalent advice for race strategy is to start running slower than your goal pace and keep increasing the pace as you cover miles. Start at a conservative pace and finish strong. Most of us have had the experience of starting a race running too fast and by the end we are running some very slow and painful miles. We can actually quantify what difference does it make to run negative splits. This means running in a way that your split times decrease as the race progresses, as opposed to running positive splits, which is to slow down as one covers miles.
For the sake of argument, I will concentrate again on data from the 2014 NYC half-marathon. This race is one of the few events that have split times at 5 km, 10 km, 15 km and 20 km. I will separate runners in 3 groups. The first group will be the negative split times group. A runner is in this first group if he or she consistently ran each 5 km split faster than the previous one. The second group will be the positive split times group. A runner is assigned to this group if he or she ran each 5 km split slower than the previous one. The third group is composed by everyone else, these are runners that for some splits they ran faster than before but for other splits they ran slower than before.
We can now look at the distribution of finishing times for each of these groups of runners. We find that runners in the "negative splits" group are indeed faster than runners in the other two groups. In fact, the slowest runners are the ones in the "positive splits" group.
We have not only confirmed the common wisdom that it is best to start a race at a conservative pace and then pick up the pace, we can now quantify how much better that strategy is. From the fitting curves for the distribution of finishing times (previous plot), we see that the typical male runner who runs negative splits finishes the half marathon in a time close to 1h48min, the typical runner that runs mixed splits finishes the half in about 1h54min, and the typical runner who runs positive splits finishes the half in about 2h06min. This indicates that most runners would be able to lower their finishing time by about 6 minutes if they follow a negative splits race strategy. This conclusion would be rock solid if one could show that the ability for running negative or constant split times is mostly determined by race strategy. Although that is the case, training makes a big difference in our ability to control our pace. In other words, choosing the right race strategy helps but it only takes you up to where your training allows.
For women we find a similar case. Form the fitting curves on the following plot the typical finishing times for our three groups of runners are 1h56min, 2h08min and 2h20min.
Most women who ran mixed split times would be able to lower their finishing times by about 12 minutes if they follow a negative splits strategy for their next half-marathon.
Running negative splits is by no means an easy task. The main difficulty is to gauge appropriately your best race pace for a given day. If you initially shoot too high, you are bound to slow down by the end of the race. From the 11,000 women who ran the 2014 NYC half-marthon only 1,345 ran negative splits, 7,845 ran mixed splits and 1,824 ran positive splits. Only 12% of women ran negative splits. From the almost 10,000 men only 14% or more precisely 1,462 ran negative splits, 7,004 ran mixed splits and 1,331 ran positive splits.
For women we find a similar case. Form the fitting curves on the following plot the typical finishing times for our three groups of runners are 1h56min, 2h08min and 2h20min.
Most women who ran mixed split times would be able to lower their finishing times by about 12 minutes if they follow a negative splits strategy for their next half-marathon.
Running negative splits is by no means an easy task. The main difficulty is to gauge appropriately your best race pace for a given day. If you initially shoot too high, you are bound to slow down by the end of the race. From the 11,000 women who ran the 2014 NYC half-marthon only 1,345 ran negative splits, 7,845 ran mixed splits and 1,824 ran positive splits. Only 12% of women ran negative splits. From the almost 10,000 men only 14% or more precisely 1,462 ran negative splits, 7,004 ran mixed splits and 1,331 ran positive splits.
3 comments:
Interesting analysis Ivan. For a 5k I definitely do negative splits, but for the longer distances, I most likely fall in the middle: start slow, pick up, pick up some more, slow again toward mile 12. I think that the people that achieve a negative split finish in a half marathon have done some serious training. Keep the posts coming, interesting reading!
It would nice to see how elevation loss/gain skews the distribution of the plots--particularly for the mixed splits group. When I finish my runs and track my splits I notice that my splits are longer when going uphills. Also, it is difficult to set a pace goal if you are unfamiliar with the course. Certainly, knowing when to speed up and when to slow down is a tremendous advantage. Just some thoughts about future implementations to these nice plots. Great start! Keep it going.
-David J.
Thanks for the comments!
I agree that quality of training and experience both impact greatly finishing times and "the ability to run negative splits". Yet again, runners perform the best when running near constant splits (i.e. all modern word records for the half and for the marathon). The question is, how much faster can a given runner run if he or she had ran constant splits?
At the end of the post I write that out of (almost) 10000 men, 1,462 ran negative splits, 7,004 ran mixed splits and 1,331 ran positive splits. If running positive or negative splits was a random variable with 50-50 chances, the expected numbers of runners would be 1250 negative, 7500 mixed and 1250 positive. I hypothesize that training and experience account for the running strategy of only ~10% of the runners.
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