Monday, 6 May 2013

The Negative Split - The Realisation that An Accepted Running Concept is Actually Flawed!


Yes, a bold post title, but I feel that rather than delicately 'tip-toeing' around the subject, I perhaps need to be a bit more forceful in exposing the negative split myth, Why such an aggressive approach to this post? Well two reasons really: (i) in response to some challenging comments left on my blog "These aren't reasons that can be easily dismissed, I've loved to see you try to come up with some compelling reason why it's a good thing to go out hard and how this overcomes the well established reasons for an even split I mentioned above." So in response to challenging words like that, a changed response is obviously called for!

And (ii) listening to last weeks MarathonTalk, where even when Martin and Tom read out some data from the recent London Marathon, they failed to then explain to their audience what this data actually means, and even worse, throughout the show, as they have pretty well done in all of their MarathonTalk shows, they continued to 'celebrate' the negative spilt, as if achieving a negative split is a sign of a good performance. Whereas the data from the recent London Marathon clearly demonstrates that achieving a negative split more than likely represents a sign of a poor performance!

Now don't get me wrong. I really enjoy MarathonTalk, and what Martin and Tom have created in terms of the positive, supportive running community is absolutely fantastic. However, as mentioned in a previous post, way back in December 2011 when I first raised this 'negative split fallacy' with Martin and Tom, pretty well everything else on MarathonTalk is 'spot on', and is really excellent advice. It therefore does seem so strange that this one aspect, the over celebration of the negative split, is so in contrast to all of their other excellent messages.

So yes, tonight,s post may go against some people’s long help beliefs, but the main aim of the post is to challenge people to re-consider their ideas. Have they perhaps got it wrong? Is the commonly accepted concept that a negative split illustrates a good performance, actually wrong? We have seen it recently where commonly accepted concepts have been wrong. Best illustrated with the fallacy of the previous marathon hydration strategy message of "drink as much as possible, before you get thirsty" which was accepted wisdom for over twenty five years!!!

So, Tom from MarathonTalk, I am directing this blog post specifically to you in response to the comment that you left on my blog back in December 2011, "My money's still on the even / negative split but I'd be delighted to be proved wrong. My quote for the day... I'd rather know I was wrong than think I was right ;)"

Hopefully, the data from the recent London Marathon will “delight you” and prove that the even / negative split is wrong. That is my challenge tonight. I am hoping that this post will attract the attention of some new readers from the MarathonTalk community, so rather that asking new readers to my blog, to search around and read some of my previous posts, I am going to repeat myself a little, so apologies to those of you that have already read some of the following material.

My intention with this post was to first present the statistical data from the London Marathon, and discuss what this data actually means in terms of pacing strategy, and the possible application of using these findings to improve performance. I was then going to follow up with the scientific evidence to explain why the London Marathon data, that clearly illustrates that the negative split isn’t a sign of good performance, actually is the reality and not because over 95% of the entire marathon field ran poorly! However, as is typical with my UltraStu blog posts, simply presenting and explaining the statistics has taken longer than expected, and the post has already reached an ultra length. So unfortunately the scientific evidence to explain why, will have to wait until part two, which should be posted by the end of the week.

I will first start with the statistics mentioned on last weeks MarathonTalk. Tom reported that from the thirty four thousand MASSED START finishers there were a total of 5 even splits, and 1369 negative splits. This gives a negative split percentage of 4.0%. You will note that I have highlighted that this data is for the massed start, so does not include the elite field data. The reason that it is important to exclude the elite filed data from this analysis, is that what the elite runners do, often does not directly correspond to what non-elite runners do. This is obvious in terms of their minute mile rates and their finish times. But often what elite runners do in other aspects, example the quantity and intensity of training, the recovery resources available to them, and their pacing strategies, also differ significantly.

An argument often used, in fact pretty well the only argument I have ever come across, in justifying that the negative split is the strategy that runners should use, i.e. that the negative split indicates a good performance, is that most of the marathon world records have been achieved on a negative split. Therefore, people often then conclude that because of this world record aspect, there is in fact no argument; the negative split must be the best approach for ALL runners! I state No! Why people believe that ALL runners can achieve the same as the elite runners, I do not know. We wouldn't expect an 'average' runner to train 100 - 150 miles per week, we wouldn't expect the 'average' runner to run at sub 2hour 10 pace, so why people think that a negative split is achievable by an 'average' runner, I just don't understand! But 1369 runners at the 2013 London Marathon, did achieve this negative split. Surely then, these runners achieved the best performances, and those that positive split, i.e. slowed down during the second half of the race, didn't perform so well.

Before I move on to explain what did actually happen within the massed start field. I will briefly provide the statistics for the men's and women's elite race. As mentioned above though, what the elite do, may not correspond to what the non-elite runner should do, as there are so many other factors that influence the elite race, their elite performances.

The London Marathon women's elite race was won with a negative split of 3:23, running 68:26, for a finish time of 2:20:15. The second placed women, also achieved a negative split of 2:06, but all of the other 15 elite women finishers positive split the race, with the largest positive split of 13:17 by the current Olympic champion, although she did get knocked down by a wheelchair racer! None of the entire men's elite field achieved a negative split. The winner ran a positive split of 2:52, and the largest positive split was 5:31 (8th place) and the smallest positive split was 0:19 (9th place).

One of the reasons that I state that we should perhaps not put too much focus on what the elite do, when comparing to the 'average' runners, is in relation to the perception of what is a long way! Looking at world records, as often pointed out, a negative split is typical for running distances of 5,000 metres, 10,000 metres and the marathon. However, for distances further than the marathon, e.g. 100km and 24 hour races, even the best in the world will positive split. Although I would like to provide evidence for all of my comments I state tonight, searching the literature to link the evidence takes time, and I do want to get some sleep tonight! So if there are some statements that I make, which I haven't provided any evidence link, please highlight by leaving a comment, and I will find the link and post it at a later date.

So even elite runners positive split a 100km. Just some quick data to illustrate this is from the recent UK 100km Championships that took place in Perth. The graph below clearly illustrates that all runners positive split the race. This positive split is also seen in all World and European 100km races, however, I haven't got to hand the data to confirm this, but I will try to search it out for those that aren't convinced.

The other interesting aspect in relation to being able to run an even pace/negative split, is that most good quality club runners are able to achieve an even pace for a 10km race, but not for the marathon.. So whereas for the elite runner the ability to hold an even pace seems to not be possible at a distance somewhere between a marathon and 100km. For the club runner, this even pace ability appears to stop somewhere between 10km and the marathon. Why the difference?

Well, I don't want to go into the role of familiarity, the impact of expectations on race performance just yet, but it does appear that perhaps ones perception of 'what is a long way', or simply the distances one has physically trained, may have an influence on the distance of the race, where the even pace is unable to be maintained. Elite marathon runners will typically cover the marathon distance in training, and typically cover weekly mileages of 125 - 150+ miles. Club runners are less likely to do these distances in training. Therefore perhaps this lack of familiarity with the distance contributes to the difference between elite and club level runners. Whatever the cause of the difference, I won't speculate any further now. But with only 4% of London Marathon finishers achieving an even pace / negative split, one cannot argue against the fact that on the whole, non-elite runners are NOT capable of running even paced for 26 miles!

Following on from this extremely low percentage of runners achieving a negative split, I thought it would be useful to see if the percentage of runners achieving the negative split varied throughout the field. Logically, due to the fact that those that run a positive split, are those runners that slow down the most during the second half of the race, one would expect that further down the field, there is an increase in runners that positive split. One would also expect the size of the positive split would increase, further down the field. The graphs below display the number of runners in each 1000 batch of finishers that achieved a negative split. What is really interesting here is that there appears to be a clearly distinctive finishing time, at 4 hours, where something interesting is happening.
Although a line of best fit has been added to the data above, the line seems to reasonably follow the data points for finish times slower than 4 hours, but not at all for faster finishing times.

It therefore appears from the graph above that the number of runners per 1000 band of finishers, is not at all influenced by the finishing time, up to the four hour mark.  The highest percentage of negative split runners was in fact at 10.6%, at a mid finish time of 3hours 28 minutes.  With the fastest 1000 finishers only having 8.4% of negative split runners.

For a finishing time slower than four hours there does appear to be a relationship, with there being a smaller percentage of negative split runners, the slower, the further down the field.
So, what does the above data tell us. Firstly, the key message is that a very low number of runners achieve a negative split. It was reported at 4.0% overall on Marathon Talk, and the table below shows how this percentage varies throughout the field for each 1000 band of finishers, for the first 25,000 finishers, i.e. up to the five hour, two minute mark..

Now I wouldn't want to upset any runners reading this post, but achieving a four hour marathon time is often a huge goal for many marathon runners, as running a sub four hour time is possibly seen as a time that indicates that one is a 'good' marathon runner. Yes, simply finishing a marathon is quite an achievement, but to finish in a time less than four hours requires substantially more preparation. Therefore the fact that there appears to be no relationship between finishing time and the percentage of runners achieving a negative split , up to a four hour finish time, warrants further attention.

To those that belief that running a negative split illustrates a good performance, perhaps they would expect there to be more negative split runners further up the field. And for me, who believes the contrary, i.e. for non-elite runners, achieving a negative split is actually a sign of a poor performance, as the negative split has only been achieved by the runner running so slowly during the first half of the race, that their overall time is slower than what they could have achieved. So surely one would expect more negative splits, the slower the finish time. But the data up to four hours, i.e. for 'good' marathon runners, the first 11,000 finishers, neither of these trends are shown. There is neither of these relationships!

I then had to really think, why there is a a lack of a relationship, either way? Why no clear relationship to indicate that a negative split is a good performance or a poor performance? In terms of my belief, surely those that run a negative split, have only achieved this because they have run the first half of the race so slowly, so the data should illustrate this. I then realised why no relationships are apparent within the data. Yes, those that negative split may have performed poorly, but they just simply move lower down the finishing place list. Throughout the field people will finish with a certain time due to many factors, so there is a massive spread of finish times. Within this spread of finish times, some runners will perform well in relation to their fitness, ability, belief, whatever else, and hence move further up the field, finish faster. Whereas some runners will perform poorly, i.e. finish slower. But the good or poor performances will not stand out within the results, they simply move upwards or downwards amongst the finish results. Hence it is not possible to observe any relationship between negative/positive splitting and finish time.

I then decided to look at the 'very good' runners within the field. Now looking at the first 500 finishers, so the top 1.5% of the field. The two graphs below display this data, first comparing positive split ranking,( i.e. those runners that slow down the most in the second half of the race, having a positive split rank of one), with finishing place. Then comparing the amount of time slowed down, i.e. the size of the positive split time, with the finishing time. Again, both ways of analysing the data failed to illustrate a relationship of any strength.

One interesting aspect did 'jump out at me' though.  That being, just how few negative splits there were in the very fastest of the runners.  The graph directly above doesn't show many dots to the left of the vertical, which are near the horizontal axis, i.e. with the quickest times.  So again back to the database, and this time looking at to see where abouts did the 84 negative split runners within the first 1000 finishers place.  So I split the first 1000 finishers into place bands of 100 runners, and 200 runners.  The data is in the table below.

Now the data in the table directly above now tells the true story! As mentioned above, those runners that achieve a good performance, i.e. those that run quicker than what their 'ability' or 'fitness', or 'talent', or 'whatever' suggests they should achieve, simply move up into the higher placing band, and are therefore 'lost' within the data. Similarly those runners that run slower than what their form suggests, simply move down into a lower placing band, and again it is not possible to identify these poor performances. However, if you move to the very top placing band, because all of the poor performers who should have finished within the top band move down to the second band, and all of the good performers move up into the top band from the second band, the top band therefore represents the qualities of the good performers, and doesn't include the qualities of any poor performers, as they have moved down to the lower band. (There is no higher band from which poor performers will move down from.) Once we move down below the top band, then one would expect that the number of negative split runners within each band would again be similar, i.e. no relationship between the number of negative split runners and finish time/place.

So if we have the place bands set at 100 places, within the top band, i.e. that band that truly represents the characteristics of a good performance, i.e. running quicker than what would be expected, then we clearly see that the negative split runner does represent a poor performance, as there is only ONE negative split runner within the top 100 place band. This has occurred, as those runners that have run a negative split, have moved out of this top band, down to the next band, as expected when achieving a poor performance. There is no longer the standard 8.4% of runners (the average for the first 100 finishers) being a negative split runner within the top band, It has dropped to only ONE percent! Hopefully, the above two paragraphs make sense. It is quite a hard concept to explain, but hopefully it is semi clear.

Having now identified that running a negative split is an indication of a poor performance, is it possible to identify how much slower have these negative split runners ran, by starting out too slowly? Asking the following question may help. How much slower does the negative split runner have to run their first half of the race in order to achieve a negative split. This answer can possibly be answered by looking at runners of similar finishing times, in this instance, for runners at the very top end of the field. How much of a positive split time, do these good performing runners on average slow down during the second half. This average positive split slow down time, would then be a close approximation of how much slower the negative split runners must have ran their first half in order to achieve an even/negative split. The average positive split time for the first 100 positive split finishes is 3 minutes 46 seconds. And for the first 916 positive split runners within the first 1000 finishes, they slowed down on average 4 minutes and 57 seconds, which for their average half marathon time of 1:21:12, corresponds to a slowing down of 6.1% of the half marathon time.

This percentage represents the average slowing down of the best performing 2.9% of the field. It is an average, some slowed down more, some slowed down less. Actually to get the true slowdown average of the best 1000 runners in the massed start field, one should also include the influence of the 84 negative split runners that sped up. Their average negative split was 1 minute 23 seconds, which in relation to their average half marathon time of 1:25:17, results in an average speed up of 1.6%. So overall the average slowdown for the first 1000 finishers is 4 minutes and 26 seconds, which in relation to the average half marathon time of 1:21:33, corresponds to a percentage slowdown of 5.4%.

This percentage slowdown value is actually quite an interesting figure. However, I mentioned above that perhaps the amount of positive split may vary across the field, hence why one should look at the value of slowdown of runners in a similar finish time to oneself. The fact that the percentage slowdown is only 5.1% for the first 100 finishers, in comparison to 5.4% being the average for the first 1000 finishers suggests that perhaps not only the actual amount of slowdown time will vary through the field, but there may also be some variation in the percentage slowdown throughout the field.

I therefore split the first 11000 finishers, those that finished under 4 hours, into bands of 1000 runners, which equated to typically a finish time band of around five minutes, except towards the top end of the field. To account for the wider finish time band near the front, I split the first 1000 place band into 0 – 100, 101 – 500, and 501 – 1000 place bands. This analysis produced some interesting results, which are displayed in the following table.

As indicated within the table above, it does appear that only at the very top end of the field is the percentage slowdown affected by finishing time. For runners finishing in a time between 3:17 and 4:00, the percentage slow down appears pretty consistent, and averages 9.9%. At the very top of the field whether finishing in the top 100, or between 101 – 500 there is a slow down percentage of 5.1%. This percentage slowdown therefore appears to represent the very least amount of time that the very best runners, i.e. the top 1.5% of the field., will slow down during the second half of the race. For finishing times, between 2:49 and 3:17 the slowdown percentage progressing rises up from 5.1% to 9.9%. I have identified three intermediate bands within the table. I guess with further analysis more bands could be added, but I will leave it at three bands, which therefore results in a total of five slowdown percentage bands. I haven’t carried out the analysis for finish times greater than 4 hours. However, I think the best proposal is that runners who plan to finish in a time slower that 4 hours should aim to maintain a slowdown percentage of 9.9%, i.e. the same percentage as for those runners between 3:17 and 4:00. With a slower planned finishing time even with the runner aiming for the same slowdown percentage, it would actually result in an increased slowdown amount of time, as their half marathon split time will be longer.

These average slowdown percentages are therefore very useful. In the future, hopefully now realising that trying to run an even pace for the entire 26 miles is not the strategy to use, resulting in a slower performance than one is capable of, it is quite easy to calculate what runner's half marathon split time should be in order to achieve a certain finishing time.

For example if a runner wants to run a 2:36 marathon time, they would simply divide this time (156 minutes) by 2.051. This represents a slow down of 5.1% on their half marathon time. So to obtain a 2:36 marathon finish time, with the average percentage slowdown, the half marathon split would be 76:04 (76.06 minutes), and then running the second half in a time of 79:56, results in the time of 2:36:00. So running a positive split of 3:52.

Interestingly, last month I was giving some pacing strategy advice to a friend that was wanting to achieve a PB at the London Marathon. His current PB was 2:38, but I felt that he could achieve a time of 2:36 if he adopted a positive split strategy. This predicted possible time was based on his recent half marathon race time, and also him getting wiser, gaining more experience as a runner over the last year. However, I hadn't carried out the detailed analysis of previous London Marathon data like I have recently carried out and illustrated above. I therefore went with my 'gut feeling', in terms of what positive split he should try to achieve, based on my 35 years of endurance running. I proposed to him that he should aim to go through half way in a time of 76:30 and then positive split by 3 minutes, i.e. 79:30 for the second half, resulting in a finish time of 2:36:00. Knowing what I know now, I would have realised that only positive splitting by three minutes (3.9%), compared to the average positive split of 5.1%, for that region of the field, is a bit ambitious. Based on his recent half marathon performances, running a time of half marathon split of 76:04 would have been most likely a wee bit beyond him. So in reality a finish time of 2:36:00 was really a wee bit beyond him. Applying a 5.1% slowdown to a 76:30 half marathon split results in an 80:24 second half time, so a total finish time of 2:36:54 was more likely for a 76:30 half marathon split that was decided upon.

What did he run? He went through half way in a time of 76:47 (76.78 minutes), a little slower (17 secs) than planned. With an average slowdown percentage of 5.1%, he should, following the 76:47 split time, therefore run the second half in a time of 80:42 (80.70 minutes), so a predicted slowing of 3 mins 55 secs, resulting in an overall predicted finish time of 2:37:29. What time did he run? He ran the second half in a time of 80:20, and finished in 2:37:07, so 22 seconds quicker than the average slowdown prediction. But still 13 seconds slower than the predicted finish time of 2:36:54, if he had ran 76:30 for the first half. Whereas in the past he would have considered running a positive split of 3:33 as a poor performance, having been 'brainwashed' with the myth that an even split is what one should achieve. He was therefore able to truly celebrate his good performance, as in the second half of the race he run 22 seconds quicker than expected.

Looking at the above one can quite clearly see the potential of this analysis. Runners can now calculate what pace they should go out at, i.e. what time they should pass halfway in, based on what finish time they are planning, specifically up to the four hour finish time. Please note that for runners that finish slower than four hours, I haven’t extended the above analysis as I feel that basing what one should aim to achieve on what the average of these 4 hours plus runners achieve, i.e. on the average slowdown of these runners, probably isn't ideal. As for these runners, their more substantial slowing down is likely to be a result of less than ideal preparation, and therefore capable of changing if the preparation had been better. This level of slowdown is therefore not as a consequence of the actual reality that for a non-elite runner, one MUST slow down. As mentioned above, I think that for runners planning to finish in more that four hours, they should plan for a slowdown percentage of 9.9%, which is quite different to the typically message given out, especially by MarathonTalk, in that one should aim for an even paced marathon, so a slowdown percentage of 0.0%!

As the statistics have clearly shown above, slowing down during the second half of the marathon is a reality. It is NOT an indication of a poor performance. Yes, if a runner slowed down by a percentage substantially more than the average slowdown percentage, for their finishing time, then this would be a poor performance. If a runner was hoping to finish in a time of 4 hours, applying the MarathonTalk strategy of running an even pace, they would then plan to go through halfway in 2 hours. With a 9.9% slowdown percentage, they would typically slowdown 11 minutes 53 seconds, so typically not achieving what they felt they were capable of. Not because they ran poorly. No, because they were given the wrong advice, and started out far too slow!
In order to achieve a 4 hour finishing time, the runner needs to divide 4 hours by 2.099, NOT by 2.000 as suggested by Marathon Talk. Dividing 4 hours by 2.099 generates the half marathon split time of 1:54:20. Slowing down during the second half by 9.9% (on 114.34 minutes) results in the second half marathon being run in a time of 2:05:40, so a positive split, i.e. slowing down of 11 minutes and 20 secs. Producing a finish marathon time of 4:00:00. Achieving what the runner set out to achieve.

As you can see, taking on board the data from the thousands of runners that successfully completed the 2013 London Marathon, and not implying that a massive 96% of them have performed poorly because that didn't run an even paced race, one is able to provide a realistic pacing strategy, which doesn't actually vary that much from the even split pacing strategy. But the difference is sufficient enough for many many runners to not achieve their goal, simply as a consequence of listening to poor pacing strategy advice. In the 4 hour marathon example above, if the runner simply went out at a half marathon pace of only 5 minutes 40 seconds quicker, based on the data from thousands of runners, the likelihood of achieving their goal is massively enhanced. Running the first half marathon split 5 minutes 40 seconds quicker, means running the first 13 miles at 8:43 second minute mile pace and then slowing for the second half of the race to an average minute mile pace of 9:35. This pacing strategy which takes into account the typical slowing down percentage of 9.9% , which is in contrast to maintaining a 9:09 minute mile pace for the entire 26 miles!

Remember this slowing down is a reality, which I will hopefully be able to show why it happens with some scientific evidence within my next blog post.

As illustrated with two examples above, the application of this slowdown percentage is really exciting. The potential benefits of this percentage slowdown is huge! Marathon runners by applying the percentage relevant for their finishing position within the field, will then know how much time they should expect to slow down, rather than trying to achieve an even pace or even worse, a negative split result!

Just one last useful bit of information before finally finishing part one of this negative split myth post. With regards to the pacing strategy, the intention is that runners should be able to run at a pretty consistent even pace for the first 13 miles. However, for the 14th mile, they shouldn't instantly slow their pace to the average minute mile pace they are scheduled to run for the last 13 miles. What tends to happen is that the slowing down begins to start not too far after half way. One could calculate an accelerated rate of slowing down, where the slowdown starts of slowly for the first few miles after 13 miles, and then the slow increase accelerates, however, for ease of application, and which probably isn't too far of what happens, one should apply a linear increase in the slowing sown for the second half of the race. The best way to illustrate this linear increase in slowing down is for the 4 hour marathon example above.

The first half is run in 1:54:20 which is 8:43 minute mile pace. The second half marathon is planned to be run at an average of 9:35 minute mile pace, so an average slow down of 52 seconds per mile. This minute mile pace should then be divided by 6.5. This value, in this example 8 secs, is then the amount the running pace slows per minute mile, every mile.

The split times for mile 14 would then be 8:51, mile 15 = 8:59, mile16=9:07, mile17=9:15, mile18=9:23, mile19=9:31, mile20=9:39, mile21=9:47, mile22=9:55, mile23=10:03, mile24=10:11, mile25=10:19, mile26=10:27. Running each mile 8 seconds slower from half way will result in running the second half at an average minute mile pace 52 seconds slower. So just with this 4 hour marathon finishing time example, where the average percentage slowdown of 9.9% has been applied, hopefully it is easy to see the benefits. When one gets absolutely shattered during the last few miles, instead on having to maintain the same pace, that was achieved during the first few miles when the runner was totally fresh. Remember this is what is proposed with the even pace strategy! (Whoever thought that this is a good approach to take, really needs to reconsider!) With an application of the 9.9% average slowdown percentage, for the last mile one is able to slow down to a 10:27 minute mile, and still achieve the 4 hour marathon goal, simply by running just that little bit faster over the first half marathon, when feeling fresh and easy. Why not run that 26 seconds per mile faster during the first half when feeling great!

Finally lets apply the same formulae to our 2:36:54 marathon example runner from above. Going through the half marathon split in a time of 76:30 is a minute mile pace of 5:50. The slowing for the second half split time of 80:24, this being the 5.1% slowdown percentage, is a minute mile pace of 6:08. The minute mile pace therefore slows by 18 seconds per mile. Divide this 18seconds by 6.5 gives a minute mile pace slowing adjustment of 2.75 seconds. The easiest approach in this situation is to round the the mile splits up or down, so rather than the following mile pace for each mile from mile 14miles=5:52.75, 5:55.50, 5:58.25, 6:01.00, 6:03.75, 6:06.50, 6:09.25, 6:12.00, 6:14.75, 6:17.50, 6:20.25, 6:23.00, 6:25.75, simply round up or down so you would then get the following mile splits from mile 14=5:53, 5:55, 5:58, 6:01, 6:04, 6:07, 6:09, 6:12, 6:15, 6:17, 6:20, 6:23, 6:26 Resulting in the required average minute mile pace of 6:08 for the second half. I guess a little bit ‘fiddly’, but I would suggest worth the effort, as at least the runner would then have realistic mile splits to aim for, rather than trying to achieve the constant running pace approach which is 96% guaranteed to fail!

I will sign off tonight with two quotes. Firstly a repeat of the quote from Tom from Marathon Talk:

“My money's still on the even / negative split but I'd be delighted to be proved wrong. My quote for the day... I'd rather know I was wrong than think I was right ;)" Tom Williams, 2011.
And the second quote from the example 2:36:54 marathon runner, who listened to the wisdom of a positive split pacing strategy, and had the humility to accept that in the past his views on the even paced strategy may perhaps have been wrong, so he took a gamble and changed his pacing strategy.
“I was delighted when I came round on to the Mall and saw the time (a PB). I think that undoubtedly your (positive split) strategy paid off and thank you so much for taking the time to advise me. It is a challenge to go in to a race with a mindset that assumes slowing down, which seems on the face of it to be a negative thing. But in reality I think that acknowledging the slow down and embracing the fact that it will require extra effort to minimise the decrease in pace is actually very positive.” Simon, 2013

Keep an eye out for part two, where the science behind why slowing down in a marathon is a reality will be explained.

All the best with your next marathon,



  1. Sorry Stu, this article shouts out that you don't understand how to go about analysing pacing strategies. You can't do it by looking at mass results and expect to be able to make individual conclusions about best pacing, the nature of the analysis you've done just doesn't sustain this at all. The only thing your analysis shows is that how hard it is to run a negative or even paced marathon.

    The only way to look at merits of different pacing strategies is look at individual results over a series of races where the athlete has similar fitness and is racing to run the fastest they can. Only by looking at individual cases can you start to see a pattern of what works best.

    As I pointed out in my recent post about the folly of positive split, elite marathoners achieve their best performances by running negative or very even splits. This evidence screams out the small negative or even spits are best, but you just dismiss that somehow Elite's and non Elite's are somehow different because they train differently, and that somehow "magically" positive split becomes best. And no you stats absolutely don't support this.

    In this years London marathon none male elite's came anywhere close to their PB's and all because of going out too fast and a later surge that destroyed the elite field, with the finish being a case of last man standing. If your theory was right then we should have been on for a massive world record, but we ended up with the slowest London marathon winning time in 7 years.

    For a good review of the elite race I'd recommend have a look at the sport scientists blog:

    While this article does just focus on Elite's the discussion about pitfalls of getting pacing wrong is something that is relevant to us all.

  2. Good to see my bro in law getting in there and making good sense. It's 'easy enough' in any race to finish faster than you start but will that give you the performance you want to achieve? For example to achieve a faster second half Stu could have suggested to his mate to go out in 85 minutes and be sure to run the second half quicker.
    I'd suggest that in the farmework Stu is talking about he's making very good sense. If he suggested to his pal that he go out in 70 minutes the plan would have been to excessive but he didn't ther suggestion was to go out faster than his overall target speed but not by too much.
    The other thing is that rather than spend ages analysing what Stu is saying and trying to 'prove' it wrong, why not try it?

  3. Hi Ken,

    I've done plenty of races and the ones that I did best came from conservative starts, while races where I've gone out fast I've suffered badly in the second half and finished slower than I should have. So for my own experience "Start steady, finish strong" has worked best. To me this suggests their may well be individual variations between runners - some seem to suffer badly after a fast start, others seem to be able to recover from a fast start and not fall apart in the second half. I suspect I'm in the former category and Stuart is the later. This variation itself is worthy of exploration, as are many other aspects of pacing that we haven't yet fleshed out.

    The last few posts from Stuart on the topic of pacing have used the same statistical analysis to "prove" that negative split doesn't work. However, this type of analysis is not appropriate for answering that question, it only really tells us how few people run negative splits, not why or what is best. The volume of stats and graphs doesn't make up for the fact that it's being interpreted in inappropriate way.

    I don't find the suggestion that because the vast majority of runners do positive splits in the marathon that this automatically means it's the best strategy. Such logic applied to the modern population trend towards obesity would have us suggests that it's best to become overweight as well. Clearly this is absurd, but it does show that it's all too easy to draw the wrong conclusions from statistical trends.

  4. Hi Stuart,

    You raise a point in your post that I believe illustrates a failure in on part of advocates of conservative pacing strategies:

    "An argument often used, in fact pretty well the only argument I have ever come across, in justifying that the negative split is the strategy that runners should use, i.e. that the negative split indicates a good performance, is that most of the marathon world records have been achieved on a negative split."

    I agree, what the elite's do is just one piece of evidence, important evidence but it's not the whole story for sure. I often have read the advice that negative split is best with little actually explanation why at it might be best due to physiological or psychological level. There are plenty of reasons why it might make sense but these often aren't explained well enough and really need to be.

    I would push this back on yourself again as well, you haven't come up with any reasons why at a physiological or psychological level why a positive split might be best. So you've fallen into exactly the same trap as advocates of negative split - preaching the cause but not explaining the foundation for it.

    In my own recent post on pacing I explored the topic of pacing from a perspective of carbohydrate sparing and here even pacing wins, whether a positive or negative split the further your pace is away from an even pace the greater the cost in carbohydrate usage. This is just one aspect of pacing though.

    I believe this is only one part of the jigsaw, observations about elite's running their best times with even or negative splits is also important, as is the fact that most races runners slow down significantly in the second half. One area I'm most in intrigued is the "why" we typically slow down so much, and how we might train ourselves and pace ourselves on the day to minimize this.

    Pacing is a complex matter that will have the truth will have to be teased out from both theory, and anecdotal evidence and from controlled studies. One set of stats, or one bit of analysis and associated blog entry won't come close to answering all the questions. Just because it's complicated should dissuade us from trying to explore the topic. While the academic exploration is rather dry, in the end I do hope we can come up with a set of easy to follow guidelines for ourselves and other runners.

    I'll attempt to contribute a bit more to the pacing jigsaw over the coming months. While I come from the position that even splits are likely best, I really don't know where the journey of exploration will take me, especially for ultra distances. I'm hoping you will also see this as journey and continue to chip in your own thoughts/experiences.

  5. Hi Stu

    thank you for this post. I have enjoyed it along with your other posts especially on this topic. I have tried positive splits and found that they suit my running style. The first time I deliberately went out fast was on a JogShop 20 run a few years ago when I managed to PB, just scrapping under 3 hours. I didn't enjoy it because I did not expect the emotional impact of having so many people passing me in the last 8 miles. Last year having read one of your posts I ran the Downland 30 by running out fast and PB-ed by about 45 minutes.

    I then ran the JogShop 20 using the negative split strategy, which I hadn't done for a few years, but knowing before hand that quite a few people would pass me in the last 5 miles. I ran 2:47-ish, again a PB. But the key thing is the difference in attitude, I guess tying in with some of your RFE ideas. Because I was not one of the top 10 runners I did not have an expectation of not being passed in the last few miles. That is a potential downside of the positive split strategy that can only be offset by the thought that you are optimising your own race. i.e. Some of the people passing you might have had an even better time if they had run quicker at the start.

    Anyway, what I really want to ask you is: how much quicker would you run the first 50 miles of a 100 mile run? And specifically how this scales with time. You've suggested about 5% quicker for 2:30 marathoners and about 10% quicker for 4 hour marathoners. I noticed in last years South Downs Way 100, there were no negative splits, with the total time per a mile being typically at least 2 mins/mile longer over the whole 100 miles than for just the first 50 miles. This equates to about a 40% split for people running the first 50 at 10 min/mile and the whole 100 at 12 min/mile (a top 10 finish). A few people managed to keep the difference down to 30 secs/mile i.e. about 10% split. What are your thoughts on the optimal split?

    Thanks again for your, as always, interesting and fun ideas,
    Jonathan Davidson

  6. Totally agree with the post, I've run 7 marathons under 3 hours on the last few years. The only negative split was when I was battling for a podium place and had lots of rfe..
    Stephen richardson

  7. Hi Stu,

    I've been working on analysing Highland Fling splits over the weekend and a few surprising things popped out. Looking at the second half/first half splits the Winner Lee Kemp's ratio was 1.124 which very the the average of the male winners years, but only 3.1% of runners this year ran a similar split or faster second half. Your own ratio was 1.251 and only 25% of runners this year ran proportionally strong or strong second halves. The average split was 1.28.

    Looking at the proportion of runners that ran close to Lee Kemp's splits only 11 out of 413 finishers the splits ratio for the 4 legs were within 2% of his, so only 2.66% ran close to the way that Lee did, and none of the other top ten males achieved this. However, if we look at the past male winners they all ran with 2% or less deviation from Lee's split ratios. So 2.66% of all runners, but 100% of winners ran similar ratio splits to Lees.

    The probability that the it's just coincidence that the male winners all ran similar split ratios is extremely low, and in fact totally improbable. The only reasonable conclusion is that for these Elite runners to come out on top that they must run within quite a narrow range of pace throughout the race. They all consistently take the first half easier and the second half faster relative to their fellow Elite's.

    I will be writing up the full analysis over the coming week. I believe in the few snippets above do illustrate that while positive splits might be highly probable, this doesn't mean than probable == optimal. Taking what runners achieve on average won't lead to an optimal performance. Optimal performance comes from optimal pacing, even when the chances of achieving optimal pacing are so rare and to achieve.

  8. I' am fan of positive split do and my best marathon was positive split abaout 2-3min was first half better (2:59:13 and first half was 1:28:20)
    but I have not speed I have a good endurance and in 15jun was my fist ultra and I wrote about this:
    last marathon was 1,25times of first marathon

  9. OMG, what utter BS. Your friend had a 74:30ish half time to his name which could equate to anywhere from 2:34-2:40 (based on a half time + 5-10 mins conversion). To split a marathon only 2 mins faster than your half pb is generally not the smartest idea (some elites can do this ok) and only adds to the number of even splits out there. I'm surprised he managed 2:37 and had he adopted a more even strategy I'm sure he would have been better off but we'll never know and your data certainly doesn't back up anything either.

    You also need to consider that as the clock ticks past 3 hours, runners are less confident in their pacing strategy and also less informed as to what they could possibly run. Not to mention the mental side of things will let them down and cause them to lose time when they could just man up and keep running and not slowing down because it is getting hard. Try that next time, your mind might be saying no but if you override it you'll probably find your body says yes. One more thing to consider is that I imagine the granularity of targets is less as the times are slower ie there's loads of "barriers" under 3hr, major ones being 3:00 2:50 2:45 2:40 2:30 2:25 2:20 and then probably every minute under that! Whereas in 4 hours + you'll ge the uniformed wanting to break 4 hours or 4:30 or 5 etc, not as much break down. So this has an effect on the faster runners who are being so precise about the half split that 1 minute too fast will result in a positive split whereas further down the field someone could split in 1:50-2:00 and still come in under the 4 hour goal time, the 1:50 resulting in maybe a positive split and the 2:00 in a negative as they were really in 3:50 shape on the day.

    I consider my best run to be a 1 min negative split even though it's not my pb. Looking back I wish I had have split 30s faster to make it more even or still slightly negative but it's one of those things we'll never know what could have been. My pb and all of my other quickest times have come off a positive split up to 2 mins. I was shattered at the end of these so I don't even want to think what would have happened had I decided to go off even quicker!! So from my experience, a 2 mins positive is still a good run but I'm sure the end result would be different if the first half was slightly slower. But what do I know, I've only run a few marathons;-)

  10. Hi Anonymous

    Thanks for your comment. It's disappointing that you interpreted my post as BS. My blog post is based on a combination of my experiences and statistical analysis. When the data from 11,000 runners supports my view, I am comfortable that my blog post makes good sense, rather than being totally blinded by the belief that ones personal view must be right, which seems to be your approach.

    All the best with your marathon running. May I suggest that rather than thinking that you could have ran quicker with an even paced split, (even though your PBs were set with a positive split), simply look at the percentage slowdown listed within the table above to guide your pacing strategy, rather than mindless guessing!


  11. Paul the builder12 March 2014 at 19:54

    I think it's not utter BS, I think that's harsh. There could be some value in this for those folk who *know* that they are under-trained and are going to slow down (at marathon distance) - and this might help them with a 'glide path' to manage that slow down.

    But to simply say that most people slow down, therefore positive splitting is the most efficient strategy is illogical. You don't justify it, why should we accept it? I don't.
    1) Huge numbers of people running a big city marathon are inexperienced, and you can put money on them going off too quickly. Foolish, but predictably foolish.
    2) You appear to have made no allowance for the course here whatsoever. Your data is (I think) all from London 2013, right? If you've run London, you'll know it has a faster first half than second. My guess is around 30 seconds faster (at around 3hr pace).

    Please don't do the analysis all over again with the even-pacing bar moved to compensate for this, because the analysis itself is flawed anyway. This is just one of the elements demonstrating that a headlong leap in to number crunching without thinking first can lead to really bizarre conclusions.

    (doesn't target a negative split, but does target even pacing)

  12. Stu, although your theory may be correct, I don't see anything in your analysis that would allow you to make the leap from correlation to cause.
    Without a within-subject analysis (comparing runners performance using a specific strategy against their performances using an alternative pacing strategy) it is difficult to look at the relative performances and pacing and draw any valuable conclusions.

    Firstly, you have no information about the best performances of each runner with which to compare. Potentially, the negative splitters may have a significantly higher likelihood of achieving a PB, or vice versa, but we don't have any data on which to consider this.
    Also, we don't know what specific strategies each individual actually attempted to use, if any, in running the London Marathon. Training, racing experience, course, previous pacing success or failure and many other factors could influence whether any individual may or may not achieve their maximum possible performance.