Thursday 9 April 2015

ReSUltS - The Reality Slowdown UltraStu Marathon Formula


(To those of you that are a little bit short of time I have copied the link to the useful webpage that this blogpost is explaining immediately below.  The remainder of this blogpost helps to explain some rationale behind the webpage slowdown formula, but one can go straight to the webapage, and hopefully the data it provides will be reasonably clear.  If not come back to this blog post.)

How fast should I run at the start of the marathon?  This is where the following webpage is really useful.   Please note that this slowdown formula has been updated form the version one which I introduced on UltraStu April last year within the post A Helpful Marathon Pacing Calculator The two improvements are that version two of the slowdown formula takes into account the gender of the runner, as this seems to have a significant effect on the percentage slowdown for the same finishing time.  I have also removed those runners that in simple terms 'blow up', and therefore have a very high percentage slowdown. Further description on the formula are detailed below.

Back in May 2013 I wrote two blog posts on the fallacy of the negative split for road marathon running, which created 'a bit of a stir'.  Which was further 'stirred up' with two other posts during April last year:  A Helpful Marathon Pacing Calculator and Road Marathon Pacing - The Positive Split Pacing Strategy - My Final Comment   At the time I stated that those posts would be my final comment on the topic, however, with marathon season 'kicking off' with the Brighton and Worcester marathons this weekend, and then Manchester, London and others during the following two weeks, I felt that one final blogpost on the topic could be so beneficial to the thousands of runners who will be running a road marathon during the next few weeks.

By now with the bulk of the physical training completed, the focus of the preparation should be on the non-physical training.  By that I mean predominantly goal setting and visualisations.  In terms of goal setting many runners will have a target marathon finish time that they would like to achieve, so this can form one of your goals, i.e. a destination goal.  This is useful as having this target finish time goal can help you in providing a counter argument to the many messages you will get during the later stages of the marathon, strongly encouraging you to slow down.  In addition to a destination goal, it is also useful to establish some journey goals for you to evaluate along the way, just to check that you are on track, and running well.  These journey goals may be related to your emotions during the run.  Are you enjoying the experience, are you 'staying within the present moment', are your race focused. are you running at the ideal intensity, right on that threshold?  Yes, it is useful to establish some journey goals, and then include what you want to be achieving whilst running the event within your visualisations leading up to race day.  Anyway, enough about goal setting, lets get back to marathon pacing.

As mentioned above, many runners will have a target finish time that they would like to achieve.  The issue is, what pacing strategy is best to increase the likelihood of achieving ones target finish time.  Now as ideal as the even paced marathon pacing strategy sounds, and with the argument typically being that most of the World records are set with an even paced, or a negative split paced strategy, in reality around 93 - 95 percent of all marathon runners who finish the marathon quicker than four and a half hours run a positive split.  That is that they slow down during the second half of the marathon, so their second half marathon time from 13 - 26 miles, is slower than their first half marathon time from 0 - 13 miles.

Now, this post isn't going to repeat my discussions on why I think this positive paced strategy is the ideal strategy.  You can go to my two posts from May 2013 if you want to read my rationale for my stand: The Negative Split - The Realisation that An Accepted Running Concept is Actually Flawed!    and The Negative Split Fallacy - Part 2 - The Explanation!   No this post is amount the reality of actually running the marathon, not opinions, theories and speculation!

So, the situation is that around 93 - 95 percent of marathon runners finishing a road marathon quicker than four and a half hours slow down during the second half of the marathon.  At last year's London Marathon within the non-elite field.  I think it is best to disregard what the elite marathon runners do, as their characteristics are quite different to the non-elite, 2:30 - 4:30 marathon runner.  Interestingly though, at last year's London Marathon only two elite men (2/18 = 11.1%) and two elite women (2/14 = 14.3%) achieved a negative split, so not that dissimilar to the 10.0 and 16.0 percent of non-elite runners in the quickest time band (see below for time band explanation).  Mo Farah also achieved a positive split of 3.30%, which is also not that dissimilar from the 3.88% for the quickest non-elite mens time band.)

     Sorry, I got distracted there!  So, the situation is that around 93 - 95 percent of marathon runners finishing a road marathon quicker than four and a half hours slow down during the second half of the marathon.  As I was going to say, at last years London Marathon 93.3% of finishers quicker than 4:18 ran a positive split.  The overall number of women runners from the first 4000 women finishers (4:18:15) that negative or even split their half marathon times totalled 292, which corresponds to a percentage of 7.3%. The overall number of men runners from the first 12000 men finishers (4:18:10) that negative or even split their half marathon times totalled 782, which corresponds to a percentage of 6.5%, which is a slightly lower percentage than for women.

So for 93 - 95 percent of marathon runners the big question is "How much time should I expect to slow down during the second half of the marathon"?  The vast majority of marathon runners aiming for a target finish time need to have an idea of the amount of slowing down that is most likely to occur, as they need to take this amount of slowing down into consideration, so even with this slowing down, which I consider IS A REALITY, NOT, I WILL REPEAT NOT AN INDICATION OF POOR RUNNING OR POOR PACING,  so that they will still achieve their target finish time.

Now I am NOT advocating for road marathons to start as fast as you can, to gain as much time as possible ahead of the even paced schedule.  No, this would be unwise.  This would be as foolish as trying to run at a constant pace for 26 miles.  No, what I am suggesting is to look at the statistics on how much slowing down occurs within the marathon, and I have used the data from 4000 women runners, and 12000 men runners from the 2014 London Marathon as the database.  And to base the calculation of how much slowdown one can expect to occur, on the AVERAGE of what happened for these sixteen thousand runners.  So quite a good sample size!

In order for the resulting percentage slowdown formula to not be influenced by those runners that absolutely 'blew up', I removed the ‘mega slowdown’ runner, those that slowed down more than two standard deviations from the mean slowdown percentage.

Those of you that are particularly observant may have noticed for the quicker runners the percentage of runners that even split or negative split the marathon was greater the quicker the finish time, with the quickest time bands being 10.0% (men) and 16.0% (women).  Yes, there does appear to be a gender difference.  The percentage slowing down, (which is calculated as the time one slows during the second half marathon, divided by the first half marathon time, multiplied by 100), is therefore slightly less for the quicker finishers.  therefore to accommodate theses characteristics of the 16000 finishers, different slowdown percentage were established for different finish time bands and for men and women runners.  The following table displays the AVERAGE percentage slowdown values for each time band, for men and women runners.

Now having these percentages in a table is interesting, but what does it actually mean for the runner.  How fast should I run at the start of the marathon?  This is where the following webpage is really useful. Please note that this slowdown formula has been updated form the version one which I introduced on UltraStu April last year within the post A Helpful Marathon Pacing Calculator As stated above the two improvements are that version two of the slowdown formula takes into account the gender of the runner, as this seems to have a significant effect on the percentage slowdown for the same finishing time.  I have also removed those runners that in simple terms 'blow up', and therefore have a very high percentage slowdown. Further description on the formula follows.  Opps, I also forgot the third improvement for version 2, in that the slowing down now doesn't start until the 16th mile, rather than the 14th mile.  I think this is more likely to be representative of what actually occurs.  As long as the runners have a realistic target finish time, maintaining a constant pace for 15 miles should be a problem.  It is during the last 11 miles when the effects of the previous miles run on the roads starts to have an impact and make the maintaining of the same constant pace a lot more difficult, hence the slowing down.

As an aside, if I recall at the time last year there was some confusion expressed regarding my perhaps wrong assumption that the accepted view at the time was that an even paced strategy pace was the standard approach, which would result in most runners not achieving their target finish time if adopting this approach.  Now I think that probably more people realise that the even paced pacing strategy doesn't work, so hopefully this year there will be less confusion.

Unfortunately the webpage calculations aren't exactly correct, due to either some mystery formatting error or simply the effect of rounding error, which we now think is the likely cause of the error.  We, actually, in reality it is good friend Tim, who is the brains behind the webpage, who has been working hard on looking to solve the problem.  Anyway it is nearly working perfect.

Just to quickly summarise.  The way the webpage ReSUltS -  The Reality Slowdown UltraStu Marathon Formula works is that you select male or female, then enter your target finish time, then click calculate.  I mentioned above that the webpage isn't working exactly right, but If you look at the minute mile pace the formula produces, the half way and 5mile, 10 mile and 15mile split times are all correct.  But when the percentage slowdown linear increase occurs at mile 16, there is a big slowdown for mile 17 and then back to a linear increase in minute mile pace until the finish.  It appears that this big slowdown at mile 17 is where the slight error occurs.  In terms of the summary table on the right the pace column is for the last mile of that 5 mile split, NOT the average pace for the last 5 miles. 

However, although the webpage isn’t exactly working, the key information, e.g. the percentage slowing down, which allows you to calculate your half marathon split time is correct.  Also the idea that one should be able to run at a consistent pace for every mile up to 15 miles is also correct.  The last 11 miles around 93 - 95% of marathon runners slow down, how they slowdown will be quite varied, but a gradual linear increase every mile from 16 miles onwards seems a reasonable guess, which the slowdown formula adopts.  Remember slowing down after 15 miles doesn’t mean that you are running poorly, or that you did the first 15 miles too fast.  Slowing down is reality. The webpage does produce a different minute mile pace for each mile from 16 miles through to the finish, however, I would recommend that you simply use the minute mile pace generated for the first 15 miles, which takes into account the average slowdown for that time band, and then from mile 16 onwards, simply run by feel.  If feeling great then reduce the rate at which you slow down.  If not feeling so great, then allow a slightly greater rate of slowing down and hope that the 'difficult patch' will pass, and that you may be able to get back 'on track' a few miles later.

Hopefully the above explanation of this ReSUltS -  The Reality Slowdown UltraStu Marathon Formula webpage makes some sense, and for those of you are able to take on the fact that 93 - 95% of marathon runners slow down during the second half of a road marathon, I hope that you find this webpage useful.  To those of you that aren't aiming for a target finish time, or are aiming for an even paced strategy, well then this webpage probably isn't relevant for you, so apologies if you have read this blogpost down to here!

To all of you running a road marathon during the next few weeks, I wish you all the best.

I will sign off with a few relevant quotes which may help during those 'challenging' moments between 16 and 26 miles.

"The way we perform is the result of the way we see ourselves.  To alter our performance we need to alter or change ourselves and it is that changing that's difficult."  Gary Elliot, New Zealand Coach to awesome NZ marathon runner Alison Roe (1983)

“A large amount of what we achieve is governed by our mental state and how we see ourselves. (It is) a lot about opening the mind to what might be possible when we throw away the self imposed limitations of our mind.” Tom Williams from MarathonTalk (2011)

“Remaining positive really is one of the most precious faculties for any athlete.  That, and an ability to stay focused and disciplined.  Develop a mind bank of positive images and thoughts – family, friends, previous successes, favourite places, a big plate of chips.  You need to build it up as you would any collection, but soon you will have a range of thoughts to flick through when next your body and soul are screaming out for relief”.Chrissie Wellington, Four times World Ironman champion,  from her book titled "A Life Without Limits".
Enjoy the journey,




  1. Last year you first published this approach and a number of commentators pointed out the flaw in using all runners in each band to compute the slow down that might be deemed acceptable. The key problem is that you are including runners that have bad days and slow down massively. Hitting the wall and slowing down massively is sure sign that a runner went out too fast and could not maintain the pace.

    By including the blow up runners you tilt all the stats towards the having a bad day runners. The amount that these bad day runners have is dis-proportionality large as there margin for slow down can be so large - it's not uncommon to see bad day runners slow by 30%+ in the second half.

    Contrast this to runners that have perfect days, the most they are likely to exceed the average for that band is the different between a even/slighlty negative split and average, for a sub 3hr runner the biggest deviation from the average is only likely to be be around 6 to 7 percent.

    I would recommend that for each band you plot the proportion of runners running different split percentages. Those who have the biggest positive splits will be the ones have the worst days. An interesting analysis would be to cut out various percentage of the bad day runners based and then see what happens to the averages of the runners have perfect to descent days.

    For our running community we actually want runners to have fun, to avoid having bad days, so for sure we don't want them using splits that are skewed by those having bad days. This is important as these bad day runners skew the results to higher positive splits than is at all comfortable to achieve - require going progressive out too fast. If you go out too fast you SUFFER MORE for a given finishing time.

    If you just look at the 3:42 to 3:45 band you are saying that they should aim for a 10% slow down. This means a 5% faster than average marathon pace for the first half, 5% slower in the second half.

    If one looks at the McMillian running calculator you'll find the difference in pace they suggest for a half marathon race vs a marathon are is actually almost exactly 5%. So what you are advising is that these runners should pace the first half as at half marathon PB pace, then hang on. (The McMillan running Calculator suggest a 1:54:02 half PB maps to a 4hr marathon time.)

    Now the McMillian running calculator isn't perfect for the average runner, it assumes too greater a resilience for an average runner so most will fall short of it's lofty estimates.

    However, your own stats will compounds things if runners use the McMillian and other running calculators to guide their pace then use your guide bands.

    These serious problems don't even touch upon what is actually most optimal way to race a marathon. This is well established by sport science as an close to even split. Calling this scientific consensus a "fallacy" is pretty daft, especially when there are numerous marathon world records that illustrate that it is indeed probably the most efficient way to pace.

    1. Hi Robert, Thanks for your comment on the slowdown formula.

      You are exactly right in that when runners 'blow up' then they can massively slow down during the second half of a maraton, and this is one of the improvements I have made to version 2 of the formula. Perhaps you missed this within by blog post yesterday, but for version 2 I have removed all of the mega slowdown runners from each time band so that there large percentage slowdown percentages don't skew the data as you highlight. I classified a mega slowdown runner as those runners who were more than two standard deviations slowere than the mean percentage slowdown, and then recalculated the mean percentage slowown for that time band with these runners removed. Interesting, if my memory is correct, this didn't actually make that much of a difference to the average percentage slowdown values. At most I recall no more than two percent. But yes, two percent can be quite a different.

      So yes, I have improved the formula due to this oversight in versio 1, and also improved due to the gender effect.

      Now in terms of the McMillian running calculator you mention, I can't commnet on this as I don't know how their values are calculated. What database they used. But what I do know is that the percentage slowdowns I present and use for the formula are based on what actually happened at last years London Marathon, from a database of 16000 runners quicker than 4:18, and with the mega slowdown runers removed. It is NOT a guess, it is what happened.

      The slowdown values are based on the AVERAGE for each time band, so yes, half of the runners will have slowed down less, but then again more than half (as megaslow runners are removed)of the runners would have slowed down more. I am simply raising peoples awareness to what the average slowdown is and that they is a really useful guide.

      If people want to try to aim to achieve zero slowdown, i.e. an even paced strategy, then yes, they can aim for this. But they need to be aware that they have a very small chance of achieving it, around 5 - 7 % chance. And achieving an even paced split doesn't automatically assume that you have run to the best of your current ability. Yes, you may have a more fun as you aren't probably really extending yourself for the majority of the race. If I want to have fun, I can go to a theme park. If I want to challenge myself, to see what I can really achieve by being really focused and giving my best I do a marathon race.

      Yes different people run for different reasons, however, one of my key reasons for running and I think for others is to achieve the best they can on the day. There is something really special in knowing that you ran well, in knowing that you focused the entire way. Running the first half at a really easy pace just so I can achieve an even paced split doesn't really appeal to me, In essence I interpret it as lacking confidence in ones ability, which is a common trait of so many runners. This lack of self belief, and the acceptance that they aren't very good at running. Other faster runners are lucky as they have better genes etc. Yes one can take it easy for the first half, get to half way feeling really comfortable as often recomended. But in reality they have turned the marathon into a 13 mile warm-up, followed by a 13 mile race. Have they really raced a marathon?

      Anway, thanks for your comments. Having other sides to the discussion really aids the understanding of this intriguing topic, which at the moment there is not clear answer. Stuart

    2. Apologies for missing the removal of the MEGA slow downs.

      I agree that only a small % of runners ever achieve close to an even split, even though a much large % will be attempting this. If you are aiming high such as beating a PB each time you race then chances are that you'll often not achieve what you set out to achieve, and this is usually because in the second half your fitness (aerobic, structural, metabolic and neurological) fails to match up to your ambitions and you slow down.

      I suspect part of this over ambition is the McMillian style runner calculators that generate overly optimistic estimates for longer races based on short races. As far as I'm aware the McMillian calculator is based age grade world bests for different distances. The progression of world bests does loosely follow what a highly trained runner can achieve, but for the average runner I believe it provide too fast times for marathon when using 5 and 10k times. The average runner simply doesn't have the resilience to keep the speed going like an elite can do.

      You can see this most clearly when you compare sprint times and marathon times. Most male runners will like to be able to do 100m in 19 seconds, so no less than twice as slow as Usain Bolt. However, looking at marathons, the average marathon finishing time is actually well over 4hrs.

      The reality is that pacing evenly by feel is really really hard to do. Pacing by even splits is just as hard, partly because of these over inflated running calculators suggested times that simply aren't possible. If you head off with splits that are too optimistic then most times a runner will crash a burn and fall short.


      As for pacing evenly not being real racing. Well go ask Robbie Britton. Have came 3rd at 24hr world champs at the weekend, he did his 162 miles over an incredibly evenly split. Was he racing for the first half or just cruising?

      I am pretty confident that he was racing even before he started the race. He will have had a realistic plan in mind, he then executed it close to perfection.

      Contrast Robbie's performance to that of Marco Consani, he looked to be having a great race, and was well ahead of Robbie at half way. He then struggled and finished with a total around 30 miles lower. I don't know yet what happen with Marco. He looked to be in 150+ mile shape beforehand. Going out faster than Robbie may well have been a factor. The team manager wrote afterwards that that those who paced evenly were the most successful on the team.

    3. Second half of reply, as it didn't quite fit...

      Just because you are running comfortably within yourself doesn't mean your not completely focused on racing. When I race by HR I am completely focused on racing, getting the absolutely best out of my race. For me it's essentially a time trial, running to get the best time I can, rather specific placing in a race.

      Being 100% focused on racing is not about running 100% effort level at all times. It's about being focused on making sure you can run your best time or place when you cross the finishing line. When you are 100% focused on achieve the best time you focus on managing your body in the best way you can so it performs at it's best overall, with the best time or placing you can achieve.

      Achieving a great time or place at half way should be 100% meaninglessly when it comes to racing. It's only the finishing line that counts.

      If you are focused on other things like "feeling like" you have been racing you'll get a different result that is you are focused on getting your best result. I fear that over the years you have conflated the two, "perception of effort level" is not proportional to "finishing result".

      My best race results I've been able to keep focused, pace well and finish strong. Often finishing strong has come automatically, it just happens if you've looked after your body well in a race. These races I've finished completely spent, but completely spent only at the finish line, not half way into the race. If you get the pacing right the pace at the start will closely match that at the finish.

  2. macmillan states on his website that the further the distance away you are using for comparison from the race distance prediction the less accurate it will be. So a 5k prediction for a marathon is much less likely to be accurate then a half for example.

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