Four things fast runners must get right when moving up to the marathon

There is a particular type of marathon blow-up I have seen many times over the years. A fast, often relatively young runner moves up from the shorter distances, having already run somewhere around 80 minutes for the half marathon and put together what looks like an excellent training block. The speed is clearly there, the workouts have been hit at exactly the right pace and everything suggests that a sub-3 marathon should be comfortably within reach. Then race day arrives. They go through halfway at something close to half-marathon pace, begin to waver at around 24 or 25km, and by 30km the wheels have come off completely. Sometimes it ends in a DNF; sometimes in a painful shuffle to a finish well over three hours.

It can be baffling because the runner is obviously fit enough to break three hours. But being fit enough to run a fast half marathon and being prepared to race a marathon are not quite the same thing. Over the years, the common mistakes I have seen tend to come down to four areas: fuelling, long runs, increased mileage and pacing. Or, conveniently, FLIP.

In most cases, the problem is not enough of the first three, and too much ambition with the fourth. Get those four things right and you give yourself a much better chance of converting your shorter-distance ability into a marathon time that actually reflects it, rather than ending a season feeling frustrated and immediately searching for another race to put things right.

F: Fuelling

This is the most literal part of FLIP: make sure you have enough fuel in the tank. The dangerous thing about marathon fuelling is that you can get away with doing it badly for quite a long time. The first 15 or 20km may feel completely comfortable, particularly for a fast runner operating well below their half-marathon effort, but by the time you start to feel as though you need energy you may already be playing catch-up.And unlike putting petrol into a car, the carbohydrate you consume is not instantly available to your muscles. It has to be digested, absorbed and transported into the bloodstream first, so fuelling works best when you stay ahead of the problem rather than waiting until you already feel yourself running low. Start properly fuelled, with a carbohydrate-heavy breakfast around two to three hours before the race and, if you have practised doing so, one or two gels before the gun. Then start fuelling early during the race rather than waiting until you feel tired.

My simple approach is a gel roughly every 7km through to 35km, with another one available if needed. Depending on the carbohydrate content of your gels, your own size and what you have trained your stomach to tolerate, you may need to adjust that slightly, but the principle matters more than the exact schedule: fuel from the beginning, not when the warning light comes on. Practise with the same gels in your long runs that you intend to use on race day and carry them yourself in a belt or secure pockets. I would never build my entire fuelling strategy around whatever happens to be available on the course, and it is certainly not worth saving a few pounds on gels after spending months preparing for the race.

I learnt this one the hard way. In my first two marathons in the early 2000s I barely fuelled at all, and I still have vivid memories of reaching the closing stages feeling as though I almost needed to physically lift my legs forward with my arms. You do not need a degree in sports science to understand what is going on here: over a marathon you are steadily burning through the carbohydrate your body has available, and if you fail to replace enough of it the final hour can become brutally difficult. It is an experience I have had no desire to repeat.

L: Long runs

A fast 5K or half-marathon runner may already have excellent cardiovascular fitness. What they may not have is legs that are accustomed to running for two and a half, three or even three and a half hours. That matters, because the marathon is not simply a longer version of a half marathon. It is partly about speed, but it is also about durability: your ability to keep running efficiently when your legs have already absorbed tens of thousands of impacts and have been working for far longer than they normally would in training or racing.

I would want several genuinely long runs in the final couple of months before a serious marathon attempt. For a well-trained sub-3 runner, four or five runs reaching at least the low-30km range is a good benchmark, and many experienced, higher-mileage runners will go further than that. The key point is not that every one of these needs to be a huge marathon-pace workout. Some can be very easy, even a minute per kilometre slower than intended race pace, because time on your feet is valuable in itself. The objective is to make the duration of the marathon feel familiar enough that your legs are not encountering completely new territory on race day.

Build those long runs gradually, recover properly afterwards and give yourself a day or two of easier running where necessary. I would also have the final long run completed around 10 days before race day, rather than trying to squeeze in one last endurance boost when the priority should be arriving fresh. By that point, the endurance work is done and the final days are about absorbing it and getting to the start line with your legs ready to use it.

I: Increased mileage

This is where some talented runners get caught out because speed can disguise a lack of endurance. Someone capable of running an 80-minute half marathon can look spectacular in training off relatively modest mileage. A 10km tempo or a set of kilometre repetitions might be completed at exactly the right pace, reinforcing the feeling that the marathon target is comfortably within reach. But the marathon rewards accumulated volume in a way that shorter races do not. There is a reason serious marathon training involves a lot of fairly unglamorous running as well as the eye-catching sessions.

For an ambitious sub-3 attempt, I would want to see at least eight weeks of sustained mileage before the taper, broadly in the 70-120km-per-week range depending on the runner's background and experience. You certainly do not need to hit 120km simply for the sake of it, and not everyone will tolerate that sort of volume, but trying to turn a 30-40km week into a fast marathon is leaving an enormous amount to chance. The individual sessions may look impressive, but they are only one part of the picture.

Nor does everything have to fit into a perfect 18-week training plan. If you already have years of running behind you, you do not suddenly lose your aerobic base because you have a holiday or an easier week. What matters much more is consistency: several consecutive weeks in which the mileage is high enough to build genuine endurance. You can bluff your way through a shorter race when slightly underprepared. The marathon has an unusually effective way of exposing the gaps.

P: Pacing

This may be the hardest one of all, particularly for quick runners. If you can run a half marathon in 80 minutes, going through halfway in 84 or 85 minutes can feel absurdly conservative. Everyone around you appears to be racing while you feel as though you are jogging, and that creates a huge temptation to let the pace creep up because everything feels so easy. The problem is that the marathon is meant to feel easy at that point.

An 80-minute half marathon requires roughly 3:47/km. An 85-minute first half of a marathon is around 4:02/km. That 15 seconds per kilometre may not sound like much, but across the first half of a marathon it represents a completely different level of effort. Going through halfway at your half-marathon pace is not banking time. You are borrowing it, at an interest rate that becomes increasingly unpleasant somewhere after 30km.

Perfectly even splits are not always realistic. Courses have hills, wind, crowded sections and congested water stations, and most runners slow to some degree late in the race. The objective is not to stare obsessively at your watch and hit every kilometre to the second. But the first half should feel controlled, and preferably almost laughably easy. The difficult skill is resisting the temptation to prove how fit you are while you still have 30km remaining.

The marathon gives you plenty of time to race later. If you reach 30-32km feeling stronger than expected, you can gradually increase the effort and spend whatever you have left over the final 10km. That is a much more enjoyable problem to have than discovering at 27km that the opening pace was unsustainable and that the final 15km are going to be about survival rather than racing.

FLIP the marathon in your favour

None of these four things is particularly complicated: fuel early, run long, build sustained mileage and pace the opening half conservatively. They are also interconnected. Higher mileage and long runs make marathon pace more sustainable, long runs give you the chance to practise your fuelling, proper fuelling makes it easier to maintain pace, and sensible pacing reduces the rate at which you burn through the resources you have spent months building.

There are no guarantees in the marathon. You can have a perfect training block and still encounter heat, illness, stomach problems, bad weather or simply a bad day. But I have seen too many talented runners arrive at the start line with all the speed required for a sub-3 marathon, only to undermine themselves through one or more of these four avoidable mistakes. The frustrating part is that they often finish knowing they were capable of much more, and immediately start looking for the next marathon to put things right (to which I would often advise: patience).

The better outcome is to respect the distance first time around. If you already have the speed, FLIP may be all you need to turn it into the marathon result your shorter-distance performances suggest you are capable of.