London Marathon 2027: The Science of Preparation

Preparing for London in April 2027

The 2027 TCS London Marathon will take place on 24 and 25 April, with 100,000 participants planned across the two days. The organiser’s official event information is the source for allocated race days, start arrangements and participant instructions. The dates and planned field were checked on 30 September 2026.

For runners already training regularly, a specific marathon block of around 16–20 weeks provides a practical structure. For London, that places the beginning of the block between December and early January. The months before it are valuable: they allow a runner to establish a routine, develop a comfortable long run and arrive at the first week with a workload they already recognise.

A plan’s starting point matters as much as its length. A runner completing 15 km each week and a runner completing 45 km each week need different progressions, even if they are entering the same event. At DVOTION, we begin with the training the runner is currently completing, then consider the race goal and the time available. The first marathon guide covers that initial progression; the marathon PB article examines the demands of improving an existing result.

Aerobic fitness and the demands of 42.195 km

Distance running relies heavily on aerobic energy production, which uses oxygen to release energy from carbohydrate and fat. Endurance performance reflects the maximum rate of oxygen uptake, the proportion of that capacity that can be sustained and the energy required to run at a given speed. These are related qualities, but they describe different parts of the task. Joyner and Coyle, 2008

The duration of a marathon adds another demand. Physiological characteristics measured when a runner is fresh can deteriorate during prolonged exercise. Researchers use the term durability to describe when that deterioration begins and how large it becomes. This helps explain why a pace that feels comfortable for half an hour may become difficult after several hours. Maunder et al., 2021

Training therefore needs to develop both aerobic fitness and experience of sustained running. Shorter runs contribute to the weekly workload, while longer sessions allow the runner to practise maintaining an appropriate effort as the duration increases. A good marathon block develops these demands together throughout the programme.

Building the week around easier running

Weekly running distance, frequency and long-run distance are associated with marathon performance across the training literature. A meta-analysis covering 85 studies and 137 cohorts supports their importance, although those associations do not establish a mileage target that suits every runner. Doherty et al., 2020

The practical implication is to build a week that can be repeated. A runner comfortable with four running days might use three shorter runs and one longer run. As training develops, some of the shorter running can include controlled faster work. The long run remains part of the overall workload: adding distance on Sunday while increasing every other session changes much more than the weekly total suggests.

Lower-intensity running should account for a substantial share of that week. Research on distance runners supports programmes combining a large amount of easier work with a smaller amount of more demanding training, rather than concentrating most running around threshold intensity. Kenneally et al., 2018

For the runner, easier effort should be recognisable. Comfortable conversation is a useful way to monitor intensity outside the laboratory. If speaking in ordinary sentences becomes difficult, the effort has moved beyond what we would usually want from an easy run. Reed and Pipe, 2014 Pace can then adjust to the route, weather and recovery from previous sessions, while the purpose of the run stays the same.

Long runs and marathon-specific preparation

The long run is where training begins to resemble the duration and practical demands of the event. Its value comes from the sustained work and what the runner learns during it: whether the opening effort is appropriate, whether breakfast sits comfortably and whether carbohydrate can be taken consistently while moving.

Distance needs to be read alongside time. A 30 km run takes 2 hours 30 minutes at 5:00/km and 3 hours 45 minutes at 7:30/km. Prescribing the same distance to both runners creates very different sessions. We consider the runner’s previous long runs, expected race duration and recovery over the following days when deciding how far the longest run should extend.

As the block progresses, experienced runners can include portions at their intended marathon effort. The purpose is to practise the demand of the race and assess whether the proposed pace remains controlled. A first-time runner may gain more from extending comfortable running and establishing a reliable fuelling routine before adding faster sections. The right session follows the runner’s preparation.

The final long runs should provide information for race day. A pace that repeatedly becomes unsustainable despite appropriate fuelling deserves revision. A fuelling plan that repeatedly causes stomach problems needs further work. These findings are useful while there is still time to adjust the plan.

Fuelling and pacing belong in the training block

Carbohydrate availability is a major consideration during prolonged endurance exercise. Established sports-nutrition guidance supports carbohydrate intake during long events, with intakes of up to around 90 g/hour for exercise lasting beyond 2.5 hours when the amount and carbohydrate blend are tolerated. Thomas et al., 2016 The marathon fuelling article explains how to choose an intake and translate it into gels and drinks.

Training gives that recommendation a practical form. Rehearsing the intended products during long runs establishes whether they can be carried, opened and consumed at the required intervals. Repeated carbohydrate exposure can also improve gastrointestinal tolerance, although the response varies between runners. Jeukendrup, 2017

Fluid intake requires its own judgement. Drinking excessive volumes can dilute blood sodium, and adding sodium does not remove the danger of overdrinking. Thirst provides a useful safeguard against excessive intake; a planned strategy should account for conditions and individual losses. Hew-Butler et al., 2015

Race pace should emerge from the training block. Recent races indicate current performance, while longer sessions show how the proposed effort holds up over time. The pacing guide brings those observations together. Set the target before race week, then allow for the conditions on the day.

Arriving at the start ready to race

The final phase of preparation reduces training volume so that fatigue can fall while some familiar intensity is retained. Evidence from endurance studies supports tapering over a period of up to three weeks, with a substantial reduction in volume. Wang et al., 2023 Our taper article explains how that principle translates into the final weeks of a marathon plan.

For London, those weeks also need to accommodate travel, kit collection and the allocated start arrangements. Complete these decisions early enough that race morning follows a familiar sequence: breakfast, transport, arrival and the opening pace. Check the organiser’s current drinks and fuelling provision before deciding what to carry.

Where training intensity is uncertain, Endurance Performance Profiling provides a blood lactate profile followed by a separate maximal aerobic test. We use the findings to inform training zones and interpret them alongside the runner’s recent training and performances. The aim is a coherent preparation in which the laboratory findings, weekly programme and race plan all inform the same decisions.