The time has approached where the London Marathon is on the horizon and everyone is thinking about their final long run of 16-20 miles. This brings the question of what should you be doing during this session to make sure you are sufficiently fuelled.
Performance nutritionist, David Dixon, offers some advice...
Unfortunately, everybody is different and there is no exact answer that will work for everyone as there are a number of external factors that need to be taken into consideration: current fitness level, average running speed, terrain, weather, current nutritional practices both generally and within current training.
However, I will attempt to give some basic tips and advice in the coming piece.
Everybody breaks food down to help us repair muscles and to provide energy to help us move around. The two main sources for this are fat and carbohydrates.
As you can see from the diagram, the amount of intensity will dictate the type of fuel we will predominantly use, with a change from predominantly fat to predominantly carbohydrates at around 50% of VO2max.
However, there may be individual reasons for this to be lower or higher than this value.
Therefore, if you run at 70% of your maximum, the fuel you will be using will be 30% from fat and 70% from carbohydrates.
As you can see, if you want to maintain that 70% of max, you will need to keep the carbohydrates topped up (it is possible to use fat stores at higher levels of intensity and it may be more beneficial for some runners, but that’s another discussion and too long for this short piece).
Assuming the following details of our athlete:
Table: How many calories are burnt running at various speeds assuming a 70% of max intensity effort
The above table is a rough guide and there will be individual differences but as you can see, at different speeds we will use amounts calories to supply energy.
If a fully fuelled body has around 2,000 Kcal of carbohydrate fuel, we can see that we do not have enough to sustain the required speeds for the entire 42km, which is why we need a strategy to keep this topped up as much as our body allows.
As you know, our stomach and intestines struggle to absorb food while we are exercising. It is important to know how much we can tolerate and to practice this before the big day.
Research shows that the body can tolerate between 30g (120 kcal) and 60g (240kcal) an hour during exercise or between 90g (360 kcal) and 120g (480g) (if using duel type fuel such as glucose and fructose).
However, I would recommend that the higher amounts are definitely only used if you have trained and used in previous races so you know that you will not suffer from upper/ lower GI distress.
As you can see, re-fuelling during the race could be important and I would suggest starting with 30g an hour and see how you go.
There are different ways to achieve this, as the diagram shows. The import thing is to find the one or combination of sources that work for you.
This might be a drink and then one of the other types. Although you may need to also use water along with the solid versions in order to stay hydrated, depending on your personal sweat rates and the weather on the day.
Once you have finished running, there is a need to remember the 4 Rs: Rehydrate, Repair, Replenish and Reinforce.
Depending on how quickly you will be training again will depend on how aggressive you need to be with your recovery.
Although I would recommend having some protein and carbohydrates immediately after finishing or at least within an hour. This could be in the form of a meal or using recovery suggestions.
The optimal amount is 1.2g per kg of body weight for carbohydrates and 25-30g of protein.
Some suggestions have been made above.
In summary, I have offered some advice with regard to fuelling and recovery. However, there is a need to practise this to find out your optimal strategy.
David Dixon
SENr Performance Nutritionist