By Joseph Agu (MSc) |
Carbohydrates to endurance athletes are what proteins are to bodybuilders. They are essential if you want to be the best endurance athlete you can be.
Despite us knowing this for over half a century, a new wave of athletes have been experimenting with low carb intakes during training and competition, through the concepts of ‘training low’ and ‘fat adaption’ (a topic for a future article!). This, combined with the popularity of low carbohydrate diets, has made many people question (athletes included) the role of carbohydrates in their diets.
As such, this article aims to reassure many, and provide a summary on the benefits of consuming carbohydrates for endurance exercise.
Why do we need carbohydrates?
The main purpose of carbohydrate is to provide energy for cellular function. It is the preferred source of fuel for the brain, central nervous system (CNS) and skeletal muscle, with a requirement of around 130g per day set for adults based on the use by the brain and CNS (FNB, 2005).
Glucose is not only required for fuelling the brain and CNS, it is necessary for the synthesis of glycogen in skeletal muscle and to a lesser extent the liver (fructose and galactose are better at being converted to glycogen in the liver) (Decombaz et al. 2011).
What are the benefits of carbohydrates for endurance athletes?
Endurance athletes often train and compete at high percentages of their VO2max (75-90% VO2max) (Joyner & Coyle, 2008).
Due to such training and performance being at the limits of aerobic metabolism, and often exceeding it, fat oxidation cannot meet the energy demands of the contracting muscles.
Because of this, carbohydrates are primarily used, whether this be in the muscle (in the form of glycogen) or delivered during exercise in the form of a sports drink or carb gel, or both (Rodbergs et al. 2004).
✓ The typical amount of maximal liver storage of glycogen (which varies depending on factors such as training status and lean body mass) is 100g compared with 300-500g in the skeletal muscle, roughly providing 1600-2400 kcal of energy before these stores deplete.
Glycogen has been shown to deplete in the thigh muscles following 90-120 minutes of steady state work at 65-75% VO2max (Goforth et al. 2003). Without sufficient glycogen, depletion will occur, forcing you to fatigue and slow down (many of you may be familiar with the concept of ‘hitting the wall’) (Maughan et al. 2015).
As such, endurance athletes must ensure that their muscle glycogen stores are sufficient for the amount of work that they need to do in order to perform at their best.
How many carbs?
Though optimal intakes depend on the individual, dictated primarily by the size of the athlete and the amount of work they perform, endurance athletes are advised to consume 7-10g of carbohydrate per kilogram of body mass, which contributes to around 60-70% of an athlete’s total energy intake (Maughan et al. 2015).
For those of you who enjoy a good run but perform significantly less mileage than more advanced runners/cyclists, then 4-6g per kilogram of body mass is a good starting point, which can be further tailored to suit your exact requirements.
In order to meet these requirements, there are ideal times that these carbohydrates should be ingested, which are outlined below.
With respect to carbohydrate ingestion, the objective of pre-exercise endurance nutrition is to maintain sufficient levels of blood glucose in order to ‘spare’ or reduce glycogen breakdown.
The pre-exercise period can be further broken down into three timeframes: days, 2-4 hours and <60 minutes before exercise.
✓ Days before exercise (AKA carb loading) – Several strategies have been popularised in order to maximise glycogen storage capacity. The most popular is carbohydrate loading. This technique is employed to cause above-normal glycogen storage (supercompensation).
The typical model includes 3-4 days of glycogen depletion coupled with exhaustive exercise, followed by 3-4 days of carb-loading (500-600g/day) with a reduced training volume (Bergstrom et al. 1967). However, linear loads (10-12g per kilogram of body mass per day for 1-7 days) have shown to be as effective as traditional carb loading (Hargreaves et al. 2004). It is worth mentioning that carb loading has no effect on exercise lasting less than 90 minutes (providing that the athlete has sufficient glycogen storage to begin with) with the exception of intermittent, high-intensity exercise (Hargreaves et al. 2004; Nicholas et al. 1997).
✓ 2-4 hours before exercise
Research recommends around 200-300g of carbohydrate to be ingested 3-4 hours pre-exercise in the instance that the intake of carbohydrates during exercise is not feasible. The glycaemic index of the carb source does not matter; eat what you enjoy!
✓ <60 minutes before exercise
As many people train in the morning before work, eating a meal 2-4 hours prior to exercise is far from practical. In this instance, I recommend consuming between 30-60g of carbohydrate, ideally in the form of a powder (e.g. sucrose, glucose, powdered oats, maltodextrin etc.) that you can mix with a protein shake.
Carbohydrates | During-exercise
The objectives of during-exercise endurance nutrition are the same as pre-exercise – to maintain sufficient levels of blood glucose in order to ‘spare’ or reduce glycogen breakdown.
✓ For exercise lasting more than 90 minutes, I recommend 30-60g of carbohydrate per hour of exercise in the form of a sports drink or carb gel (Jentjens et al. 2004).
✓ For exercise lasting greater than three hours, 60-90g would appear to be the sweet spot. For these higher intakes, a ‘multiple transportable carbohydrate source (e.g. glucose and fructose) is recommended for better absorption and to minimise risk of stomach upset (Jeukendrup, 2014).
Carbohydrates | Post-exercise
Following a bout of exercise, the carbohydrate consumed should be enough to replenish glycogen stores, as insufficient intakes will ultimately lead to progressive glycogen depletion across training sessions.
✓ For this reason, endurance athletes are advised to consume 200-300g of carbohydrate in the hours following training, ensuring this fits in with your daily requirements. Higher glycaemic index carbohydrates (e.g. white potato, jasmine rice, white pasta) are known to replenish glycogen stores more quickly than low GI sources.
For those with less demanding training schedules, however, my advice would be to consume the carbohydrates that you prefer and are more likely to stick to (Jentkens & Jeukendrup, 2003).
Take Home Message
There you have it! I have hopefully convinced you of the importance of carbohydrates for endurance activity. In doing so, I have outlined some recommendations that you can try out for yourself to help with your training goals.
It is worth bearing in mind that these recommendations are pretty generic and therefore may not be ideal for everyone.
I would advise that you use these recommendations as a starting point, from which you can tailor to suit your exact needs based on how you feel and perform during your training sessions.