The use of carbohydrate for sports has been well-known for several decades. The amount and timing of carbohydrate intake depends on many factors, including the duration, intensity and type of exercise.
Roles of carbohydrate in sport
As seen in the previous article, the main role of carbohydrate in the body is the production of energy. During exercise, this can translate to:
- Increased capacity to perform physical activity, particularly when duration is long
- Improved performance
- Maintenance of blood sugar levels
- Delayed time to fatigue (mostly in endurance sports)
- Improved skills in team sports
In the time between training or competition bouts, carbohydrate intake is important to:
- Top up glycogen stores
- Recover from exercise
- Maintain good immune function
The amount of carbohydrate an athlete requires during and around exercise depends on several factors:
- Exercise duration, intensity and type. Longer duration and higher intensity, particularly when the effort is constant as opposed to intermittent, requires more carbohydrate.
- Individual factors: oxidation rates, tolerance and preferences
- Practical factors: availability of carbohydrate-containing food or fluids and opportunity (or lack thereof) to consume those foods or fluids
It is important to mention the fact that the individual factors listed above can change with habits. When it comes to carbohydrate tolerance, this is commonly known as “training the gut”.
Sources of energy during exercise
The first few seconds of effort during exercise (8-10 seconds) are fuelled by existing intracellular ATP, which depletes in 1-2 seconds and phosphocreatine, which depletes in 8-10 seconds. Beyond that, exercise is typically fuelled by the oxidation of carbohydrate and fatty acids.
The rate of carbohydrate vs fatty acid oxidation depends on several factors, including the intensity of exercise but also the athletes’ dietary macronutrient composition and fuel stores. Regardless, in general terms it is easier for the body to generate energy from carbohydrate than from fat, which is why carbohydrate is the fuel of choice for most athletes.
Sources of carbohydrate during exercise
During exercise, the body obtains carbohydrate from 2 sources: endogenous and exogenous.
- Endogenous = inside the body (i.e. breakdown of glycogen from the muscles and liver to produce glucose)
- Exogenous = outside the body (i.e. food and fluids containing carbohydrate)
Carbohydrate for sports
Daily carbohydrate requirements are often expressed as grams per kilogram of bodyweight. The ranges are based on the duration and intensity of exercise:
- Low intensity: 3-5 g/kg
- Moderate intensity: 5-7 g/kg
- Endurance (1-3 hours per day) at moderate-high intensity: 6-10 g/kg
- Extreme (4+ hours per day) at moderate-high intensity: 8-12 g/kg
The requirements for sports that are not entirely glycolytic in nature (e.g. strength sports, team sports, martial arts) will likely reside somewhere in the lower ranges.
Consuming carbohydrate in the days prior to an event is known as “carbohydrate loading”. This process can lead to increased glycogen stores, which can be utilised in long endurance events or even medium duration events (e.g. 80-90 minutes) where glycogen availability can provide a competitive advantage. Typically, a high intake of carbohydrate in the 1-3 days leading to the event can help achieve a high level of glycogen storage.
Many people, including elite and professional athletes, choose to train or compete fasted. The main reasons are the belief that fasted exercise is more effective at burning fat and gastrointestinal discomfort.
In reality, training or competing in a fasted state when carbohydrate is an important fuel source (i.e. exercise lasting >60 minutes and/or of moderate to high intensity) benefits from a pre-exercise meal consumed 1-4 hours before exercise.
The amount of carbohydrate in the pre-exercise meal should contain 1-4 g carbohydrate/kg bodyweight, depending on exercise demands. There is evidence for and against of both low and high glycaemic index (GI) carbohydrate consumption in the pre-exercise window. In general, low GI carbohydrates tend to provide a more stable release of glucose into the bloodstream, however it should be noted that excessive fibre (along with excessive fat and protein) is not recommended before competition due to potential digestive discomfort. As a reminder, fruit and dairy foods are both low GI and tend to be easy to digest, making them suitable choices.
In shorter events (30-60 minutes), rinsing the mouth with a carbohydrate solution may be enough for improving performance due to the effects of the carbohydrate in neurons.
Not every athlete needs to consume carbohydrate during exercise, and those who need to may not be able to. Endurance events lasting 60 minutes and over, as well as team sports warrant the use of carbohydrate at the following rates:
- 60-150 minutes: 30-60 g/h
- 150+ minutes: up to 90 g/h (this can be achived with a mix of carbohydrate sources, as mentioned above)
Carbohydrate taken during exercise should be easy to consume, absorb and digest, e.g. sports drinks and gels containing high GI carbohydrate.
Note: the hour before the event is considered to be within the “during exercise” window.
When consuming carbohydrate in liquid form, it is important to take into consideration the hydration needs for the athlete to ensure the right amount of fluid is consumed.
When there is little time in between demanding sessions (i.e. less than 8 hours), the optimal protocol is to consume 1-1.2 g high GI carbohydrate per kg bodyweight per hour for about 4 hours after the event.
When the athlete has more time to recover, normal daily carbohydrate intake should be enough to replenish glycogen stores.
- Burke, L. Clinical Sports Nutrition. [VitalSource]. Retrieved from https://bookshelf.vitalsource.com/#/books/9781743763124/
- Jeukendrup A. Carbohydrate Supplementation During Exercise: Does it help? How much is too much? [Internet]. Vol. 20, Gatorade Sports Science Institute. Gatorade Sports Science Institute; 2007. p. 1–6. Available from: target=”_blank”>https://secure.footprint.net/gatorade/stg/gssiweb/pdf/2008130121226248.pdf
- Jeukendrup A. A step towards personalized sports nutrition: carbohydrate intake during exercise. Sport Med. 2014/05/06. 2014;44 Suppl 1(Suppl 1):S25-33.
- Williams C, Rollo I. Carbohydrate Nutrition and Team Sport Performance. Sport Med. 2015/11/11. 2015;45 Suppl 1:S13-22.
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