Carbohydrate Loading: Enhancing Aerobic Performance
What is Carbohydrate Loading?
The aim of Carbohydrate loading is to increase the body’s limited stores of glycogen, ultimately increasing endurance performance. As exercise intensity increases, the rate of glycogen use also increases. Endurance events longer in duration will also increase the amount of glycogen used. The majority of glycogen is stored within skeletal muscle: ~300 – ~600 g depending on fat free muscle mass, equating to ~1200 – ~2400 kcal. Glycogen is also stored within the liver: ~80 – ~110g, equating to ~320 kcal – ~440 kcal, but this source of glycogen is mainly used to keep blood glucose levels constant, preventing hypoglycemia (drops in blood glucose levels). Exercise durations greater than 60 minutes show the greatest performance improvements when using carbohydrate loading.
The science of Carbohydrate Loading
Muscle glycogen is a readily available energy source that is oxidized at a rate dependent on the exercise intensity. At lower exercise intensities energy is obtained through oxidative phosphorylation of acetyl-CoA of both fat and carbohydrate substrates. As exercise intensity increases the oxidation rate of fat is not sufficient to meet exercise demands, meaning the majority of energy is derived through glycolytic pathways, resulting in an increased need for glycogen. Studies have shown that glycogen stores can be increased through carbohydrate loading, increasing endurance performance.
Carbohydrate Loading Strategies
Carbohydrate loading strategies should be employed in the days leading up to the event not just the night before. Increasing carbohydrate intake 36-48 hours leading up to an endurance event has been shown to increase performance. To increase muscle glycogen stores by as much as ~150%, consume 10-12 g of CHO•kg-1•BW-1•day-1 36-12 hours before the start of your competition
Practical example: for a 80 kg male this equates to 800 g of carbohydrate per day, if following 10 g•kg-1•BW-1•day-1 meaning 3200 kcal. This has been shown to increase muscle glycogen stores by ~150%.
3-5 hours pre event
Studies show that a carbohydrate rich meal 3-5 hours pre event of 140 – 330 g of carbohydrate, equating to 560 – 1320Kcal significantly increases endurance performance. One study found that consuming a meal containing 2.5 g of CHO•kg-1•BW-1 increased muscle glycogen store by 11% after following a carbohydrate loading protocol.
Using the practical example above of 2.5 g of carbohydrate per kg of bodyweight, the same 80 kg male would need a consume a meal containing 200 g of carbohydrate, equating to 800 kcal 3-5 hours pre event.
Carbohydrate Loading Considerations
It should be noted that for every 1 g of stored muscle glycogen, 3-4 g of H2O (water) binds to each molecule of glycogen. Additional fluids should be consumed to aid digestion and absorption of carbohydrates. Another consideration to carbohydrate loading is the increased bodyweight associated with the additional glycogen and water.
Another consideration of consuming high amounts of carbohydrate (6-12 g of CHO•kg-1•BW) is that it can cause gastric distress. Ingesting foods high in protein and fat slows digestion rate, degreasing glycemic load and avoiding significant increases/decreases to blood sugar, which should all help to reduce gastric distress.
Glycogen Depletion Strategies
Individuals using depletion and loading protocols should taper their training during the days leading up to carbohydrate loading. Failing to rest or decrease exercise intensity can compromise race performance and reduce immune function, increasing risk of respiratory infections. Depletion strategies preceding carbohydrate loading are usually unnecessary and will not offer a significant performance benefit to most individuals competing or participating in an endurance event.
Carbohydrate intake 30-60 minutes pre event
Conflicting research exists over the type and amount of CHO to consume in the hour leading up to an endurance event. Studies show that ingestion of a high glycemic carbohydrate (e.g energy gel/hypertonic energy drink) results in a large rise in plasma glucose, causing a large insulin response. The onset of exercise causes a rapid drop in blood glucose, causing a phenomenon known as ‘rebound’ or ‘reactive hypoglycemia.’ Research opinion has varied in recent years with studies showing the use of lower glycemic sugars such as fructose preventing against this rebound effect. Most studies use highly trained or elite athletes during CHO studies, which are not a true representative of the whole population, so keep it simple, do a few race simulations in which you try different pre-event nutritional strategies and get to know what your gastric tolerance is.
Try natural foods high in fructose such as raisins and dried apricots 60 minutes pre warm-up if energy gels/energy drinks give you gastric distress.
Whether you are looking to improve your performance for a Tough Mudder, half marathon, marathon or ultra-endurance event, performance will be significantly improved following carbohydrate loading protocol. Need some further advice? Visit your nearest Decathlon retailer for expert nutritional advice and a range of nutritional supplements to help you through your next event. With products including energy gels/energy drinks, isotonic powders, electrolyte tablets and energy bars, we have the perfect product to meet your exercise needs.
(Notes on the Author – Danny Foster is an avid runner and nutrition expert currently studying sport and exercise science at Sheffield Hallam University. He works in our Sheffield Decathlon branch and currently works as an expert sports adviser ensuring each running/nutrition customer leaves the store kitted out with everything they need for their next race. Are you interested in a job that lets you pursue your passion? Why not scoot over to our careers site and discover the many positions available – http://www.decathlon-jobs.co.uk/ )