Pre exercise carbohydrate – is it still King when it comes to performance?

If you are like me you will have been fascinated recently at the attempts to break the 2 hour marathon. Whist there were many novel marginal gains implemented in an attempt to achieve this remarkable sporting barrier, one “old fashioned” gain that was frequently discussed were the attempts to optimise the runners pre-race and during race carbohydrate. I will have a look at the during-race carbohydrate strategies in a future “Fact Friday” but for today I am going to look at the science and practice of carbohydrate loading the day prior to competition.
Over the last few years you will have no doubt read articles suggesting that we do not need carbohydrates for maximum athletic achievements and that athletes are now fuelling winning performances on fats. To give credence to this claim, some excellent researchers have published interesting reviews on this topic suggesting that this may well be the case[1]. Whilst I could agree that low-intensity long duration exercise could be fuelled this way, or even some aspects of training, I am still convinced that for high intensity performance carbohydrates are still King. Let me try and convince you why I feel this way.
I really enjoy reading early studies in sport science and with carbohydrate we can go back as far as 1920 when Krogh and Lindhart first reported that there were distinct differences in the difficulty to perform exercise when on differing diets[2]. These authors noted that high fat diets resulted in excessive fatigue compared with diets rich in carbohydrates.  Perhaps the most well-known and informative study came from Bergstrom and colleagues in 1967[3]. These authors took muscle biopsies to look at the relationship between stored carbohydrate in the muscle (glycogen) and endurance performance. The figure below clearly shows the association between glycogen and performance capacity with athletes on the high carbohydrate diets being able to maintain performance much longer than those on the low carbohydrate or even mixed diets. Professor John Hawley  tried to summarise this in a great review where he suggested that in carbohydrate loaded athletes the elevated glycogen postpones fatigue by approximately 20% in events lasting >90 mins [4]. I am sure most of us would welcome a 20% improvement in performance!

Figure 1. The effects of muscle glycogen on endurance capacity. Redrawn from Bergsrom et al., (1967).

Recently, arguably the best sport nutritionist of our generation, Professor Louise Burke (from the Australian Institute of Sport), performed an amazing study to test this hypothesis. In a brilliantly designed study, elite race walkers were given time to adapt to a high fat diet or a high carbohydrate diet and performed a maximum 50 km time trial[5]. Despite achieving really high fat oxidation rates, the results again showed a significant performance advantage of carbohydrate over high fat diets. Given the historical data, combined with such well-designed and performed recent studies, I am more convinced than ever that if we want to maximise high-intensity performance we must start the event loaded with carbohydrates. 


It would be wrong of me not to point out that in 2017 we are becoming increasingly aware of the performance benefits of performing some training sessions in a low carbohydrate state to promote adaptions to training[6]. This style of eating is also seen as a good way for athletes to maintain muscle mass whilst dropping body fat (reducing carbohydrates allows protein to be consumed regularly to maintain muscle whilst still creating a calorie deficit) as recently demonstrated in some of our jockey research[7]. Our recent work in Rugby has shown that some rugby players who eat a low carbohydrate diet in the 24 hours prior to a game, commence the match with lower muscle glycogen and end the game with glycogen levels that could affect performance[8]. It is therefore more crucial than ever that athletes know how to load the day before performance to make sure they arrive at the start line loaded and ready to go. But how do we do this? 


The original studies looking at carbohydrate loading described a method by which athletes performed a hard training session approximately 1-week prior to competition to initially deplete muscle glycogen. Training was then gradually tapered over the week with carbohydrate increasing daily up to about 10g of carbohydrate per kg of body weight. Whilst this strategy may well lead to the maximum carbohydrate stores, it is often not practical in sport given that on many occasions we do not have a full week to taper for performance. Fortunately, it has been shown that muscle glycogen concentrations can increase from 95 mmol/kg to 180 mmol/kg in as little as 24 hours providing that approximately 8g of carbohydrate per kg body mass are consumed and that some of this is in the form of high glycemic index carbohydrates [9]. This is great news as this allows us to eat some of the foods that we may have been restricting during the week.


In reality, I often use between 6-8 g per kg body weight 24 hours pre-game to load my athletes, especially if they are not used to high carbohydrate diets. A typical diet giving these levels of carbohydrate may look a little like this:


Breakfast: Poached eggs on toast, with beans and a fruit smoothie (plus an extra banana)


Mid morning snack: Mint protein get buzzing bar

Lunch: Chicken with large portion of white rice, garlic bread. Fruit and Yoghurt. Large glass of fresh apple juice


Mid Afternoon Snack: Cherry protein get buzzing bar and smoothie.

Dinner: Cod with potato wedges (2 potatoes), mixed seasonal vegetables


Evening Snack: Greek Yoghurt with Muesli, pint of milk


So why not try it? The next time you have a big performance, see if this can be improved by a one day carbohydrate load. You may just find you achieve your personal equivalent of the sub 2 hour marathon. Good luck with your training and competition.





1. Volek, J.S., T. Noakes, and S.D. Phinney, Rethinking fat as a fuel for endurance exercise. Eur J Sport Sci, 2015. 15(1): p. 13-20.

2. Krogh, A. and A. Lindhard, The relative value of fat and carbohydrate as sources of muscular energy. Biochem J, 1920. 14(3-4): p. 290–363.

3. Bergstrom, J., et al., Diet, muscle glycogen and physical performance. Acta Physiol Scand, 1967. 71(2): p. 140-50.

4. Hawley, J.A., et al., Carbohydrate-loading and exercise performance. An update. Sports Med, 1997. 24(2): p. 73-81.

5. Burke, L.M., et al., Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. J Physiol, 2017. 595(9): p. 2785-2807.

6. Bartlett, J.D., J.A. Hawley, and J.P. Morton, Carbohydrate availability and exercise training adaptation: too much of a good thing? Eur J Sport Sci, 2015. 15(1): p. 3-12.

7. Wilson, G., et al., Fasted Exercise and Increased Dietary Protein Reduces Body Fat and Improves Strength in Jockeys. Int J Sports Med, 2015. 36(12): p. 1008-14.

8. Bradley, W.J., et al., Muscle glycogen utilisation during Rugby League match play: effects of pre-game carbohydrate intake. Journal of Science and Medicine in Sport, 2016: p. in press.

9. Bussau, V.A., et al., Carbohydrate loading in human muscle: an improved 1 day protocol. Eur J Appl Physiol, 2002. 87(3): p. 290-5.

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