Fuelling for exercise – Part 1 – Pre-Exercise Caffeine & Carbohydrate

by our Sports Scientist Stephen Morehen

Optimal physical performance isn’t all down to how quick, strong or powerful you are. In the same way that the Apollo 11 wouldn’t have made it to the moon using standard petrol that we put in our cars – the human body simply cannot perform to its best ability without appropriate fuelling. In this next series of blog posts, we will take a look at some of the most researched and effective (backed by robust scientific evidence) ways to fuel our bodies for exercise.

Carbohydrates

Carbohydrate is the primary source of fuel for our bodies during exercise. Carbohydrate is stored in our bodies as glycogen and is broken down into glucose as and when we need the energy to perform a given workload – this could be leg day in the gym or a 10km park run. The average person can store ~600g of glycogen, though this is dependent on many factors such as body mass, fitness levels and diet. Skeletal muscles store the most glycogen (300-700g) whilst the liver contains a smaller stash of anywhere up to ~160g.

Research has shown that exercise which exceeds 2hrs in duration is the most likely to see improvements in performance due to pre-exercise consumption of carbohydrate, although no negative effects are seen in shorter-duration exercise [7]. For example, if you’re planning a long Sunday bike ride it is definitely worth considering your carbohydrate intake prior to starting. Just how much you need to consume depends on the duration of your ride [8] but a rough guide is as follows (to be consumed 3-4 hours prior to exercise):

~1hr                 1.5-2.5g/kg of bodyweight

1-2.5hrs           2.5-3.5g/kg bodyweight

3hrs+               4g/kg bodyweight

Be wise with your choice of carbohydrate, foods with a lower glycaemic load (oats, sweet potato, brown rice) will offer a slower and more sustained release of energy compared to foods with a high glycaemic load (high-sugar cereals, white bread, white rice). High levels of carbohydrate can elicit gastrointestinal discomfort for some individuals [9] so, as mentioned with caffeine above, try lower doses first and build up to higher doses if necessary.

Caffeine

Responsible for the buzz you get from your morning coffee, caffeine is one of the most widely used supplement in sport. One study, by Del Coso et al (2011) found that in a sample of over 20,000 urine samples collected from elite athletes between 2004-2008, over 70% contained measurable levels of caffeine [1]. Indeed, a recent review of evidence regarding caffeine and performance concluded that caffeine elicits ergogenic (performance enhancing) effects in endurance exercise, repeated high-intensity exercise and submaximal strength-based exercise [2]. At the time of writing, the effects of caffeine on maximal strength are ambiguous [3].

General recommendations are a dose of 3-6mg/kg of bodyweight, 60 minutes prior to exercise, with no additional benefits seen at doses higher than 9mg/kg [4]. There is, however, growing evidence which suggests a degree of inter-individual variability in responsiveness to caffeine [5]. As such, a good idea would be to start with lower doses and build up gradually to determine whether you respond to lower doses and therefore don’t require higher doses. Some typical caffeine contents are listed below:

Double espresso – 80mg

12oz brewed coffee – 120mg

250ml can of redbull – 80mg

Caffeine is also available in powder or tablet form although research has shown no difference in ergogenic effects between coffee and pure caffeine [6].

References

1. Del Coso, J., G. Munoz, and J. Munoz-Guerra, Prevalence of caffeine use in elite athletes following its removal from the World Anti-Doping Agency list of banned substances. Appl Physiol Nutr Metab, 2011. 36(4): p. 555-61.
2. Grgic, J., et al., Wake up and smell the coffee: caffeine supplementation and exercise performance-an umbrella review of 21 published meta-analyses. Br J Sports Med, 2019.
3. Grgic, J., et al., Effects of caffeine intake on muscle strength and power: a systematic review and meta-analysis. J Int Soc Sports Nutr, 2018. 15: p. 11.
4. Goldstein, E.R., et al., International society of sports nutrition position stand: caffeine and performance. J Int Soc Sports Nutr, 2010. 7(1): p. 5.
5. Pickering, C. and J. Kiely, Are the Current Guidelines on Caffeine Use in Sport Optimal for Everyone? Inter-individual Variation in Caffeine Ergogenicity, and a Move Towards Personalised Sports Nutrition. Sports Med, 2018. 48(1): p. 7-16.
6. Hodgson, A.B., R.K. Randell, and A.E. Jeukendrup, The metabolic and performance effects of caffeine compared to coffee during endurance exercise. PLoS One, 2013. 8(4): p. e59561.
7. Murray, B. and C. Rosenbloom, Fundamentals of glycogen metabolism for coaches and athletes. Nutr Rev, 2018. 76(4): p. 243-259.
8. Thomas, D.T., K.A. Erdman, and L.M. Burke, American College of Sports Medicine Joint Position Statement. Nutrition and Athletic Performance. Med Sci Sports Exerc, 2016. 48(3): p. 543-68.
9. de Oliveira, E.P., R.C. Burini, and A. Jeukendrup, Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports Med, 2014. 44 Suppl 1: p. S79-85.