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Running: How to Fuel for Training vs. Race Day

Whether you’re preparing for a 5k or a marathon, the aim of fuelling strategies for training and race-day are different. Fuelling for training should support training intensity and recovery whilst also promoting optimal training adaptations i.e. actually helping our muscles to better withstand the demands of the event. In contrast, race-day fuelling is all about reducing the stress of the exercise in order to support maximal performance.


When carbohydrate is restricted before or during exercise (during morning runs for example), enhanced training adaptations (such as making our muscles become more “endurance like”) are commonly reported. Training sessions deliberately performed with low carbohydrate availability are termed ‘train-low’ sessions(1). Training ‘low’ appears to enhance the amount of mitochondria in our muscles, and may improve endurance performance(1). Providing that race-day carbohydrate loading and in-race fuelling is optimal (e.g you hit 60-90g of carbohydrate per hour), these enhanced training adaptations could therefore improve race-day performance.

Despite the potential benefits of training ‘low’, there are negative implications of persistently training ‘low’(1):


  • Prolonged or high intensity runs are unlikely to be maintained because carbohydrate is the primary energy source during high-intensity exercise.
  • The Immune system can be suppressed, increasing the risk of illness.
  • Muscle protein breakdown is increased(3). Continually raised muscle protein breakdown can reduce overall muscle mass, which can reduce power output and running performance.
  • The muscles need to ‘remember’ how to utilise carbohydrate as a fuel.


As opposed to “training-low” all the time, it therefore seems better to adopt a “train-smart” approach whereby some sessions are performed with high carbohydrate availability and some sessions are deliberately performed with low carbohydrate availability.



‘Train-smart’ recommends that a runner performing exercise fuels for the work required. Carbohydrate can be reduced or restricted for selected training sessions (ideally before breakfast) where the intensity or duration of the session is not likely to be compromised by low carbohydrate availability. However, when the aim is to perform the highest workload possible, practicing your fuelling strategy will allow the body to learn to utilise carbohydrate as a fuel source. Here, a restricted carbohydrate approach is unlikely to be appropriate(2).

Multiple ‘train-smart’ strategies that appear to enhance training adaptations are reported in the scientific literature:


  • ‘Sleep-low & train-low’ uses overnight carbohydrate restriction followed by a moderate-intensity, ‘train-low’ running session in the morning. High-intensity sessions are performed in the afternoon/evening with high carbohydrate availability, having consumed carbohydrate during the day(4).
  • ‘Twice per-day sessions’ suggests training twice per-day every other day rather than once every day. The second session of the day is a ‘train-low’ session, having restricted carbohydrate intake following the first session(5).
  • During a ‘train-low’ session carbohydrate should be restricted during training to enhance training adaptations(6).
  • ‘Train-low’ sessions can be protein-fed rather than fasted to reduce muscle protein breakdown(8).
  • Consuming caffeine before a ‘train-low’ run appears to increase exercise performance by mitigating some of the loss in exercise intensity(7).


Race-day strategy

When optimal performance is the goal, high carbohydrate intake is necessary because carbohydrate is the primary energy substrate for high-intensity and prolonged runs. Even one day of carbohydrate loading before a race is effective to increase muscle glycogen concentration(9), therefore the day before race-day; 8-12 grams per kilogram of body mass of high glycaemic index (GI) carbohydrate is recommended. High GI carbohydrates are easily and quickly absorbed e.g. breads, cereals, rice, pasta, potatoes etc. This increases muscle glycogen resynthesis to a greater extent than low GI carbohydrate sources(10).



To maximise running performance and carbohydrate loading, training should be tapered leading up to race-day. Tapering should begin two weeks prior to race-day with a steady reduction in training volume(11). The final training session should take place in the afternoon/evening two days prior to race-day and carbohydrate loading can begin with the post-training meal. By doing this, muscle glycogen resynthesis is enhanced in the 1-4 hour period after your final run.

On race-day:


  • Large quantities of fibre, protein, fat, and fructose (typically found in sports drinks) should be avoided as these have been associated with gastrointestinal problems during exercise, individual preference is also important in this regard.
  • The pre-race meal should contain some carbohydrate (e.g. 2-3 g/kg body mass), however if the individual is sufficiently loaded the day before, it doesn’t have to be especially high in carbohydrate.

Carbohydrate consumed during a race provides the muscles with an additional source of carbohydrate as opposed to muscle glycogen only. Carbohydrate should be particularly consumed during training sessions and events lasting greater than 1 hour (e.g half marathon) to help promote performance.


‘Train-low’ sessions:

  • Only for moderate or low intensity training lasting less than 60 minutes.
  • Consume protein beforehand rather than being fasted.
  • Consume caffeine approximately 30 minutes beforehand.


Performing carbohydrate loaded:

  • For high-intensity training and/or sessions lasting longer than 90 minutes.
  • For events lasting longer than 90 minutes consume 8-12 grams per kilogram of body mass of mainly high GI carbohydrate the day before race-day.
  • Consume 60-90 grams of carbohydrate every hour during a race, aiming for 20 grams every 20 minutes. Achieve this using a mix of GO Electrolyte Powder and GO Isotonic Energy Gels.
  • Consume 1.2 grams per kilogram of body mass of carbohydrate following high-intensity and/or long duration exercise to replenish energy stores. Achieve this through a mix of REGO Rapid Recovery Plus and carbohydrate rich foods.



    1. Bartlett, J. D., Hawley, J. A., & Morton, J. P. (2015). Carbohydrate availability and exercise training adaptation: too much of a good thing?. European Journal of Sport Science, 15(1), 3-12
    2. Impey, S. G., Hammond, K. M., Shepherd, S. O., Sharples, A. P., Stewart, C., Limb, M., Smith, K., Philp, A., Jeromson, S., Hamilton, L. D., Close, G. L., & Morton, J. P. (2016). Fuel for the work required: a practical approach to amalgamating train-low paradigms for endurance athletes. Physiological Reports, 4(10), e12803
    3. Howarth, K. R., Phillips, S. M., Macdonald, M. J., Richards, D., Moreau, N. A., & Gibala, M. J. (2010). Effect of glycogen availability on human muscle skeletal protein turnover during exercise and recovery. Journal of Applied Physiology, 109(2), 431-438
    4. Marquet, L. A., Brisswalter, J., Louis, J., Tiollier, E., Burke, L. M., Hawley, J. A., & Hausswirth, C. (2016). Enhanced endurance performance by periodisation of carbohydrate intake: ‘sleep low’ strategy. Medicine and Science in Sports and Exercise, 48(4), 663-672
    5. Wee, K. Y., Paton, C. D., Garnham, A. P., Burke, L. M., Carey, A. L., & Hawley, J. A. (2008). Skeletal muscle adaptation and performance responses to once a day versus twice every second day endurance training regimens. Journal of Applied Physiology, 105(5), 1462-1470
    6. Morton, J. P., Croft, L., Bartlett, J. D., MacLaren, D. P. M., Reilly, T., Evans, L., McArdle, A., & Drust, B. (2009). Reduced carbohydrate availability does not modulate training-induced heat shock protein adaptations but does upregulate oxidative enzyme activity in human skeletal muscle. Journal of Applied Physiology, 106(5), 1513-1521
    7. Lane, S. C., Areta, J. L., Bird, S. R., Coffey, V. G., Burke, L. M., Desbrow, B., Karagounis, L. G., & Hawley, J. A. (2013). Caffeine ingestion and cycling power output in a low or normal muscle glycogen state. Medicine and Science in Sports and Exercise, 45(8), 1577-1584
    8. Taylor, C., Bartlett, J. D., van de Graaf, C. S., Louhelainen, J., Coyne, V., Iqbal, Z., MacLaren, D. P. M., Gregson, W., Close, G. L., & Morton, J. P. (2013). Protein ingestion does not impair exercise-induced AMPK signalling when in a glycogen-depleted state: implications for train-low compete-high. European Journal of Applied Physiology, 113(6), 1457-1468
    9. Bussau, V. A., Fairchild, T. J., Rao, A., Steele, P., Fournier, P. A. (2002). Carbohydrate loading in human muscle: an improved 1 day protocol. European Journal of Applied Physiology, 87(3), 290-295
    10. Wee, S. L., Williams, C., Tsintzas, K., & Boobis, L. (2005). Ingestion of a high-glycemic index meal increases muscle glycogen storage at rest but augments its utilization during subsequent exercise. Journal of Applied Physiology, 99(2), 707-714
    11. Bosquet, L., Montpetit, J. Arvisais, D., & Mujika, I. (2007). Effects of tapering on performance: a meta-analysis. Medicine and Science in Sports and Exercise, 39(8), 1358-1365
Written By

Ted Munson (Performance Nutritionist)

Ted is a Performance Nutritionist here at Science in Sport.