Carbohydrates

Jessica Ennis

Like any engine, your muscles need fuel. Your energy comes from three major sources: carbohydrate, fat, and protein, with carbohydrate acting as the preferred muscle fuel for intense and prolonged exercise. There are a number of factors that affect how our bodies consume these, including:

  • Type of exercise
  • Training intensity
  • Duration of exercise
  • Frequency of training sessions
  • Fitness level
  • Diet

Types of exercise

All the carbohydrates you take in are converted to glucose and stored in the muscles and liver. We have a limited capacity to store carbohydrate (glucose or glycogen) in our body, so if you exercise regularly, you’ll require additional supplies from their diet to maintain adequate stores.Having a good supply of carbohydrate is directly linked to how you perform when training. When you’re doing an endurance event, such as a marathon, you primarily use carbohydrates for fuel. By contrast, a middle-distance run of 5-10k would use a combination of all three fuels.

During low-intensity exercise (defined as using less than 300kcal per hour) the body uses a greater proportion of fat, a smaller proportion of carbohydrate and fewer calories. As a general rule: the higher your exercise intensity (the harder you work), the more of the fuel you use comes from carbohydrates.

Why are carbohydrates important for performance?

Giving you an edge and enhancing performance
“Pre-loading” with carbohydrates before a session ensures that you have a “full tank” to start your exercise. Timing is important: if you have a low carbohydrate intake, then give yourself a sudden boost, this increases your fuel reserves and helps your endurance and performance1-6. Studies have shown that footballers rely heavily on carbohydrates, and that boosting their intake before and during a match can help enhance performance during its final stages1.

Before, during and after exercise

Before exercise
 It’s generally recommended that you eat a high carbohydrate meal (such as a pasta or rice) 2-4 hours before exercising, although precise timings and amounts can vary from person to person. Some people also consider a high carbohydrate snack (such as a sports drink or cereal bar) 30-60 minutes before exercising. It’s advisable to avoid bulky (fibre-rich) carbohydrates in the hours immediately before exercise, as these can cause abdominal discomfort.

During exercise
During exercise, it helps to maintain your flow of glucose. Taking on carbohydrates immediately before exercise, or during rest periods in strenuous sessions (lasting over 60 minutes), is a good way to do this: 30-60g of carbohydrate per hour is a useful benchmark figure, although obviously this will vary depending on your weight, fitness, and the intensity of your session. Try to spread your intake, taking on small quantities frequently (i.e. every 15-30 min) rather than all at once, to get a steady flow of carbohydrate into your bloodstream.

Sports drinks, such as Powerade ION4, contain both the carbohydrates and fluids your body needs to maintain performance.

Recovery
Recovery is not a passive process: replacing lost carbohydrates is one of the most important things you can do to help your body recuperate. Consuming foods or fluids high in carbohydrates immediately after a strenuous session will help the muscles begin their recovery, and take advantage of your body’s heightened rate of glycogen storage. As a general rule, glycogen storage rates rise for around a 2-hour window after exercise, giving you the chance to replenish your stocks.

If you are training more than once a day, recovery is particularly important. As it might not be practical to plan a meal straight after exercising, consider a snack high in carbohydrates. Replacing your lost carbohydrates quickly will help you get the most out of any subsequent workout.

Remember: “hitting the wall” is usually caused by exhausting your glycogen – the vital fuel stores in your muscles. Signs of “hitting the wall” include fatigue, reduced stamina, and slowing in pace and reaction time. Try to start each session you do with a full tank of glucose (fuel): this will help you maintain your performance for longer.

References
  • 1Bosch, A.N., Dennis, S.C. ja Noakes, T.D. (1993). Influence of carbohydrate loading on fuel substrate turnover and oxidation during prolonged exercise. Journal of Applied Physiology, 74, 1921–1927

This information is not medical advice and should not replace consultation with your health care provider or nutritionist before starting a new exercise program or eating plan.