Soccer performance: to load or not to load?

Assuming your diet is healthy and you’re drinking ample fluid, it’s no exaggeration to say that when it comes to endurance, your carbohydrate nutrition can make the difference between merely adequate and truly excellent performance. That’s because carbohydrate can be considered as your body’s 5-star fuel. Consuming the right amount of the right type of carbohydrate at the right time can dramatically extend your endurance and delay fatigue.

The fundamental importance of carbohydrate

The study of carbohydrate metabolism in relation to the field of sport and exercise is an area of investigation that is now over 100 years old. It was almost a century ago, when researchers first demonstrated that fatigue occurs earlier when subjects consume a low-carbohydrate diet (as compared with a high-carbohydrate diet) in the days preceding an exercise⁽¹⁾. Shortly afterwards, researchers also observed that runners who completed the 1923 Boston marathon exhibited hypoglycaemia (low blood sugar) immediately post-exercise, thus suggesting that low carbohydrate availability may be linked to fatigue⁽²⁾.

These very early studies provided the initial evidence that carbohydrate was an important fuel source for sustaining exercise performance. However, it wasn’t until the development of muscle biopsy techniques in the late 1960s that sports science researchers were able to fully grasp the fundamental importance of carbohydrate for endurance exercise performance. In a series of studies by Scandinavian researchers, scientists discovered three key principles, upon which our current-day understanding is built upon^(3-6). These key principles are as follows:

       I.          Muscle glycogen (stored muscle carbohydrate – the body’s 5-star fuel for high-intensity exercise performance) is depleted during exercise in an intensity dependent manner (see figure 1).

     II.          High-carbohydrate diets increase muscle glycogen storage and subsequently improve exercise capacity.

    III.          Depleting muscle glycogen with prior exercise then consuming a high-carbohydrate diet can boost muscle glycogen storage above and beyond normal storage levels.

A half a century later, these three principles still serve as the foundations for the current recommendations for modern-day sports nutrition practice⁽⁷⁾.

Figure 1: Exercise intensity and glycogen depletion*