Marathon training is serious business and researchers have found that consuming carbs before and during a half marathon can help improve racers' performance.

In a study published in the Journal of Applied Physiology, Jill Leckey and her colleagues showed that carbohydrates are the main source of energy for the body when it comes to prolonged, high-intensity running. Both carbs and fat can be used as fuel for exercise. However, the two differ in availability. Carbs are easily accessible but are present in limited quantities while fat requires further processing before use but is attainable in bigger volumes.

Earlier studies have explored how muscles' fat-burning ability can be altered to improve performance as there are larger fat stores in the body, which will then translate to a larger energy supply for intense physical activity.

For this study, however, researchers examined the importance of fuel source in sports endurance. To do this, they blocked the use of fat in the bodies of male competitive half-marathon runners. The subjects were tasked with running until exhaustion on a treadmill at the same pace as 95 percent of their best time for a race. They were given carbohydrates or calorie-free meals before and during their run. Nicotinic acid was also administered to the runners to prevent their bodies from tapping into fat stores during physical activity.

Based on the results, blocking fat use did not hamper distance covered by the runners before they were exhausted, nor carbohydrate use. In fact, carbohydrates accounted for approximately 83 to 91 percent of total energy used. These results show that muscles used during long-duration, high-intensity runs prefer carbohydrates as fuel source, whether or not the runner has eaten.

It would be wise for competitive runners to turn to dietary strategies to optimize performance in race events lasting up to 90 minutes, said Leckey, the study's primary author.

The study was carried out with competitive runners as subjects but the researchers said that their findings will also apply to recreational runners. Instead of running pace, relative exercise intensity is the deciding factor that determines how much fat and carbohydrates muscle will use as fuel.

Other authors for the study include John Hawley, James Morton and Louise Burke.

Photo: Charlie Llewellin | Flickr

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