Although sports drinks and sweets are known to improve performance, it seems the sugar does not even need to be absorbed by the body’s muscles to have an effect.

Simply rinsing the mouth with a drink and spitting it out – instead of swallowing – helps boost performance.

The small study, published in The Journal of Physiology, was carried out by experts from the University of Birmingham and Manchester Metropolitan University.

They gave eight endurance-trained cyclists a drink containing 6.4% of glucose (a form of carbohydrate) and compared the results with those for a drink containing the artificial sweetener saccharin.

A second group were given a drink containing 6.4% of maltodextrin (a tasteless form of carbohydrate) and the results were compared with those for a drink containing another artificial sweetener.

Everybody taking part in the trial rinsed their mouths with their drink and spat it out before completing a one-hour cycle challenge.

All the drinks were sweetened artificially with another sweetener to make them all taste the same.

In both trials, the cyclists swilling their mouths with the carbohydrate drink performed significantly better than those given the artificial sweetener drink.

It took them an average of 2% less time to complete the set workload and they displayed an increase in average power to help them cycle, even though they did not feel they were working any harder.

Brain scans enabled the researchers identify regions in the brain that were activated by the drinks.

They found the carbohydrate drinks sent reward and pleasure signals to areas of the brain that were unaffected by the artificial sweeteners.

This helped reduce the athletes’ perceptions of how heavy the workload was, which in turn enhanced their performance.

The authors concluded: “The results suggest that the improvement in exercise performance that is observed when carbohydrate is present in the mouth may be due to the activation of brain regions believed to be involved in reward and motor control.

“The findings also suggest that there may be a class of so far unidentified oral receptors that respond to carbohydrate independently of those for sweetness.”

Dr Edward Chambers, from the School of Sport and Exercise Sciences at the University of Birmingham, who led the study, said: “Much of the benefit from carbohydrate in sports drinks is provided by signalling directly from mouth to brain rather than providing energy for the working muscles.”

He said the findings support the emerging ’central governor hypothesis’ – the theory that it is not the muscles, heart or lungs that ultimately limit performance, but the brain itself, based on the information it receives from the body.