Physical fitness has been linked to a having a "younger" brain for the first time.

Scientists at the University of Tsukuba in Japan have found that fitter men are able to access certain parts of the brain more associated with youth.

The left side of the brain, which deals with short-term memory and the meaning of words, is used frequently when we are younger, whilst the right side of the brain is favoured more as we age.

Fitter men were more able to use the youth-like, task-related side of the brain, scientists found in their test.

Professor Hideaki Soya said the white matter that connects the two sides of the brain might be kept in better condition if someone is fitter.

"One possible explanation suggested by the research is that the volume and integrity of the white matter in the part of brain that links the two sides declines with age," he said according to Science Daily.

"There is some evidence to support the theory that fitter adults are able to better maintain this white matter than less fit adults, but further study is needed to confirm this theory."

In the study, 60 older men aged between 64 and 75 years reacted to a card showing them a particular colour, but with a word of a different colour on top. Their ability to say the colour they can see, and not the word they can read, is the Stroop test of brain-function speed.

Their aerobic fitness was measured by the amount of oxygen in their blood. The men with better aerobic fitness had shorter reaction times, with the authors concluding they might have more youth-like brains.