If you needed yet another reason to exercise, here it is: regular physical activity helps keep your brain young. Studies on humans suggest that exercise helps protect against cognitive decline as we age.
But how does it work? Dr Áine Kelly at Trinity College Dublin is trying to find out.
"There aren't very many studies on humans and there are lots of questions to be answered as to whether exercise taken up in later life is as effective as someone who has been active throughout their lifespan, but certainly it appears that there are benefits to be gained by physical activity, even if it is in old age," says Kelly, who is a senior lecturer in physiology.
"With humans you can do psychological tests or look at something in the bloodstream but when you want to go down to the cellular level, you can't do that in humans."
So to get to the root of the matter, she is examining a small region of the brain called the hippocampus in animal models.
"The hippocampus is a brain region that is indisputably involved in learning and memory," says Kelly. "We need the hippocampus to store information in the short and long term."
Young rats are able to learn faster than their older counterparts, but Kelly's research is finding that if the animals take exercise in middle and old age, they are better able to learn as they grow older.
"It probably equates to fast walking in humans," she says. "You are not talking about going flat out, it was just consistent exercise over that period from middle age to old age and we found that the older animals who exercised performed the hippocampal function test just as well as the younger ones did."
She has also found that the physically active animals had higher levels in the hippocampus of a protein called BDNF, which is believed to be involved in the growth of new brain cells.
The research is basic at present, but it could eventually inform new therapies to help stave off cognitive decline as we age, according to Kelly.
And, in the meantime, it bolsters the advice that keeping physically active into old age has a protective effect on the brain, she adds.
"It's reinforcing that lifestyle changes like increasing exercise could be very helpful for your brain health as well as your general physical health. In terms of fighting the degenerative changes associated with ageing, it's important to know that there are cheap and easy beneficial interventions that you can undertake like increasing physical activity."