London: Ever wondered why some people have endless energy and others don't? It's all in the genes, scientists claim to have discovered.
A team at McMaster University in Canada, in fact, claims to have identified two genes which produce an enzyme in one's muscles during exercise called AMP kinase that controls the way one turns food into energy.
Those who generate large quantities of AMPK have more energy, whereas those with lesser amounts are likely to tire almost immediately, say the scientists.
Dr Gregory Steinberg, who led the research, said the discovery could lead to treatments for those who find it difficult to exercise, including the obese and those with asthma, daily reported.
His team found dramatic results in tests on two groups of mice, one bred without the two suspected genes behind AMPK production.
When given an exercise wheel, the mice who still had the genes could go for 1km in just 20 minutes. By contrast those without were "extremely exercise intolerant" and could achieve only a fast walk for around 40m before giving up.

The scientists believe the same effect would be seen in humans. AMPK is present in our cells and is known to be responsible for boosting the number of mitochondria, the tiny batteries which break down food and turn it into energy.
This is the first time scientists have demonstrated that AMPK is controlled by two genes and that removing them hugely impairs our ability to exercise.
Dr Steinberg added, "The mice looked identical, but within seconds we knew which ones had the genes and which ones didn't because the difference in ability was so significant."
But the good news or bad news, depending on your outlook – for couch potatoes is that exercise itself appears to stimulate the production of AMPK. So if you force yourself to keep going for a jog it will eventually get easier.
Dr Steinberg added, "When you become obese and sedentary that is what makes it so hard to get started. The message is don't let yourself get to that stage, but if you do this is not a genetic defect, there is something you can do about it."
The findings have been published in the 'Proceedings of the National Academy of Sciences' journal.