Finally: Scientists discover the couch-potato gene

Scientists have discovered why some of us have the energy to work out for hours while others can barely summon the get-up-and-go to reach for the TV remote.

They believe they have pinpointed the genes that produce an enzyme in our muscles during exercise called AMP kinase, which controls the way we turn food into energy.

Those who generate large quantities of AMPK have more energy, whereas those with lesser amounts are likely to tire almost immediately.