It's a paradox. We know exercise is good for us. We know staying still all the time isn't. So why do so many of us live such sedentary lives?

In short, it's our brains. New research suggests that laziness may in fact be hardwired into them, as a kind of evolutionary survival mechanism – much like it seems to be for hundreds of species in the animal kingdom – so there's a perfectly good reason for lying on the couch, even if it's not a great idea.

"Conserving energy has been essential for humans' survival, as it allowed us to be more efficient in searching for food and shelter, competing for sexual partners, and avoiding predators," explains neuroscientist Matthieu Boisgontier from the University of British Columbia in Canada.

"The failure of public policies to counteract the pandemic of physical inactivity may be due to brain processes that have been developed and reinforced across evolution."

In a new study, Boisgontier and his team tried to find out just how deeply rooted laziness is in our brains, by using electroencephalography (EEG) to measure our cognitive responses to different stimuli representing physical activity and sedentary behaviour.

In an experiment, 29 young adults were recruited to take part in a computer exercise, where they could control an on-screen avatar.

Different images would flash on the screen, depicting behaviours associated with either physical activity (a figure climbing a staircase, or riding a bike, and so on) or physical inactivity (such as lying in a hammock).

Using keyboard controls, the participants had to move their avatar towards the images depicting physical activity and away from the ones suggesting sedentary behaviour. They also had to do the opposite: making the avatar avoid the physical stimuli, and approach the sedentary examples.

The experiment, which was timed, confirmed something researchers have seen before in similar studies – people are quicker at avoiding the sedentary behaviours and moving toward active behaviours.

But it also showed up something that was new – thanks to the EEG sensors recording the participants' cortical responses during the simulation.

"The exciting novelty of our study is that it shows this faster avoidance of physical inactivity comes at a cost – and that is an increased involvement of brain resources," says Boisgontier.

"These results suggest that our brain is innately attracted to sedentary behaviours."

It's only a small study, so we should be careful how many conclusions we draw from the data.

But if the researchers' hypothesis is correct, it could mean that higher levels of cognitive effort are required to override a disposition towards laziness in all sorts of areas of life.

One example Boisgontier gives is choosing to take the lift when visiting a gym – an almost unconscious choice that defeats the whole purpose of why you're there (engaging in physical activity).

"When you go to the gym, and you take the elevator or the escalator it doesn't make sense, because you go to the gym to exercise," he explained to The Star Vancouver.

"I try to fight this too. I would never take the elevator or escalator to go to the gym now, because I'm aware of this."

That kind of takeaway – being aware that parts of our brains are just wired to take the easier path – is something the team hopes can be appreciated by public health organisations too, since they have an uphill battle trying to keep populations fit.

Here's hoping these new insights make the effort easier. But not too easy.

The findings are reported in Neuropsychologia.