If you find it hard to lose weight – here's why it's not your fault

If you go to the gym or walk the dog to burn as many kilojoules as you can, you’ll be disappointed to learn that your nervous system is sabotaging your efforts.

Researchers reporting in the Cell Press journal Current Biology have found that our nervous systems are remarkably good at changing the way we move so that we expend the least amount of energy possible. Our bodies are good at being fuel efficient, and we are hard wired to be lazy cheats.

The findings, which were made by studying the energetic costs of walking, likely apply to most of our movements, the researchers say.

“We found that people readily change the way they walk – including characteristics of their gait that have been established with millions of steps over the course of their lifetime – to save quite small amounts of energy,” says Max Donelan of Simon Fraser University in Canada. “This is completely consistent with the sense that most of us have that we prefer to do things in the least effortful way, like when we choose the shortest walking path, or choose to sit rather than stand. Here we have provided a physiological basis for this laziness by demonstrating that even within a well-rehearsed movement like walking, the nervous system subconsciously monitors energy use and continuously re-optimises movement patterns in a constant quest to move as cheaply as possible”.

There is a bright side to this, lead author Jessica Selinger adds: “Sensing and optimising energy use that quickly and accurately is an impressive feat on the part of the nervous system. You have to be smart to be that lazy!”

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The research team wanted to understand why people move the way they do, and it’s partly a question of evolution and learning. But, the researchers wanted to know, to what extent can our bodies adapt movement based on real-time physiological inputs? In other words do our bodies cheat as we exercise, so that it’s difficult for us to work as hard as we want to to reach those fitness goals, and burn those kilojoules?

To find out, the researchers asked people to walk while they wore a robotic exoskeleton. This allowed the researchers to discourage people from walking in their usual way by making it more costly to walk normally than to walk some other way.

This allowed the researchers to test whether people can sense and optimise the cost associated with their movements in real time. And it turns out we can. We are hard wired to be lazy!

The experiment revealed that people adapt their step frequency to converge on a new energetic optimum very quickly – within minutes. What’s more, people do this even when the energy savings is quite small: less than five per cent.

So if your exercise plan just isn’t working, it may not be your fault, your body is hard wired to be lazy!


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