丁香园AV

Do you feel lazy? Most of us do when we choose to drive somewhere when we could have walked or skip daily exercise to binge watch 鈥淕ame of Thrones鈥�. New research from 丁香园AV professor Max Donelan and his team demonstrates that this inherent laziness extends to our subconscious nervous system.

Published in the Sept 10 issue of Current Biology, their research shows that even within a well-rehearsed movement like walking, the nervous system subconsciously monitors energy use, and continuously re-optimizes movement patterns in a constant quest to move as cheaply as possible.

This finding arose through experiments designed to test theories of how people learn to move. The central claim of these theories is that the nervous system does not move as accurately as it possibly can, but instead selects coordination patterns that are a compromise between accuracy and energetic cost. These theories, while influential, have proven difficult to test resulting in little scientific evidence to support the role of continuous energy optimization - until now.

PhD student and lead author Jessica Selinger explains how she tackled this problem: 鈥淲e asked participants to wear a robotic exoskeleton that made certain abnormal ways of walking energetically easier than walking in a 鈥榥ormal鈥� way. They accomplished this by applying high energetic penalties to 鈥榥ormal鈥� ways of walking, and much smaller penalties to specific abnormal way of walking.鈥�

Researchers found that after just minutes of wearing the exoskeletons, people changed fundamental characteristics of their gait鈥攃haracteristics that have been established with millions of steps over the course of their lifetime. 鈥淎nd, they did this even to gain just a few percent savings in energetic cost,鈥� notes Selinger. 鈥淪ensing and optimizing 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!鈥�

Donelan adds: 鈥淲hile we suspected that the nervous system could optimize energy use, it was surprising to us how small of a cost it cared about. We found that people would adapt their gait even in response to remarkably small energetic savings, at times for less than five per cent of their total cost. Had they simply suffered this small penalty, their energetic debt after one hour of walking would be roughly equivalent to the energy contained in a single peanut. The savings were literally peanuts!鈥�

It makes sense that our movements remain malleable because people鈥檚 bodies, and the tasks they are presented with, can change, Donelan adds. 鈥淐ontinuous energetic optimization benefits our ability to adapt our movements by keeping them close to energetically optimal. It helps backpackers efficiently adapt to changing terrains, it helps patients compensate for movement deficits after injury or disease, and, for better or worse, it helps all of us move with as little energy as possible.鈥�

Support for this work came from a Vanier Canadian Graduate Scholarship (J.C.S), a Michael Smith Foundation for Health Research Fellowship (J.D.W), and a grant from the U.S. Army Research Office.

Click  for videos, photos and more details about the study.