Shall we walk?

Humans long ago made the evolutionary leap from walking on four legs to walking on two. As far as not-falling-over is concerned, this adaptation was a strange one. There’s a reason chairs tend to have, at the least, four legs.

Very few other mammals have gone the two-legged route: kangaroos spring to mind (sorry), but they benefit from a stabilising tail and clown-shoe-sized feet. Plus, they usually walk around as pentapeds (i.e. using all four legs and their tail). I’ve never tried to push a kangaroo over, but I’m guessing I’d be unsuccessful if I gave it a go. You, on the other hand, I could topple right over, if I timed it just right and gave you a vindictive enough of a shove.

To make matters worse, humans walk by balancing on one foot while swinging the other one forward. Paleoanthropologist John Napier describes walking as “a unique activity during which the body, step by step, teeters on the edge of catastrophe”. It’s a frankly ridiculous way to get around.

Movement scientists describe walking as controlled forward falling. We propel ourselves forwards – precariously – and then we swing out our other leg to avoid catastrophe. And then repeat, repeat, repeat, until we get to where we need to be. Just as in life, walking involves venturing towards an uncertain future in the hope that we arrive safely. Sometimes, however, we find ourselves arse-over-tit on the pavement.

There is, of course, a method to this human madness. Walking and standing on our hind legs opened up new opportunities for our ancestors. With our forelimbs freed up, they could use their hands for touch, exploration, tool-making and Googling how to make fires.

Modern-day humans continue to compensate for our ancestor’s sacrifice of stability in favour of constant access to skillful, handy hands. Staying upright in the outside world – with its kerbs, uneven paving stones and discarded banana skins – requires mind-boggling levels of neural computation to integrate multiple sensory inputs from the eyes, inner ear, and internal position sensors. All these inputs must then be transformed into accurate commands to our joints and muscles to maintain posture and allow purposeful locomotion.

Advancing age and neurodegenerative conditions such as Parkinson’s disease reduce the fidelity of these computations. It’s no surprise, then, that falls are common amongst older people and those with Parkinson’s disease. In fact, falls are the leading cause of death from injury in the over 65s. Non-fatal falls cost the NHS more than £2bn and four million bed days a year. Moreover, falls can be life-changing. They can make the difference between living well in your own home for the rest of your life, or losing your independence entirely.

The good news is that there are things people can do to mitigate their risk of falling. Studies show that staying active and physically strong is highly effective in preventing falls. As is maintaining connection to social networks.

At Manchester Met we’re developing new treatment approaches for people with Parkinson’s with balance impairment. With funding from Wellcome Trust and the Medical Research Council, we’re revealing how changes in the brainstem in Parkinson’s impair balance. A closer look at our project and its potential to improve treatments for Parkinson’s can be found here.

Importantly, we’ve co-designed our approach with people with Parkinson’s, leading to a new understanding that there is no one treatment that will work for everyone. We also now realise that there are periods in life when staying balanced is particularly important, like when you’re recovering from a hospital procedure (i.e., when you don’t want to go back into hospital anytime soon). Dr Chesney Craig is leading a new project to provide balance and mobility interventions targeted to these life events.

In short, we have lots of exciting new work to tell you about in 2025. We’re all falling forward, but we’re swinging out a leg to prevent catastrophe.