What happens when we walk?

The gait is essentially a style or manner of walking. Obviously the general gait for humans is bipedal walking. Walking is controlled falling, and it always is. We are perpetually in danger of falling over. The adjustments we make to balance are to prevent us falling over. Essentially, the risks that we have in walking are mostly associated with the risk of falls. The biggest risk comes in turning. Turns are about 30% to 40% of all steps. In turns we have to decelerate the body, accelerate the body, and we’re doing this within about two steps. In order to measure all this, we need high-speed cameras which are recording body motion - the motion of all segments.

We need to record actually not just the linear accelerations, changes in speed of the body segments and where they’re moving in space, but axial rotations - how a limb segment is rotating upon itself. All these things are telling us about how the body is moving, and then we need to look at muscle contractions, which are driving the motion, driving the balance. And then we need to look at the ways that we control that with our vision and the effect that listening to sounds in the environment has on our walking. So it’s a very complicated subject. It can’t just be the musculoskeletal system, I have to say that it’s cognition as well.

For a full understanding of gait, obviously, you need to look at all of these, because for people who’ve had strokes, for people who are elderly, the cognitive system is that which is primarily involved in the problems. We only have a certain number of brain cells. We talk about our brains as if they’re billions of cells where we’ve got plenty left over. It’s not like that. The control systems of the musculoskeletal system are actually rather short of processing power, if anything else.

And so there is, if you like, a competition for attention between the parts of the brain which interpret sound, which tell us which sounds we should be listening to, which sounds we should remember, which sounds we should try and analyse, and those we should ignore. Similarly, with vision, the things in front of us - which can we safely ignore? Which are really important to us? And unfortunate for humans, the system which comes at the bottom of the list appears to be that which controls walking. For some reason our attentional system in the brain is actually geared towards sound and vision, not walking, perhaps because these things are associated with predation - both avoiding being eaten and avoiding predators.

So, we have problems when we’re challenged with sounds in a busy street environment, where you have lots of signs to look at, where lighting is changing when we’re going in and out of doors. All of these things are a major challenge to us, and particularly as we’re getting older. What’s driving gait, what’s driving our control of walking and driving our ability not to fall over when we’re walking is the application, obviously, of force to bones through muscles. Ultimately there is one part of the body which matters in terms of walking, and that’s the one down there. We move our trunk around, we move our head around, we move our legs around.

But all that is doing ultimately is changing the interactions - the force interactions, the pressures - between the foot and the ground. So that’s all we’re doing. Everything else is acting sequentially down the body, from top to bottom, to change the pressures under the feet, between the foot and the ground. For example, if I lean over sideways or I feel unstable sideways, I will increase the pressure on the opposite side of my foot by changing the pressure under my toes. And again, if you’re wearing shoes and the shoes are stiff, well, you’re not very good at doing that, and so your risk of falling is higher.

The footwear that people have chosen or adopted is actually largely very bad for us. We obviously didn’t evolve to walk around in shoes or boots. We evolved to control, in particular, the lateral sway of the human body by using the lateral and medial sides of the foot, by using the toes. And obviously if the toes are bound together in the front by tight-fitting shoes, that’s gone. By the time people are, say, 40 or thereabouts, their toes have been squashed together by fashionable shoes - for men and women - and again, in the case of women, high-heeled shoes are further disrupting the normal muscular function. So unfortunately most of the effect of clothing is negative.