It’s a pleasure to once again write about a new paper by EMB researchers, with this months blog put together by the first and last authors of our latest contribution. This one is led by PhD student Juliet McClymont, whose research you can read more about here, and final author Karl Bates. The paper is published in the open access journal Royal Society Open Science and can be downloaded for free from here (http://rsos.royalsocietypublishing.org/content/3/8/160369). In this paper we wanted to research something that no one had looked at before: how the pressure you exert on the ground when you walk varies from step-to-step. It’s quite surprising that this is the case, considering it has much wider implications (see below), and it seems that problems with methodologies are the cause of this gap in knowledge.
Humans are by far the most intensively studied animals in the context of locomotion or ‘gait’ analysis. This stems not only from a natural scientific curiosity about how we move but also for more practical reasons: understanding ‘normal’ movement patterns can help in diagnosis, prevention and treatments (such as orthotic insoles), for all kinds of musculoskeletal injuries and diseases. It’s also crucial in sports performance and the design of sports equipment, as keen observers of the Rio Olympics may have picked up on. Furthermore foot pressure records are studied in clinic and in sports biomechanics analysis. So why hasn’t variation (how one pressure pattern is different to the next one) within people been extensively studied?
Well, probably a combination of reasons. Firstly, assessing how foot pressure varies step-to-step requires data from lots and lots of footsteps, which takes a long time to collect and perhaps even longer to analyse using traditional approaches. Secondly, current convention suggests that actually foot pressure doesn’t vary much step-to-step and that you can capture most of person’s natural variation in around 12 steps. However, this convention itself is based on analyses of small numbers of steps and so it’s not a very comprehensive one. In her study Juliet, along with EMB colleagues, collected and analysed variation in over 2,500 steps, captured when people walked at 5 difference speeds for 5 minutes. This allowed us to capture enough prints to capture a holistic picture of how pressure varies from one step to the during a decent bout of walking.
So, what did we find out? Well quite a lot as it happens, but here are the major highlights. Firstly, some people are a lot more variable between steps than others, up to eight times more variable in some cases! During walking, your brain co-ordinates your arms and legs through feedback from your eyes (through the vestibular system) and through touch (the sensorimotor system), your feet against the ground. The amount of inputs, and the minuscule amount of time that the brain facilitates changes in step mechanics, perhaps is at least partly responsible for this huge variation.
So people are really variable in their pressure at all walking speeds, and interestingly, this means that in this healthy group of people, pressure didn’t increase or decrease because of different speeds. This is a great result because variance in the motion and forces in other parts of the body, go up or down as you walk faster or slower. But not, as far as we can tell, with foot pressure. Not even when we looked specifically in the midfoot which stiffens as speed increases to power the big toe against the ground and into the next step.
While each subject had a wide range of pressure values that overlapped across the whole range of speed, the total variance was low compared to other parts of the body. For example, the variability in step width decreases when you walk faster to keep you balanced and upright. Variation is considered low when it is less than 5%, and foot pressure; well it’s less than 2.5%. Really low. We think variation is low because your foot has to adapt to anything and it has to do so rapidly, based on change in speed, walking from concrete to grass, and going up and down hills. These changes all require different motor patterns but the results show that on a treadmill, the variance in motor patterns in super low – because you can see and sense that nothing is changing.
We showed that the variability in pressure is low which suggests the foot has a lot of mechanical options to complete a single task. Speed does not influence the patterned behaviour of pressure, which further points to the foot being an adaptable and reliable unit.