Our feet are a continuous proof of the ability of our body to adapt to the environment. They represent the link that connects us to the ground on our daily activities and they withstandthe burden of gravitational forces. Luckily enough, shoes support and mediate this interaction between us and the earth, often softening our relationship with massive pleasant cushioning while providing a fashionable interface with others.
I often wondered what we would be if Nike did not invent Air, Zoom, Shox and counting, those devices which act as a pillow for our heels, making its impact more comfortable. Reality is that we are no longer hunters and apart from few exceptions we need to run and jump just for pleasure and to feel alive.
So how did our ancestors cope with their feet in complete or almost nudity and the poor heels having to sustain all the pressures of hunting a wild beast among the rocks of a forgotten valley?
There is a chance they coped quite well. And us? It seems that tendinitis, overuse injuries and uncomfortable pain have certainly not left our limbs after the introduction of cushioned shoes.
Here there is something missing, but as naturally happens in human business rather than individuating the source of a problem it is often more convenient to act on its consequences, working on the effects of it. Not only shoe brands benefit of this fashion but this also creates the niche of therapists and sorts whose intent is stopping the discomfort, first.
I’m talking about that lovely cushioning that cuddles your feet. Indeed the resilient material inserted in the sole of a running shoe assists the heel in absorbing those forces produced with the ground contact, especially when running.
Problem is that heel-first contact should not happen at all, according to Lieberman et al, who studied the biomechanics of shod and barefoot running. The study was performed comparing regular shod runners to Kenyan barefoot runners or to regular US shod runners using minimal footwear (Vibram, Nike Free…), so it was also possible to understand if there was any difference between those who grew up barefoot and those who did not but now opted for minimal shoes.
The clear finding is that those with cushioned footwear strike the ground with the heel first (rear foot), while those running barefoot land with the front foot or flat foot, in a more plantar flexed stance.
Looking at the forces in play, barefoot running results in smaller collision forces with the ground and front foot impacts generate ground reaction forces lacking of a transient, which is a sudden collision force occurring in rear foot strikers in the first 50 milliseconds of contact and corresponding to 1.5-3 times body mass.
Thick soles hinder proprioceptors, decreasing mechanical sensitivity of the foot, which may in turn influence postural control and affect foot strike. A large study on marathon runners curiously found that the rate of injury was negatively correlated to shoes cost, in other words those wearing the most expensive shoes were also those who had the higher injury chance, perhaps suggesting that more sophisticated cushioning technologies are not necessarily better.
A final remark is on performance. Every action has a reaction and every time we hit the ground ideally we should receive an equal force from the ground, although in the real world part of this energy is dissipated. When fore-striking, the foot’s longitudinal arch is passively stretched much earlier than when rear-striking, meaning that in the first case more energy is returned to the foot. This means that front-strikers are more energy efficient and their run has a lower energetic cost, with an estimated 5% difference in a study by Divert et al and barefoot, front-striker runners, might benefit of a better running economy.
Perhaps going back to the past can be a good idea sometimes.
Lieberman et al 2010 Foot strike patterns and collision forces in habitually barefoot versus shod runners
Marti et al 1988 On the epidemiology of running injuries. The 1984 Bern Grand Prix Study
Divert et al 2005 Mechanical comparison of barefoot and shod running