foot structure & injury rates

Does the structure of your foot affect your injury rate? There’s been considerable confusion concerning the effects of foot structure on injury rates. Some researchers – and large numbers of people in the population at large – believe that individuals with low-arched feet have weak foot structures and are more predisposed to injuries in the lower extremities. In the US, would-be recruits with low-arched feet have actually been denied the opportunity to serve in the US Army because it was believed that their risk of injury would be unacceptably high. On the other hand, some scientists have suggested that low-arched feet may in fact be protective against foot injuries and that high-arched people are at higher risk, especially for problems such as stress fractures in the feet and legs. They theorise that low-arched feet absorb more energy during footstrike and that high-arched trotters are so rigid that they transmit impact forces directly up the leg, increasing the risk of bone damage. If low or high arches did actually increase the risk of injury for football and rugby players, walkers, tennis players, runners, etc, they would probably do so by increasing the impact forces passing through the lower parts of the legs each time the feet hit the ground. To determine whether those impact forces are significantly different between low- and high-arched people, scientists at the University of Calgary recently studied 18 female and 19 male adults as they ran at a pace of about seven minutes a mile.

Actual arch heights of the subjects ranged from 1.38 to 3.56 cm (about half-an-inch to almost 1.5 inches), and ‘arch flattening’ (the degree to which the arch collapsed) during running ranged from 0.1 to 0.8 cm (from one twenty-fifth to one-third of an inch). However, there was no connection between arch height and arch flattening. In other words, high-arched people did not actually have more rigid arches, as many researchers have suggested. Further, impact forces were identical in high-arched and low-arched people, indicating that shock absorption was similar in the two types of feet. Neither the low-arched or high-arched person seems more likely to send injury-producing shock waves through the legs. Why were there no differences? As the Calgary scientists pointed out, if when people run they first land on their heels as their feet hit the ground, the resulting impact forces tend to be transmitted directly up through the heel bones into the lower part of the leg. In other words, the arch region plays little part in modulating impact forces. In fact, many people are indeed ‘heel strikers’.

True, it seems that the impact forces for midfoot strikers (people who land on the middle of the foot with each step) would be affected by arch height. However, arch flattening would influence these forces, and neither low- nor high-arched people are better at arch flattening, according to the Calgary research. In addition, other factors unrelated to arch height, including knee flexion during footstrike, ankle supination (the degree to which the foot rolls outwards during footstrike), and pronation velocity (the speed at which the foot rolls inwards during footstrike) also have an effect on impact forces and may over-ride any specific effects of arch height. So if your shoe salesperson tells you that you need extra shock absorbency in your athletic shoes because you have high (or low) arches, be wary. Research just doesn’t support the idea. In fact, as the Canadian scientists pointed out,’ arch height cannot be used clinically to define a general foot type that is at risk of injury’. Another time-honoured belief – that individuals who pronate (roll their feet inwards) excessively during running are also at greater risk of injury – was exploded by the same Canadian team. In a prospective study the researchers were able to show that runners with high degrees of pronation did not injure themselves more frequently during training than those who pronated very little. This latter finding casts new light on efforts by the running-shoe companies to produce shoes which control pronation, or, as the companies like to call it, ‘excessive motion’. But if higher amounts of pronation don’t in fact produce higher injury rates, why does pronation need to be controlled?

(‘Effects of arch height of the foot on ground reaction forces in running’, Medicine and Science in Sports and Exercise, vol. 24(11), pp.1264-1268, 1992.)