PART 2 – SHOES AND INJURIES
For the last fifteen years or so, buying a pair of runners has always been accompanied by a warm fuzzy feeling inside, a feeling that comes from the certain knowledge that you’re investing in a high-tech device purpose-designed to protect you from injury and improve your performance. You can just see all those smart dedicated NIKE mechanical engineers hard at work developing and testing newer and better space-age materials to shield you from the terrible pounding you submit yourself to in order to “Just do it!’ Gel, air, channels, honeycomb, microspheres, super-light materials, foam springs and soon…yes, you guessed it, micro-chips in the soles of your shoes (better than diamonds, I suppose). New round laces and ribbon eyelets result in that custom-fitted feel supplemented by molded sorbothane insoles or special orthotics from your local prosthetist and you’re ready to tackle any distance.
Now here’s the catch. If all this high-tech stuff is supposed to be preventing running injuries by shielding us from impact, why is it that two out of every three runners are sidelined every year because of a running injury? Why is it that since the great jogging boom of the mid-seventies, there has been no decrease in the incidence (some authors say there has been an increase) of running injures in spite of yearly ‘improvements’ in running-shoe technology? Why is my office filled with runners who have injured knees (26% of running injuries), tibias (13%), Achilles tendons (6%) and plantar fascias (5%)? The cause of all these injuries is quite evident: cumulative micro-trauma caused by repetitive impact experienced during running. The heel of a runner upon striking the ground generates a force that can equal 2.5 times body weight at the foot and as much as 7 times body weight at the hip. Repeat this 1000 times per mile and it’s easy to appreciate the stress the old bones are under. Add to this the hardness of urban roadways compared to naturally deposited surfaces and eventually, something gives, inflammation sets in and pain results…and you end up working at the finish-line pulling bar-codes off finishers. Now, where’s our high-tech shoe in all this? With all the improvements in recent years, you’d think we’d be seeing a marked decrease in running injuries. Just keep reading.
It wasn’t till the mid-eighties that some researchers smelled something rotten in the athletic footwear world and it wasn’t just dirty socks. Footwear manufacturers were well aware that impact was the cause of running injuries and reasoned that the way to attenuate impact was to interpose a soft impact-absorbing midsole between the foot and the ground. The first major problem was the method used by essentially all the footwear development labs to test the impact absorption of footwear mid-soles. Dr. Benno Nigg from the University of Calgary showed that machine testing of these materials by dropping a 5-kg object onto the shoe-sole and measuring the impact on a pressure-plate did not accurately predict human impact with the same materials. In fact the correlation turned out to be inverse, that is when you drop a 5-kg ball on materials of increasing softness, you measure decreasing impact. However, when the impact from a running human is measured, the result is the reverse, and the impact increases with softer materials! WHOOPS! (You’ll find out why later.)
Next problem. In 1989, Dr. B. Marti published a paper which still makes the throats of footwear executives go dry. He studied 5,038 runners who participated in a 16km race and had them fill out an extensive questionnaire about their running in the year preceding the race. Here’s what he found: The incidence of injuries in runners using shoes costing more than $95 was more that twice as great as in runners using shoes costing less than $40. (Note that this result includes correction for other influencing factors such as training mileage and history of previous injury.) In other words, the fancier (high-tech, advanced) the shoe, the more dangerous it is! Now a study of over 5,000 runners is not something to thumb your nose at and you would think the shoe manufacturers would have taken some notice. Not on your life. Yearly athletic shoe sales were in the billions of dollars and this was no time to fiddle with a successful product. In any case, it is felt by many observers that by the mid-eighties researchers, in-house or independent, had effectively been forced out of the loop of new product development and that research and development was now exclusively in the hands of the marketing people. Athletic shoes had become a fashion item and were designed as such, as they are to this day.
The big question: Why are super shock-absorbing athletic shoes causing more running injuries? Dr. Steven Robbins from the Centre for Studies in Aging at McGill University in Montreal is the man who came up with the answer. Dr. Robbins pointed out that the human lower extremity is not a delicate, rigid, passive structure requiring ‘packaging’ to protect it from impact. This becomes blatantly obvious when one observes the nearly complete absence of foot disorders in unshod populations. People who go around barefoot just don’t get plantar fasciitis or any of the other lower extremity injuries so common in shod populations. The lower extremity, he points out, is a rugged, flexible, active, well designed (teleologically) structure. Wire this structure to a spinal cord and a brain and what you’ve got is a system fully capable of handling the impacts of running. So, how does this system work exactly and why do modern running shoes screw it up?
Allow me for a moment to compare the human locomotor apparatus to a modern luxury car. The bones of the foot, leg, thigh and pelvis act as the frame, linked by joints and all held together by fairly inelastic ligaments and fascia. The bones and joints are surrounded by contracting muscles which act as the suspension system. This is especially evident in the arch of the foot which is formed by both the passive, rigid plantar fascia as well as the active, flexible intrinsic muscles. The bones and muscles are covered by fat and skin within which reside receptors or sensors that send information to both the peripheral computer (the spinal cord) and the central computer (the brain). The skin on the sole of the foot (glabrous skin) is very well suited to its function possessing about 600% of the toughness of hairy skin (the skin everywhere else on our bodies except our palms). The receptors in the foot are specially designed to sense both impact (vertical force) and shear (horizontal force). Add to this information streaming in from pain receptors as well as joint position receptors throughout the lower extremity and you’ve got a Hummer! (Got carried away a little…sorry.)
During barefoot running, the ball of the foot strikes the ground first and immediately starts sending signals to the spinal cord and brain about the magnitude of impact and shear, getting most of its clues about this from the skin contact with the surface irregularities of the ground. Take away this contact by adding a cushioned substance and you immediately fool the system into underestimating the impact. Add a raised heel and the shod runner is forced to land on it. Strap the cushioning on tightly with the aid of a sophisticated lacing system and you block out shear as well, throwing the shock-absorption system even further into the dark. The system responds by landing harder in an attempt to compress the cushion and ‘feel’ the ground. The weight is then transferred to the outside edge of the foot, completely by-passing the skin of the arch. The heel then touches down and the weight is transferred to the ball again with final push-off through the toes. While the weight is being transferred, the arch carries out its function as the suspension system of the foot and flattens under the active control of the intrinsic muscles. The ankle, knee and hip joints flex to absorb impact in response to information flowing in from the foot. The cushioned midsole of the modern running shoe robs the system of important sensory information necessary for ankle, knee and hip response to impact. The arch support (or orthotic) in modern running shoes not only prevents the arch suspension system from absorbing energy by preventing flattening but eventually leads to intrinsic muscle atrophy and complete loss of active muscular control of the arch leaving only the inelastic plantar fascia as a checkrein to flattening. The barefoot runner’s ‘foot position awareness sense’ which relies heavily on sensory input from the sole of the foot minimizes his risk of sustaining an ankle sprain on uneven ground. The shod runner is at marked increased risk of ankle sprains because his ‘foot position awareness sense’ is handicapped by the paucity of sensations coming from his soles. The barefoot runner is constantly alert scanning the ground before him for irregularities and dangers that might cause him injury. The barefoot runner is a cautious runner and actively changes his landing strategy to prevent injury. He treads lightly. The shod runner is bombarded by convincing advertising stating or implying that the shoe he is wearing will protect him well over any terrain and he becomes a careless runner. He is heavy footed. Finally, certain diseases in humans can cause a gradual destruction of the sensory nerve endings in the foot (and elsewhere) resulting in a significant increase in lower extremity injuries. Diabetes and tertiary syphilis are two. Extremities so affected are termed ‘neuropathic’. The shod runner, because of his sensory deprivation and high risk of injury may be termed as having ‘pseudo-neuropathic’ feet, a term coined by Robbins.
The conclusion that shoes are the primary cause of running injuries is strongly supported by the scientific literature. I’ve already mentioned Marti’s work showing more than twice the incidence of running injuries with expensive shoes compared with cheap ones. Rao and Joseph (1992) examined 2300 Indian children between the ages of 4 and 13 and found that the incidence of flat feet was more than three times greater in those children who used footwear than in those who did not leading them to conclude that shoe-wearing in early childhood is detrimental to the development of a normal arch. In 1988, Hamill and Bates showed that as running shoes lose their cushioning through wear and tear, subjects improve foot control on testing and presumably decrease their risk of injury, i.e. shoes get better with age. Robbins and Gouw showed in 1991 that modern athletic footwear creates a perceptual illusion in subjects whereby they consistently underestimate impact. Simply adding surface irregularities on the insoles (to simulate barefoot like conditions) markedly improves subjects’ estimates of impact. Robbins and others (1994) studied the balance ability of men walking along a beam wearing shoes with soles of varying thickness and hardness. Results confirmed that the thinner and harder the soles, the better the balance. In one of their most elegant and widely publicized studies, Robbins and Waked (1997) examined the effect of advertising on landing impact. They asked subjects to step down barefoot ten times onto four pressure measuring platforms, the first one being bare and the other three covered by identical shoe sole material made to look different by different colored cloth. The subjects were given different messages for each of the covered plates: the message for the first covered plate suggested superior impact absorption and protection (deceptive message), the second suggested poor impact absorption and high injury risk (warning message) and the third suggested unknown impact absorption and safety (neutral message). Results showed that subjects landed with the highest impact when given the deceptive and neutral messages and with the lowest impact when given the warning message or with the bare plate. The authors conclude that running injury rates are greatest in users of the most expensive shoes because advertising has deceived these users into believing that the shoes provide a superior level of safety thereby inducing an attenuation of impact moderating behavior, increasing impact and injury. The authors add that deceptive advertising of protective devices is a public health hazard and should be addressed. Humans are less cautious even when they use truthfully advertised products because of excessively positive attitudes toward new products and wrong impressions of the standards of truth in advertising.
“So,” you think, “is this guy telling me that NIKE, REEBOCK and all those big corporations just put this new stuff out on the market without any proof that its safe? Can’t be!” Well, that’s exactly what I’m telling you. I can be a real pain in the ass when I try, and some years back, I was in the mood. I got on the phone and tried to talk to the directors of research at all the big athletic footwear companies. I tell you, getting to talk to one of these guys is harder than talking to the Pope. I finally got to speak with Mr. Gordon Valiant, then director of research at the NIKE Sports Research Lab in Beaverton, Oregon. JF:” Mr. Valiant. My name is Dr. Froncioni and I’m an orthopedic surgeon. I treat a lot of runners and I was just wondering what your thoughts were on the whole issue of running injuries possibly being caused by your running shoes.” …long pause…GV:”Umm…well…I’m afraid I’m not at liberty to discuss that matter.” SAY WHAT!!!?? JF:”Mr. Valiant, in case you missed it, I’m NOT a reporter. I’m just an orthopedic surgeon who’s looking for some answers for his patients. Let me rephrase. Surely you have data to support the injury protection claims you make about your running shoes….surely sir..” GV: “Well…I could refer you to our marketing people and I’m sure they could send you something.” Nope. We’re not on the same wavelength at all. I’m sure the lawyers have given these guys a gag order. JF: “Mr.Valiant, your marketing people send me stuff all the time; it’s all over the Runner’s World I get every month. Anyway, nice talking to you.”
I’ve also had a few chats with Dr. Steven Robbins. He feels very strongly that the athletic footwear manufacturers are painting themselves into a very tight corner by not acting on the available information. After all, it is within their power to effect changes in their shoe design based on the available data and in doing so decreasing the running injury rate by up to 55%. By not acting now, Dr. Robbins predicts the footwear manufacturers may end up in the same situation as the tobacco companies with massive class-action lawsuits brought against them.