Soft Soles Could Be Hurting Runners23 May 1997
SOURCE: Archives of Physical and Medical Rehabilitation (1997;78:463-467)
Frequent injuries common to runners and gymnasts may be due more to soft shoe inner soles or floor mats than to repetitive impact from these activities, a study suggests. New findings indicate that people come down harder and more straight-legged when wearing modern athletic shoes than they do barefoot, and that these shoes (and foam floor mats) make the landing more unstable -- a precursor to injury.
"There's a prevalent myth that these shoes with thick soft soles, like typical running shoes, help you absorb impact and give you good cushioning," says Dr. Steven Robbins, a biomechanics expert and sports medicine doctor in Montreal, Canada. "Even though the running shoe companies sell these shoes as great protective devices, there's no evidence that they actually protect." Among the common injuries associated with running and gymnastics are foot, ankle, and knee problems, and shin splints -- pain in the front and sides of the lower leg that worsens during exercise. "The injury frequency in these sports remain high with these thick shoes," Robbins says, noting that it is probably because impact with the landing surface also remains high when wearing shoes.
According to the researcher, the shoes and floor mats do not really absorb impact well. "It's been shown that when people land on thick soft surfaces, they land harder," he explains. "And they land harder by landing with straighter legs. The leg doesn't bend, sink down, which is a very effective shock absorber." He notes that the increased impact with straighter legs "overcomes the little advantage that the shoe has," but Robbins adds that although researchers ("but not the public") have known about this phenomenon for years, no one has understood why.
In earlier scientific reports, Robbins has shown that thick athletic shoes and mats cause people to lose balance. "We had a hypothesis that the 'landing harder strategy' on these materials was a strategy to improve the stability, the balance," he says. In his new study, participants were asked to jump off a platform barefoot "from a height as high as one lands when one is running -- six inches or so" and land on a platform containing a device that measures impact and stability. The researcher and his colleagues measured the impact after repeated landings on either a bare, rigid platform or one covered with materials similar in thickness to that of a gymnastics mat. "We found that the greater the instability the material produced, the greater the impact," Robbins says, pointing out that the covered platform produced greater instability. "This explains why thick running shoes don't actually have the desired effect of reducing impact when humans use them," he says. "They do reduce impact when tested by a machine, which doesn't have changed running strategies -- there's no behavior associated with the machine." Because of the "changing strategies," the impact load is not uniform, the researcher explains. "If it were a uniform load, the thick shoes would be good, but they're actually terrible," he asserts. "And not only do they not absorb impact, but they also produce instability. And balance, of course, on those shoes is much worse, too, which is a big factor why elderly people fall."
On that last point, Robbins says his studies in the elderly indicate that thin, firmer shoes provide better stability. "They also provide better impact absorption" because people do land in them "with greater flexion of their knee and hip," he adds. "This myth about needing the thick soft shoe for cushioning should be exposed," he says. "Sports shoes and mats should be redesigned to protect the people who use them."