A female runner came in today, who hasn’t been able to run for the past two weeks because of increasingly severe left ankle pain. She has been wearing a pair of Mizuno Wave Alchemy running shoes for the past 6 months and when I set the shoes on a flat table, this is what I found.
Notice how the back of the left shoe is tilted outward and the right shoe is more upright?
In this case, the shoes outsole is made of soft EVA (ethylene vinyl acetate), whereas this person should have hard EVA to support heel strike, especially on her left side. EVA is made soft by pumping in air, which is great for shock absorption, but accelerates outsole wear because of compression.
In this case, because the outsole compressed unevenly, this runner sustained significant peroneal tendon injury. At this point I’ve ordered an MRI to determine the extent of the tendon damage…A big price to pay for an excessively worn shoe.
This injury could have been completed avoided, had this runner known how to evaluate her running shoes. Lots of runners have rules when it comes to replacing shoes. The most common ones I hear are replace your shoes every 500 miles or every 6 months.
Unfortunately, because shoes vary so much in construction, an arbitrary rule can lead to injury. Instead, place your running shoes on a flat surface monthly and when they start to tilt, it’s time for a replacement pair.