BY MARC LINDSAY MAP MY RUN BLOG

One of the great things about running is you don’t need a lot of gear. That said, a good pair of running shoes is a must — and you’ll need to replace them frequently to avoid common overuse injuries.
When you need to replace them is subject to debate. If you ask 10 different experts, you’ll likely get 10 different answers. While there is no one right or wrong answer for everyone, there are a few general wear-and-tear signs that can signal it’s time for a new pair of kicks.
Why Running Shoes need to be replaced.
Running shoes are designed to be protective and supportive. Once the exterior sole or tread, midsole and upper begin to wear, your feet, ankles, knees and hips will have to absorb more of the pounding as you run on the road.
When the midsole, (which provides a majority of the cushion on impact), has been compressed enough times, it won’t provide those shock-absorbing qualities that can help to reduce the likelihood of an overuse injury like patellar tendonitis, Achilles tendonitis and plantar fasciitis among others. “Air is one of the key ingredients to the foams that are used in running-shoe midsoles. This is what allows the shoes to be light and comfortable underfoot,” says Cori Burns Run Category Manager at Under Armour. “In turn, over time and under the repetitive stresses of running, the foam structure can break down or compress.”
The general range for when a midsole begins to break down is between 300–550 miles. The number of miles you run until the midsole breaks down varies so greatly due to a number of factors that can differ from person-to-person and shoe-to-shoe. It isn’t recommended to judge midsole breakdown based on time, since the number of miles you run from month-to-month can differ. “In addition, the outsole rubber, under the sheering forces of foot-strike will also wear down over time. Similar to the tread on tires,” says Burns. “To maximize the cushioning underfoot and keep your feet and joints feeling fresh, it’s best to refresh your shoes.”
Factors that affect Midsole Breakdown
Because of the variances of anatomy and training habits, midsole breakdown can vary greatly between runners. “The amount of load (weight of the runner, number of miles run in the shoes, wearer’s efficiency and foot-strike) plays a significant role in the breakdown of a shoe over time. However, the foam composition and how resilient it is to ‘compression set’ will also play a major role,” says Burns.
Below are a few factors that should be considered when determining how often your running shoes need to be replaced:
• How much do you weigh? Larger runners need to replace shoes more often since the compression of the midsole will be much greater than it is from a smaller runner.
• What’s your running style? Runners who have an efficient stride and are light on their feet will not wear out running shoes as quickly as runners with an excessive heel strike who pound the pavement.
• Where do you run? If you run primarily on the road, your running shoes will wear faster than they will if you run on grass or dirt trails.
• What kind of shoe do you have? Different models wear at different rates depending on the quality of the materials in the midsole. Minimalist shoes can wear even quicker than other models.
Signs that it’s time to replace your shoes
Not everything needs to be scientific. If your running shoes have started to feel flat and you begin to notice aches and pains in your feet, ankles and knees, it’s probably a safe bet it’s time for a new pair. “It’s often said that a runner should replace their shoes after about 300 miles,” notes Burns. “But it’s important to consider the underfoot feel and the outsole tread pattern as well. If the shoe still feels lively, it is likely fine to continue pounding out the miles. But, if the midsole feels dead and if the outsole traction has worn away, it’s a good sign to refresh your shoes.”
Here are some other basic wear-and-tear signs that signal the need for a trip to your local running store:
• Visible creases or cracks in the midsole.
• A worn outer sole showing the midsole, or an outer sole that’s rounded or bald like a car tire.
• An unsupportive heel counter.
• Tears in the upper.
• The shoe sole is visibly worn on either side so that it leans to one side on a flat surface.
• The midsole doesn’t feel as springy as it did when they were purchased.
If you’re still on the fence, try on the same model you already own. If there is a noticeable difference in how they feel, you might want to go ahead and make the purchase.
Tips to make your running shoes last longer
Whether or not you’re a high-mileage runner, replacing your running shoes every few months can get expensive. To make your running shoes last as long as possible, there are a few things you can do to improve their longevity.
While it might seem expensive at first, purchasing two or three pairs of running shoes and alternating them can help them to last much longer than they would if you only run in one pair. “having a couple of pairs to rotate throughout the week can alleviate the stress on a single pair, and ultimately allow both shoes to last longer,” says Burns. This is due to the compression of the midsole, which takes close to 24 hours to return to its normal shape. By alternating pairs if you run one night and then again the next morning or afternoon, you’ll give your joints more protection and increase the longevity of your shoe.
It’s also a good idea to switch up your running surfaces instead of sticking to the sidewalk. “Running on softer surfaces, such as grass or a treadmill can help to preserve your shoes,” says Burns. Since concrete is a much harder surface, your shoe’s midsole will have to compress more to absorb the impact of your foot strike. By alternating runs on softer surfaces like dirt, grass or even the treadmill every once in awhile, your shoes won’t have to work as hard to provide the cushion and support your body needs.
If you’ve gotten into the habit of wearing your running shoes while running errands, this also decreases their lifespan. Only wear your running shoes while running and get a separate pair of shoes to wear while you’re out in town.