You may think you’re being financially savvy by holding onto your old sneaks, but their worn-down cushioning could actually be causing your feet some serious harm.
How frequently you need to buy a new pair of sneakers is going to depend on a ton of factors: your body mass, the shoe’s quality, the environment you wear them in, the type of workout you’re wearing them for, and how often you wear them, says Phillip Vasyli, an Australian podiatrist and chairman of Vionic Shoes. Owning a pair of shoes for four months is going to mean vastly different things depending on whether you’re wearing them for triathlon training or lacing them up three times a week to walk your dog around the block.
So how do those factors above play into how long kicks will last? “Assuming you purchase the appropriate shoe for your chosen activity, the frequency of wear basically determines how long a shoe will last structurally,” says Vasyli. And when we talk about shoe structure, the key component is the midsole. The most common material for these is Ethyl Vinyl Acetate (EVA): “EVA is a cellular foam which is lightweight, supportive, flexible, and absorbs shock,” says Vasyli. Over time, the EVA in your shoes compresses, meaning you lose out on your shoe’s “rebound” and shock absorption abilities.
We asked Vasyli for some activity-specific hints that you should probably replace your kicks, like, yesterday:
You’re 100 Percent a Runner
Runners tend to put the most wear and tear on their shoes, says Vasyli. So when is it time to toss a pair? “300 to 400 miles is a reasonable indicator,” he says. Try to keep track of your miles, and really start to evaluate the midsoles of your shoes when you creep up near the 300-mile mark.
You’re Not into Running, but You Walk Everywhere
Walking shoe replacement is going to follow similar protocol to running shoe replacement: Mileage is key. But because walking is significantly lower impact than running, Vasyli says your shoes can last more like 500 miles. That’s not to say, though, that you can walk five miles a week and your shoes will last 100 weeks. “EVA and the adhesives used in sports shoe constructions have shelf lives and will deteriorate while sitting in your shoe cupboard,” says Vasyli. As a rule of thumb, even if you’re not using them often at all, the adhesives in shoe construction typically have a shelf life of six to nine months. Although this doesn’t mean that the entire shoe construction will spontaneously deteriorate after the nine-month mark, the seams that bind the shoe together can become brittle or less flexible, which means the shoe could start coming apart.
You Swear by the Elliptical and StairMaster
Cardio machines like these don’t require as much impact as running on pavement, so “structurally, these shoes should last longer than running shoes,” says Vasyli. But pay attention to the shelf life factor here, too, he warns.
You’re More of a Dance Cardio Kind of Girl
Vasyli describes these classes as “medium impact,” which he says is pretty similar to the impact of walking. But since you can’t calculate mileage for your grapevines, you’re going to need to go by feel here, says Vasyli. “Compression in the midsole will lead to a ‘harder’ feel,” he says. “Where the shoes once felt more cushioning and flexible, they can become less flexible and firmer.” You know what that means: You’re overdue for new shoes.
This article originally appeared on Women’s Health.
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