When is it time to replace running shoes?
How do you know when it's time to retire your running shoes? When is it time to say, enough, I need some new shoes (or I want some new shoes)? Without sounding like I'm beating around the bush, it really all depends. Let's take a look at the three basic attributes of a shoe and see how they change over the course of the life of the shoe. And maybe based on this knowledge we can come up with some logical reasons why you may or may not need to change your running shoes out.
Think back to the days when you ran in your Chuck Taylor's and how things have improved. The difference today is that good running shoes are really a knock-off on a traditional Oxford shoe. Sure, they're lighter and more able to adapt to a recreational activity than a heavy leather Oxford. But to make a good running shoe, we need to incorporate some of the attributes that make an Oxford a supportive shoe. The three attributes of an Oxford include a slight heel, a rigid shank and a laced upper. Combined, all three attributes of the Oxford shoe create what is a very eloquent brace, that we call a shoe. Let's take a quick look at each attribute and how they may wear out and create a need for replacement.
The heel of the shoe is used to weaken the calf. Running and walking is really a controlled forward fall regulated by the calf and Achilles tendon slowing the forward excursion of the leg over the foot. As your body moves forward over the foot, the calf can no longer limit that forward motion of the lower leg and you enter the 'heel off' phase of gait. By placing a heel on the shoe, you elevate the heel just a wee bit. This results in early heel off which decreases the effort required to walk or run.
The shank of the shoe is used as a brace to carry the mechanical force (eccentric muscle contraction) from the heel to the ball of the foot. Really simply put, place a doctor's wooden tongue depressor on the bottom of your foot, secure with some duct tape and you have a shank (don't try this at home). But for sake of example, I think you get the point. The shank is a brace. It decrease the amount of effort needed to walk or run by splinting the bottom of the foot.
And lastly, the laced upper. By definition, the upper of the shoe includes the walls of the shoe and the mechanism that holds the walls together. The upper could be bound by laces (most common), slip tie or perhaps Velcro. The upper (hopefully laced) is what really holds the whole shoe together. The laced upper is what binds the foot and forces it to utilize the shank and heel raise.
So when do you swap out your running shoes? The first consideration is foot health and foot comfort. Some people are lucky to have good feet. They could run 10 miles barefoot or in a pair of loafers and it really wouldn't faze them either way. But for most of us, we use our shoes to protect the feet and to make the foot more efficient. And this is where the three attributes of the traditional Oxford start to come into play. When the heel wears, running becomes a bit harder. As the shank breaks down, the foot becomes less efficient and tires more easily. And lastly, the laced upper - as the walls of the shoe stretch, the support provided by the laced upper becomes increasingly less supportive.
I've never been a fan of swapping shoes every 400 miles or every 4 months (or whatever formula you may read about). You may have a formula that works for you but I'll bet that formula came from a history of wearing out multiple pairs of running shoes. Try this as an alternative; wear a pair of running shoes for a dedicated period of time (say 3 months), and then pick up another pair of the same shoes. Start to rotate them and see if you can tell the difference. Run with the new shoes only once a week. As you get into the 4th - 6th months, you'll start to see the difference. The old shoes, although comfortable around town just don't have the support anymore. Why? The heel is wearing down, the shank is becoming weak and the laced upper is no longer able to support your foot in running.
Swapping out running shoes in this manner is a way I've helped runners over the years determine the right time to swap out their running shoes. Give it a try and let me know - how long until you need to swap out your shoes?