Okay, so I have been reading some weird things on the internet. “There is no excuse to throw out minimalist shoes, you bought them for the lack of cushioning to begin with!” —this is so, so very wrong.
Yes, indeed, minimalist shoes are built with less cushioning, but they are built with cushioning nonetheless. Furthermore, they are built with arch support. When one, or both of these aspects degrade, the quality of the shoe is compromised, and thus so is your running. This can lead to injuries when your gait is compromised by an old/misshapen shoe. Take a look at my two pairs of Saucony Kinvara2s:
Both of these pairs of shoes are worn out, how can you tell? They look nearly as good as they did when I bought them (the pink ones have 400+ miles, the blue have ~300/350). The fact is, the quality of your shoes is not reflected in the wearing of the tread on the bottom. A better sign of quality is to look at the midsole (in these two pairs, the white strip of foam bordering the blue upper on the top photo). While that is an incredibly terrible photo, if my camera had better resolution, you would be able to see stress lines in the foam where it has compressed and has not been able to recover. When you shoes begin getting deep lines, it may be time to buy a new pair and begin rotating them in with you current pair. I will discuss this more later.
Due to my particular gait, the foam gets worn out in certain places faster than others. this causes certain areas of the shoe to become more compressed, so the shoes do not lay flat when they are placed on a level surface. My particular stride causes my right shoe to rocker outward when you touch the outer heel, meaning that the cushioning in the outer area of the midsole has been worn away. This matches my known pattern of supinating, where I land first on the outside of my foot and roll minimally inward. On my left shoe, the cushion near the toes is worn out more than the sides, meaning I have a more neutral footstrike on that side of my foot. This is also indicated by my stride, where my right ankle rolls more than my left one. Take a look at these photos of my shoes lying on a flat surface, they do not lie perfectly flat anymore (very hard to tell—crappy camera and angle. My apologies).
The important part of this information is that when the cushion degrades in one place more than others, it compromises the fit of the shoe. My gait is affected when I run in these old pairs, and causes me minor pain in areas I associate with “worn out shoes.” This is typically in my upper hamstrings, which have to bear a greater impact burden as the cushion is worn away. While these minimalist shoes were intentionally bought for their lack of cushioning, when it is worn away, the shoe causes injury. It does not matter that they have less cushioning now, it is the way it is distributed which is of great importance.
That being said, how do I know when I need to buy new shoes? The easiest answer is the “6-month or 300-400 miles” rule, where a shoe is usually degraded after running through either of these two minimums. This is not entirely true, but is a good basis. Some people will find that they can run 1000+ miles on a shoe, others may only get 150 (especially with racing flats). It depends on the surfaces you run on, your weight and running efficiency, how you footstrike, and if you use your shoes for other purposes. Shoes used in the rain will deteriorate quicker, as well as shoes that are also used for lifting or recreational walking (which will acquire more miles). Running on wet surfaces or in the rain will allow your shoes to absorb the water and damage the cushioning irreparably. Hence, I only run in the rain in older shoes that are already delegated to the “treadmill and rainyday” pile.
Minimalist shoes will also degrade quickly due to their lack of a rubber outsole. The white foam on my kinvaras is an unprotected area where the foam degrades quickly. This causes these shoes to have a shorter lifespan than “regular” rubberized trainers. The pink and blue triangles in the forefoot of my kinvara have worn down, but not nearly as much as the white foam around it. The two used to be level, so you can clearly see how compressed the foam has become.
Shoe Rotation: keeping this one quick; when you record the mileage of your current shoes, you can begin to tell when they start degrading. Once the shoes have reached their half-life, it is wise to buy a new, different pair, and begin using both together during the week. This reduces stress injuries from the repetitive striking in one type of shoe; as well as allows you the reference of a new shoe versus an old one, allowing you to properly gauge when the old ones need to get chucked!
Thanks for the thought :) The same rule still applies, mostly. Barefoot-like shoes also have some “cushioning” through the rubber in the sole (I’m thinking vibrams here). When the sole wears away to a hole in once place, is that not comparable to the cushioning being worn out a shoe? It is not the amount that matters (wearing vffs you’re probably trying to work to running full barefoot, so why not shoes with holes??) but the distribution of it. If the rubber were simply thinner all around, it’d still be fine. But if the rubber is worn too thin in one place and causes problems (cuts and bruises if there were a legit hole in your vffs) then that is an issue.