Your Shoes are the Window to Your Sole

What do your shoes say about you??

The older your shoes get, the more valuable they become - definitely not in terms of monetary worth (or benefit to your running) - but in what they reveal about you and the way you run, walk and move. They’re like a window to your sole. Wear patterns tell a story, and are strongly correlated with specific foot types. So, looking at your old shoes will tell you lots of information about your natural biomechanics - the structure of your feet, and how they function during both walking and running gait.

Wear of course is also one of the best ways to determine whether or not your shoes are worn out. The life expectancy of running shoes differs significantly, and is dependant on a number of factors, including how cushioned the shoes are, and the types of materials used to manufacture them. Whilst each brand produces their own cushioning compounds with slightly different characteristics and feel, essentially they’re all synthetic, and are often derivatives of EVA (ethyl vinyl acetate). This means the cushioning contains at least some proportion of air (how else would shoes be so lightweight with such a significant volume of cushioning underfoot?). As such, the cushioning in your shoes will compress and deteriorate with use, and once your shoes have expired, they will no longer provide adequate shock attenuation. Unfortunately, regardless of use, shoes will deteriorate over time, so even if you leave your shoes untouched in the cupboard, they will wear out - so don’t hoard shoes!

How you wear your shoes (are you hard on your shoes?) and how often you wear them will also influence their life expectancy dramatically. You could get anywhere from about 200km up to 1000km out of your shoes before they should be retired. Though many runners will attest to using their shoes for many 1000s of kms, due to the lack of cushioning, the injury risks associated with running in dead shoes are far too great. Because there is significant variation in the life expectancy of running shoes, it’s really important to check your shoes regularly for wear, and to understand the signs indicating that your shoes are dead.

Five Signs Your Running Shoes are Dead

1) Dead Shoe Test

Remember that resistance is cushioning. Your shoes should flex in the forefoot with the toes up (as your foot would). New shoes should not flex in the opposite direction - toes down, because they will be strong and cushioned enough to resist this movement. If you can bend your shoes the wrong way at the forefoot, they’ve lost their resistance and failed the test. They are dead!

2) Visible creases and wrinkles in the midsole

Permanent creases in the midsole indicate the cushioning has compressed, and that your shoes are worn out

3) Palpable soft spots

Typically this occurs with particular biomechanics or gait types, but you might wear significantly to just one spot on the midsole. This type of wear is more difficult to identify, but if you push focal pressure to different areas of the shoe and find one portion that’s particularly soft (lacking resistance), then it could post an issue.

4) Complete wear through the outsole

If you’ve worn through the outsole, then obviously that’s an area of high-wear, and will continue to be as you wear the shoes. Without the protection of the more durable outsole, you will wear through the midsole very quickly.

5) Wedging and compression of the midsole

Do your shoes lean to one side or the other? Place them on the ground and take a look from the back. Wedging can occur with significant compression to the entire lateral or medial cushioning of the shoes, and will mean the shoes are no longer providing adequate support for your feet.

6) Injury Niggles

Many runners will start to experience niggling pain when their shoes are dead, likely because they’re no longer offering the cushioning and shock attenuation required, and your joints, tendons, ligaments and muscles will be working harder as a result.

Shoe Wear Explained

When examining wear, it’s important to consider all parts of the shoe - not just the outsole, but also the midsole, upper and the insole. Wear to each of these different parts are like pieces of the puzzle, and help to build a better picture about your feet, and the suitability (or not) of the shoes.

Outsole Wear

Visible wear and abrasions can only occur with friction. It’s somewhat counterintuitive, but this means runners who are really heavy and loud in their feet, are much less likely to have visible outsole wear on the outsole of their shoes. A heavy, pounding strike typically occurs because there is a flat strike with no movement or pronation to attenuate shock, so instead of being converted into momentum, that energy is lost as sound. These runners will need to use midsole wear to indicate shoe deterioration.

Given that a majority of runners heel strike, wear to the heel outsole is common, but the aggressiveness and location of wear differs, and is important to consider. Really aggressive wear is a sure sign that scuffing is occurring at strike, and commonly suggests over-striding. An aggressive heel strike can also cause midsole compression and wedging over time. Wear to the postero-lateral heel is normal, but wear more directly to the back of the heel, or medially, is unusual and can suggest issues.

Looking at the forefoot outsole, there are again different wear patterns to identify. Being the largest and strongest joint in the forefoot, the 1st MPJ (big toe) is designed to take a majority of the load through propulsion. Therefore, wear should ideally be focussed through the central and medial forefoot. Lateral forefoot wear can suggest that your shoes are providing too much control, resulting in a lack of pronation and insufficient 1st MPJ utilisation. A circular wear pattern through the forefoot commonly suggests 1st MPJ dysfunction - where the joint is stiff and doesn’t flex properly during gait. To counteract this stiffness, a twisting motion is typically seen during forefoot loading, which allows a more lateral toe-off.

Midsole Wear

The midsole is arguably most critical part of your shoes with regard to their life expectancy. Compression wear is by far the most common, and predominantly manifests as wedging or focal soft spots in parts of the shoe that take the most load. With compression, the midsole looses resistance and cushioning ability. As such, the Dead Shoe Test is a great indicator of overall midsole wear and deterioration. Wearing your shoes for daily wear (ie. work/casual), and walking and running on consecutive days will drastically increase the amount of compression wear to the midsole. Just like us runners, your shoes need rest to help the midsole recover between uses.

Wedging occurs as an entire portion of your shoes becomes significantly compressed, and it can significantly affect the way they function. Stability shoes are most commonly affected by wedging, particularly if they are too controlling for the wearer. Being a denser material, the medial support is generally more resistant to wear compared to the rest of the midsole. If the shoes are providing too much control, there will be increased wear to the softer lateral border of the shoes, in combination with the increased wear-rate compared to the medial border, this will lead to compression and subsequently exacerbate the medial support provided by the shoes. In addition to shoe suitability, sizing issues can also cause midsole compression. Similar wedging is often seen if shoes are too narrow for the wearer, and their feet fall off the lateral the side of their shoe. Again, this will increase compression wear to the midsole and wedging is likely to develop.

Although less common, scuffing wear to the midsole also occurs with certain gait types, when one shoe brushes or scuffs against the other during the swing phase (some runners will scuff against their medial leg instead, evident with scratches or dirt). Typically there is corresponding wear seen on each shoe, which may be to the medial rearfoot or forefoot midsole, or even to the medial collar (upper). Medial scuffing can indicate gait characteristics such as a narrow base of gait and circumduction, which can be a sign of glute or knee instability, or a twisting at propulsion due to forefoot pathology or dysfunction.

Insole Wear

Generally being a low density, relatively thin material, insoles are not very resistant to wear, which means they are a great indicator of what’s going on inside your shoes. Movement of your feet within your shoes, and areas of high pressure and load can be determined by examining insole wear. Movement and friction will be seen as pilling or abrasions, whilst compression and thinning of the insole would indicate high pressure. Commonly, insole wear will be seen in conjunction with corresponding or related wear to other parts of the shoe. For example, 1st MPJ dysfunction could be seen as minimal pressure through the 1st MPJ and higher pressure load through the lateral forefoot (on the insole), as well as a circular wear pattern to the forefoot outsole. Alternatively, a runner with a scuffing lateral midfoot strike would likely see wear and compression to the lateral midsole and outsole, plus also some abrasion to the lateral portion of their insole.

Ideally, pressure and load should be spread as evenly as possible throughout the foot, because the same amount of load distributed across a larger surface area will greatly reduce load to specific structures and reduce the risk of overuse injuries. Someone with a rigid, high-arched foot type might see significant pressure through the forefoot, and no wear through the arch. In addition to enhancing comfort and function, this is the main premise behind orthotics - to spread load across the foot and reduce areas of high load and pressure. A custom orthotic is designed and shaped specifically, such that it will contour naturally to your foot, and enhance comfort and function. Of course, this can be achieved in various ways, but the end result is highly dependant on dynamic function during gait, and relies heavily on the interaction between the insole or orthotic, your feet and your shoes.

Upper Wear

Although upper wear very rarely affects shoe life expectancy, it can be unsightly, frustrating, and often uncomfortable. The key is understanding why the wear occurs, so that you know what to expect and whether or not it’s something worth worrying about. Upper wear is highly indicative of structural and biomechanical abnormalities.

One of the most common wear patterns is seen when the big toe pokes a hole through the forefoot upper, which is highly indicative of 1st MPJ dysfunction during gait. The big toe has hyperextended to compensate for lack of 1st MPJ flexion, and repeated pressure to the upper has causes material failure. Some shoes will offer a firmer material toe cap to decrease the likelihood of this occurring. However, this solution is like a bandaid - if your big toe is always lifting, although you will not wear through the upper, wearing a shoe with a reinforced toe is more likely to cause discomfort (ie. black toenail). Addressing the 1st MPJ dysfunction with insole padding or an orthotic, searching for shoes that offer more depth in the forefoot, or tolerating the upper wear will be more effective remedies.

Heel counter wear, within the posterior heel of the shoe, is also very common. Having a Hagland’s deformity (large prominence on the posterior calcaneus) can certainly predispose you to this type of wear, although often friction will also play a role. If the heel counter of your shoes doesn’t fit properly (due to shape), or the fit is insecure, then your heel is much more likely to slip and cause friction, which will result in excessive wear. Increased direct pressure can also cause increased wear, and often discomfort - in some cases, pressure from the heel counter (particularly in ill-fitting running shoes or work boots) can contributed toward insertional Achilles tendinopathy or bursitis. All shoes have a slightly different heel counter construction in relation to materials, shape, flexibility and depth, so if you’re having

issues with heel counter wear or discomfort, it is likely that alternative shoe that will provide relief.

There are many more examples of upper wear, such as:

- Holes to the medial or lateral forefoot upper can indicate a poor fit, and lack of width or depth, so you should use such wear as a guide when purchasing your new shoes.

- Wear to the collar is often a result of scuffing during the swing phase of gait.

- Bunching of the forefoot upper - a sign that the shoe is too wide and laced too tightly to provide a secure fit.

Extending the Life of Your Shoes

The best way to extend the life of your shoes is to look after them. Two simple ways to achieve this are:

1. Wear different shoes for different activities to ensure suitability

2. Run (or walk) in multiple different pairs, and alternate between them on consecutive days to allow your shoes adequate recovery between uses

For example, A runner using the same pair of shoes for five sessions per week might expect the pair to last 500km. However, if the same runner used that same pair of shoes for only three of those runs each week, and a different pair for the other two runs, those shoes might last 600km instead (each pair - assuming they had the same characteristics). Just by alternating his shoes between sessions, both pairs would last much longer in terms of time, but he would also get more volume from them.

Remember that your shoes are unlikely to last as long as you would like or expect, and if you think they’re dead, they almost certainly are! Take good care of your shoes, check them regularly for wear, and replace them often. It will benefit your running and greatly reduce your injury risk.