When rubber meets road: what your running shoes can tell you

Mark Richardson reveals the story that our running shoes can tell us, and how it can help you avoid running injury

As a physiotherapist I see many runners in my practice, and one thing I like to do is examine their running shoes. That’s because there are a lot of things we can learn about someone’s biomechanical alignment, foot posture and running style by examining the soles of their running shoes. Why does it matter if we identify more wear on the inner or outer part of the shoe? And assuming this does matter, can anything be done to change this anyway? In this article we will consider why abnormal wear on running shoe soles is important to identify, and what corrective measures can be taken.

Normal wear

To understand normal wear on our soles, we first need to understand what ‘normal’ biomechanics for the foot during running looks like. We can split the running cycle into weight bearing and the non-weight bearing phases, but when considering the sole of our shoes, we are really interested in the weight bearing phase of the cycle. This weight bearing phase can be further subdivided into:

1. Contact
2. Midstance
3. Propulsion

These three different parts of the weight-bearing phase relate to different parts of the shoe’s sole. When considering the contact phase we need to look at the back section of our sole. For the midstance, the the mid-section is important while propulsion relates to the front section of the sole. So the first thing we should do is divide our shoe into these three sections (see figure 1).

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Figure 1: The three sub divisions of the stance phase

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THE CONTACT PHASE – The contact phase occurs when the heel hits the ground. At heel contact, your foot should be slightly tilted outwardly or supinated^{J Orthopaedic Sports Physical Therapy, October 1987, 9(4), 160-165}(see box 1 and figure 2). In other words you should be landing slightly on the outer part of your heel. So you should be noticing more wear on the outer part of the heel as compared to the inner part. This is perfectly normal. If you notice more wear on the inner aspect or that the wear is spread evenly across the whole of the heel then this means you are landing on your heels with too much inward tilt (pronation – box 1). This problem would be classed as ‘excessive pronation at heel strike’.

THE MIDSTANCE PHASE – The midstance phase is when the foot is in full contact with the ground. As your foot lands in midstance, it should become more pronated to allow for shock absorption and any ground terrain changes^{J Orthopaedic Sports Physical Therapy, November 1985, 7(3), 91-95}(see figure 2 and box 1). Therefore, at the mid-section of your shoe, there should be more wear on the inner aspect as compared to the outer aspect. One thing you should not see here is excessive wear on the outer aspect. This would be a sign of ‘excessive supination at midstance’.

THE PROPULSION PHASE – During the propulsion phase, the heel begins to rise followed by the whole foot in order to propel you into the swing phase. As you push off, your foot should supinate^{J Orthopaedic Sports Physical Therapy, November 1985, 7(3), 91-95}(see figure 2). Put simply, you should feel like you’re pushing up from the mid to outer aspect of your foot. When examining the front part of your shoe (where the tips of the toes sit) you should notice that there is more wear on the mid to outer part. There should not be excessive wear at the tip of the sole in the region of the big toe. This is a very common problem we observe, and is a sign of ‘excessive pronation at propulsion’.

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Figure 2: Gait cycle during the stance phase

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Box 1: What is pronation and supination?

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The importance of sole wear

Why is all this important I can hear some of you ask, especially if you currently have no symptoms? Well, a lot of the patients I see who experience pain when running due to biomechanical imbalances are likely to have had these problems for years without symptoms. Over time however, the subtle changes in the foot and lower limb can mean that if not addressed, these symptoms will eventually develop.

Running gait problems such as those described above have long since been linked with problems of the lower limb and lumbar spine area^{Sports Med, September 1998, 26(3), 169-176 Am J Sports Med, January 1991, 19(1), 66-71 J Manipulative and Physiological Therapeutics, October 1988, 11(5), 373379}. While it’s true that many runners can get away without symptoms by becoming less active, this is not a good way to deal with the problem. Moreover, many could remain active by correcting their biomechanical problem. So it’s worth checking for this reason.

Secondly, there may be a link to running performance. In 2001 a very interesting study looked at calf muscle strength in two groups of runners^{Foot and Ankle International, March 2001, 22(3), 234-240}. One group had excessive pronation during propulsion while the control group had ‘normal’ foot alignment at propulsion. Subjects with excessive pronation at propulsion were found to have significantly less calf muscle strength than the control group, with implications for running efficiency. These results suggest that reducing biomechanical imbalances and improving your running gait could also help you run faster!

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Box 2: Measuring pronation/supination

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Optimising your running gait

The three most common problems identified so far are excessive pronation at heel strike, excessive supination at mid stance and excessive pronation at propulsion. While it’s possible to have different imbalances such as excessive supination at heel strike and excessive pronation at midstance, these are relatively rare. In the final section of the article therefore, we will consider how to correct these more common abnormalities (see figure 3).

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Figure 3: Common abnormalities

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Excessive pronation at heel strike

• In a sitting position, place your foot into a position that mimics the heel strike phase. In this position you should aim to turn your foot inwardly.
• Perform 10-20 repetitions and  3-5 sets.
• Progress by adding resistance  using a resistance band as illustrated, or simply pushing your foot against a solid surface.
• A further progression is to perform this exercise in standing.

Excessive supination at mid stance