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).


Figure 1: The three sub divisions of the stance phase


THE CONTACT PHASE – The contact phase occurs when the heel hits the ground. At heel contact, your foot should be slightly tilted outwardly or supinated1(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 changes2(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 supinate3(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’.


Figure 2: Gait cycle during the stance phase

The foot should be supinated at contact phase, pronated at midstance and supinated at propulsion.


Box 1: What is pronation and supination?

When talking about the foot, we talk a lot about pronation and supination. It is important to understand these movements before discussing what happens during running. Pronation refers to the flattening of the inner arch of the foot whereas supination refers to the rising of the inner arch of the foot. These movements are illustrated below. Each of the feet below is the right foot viewed from behind.


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 area4 5 6. 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 runners7. 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!


Box 2: Measuring pronation/supination

There are other ways we can measure pronation/supination. One way is to measure the distance between your navicular tuberosity to the floor. The navicular tuberosity is a bony protrusion on the inner aspect of your foot, as illustrated below. The navicular tuberosity drops down closer to the floor in pronation, and rises up away from floor in supination. Navicular height has been found to be a valid and reliable measure of pronation and supination. In single leg stance – ie mimicking the mid stance phase of the gait cycle – navicular height should be about 4cm. Less than this and pronation can be assumed. Greater than this and supination can be assumed. Granted, this measurement only concerns the mid stance phase we can assume that if there is over pronation or supination in this position, it is likely to be transferred to other phases of the gait cycle.


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).


Figure 3: Common abnormalities


Excessive pronation at heel strike

If you have identified yourself as having excessive pronation at heel strike you need to try and retrain supination at heel strike. This can be achieved as follows:
  • 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.
Note that your foot should remain in a pointed up position. This is in order to mimic heel strike. You may notice that if you were to point your toes downwards you feel much more range of movement. This is true, but performing the exercise with toes pointed down is ineffective because it is non-functional –ie not applicable to the position of the foot at heel strike during running.

Excessive supination at mid stance

If you have identified yourself as having excessive supination at mid stance you should retrain pronation at midstance:
  • In a sitting position with your foot flat on the floor, try to lift up the outer aspect of your foot from the floor (see figure 3). You should feel like your big toe squashes down into the floor while the little toe should lift from the floor.
  • Perform repetitions and sets as suggested previously.
  • Progress to performing this exercise in a standing position with the knee straight (important).
This exercise will re-train the muscles that pronate the foot during the midstance phase. A good tip is to hold on to your knee and not let it move. This is to ensure it is your foot doing the work and not your knee or hip.

Excessive pronation at propulsion

If you have identified yourself as having excessive pronation at propulsion, you need to retrain supination at push off:
  • Start off in a sitting position and mimic the ‘push off’ foot position by lifting your heel from the floor.
  • Transfer your weight onto mid or outer aspect of the ball of your foot.
  • Move between midstance position (foot flat) and push off (heel lift), ensuring you resist pronation (see figure 3 overleaf).
  • Perform repetitions as previously suggested.
  • Progress to a standing position and perform calf raises but ensure you avoid pronation.
  • Take care not to go into extreme, end of range supination. You should be aiming for your weight to be centred on the base of the third toe.
This exercise will retrain the  muscles that supinate the foot during propulsion.

The tricky bit!

Dedicating time every day to performing these specific exercises is all well and good. But the key is whether you can you put this into practice on the road. All the analysis and exercises are useless unless you make a conscious change while running. This is undoubtedly the most important aspect of rehabilitation.
It’s true that insoles may help to achieve some of the things we have discussed in this article by passive correction. However, you should be aiming to retrain your foot muscles actively by thinking about how your foot moves during running.
So for example if you have excessive pronation at heel strike, you must actively try to land with more supination – ie on the outer aspect of the foot. Likewise, if you have excessive supination at midstance, you should subtly allow your foot to pronate midstance by thinking about transferring body weight onto the inner aspect of your foot slightly. Finally, if you have excessive pronation at propulsion, you need to mentally focus on pushing up from the outer aspect of your foot during push off. However, it is worth emphasising that these movement changes when running should be subtle. You can be more aggressive in your specific exercise program done at home, but when out running, a gentler change is needed. This is the trickiest and yet arguably the most important part of the rehabilitation process.

Key learning points
  • Your running shoes can give you lots of information about your biomechanical alignment
  • Altered biomechanics can predispose to injury and negatively impact your peak performance
  • Analysing your running shoes is quite simple to do
  • It is possible to actively improve your biomechanical alignment to prevent injury and improve performance

SEE ALSO:

 

References

  1. J Orthopaedic Sports Physical Therapy, October 1987, 9(4), 160-165
  2. J Orthopaedic Sports Physical Therapy, November 1985, 7(3), 91-95
  3. J Orthopaedic Sports Physical Therapy, November 1985, 7(3), 91-95
  4. Sports Med, September 1998, 26(3), 169-176
  5. Am J Sports Med, January 1991, 19(1), 66-71
  6. J Manipulative and Physiological Therapeutics, October 1988, 11(5), 373379
  7. Foot and Ankle International, March 2001, 22(3), 234-240
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