Over-pronation (fallen arches and rolling inwards of the feet & ankles) is a very common condition, affecting at least 70% of the population. The opposite of pronation is supination: the feet tend to roll outward and the arch remains high during the walking process. Only 5% of the population has this problem (often referred to as Pes Cavus - latin for high arched foot).
Interestingly, many people are convinced they don't over-pronate at all, because their shoes tend to wear out faster on the outside, not the inside! In other words, they believe that over-supinate, rather than over-pronate...
Shoewear (at the bottom of the shoes) can provide helpful information when assessing a person gait pattern. Podiatrists and phyiotherapists often will look for irregular shoewear when a patient presents with a foot or knee problem.
The simple assumption that excessive outside wear of sole indicates supination and conversely excessive inside shoewear indicates over-pronation, is incorrect.
Firstly, we need to understand normal human gait pattern. When we walk our feet always land on the outside heel first (heel strike). This is simply because the distance between our hips is wider than the distance between our feet when they land during walking or running. Women especially place their feet very close together, almost in a one line, during walking and running. The photo below illustrates how our legs are always angled inwards, during walking and running. With women the angle tends to be slightly greater than with men.
Because of this leg angle, when the foot lands it always hits the ground first with the outside of the foot. During our gait our heels touch the ground first, so it comes as no surprise that our footwear wears out first on the outside heel area of the shoe.
This excessive wear on the outside heel is totally normal and occurs in both over-pronators and over-supinators. Some people will only notice slight outside wear, others a lot. Supinators will notice excessive wear not just in the outside heel area, but more likely across the entire outside area of the shoe.
Now let's have a look at what happens after heel strike. After our heel strikes the ground, the foot makes full ground contact (this is called the midstance phase of gait) and pronation occurs. I.e. the foot muscles loosen allowing the foot and ankle to roll inwards and the arch to flatten. Pronation is a normal process: it is nature's own shock-absorbing mechanism.
Next the heel lifts off the ground and the foot prepares itself for take-off: a propelling motion to move the body forward (the propulsive phase of gait). At this stage the foot should become rigid and supinate (roll outwards). Unfortunately, this the moment where things go wrong. Most of us don't supinate, instead the foot remains loose and stays in a pronated position (ankle inwards and arch lowered). This situation is referred to as over-pronation.
So in conclusion, if your shoes wear out faster on the outside heels of your shoesoles, it doesn't mean you're not an over-pronator! Most likely you are, like 70% of the population.
Over-pronation can be a real problem as it makes walking and running quite inefficient, costing us more energy and increasing the chances of pain and injury such as plantar fasciitis, shin splints, knee pain and lower back pain. To combat over-pronation you can 2 things: strengthen the muscles in your feet and legs with exercises and wear a (flexible) orthotic like Footlogics orthotics. The good thing about flexible orthotics (as opposed to hard, rigid) orthotics is that they still allow the foot to pronate naturally, but at the same time they prevent over-pronation.