When you go into a specialist running store you may hear the term 'Gait Analysis' thrown about. The store assistant may well ask you to run on a treadmill whilst watching (or recording) the way your feet strike the ground. This will be followed by them telling you that you overpronate, underpronate (suppinate) or have a neutral gait. They will then use this information to direct you to the 'appropriate' running shoe for your gait. The problem is that this process can occur without you, the buyer, truly understanding what is going on and why they are suggesting a particular shoe. We are here to help.
Overpronation is essentially when your ankles roll inwards (towards one another). Many articles on the topic will state that overpronaters may see a higher incidence of injuries such as shin splints. Unfortunately for every piece of research suggesting this there is another piece refuting that this is the case. There is no definitive evidence that overpronation leads to more injuries.
Running stores offering 'Gait analyses' are oftentimes simply using it as a marketing tool. Given the abundance of great running shoes the presence of a 'test' to direct a buyer to an appropriate pair of shoes often makes decision making a lot simpler. Recently some running stores here in the UK have stopped offering gait analyses for this very reason.
Given this, it is important that you know/understand what you are looking at and can make an informed decision.
If you have access to a treadmill or simply a friend/family member with a camera you can ask them to record you as you run a short distance. Most significant issues with running form/gait can (in my opinion) be seen simply by looking at such a video and asking yourself as to whether anything looks obviously unnatural. If it does we would always recommend that you seek professional advice. Similarly if at any point you feel any discomfort or pain whilst running.
It is not often the case that you find someone who starts running and then a week later is running marathons. Your body needs to adapt to the stresses that you are going to place on it. This need for a slow and steady buildup of mileage is in itself a protection mechanism. That is to say that if you do overpronate it is not imperative that you are running in a support shoe (see below) from the get go. Rather, as/when you encounter issues as you increase your mileage you should seek appropriate advice and adjust the shoes you wear as appropriate.
Once you have worn a pair of running shoes for a number of miles one way of discerning how you strike the ground is to simply look at the wear patterns on the sole of your shoes. Running shoes often have indentations on the soles (to provide grip) which (if you overpronate) will be more obviously worn on the inside edge of the shoe.
I myself overpronate quite significantly. A gait anaylsis (and the advice that came with it) told me that I would need a pair of support shoes - shoes that are appropriately built up on the inside to prevent the ankle from rolling inwards.
During my time working in a large running specialty store I was able to try on every pair of support shoes (that we stocked) and record myself running on the treadmill. 2/16 pairs actually corrected the inward roll of my ankle.
The point here is that different companies use different technologies to provide the 'support' to those who overpronate. Your results will vary and the efficiency of a support shoe for your specific biomechanics will be different to those of any other individual. You should try on any/all potential running shoes, test them on a treadmill and make sure it is actually doing what you expect it to.
At the end of the day, running shoes are an expensive (albeit worthwhile) investment and as such you want to get it right !