I think it is important not to use just one pair of shoes for running and it is definitely not a good idea to start thinking about buying the next pair only when the pair you are using starts to wear out. In the last part of a shoe’s life it loses its shape or at the very least provides less cushioning and therefore poses a danger to the runner. In short, less protection leads to increased risk of injury.
In order to take advantage of a shoe’s average life (usually around 500 km), you should start rotating it with the new shoes you have bought. Even if “the old pair” offer less guarantee, you reduce the risk by running only part of your weekly distance in them.
My advice is actually to buy different types of shoe.
I always preferred to have three types:
– Shoes for easy running, medium and increasing pace; average protection
– Shoes for repetitions, intense intervals and short bursts of speed; an intermediate shoe with a balance of protection and bounce.
– Shoes for races or sprint sessions. Shoes that, once tested out a few times, are reserved exclusively for competitions. Offering little cushioning, they are purely for ‘performance’. They are also the type of shoe that wears out quickly and should therefore be used for your best running.
By constantly changing the first shoe types I mentioned, you keep yourself safe from support issues. Every shoe has its own characteristics and after a few hundred kilometres of running you will find you are conditioned to wearing them on the ground. Rotating shoes therefore means that you avoid your feet behaving abnormally in contact with the ground. As well as changing the features of your shoes, it is not a bad idea to try different shops every so often. That way, you don’t fall victim to just one construction type. A competent sales assistant can even help you choose the correct shoes.
Finally, it is a good idea to look at support carefully, especially if you have a specific defect, as you mustn’t forget that your feet are different from anyone else’s. Make sure your running shoes feel at one with your feet, they should fit like a glove. Your shoes are there to protect you and at the same time enable thrust. Your shoes are what connect you to the ground and allow you to convert all your energy into speed.