“Athletic shoes should be replaced once a year or every 800 – 1000km. Your body will also start telling you when you need new shoes, as old shoes can cause knee pain, shin splints and other problems. The midsole is the first part of the shoe that starts to deteriorate and collapse, which is when the shoe should be replaced. An untrained eye cannot always identify a collapsed midsole however – in most cases the outer sole and upper of the shoe is still perfect by the time it needs to be replaced.”

Ref; http://www.runnersworld.co.za/shoes-gear/your-shoes-

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