A running shoes purpose is to protect the foot and to achieve your maximum potential while running. There are some great runners and some may even say legends from Ethiopia and Kenya that run barefooted but for most runners in the west we must wear running shoes. A general purpose trainer is exactly what the name suggests; it can be used for all types of sports. Sports specific shoes are essential and in the case of runners a cross trainer is ideal.
The general concept of the running shoes is that it should facilitate horizontal running. Running shoes usually have a slightly larger toe box to accommodate the increased pressure on the mid foot during the running stride. Most running shoes have a slight heel raise to reduce stress on the lower leg and increase ankle stability. Greater shock absorption and medial posts (arch support) are also a feature of many running shoes.
Research suggests that you have a 1 second per mile improvement for every ounce less of running shoes you use. This can help many runners achieve personal bests but if you have a biomechanical complaint or are prone to injury than the lighter running shoes may cause further problems. The lighter running shoes are usually racing shoes. Do not wear racing shoes for races only as this can lead to a running injury. An important point to remember is that racing shoes are lighter but have less shock absorption and stability.
Shoes buying tips
Taken from: www.shoeguide.co.uk