The outsole: This is the treaded layer on the undersurface of the shoe, usually made from carbon rubber or similar material. It resists wears and provides traction. It may also have a studded or waffle design to enhance traction on softer surfaces.

The midsole: This is considered the most important part of running shoes as it is the cushioning and stability layer between the upper and the outsole. The most common materials for the midsole of running shoes is ethylene vinyl acetate (EVA), polyurethane (PU) or a combination of the two. Often there is a dual-density midsole that has a firmer material on the inner side (medial side) to help limit pronation (rolling in) of the foot. A lot of proprietary technologies developed by different manufacturers go into the midsoles of running shoes (eg air, gel and high-tech plastics materials).

The upper: This is the part of the shoe that wraps around and over the top of the foot. It may be made of leather or a synthetic material that is lighter and breathable (to reduce heat from inside the running shoe). The tongue of the upper should be padded to cushion the top of the foot against the pressure from the laces. Often, at the back of the running shoe, the upper is padded to prevent rubbing and irritation against the achilles tendon.

The heel counter: This is a firm and inflexible cup which is built into the upper of running shoes and surrounds the heel. It is usually very firm so that it can control motion of the rearfoot.

Post or footbridge: This is the firm material in the midsole which increases stability along the inner side (arch side; medial side) of the running shoe.

Usually, most runners who develop an injury either supinate (roll out) or pronate (roll in) too much. Normal amounts of pronation and supination are needed for normal function, but abnormal amounts increase the risk for injury.

Excessive pronation is the most common cause of running injury. A pronated foot rolls inwards at the ankle, the midfoot bulges inwards and the longitudinal arch flattens. Those who over-pronate generally have very flexible and unstable feet, so need running shoes with a lot of motion control. A motion control shoe has design features that give a high level of support - a firmer anti-pronation post on the inside of the midsole; a firm or dual density midsole; and a a firm heel counter.

A supinated foot rolls outwards at the ankle and has a high arch. They tend to be more rigid and are very poor at absorbing shock, so they will need running shoes with a lot of cushioning. Cushioned shoes tend to be poor at motion control.

The amount of excessive pronation or supination present will determine if you need a neutral running shoe with an even amount of mild motion control and mild shock absorption; or a running shoe designed for mild, moderate or severe amount of pronation, with mild, moderate, or severe motion control or stability; or a running shoe for mild, moderate or severe amount of supination, with varying degrees of shock absorption or cushioning.

As a general rule, you should be able to get up to 1000km from a running shoe.