Paralympics: Competitors scrutinised

Paralympics athletes compete under a complex system of classification that is as crucial to their sports as drug testing is to Olympians.

They will be tested for drugs in Sydney but will also be assessed by teams of doctors and specialists.

The Games have six main categories of disabilities: amputee, cerebral palsy, intellectual disability, vision impaired, wheelchair and special category.

Visually impaired and intellectually disabled athletes compete in separate events. Athletes from other disability groups can compete separately or together in, for example, wheelchair events.

Within these groups, degrees of disability are determined by assessment panels. There are three classes of visual impairment from total blindness to athletes who can see at six metres what a person with normal vision can see at 60 metres.

There are four classes in wheelchair events to allow for differences in disability. between tetraplegics, whose entire body is weakened by a spinal injury near the neck, and paraplegics, whose injury is in the lower spine.