BEIJING, Sept. 5 (Xinhua) -- Wheelchair tennis athletes from 34 different countries and regions have gathered in Beijing for the 2008 Paralympic Games as the draw will come out on Saturday.

    Four-time Paralympic gold medallist, Esther Vergeer from the Netherlands, will bid for her third successive gold medal in both singles and doubles in Beijing.

    The 26-year-old has remained unbeaten in the women's singles since 2003.

    Her strongest challenges will come from Frenchwoman Florence Gravellier, Marie-Annick Sevenans of Belgium and Dong Fuli from China.

    Dong was among the first two Chinese wheelchair tennis players to attend a Paralympic Games, competing in Athens in 2004.

    There is also a strong Dutch entry in the men's singles, with Robin Ammerlaan, defending his title, alongside Maikel Scheffers and Ronald Vink.

    The title favourites also include world No. 1 Shingo Kunieda of Japan, who will bid to add the men's singles gold medal to the men's doubles he won with compatriot Satoshi Saida, at the Athens 2004 Paralympic Games.

    There will be six wheelchair tennis events, beginning on Sept. 8to 15. They include men's singles and doubles, women's singles and doubles, and quad singles and doubles.

    The game follows able-bodied tennis rules. The only difference is that the ball is allowed to bounce twice before the player must return the ball. The first bounce must be within the bounds of the court but the second bounce can be either in or out of the court boundaries. The winner is the player or pair to win two sets.

    The wheelchair is also considered to be part of the body, so allrules which apply to a player's body, also apply to the wheelchair.

    Athletes must have a permanent substantial or total loss of function in one or both legs. There is a special class of competition for quadriplegics, known as the quad division. Players in this event have a disability in three or more limbs.

    The game featured as an exhibition sport at the Seoul 1988 Paralympic Games and became an official event at the Barcelona 1992 Paralympic Games. Quadriplegics were able to participate in singles and doubles competitions for the first time at the Athens 2004 Paralympic Games.