The six races that make up the omnium are spread across two days with points scored in each event deciding the winner of the medals. The racing begins with the 15km scratch race and is followed by the 4km individual pursuit and the scratch race. Monday see the riders in action in the kilometre time trial, the flying lap and the final points race, where every point counts towards the final classification. The omnium tests the sprinting, pursuiting and points racing skills of the riders, with only the best emerging during the two days of action.
Gaviria is arguably the favourite for gold after winning the last two world omnium titles and also showed his road skills with Etixx-QuickStep this season. However, both Cavendish and Viviani have sacrificed part of their road racing season to ensure qualification and peak for the omnium in Rio. Lasse Norman Hansen should not be discounted despite his lesser palmares on the road. He helped Denmark secure a bronze medal in the team pursuit behind Great Britain and Australia and is the 2012 Olympic Omnium winner. Other names to watch out for include Robert Kluge of Germany, Australia's Glenn O'Shea and Thomas Boudat of France.
Cavendish won four stages at the Tour de France but quit the race on the second rest day to recover and prepare for the track events in Rio. He was disappointed not to be considered for the team pursuit but is hungry to win a medal after missing out in Beijing in 2008 when he rode the madison with a tired Bradley and in London in 2012 when he was team leader of the road race team.
"Either it's third time lucky or it's not meant to be," Cavendish said.
"I'd like to win, I've put a lot into this - people around me have put a lot into this. Ultimately, I'd like to come home with a medal from Rio," he told British Cycling from Rio, aware that he will face tough opposition during the two days of racing.
"It's such a strong competition now the omnium; it's got some of the best bike riders in the world – all the guys who were there in the world championships in London. You've got Elia Viviani, Fernando Gaviria, Roger Kluge, Glenn O'Shea, and Lasse Norman Hansen who won in London. It's a list of hitters doing it."
Viviani rode the Giro d'Italia in May and has been focused on his track preparation since then, only doing road racing when it fitted in with his plans for Rio. Viviani was leading the omnium after five events but then slumped to sixth after the final points race. The points system of the event has changed since then and Viviani has matured and improved after two seasons with Team Sky.
Viviani was gutted after missing out at the world championship in March. Then Cavendish lead out the final sprint and Gaviria came past to win and snatch the world title. However Viviani believes the Olympic omnium will be a different race, with the fight for the three medals making it a more tactical event, especially in the final points race.