Keirin Racing began in 1947 as a way to regenerate Japanese communities devastated by World War II. It was also seen as a tool to develop the bicycle industry, and companies such as Shimano have forged their success on keirin.
Though not as big as football, baseball or golf, the sport has a large following and the best exponents are cult heroes.
At the end of each season, the top nine money earners compete in the Grand Prix final (though foreigners are not eligible at this level). It's a single race, which lasts a minute but is worth a staggering 100 million ($1.4 million) to the winner, one of the biggest purses of any sport in the world.
More than 1000 hopefuls apply to the keirin school each year, with only 75 accepted. They live in spartan conditions, with no access to email or mobile phones and just one call home allowed a week. Successful graduates are registered as professional keirin riders and, if they maintain their standards, can enjoy 30-year careers.
The top Japanese riders don't always compete on the world stage, preferring to concentrate on the riches and prestige available at home, though there has been some crossover. Koichi Nakano was a professional keirin racer who won 10 consecutive world championship sprint finals from 1977, while Kiyofumi Nagai took Olympic bronze in 2008 in Beijing, eight years after the event was first admitted to the Olympics.
Van Velthooven is one of four foreign Olympic medallists competing on the Japanese circuit, alongside Shane Perkins (Australia), Michael D'Almeida (France) and Teun Mulder (Holland).