There are just four sports that patrons in Japan can bet on legally. A form of bicycle racing known as keirin is one of them.

Keirin cyclists compete in two-kilometer track races; they start by following a pacer, then sprint to the finish line.

The sport started in 1948 and was created with gambling in mind. For a while its popularity grew, but it faced a decline in the 1990s and never fully recovered.

Even so, many still seek to join the professional ranks. But becoming a registered keirin racer isn't easy.

There is a special school that riders must attend; it has an acceptance rate of 10%. The training is intense, lasting six days a week for 15 hours a day for almost a year.

These photos, taken by Chris McGrath for Getty Images, take you inside the Keirin School in Japan and its intense athletic regimen.