Fighters where brought in from Pure Pain Thai Kickboxing in Winter Springs Florida, Gracie Bara in Orlando Florida, Kokopelli's Gym in Longwood Florida, and Shogun Fight School in Orlando Florida.
It's a song by Kanye West called "Stronger". However the song takes samples from two other songs. One is "Harder Better Faster Stronger" by Daft Punk. The other is "Cola Bottle Baby" by Edwin Birdsong. For the rest of the songs and their corresponding scenes try here.
In the US, the movie was rated PG-13 and made available on DVD in the meantime. At the same time a so called "Extended Beatdown Edition" was released. It offers slightly more fight scenes and some more explicit nudity.