The real Frank Dux was the fighting coordinator for this film. When Jean-Claude Van Damme was cast, Dux announced that Van Damme wasn't nearly in good enough shape, and put him through a 3-month training program. Van Damme called those three months "the hardest training of his life" - this despite being a world-championship martial artist in his own right.
The movie was touted as a true story. However, since then much doubt has arisen about the veracity of Dux's story and now the majority of martial-arts enthusiasts view his accounts of competing in secret tournaments as complete fiction, as well as his claims of military service and being an undercover CIA operative. Some have pointed out that he is the only source that these secret tournaments exist, and that nobody else has come forward to confirm his story or tell their own version.
Michel Qissi, who plays "Suan Paredes," would go on to play the more more famous Tong Po, the main villain in Jean-Claude Van Damme's Kickboxer series. He also knew Van Damme as teens and together came to the US to become action stars.
Though Frank Dux's brick-breaking demonstration is purely fictional, the Dim Mak ("Death Touch") is a legendary move fabled in Chinese martial arts folklore. The Dim Mak is an accu-pressure attack where the attacker quickly strikes his opponent several times (in sequence) at various spots on his body. Striking an opponent in this method can result in broken bones, paralysis/painful muscle spasms or even instant death. Pei-Pei Cheng's character Jade Fox uses a paralyzing Dim Mak-type attack in Crouching Tiger, Hidden Dragon (2000).
The Dim Mak is actually a purely fictional martial arts move that has its roots in Chinese Wuxia novels. It was popularized in the 1960's and 70's by "Count Dante" who ran ads in Black Belt magazine and other magazines of the day claiming to be able to teach it for a small fee and joining the "Black Dragon Fighting Society."
The shorts worn by Paulo Tocha's character bear the words "Sor Thanikul," printed in Thai syllabary. This is the name of the gym that Tocha trained at as a legitimate kickboxing competitor. In the future, Tocha used his connections to the gym to make it a filming location for the filmmakers' subsequent project, Kickboxer (1989).
In the tournament scenes, Jean-Claude Van Damme is seen trading kicks when fighting a guy in a grey karate suit with long hair. This fighter is veteran Hong Kong stunt performer and top notch martial artist Yu-Shu Wu. He was told to tone down his kicking skills to make Van Damme look better on screen.
Midway's Mortal Kombat (1992) took huge inspiration from the film and even used a parody of Jean-Claude Van Damme for the character Johnny Cage, who has a similar costume, back story and a familiar split punch. According to game creator John Tobias, they wanted to make a "gritty" game based on the film.