CARTHAGE, Mo. -- Ultimate fighting once was the sole domain of burly men who beat each other bloody in anything-goes brawls on pay-per-view TV.
But the sport often derided as "human cockfighting" is branching out.
The bare-knuckle fights are attracting competitors as young as 6 whose parents treat the sport as casually as wrestling, Little League or soccer.
The changes were evident on a recent evening in southwest Missouri, where a team of several boys and one girl grappled on gym mats in a converted garage.
Two members of the group called the Garage Boys Fight Crew touched their thin martial arts gloves in a flash of sportsmanship before beginning a relentless exchange of sucker punches, body blows and swift kicks.
No blood was shed. Both competitors wore protective gear.
But the bout reflected the decidedly younger face of ultimate fighting. The trend alarms medical experts and sports officials who worry that young bodies can't withstand the pounding.
Tommy Bloomer, father of two of the "Garage Boys," doesn't understand the fuss.
"We're not training them for dog fighting," said Bloomer, a 34-year-old construction contractor. "As a parent, I'd much rather have my kids here learning how to defend themselves and getting positive reinforcement than out on the streets."
Bloomer said the sport has evolved since the no-holds-barred days by adding weight classes to better match opponents and banning moves such as strikes to the back of the neck and head, groin kicking, and head butting.
Missouri appears to be the only state that explicitly allows the youth fights. In many states, it is a misdemeanor for children to participate. A few states have no regulations.
Cops: We'd 'look into' bouts
While minors in California may participate in events such as Police Activities League boxing, the California State Athletic Commission prohibits people younger than 18 from being "a contestant in any contest or match or exhibition, except that any person 16 years or over may be licensed as an amateur ... ."
Sgt. Craig Gundlach, a Modesto Police Department spokesman, said authorities would investigate any event where children's health might be in danger.
"If there was a gym in Modesto where young 8- and 10-year-olds were paired with another child and instructed to hit each other without protective gear and causing injury, that is something we would look into," Gundlach said.
Supporters of the sport acknowledge that allowing fights between kids sounds brutal at first. But they insist the competitions have plenty of safety rules.
"It looks violent until you realize this teaches discipline. One of the first rules they learn is that this is not for aggressive behavior outside (the ring)," said Larry Swinehart, a Joplin police officer and father of two boys and the lone girl in the garage group.
The sport, which also is known as mixed martial arts or cage fighting, has spread far beyond cable TV. Last month, CBS became the first of the major networks to announce a deal to show primetime fights. The fights have attracted such a wide audience, they are threatening to surpass boxing as the nation's most popular pugilistic sport.
Hand-to-hand combat also is popping up on the big screen. The film "Never Back Down," described as "The Karate Kid" for the YouTube generation, has taken in almost $17 million in two weeks at the box office. Another mixed martial arts movie, "Flash Point," an import from Hong Kong, is in limited release.
Bloomer said the fights are no more dangerous or violent than youth wrestling. He watched as his sons, 11-year-old Skyler and 8-year-old Gage, locked arms and legs and wrestled to the ground with other kids in the garage in Carthage, about 135 miles south of Kansas City.
The 11 boys and one girl on the team range from 6 to 14 years old and are trained by Rudy Lindsey, a youth wrestling coach and a professional mixed martial arts heavyweight.
"The kids learn respect and how to defend themselves. It's no more dangerous than any other sport and probably less so than some," Lindsey said.
Rules vary by state
Lindsey said the children wear protective headgear, shin guards, groin protection and martial arts gloves. They fight two-minute bouts. Rules prohibit elbow blows and blows to the head when an opponent is on the ground.
"If they get in trouble or get bad grades, I'll hear about it and they can't come to training," he added.
In most states, mixed martial arts is overseen by boxing commissions. In Missouri, the Office of Athletics regulates the professional fights but not the amateur events, which include the youth bouts. For amateurs, the regulation is done by sanctioning bodies that must register with the athletics office.
The rules are different in Oklahoma, where unauthorized fights generally are a misdemeanor offense. The penalty is a maximum of 30 days in jail and a fine of up to $1,000.
Joe Miller, administrator of the Oklahoma Professional Boxing Commission, said youth fights are banned in his state, and he wants it to stay that way.
"There's too much potential for damage to growing joints," he said.
Miller said mixed martial arts uses a lot of arm and leg twisting to force opponents into submission. Those moves, he said, pressure joints in a way not found in sanctioned sports such as youth boxing or wrestling.
But Nathan Orand, a martial arts trainer from Tulsa, Okla., said kids are capable of avoiding injuries, especially with watchful referees in the rings. He thinks the sport is bound to grow.
"I can see their point because when you say 'cage fighting,' that right there just sounds like kids shouldn't be doing it," Orand said.
"But you still have all the respect that regular martial arts teach you. And it's really the only true way for youth to be able to defend themselves."