They range in height from 3 1/2 feet to 5 feet, 9 inches, in shape from chubby to lithe, but when Shaun Wilson claps or shouts, the boys and girls in the white gis and sweat shirts move as one -- crab-walking, sprawling to the mat and back to their feet, striking the padded walls with resounding thump-thump-thumps.

It's early evening at the Baltimore Martial Arts Academy in Ellicott City, and Wilson, a veteran instructor and competitor, is putting his advanced youth class (ages 8-14) through its paces.

"C'mon! C'mon!" he bellows, slapping his palms together in an escalating rhythm. "Let's earn it, everybody. Earn your belts!"

During the next 60 minutes, the 14 yellow, green and blue belts from around the Baltimore area work their way through pulse-pounding exertions in two venerable fighting traditions (karate and kung fu) and a newer, more rapidly evolving one (Brazilian jiujitsu).

"We expose them to different [disciplines] early," Wilson says. "Later on, if they want, they can specialize."

The class reflects the growing number of choices available to those who want to learn or practice one or more of the martial arts.

"Not everybody has talent at striking or kicking," says Wilson, 34, a black belt in multiple traditions who has taught at BMAA for 12 years. "Not everybody is as natural at grappling. These techniques are all valuable, and we offer a variety."

Martial arts -- codified forms of combat and self-defense, often associated with one or another philosophical tradition -- generally focus either on striking (punches, as in karate, or kicks, as in tae kwon do) or grappling (judo, Brazilian jiujitsu). The local Yellow Pages lists more than 80 schools under "Karate and Other Martial Arts" -- often, the word "karate" is used to denote martial arts in general. Some of the schools specialize in a single discipline. Others offer an array of the many available options.

"The choices can be confusing," says Gary Berger, 39, who founded BMAA in Catonsville in 1995 and moved it to its current, 2,000-square-foot location in Normandy Shopping Center on Baltimore National Pike five years later. "Taught properly, most are great for fitness, self-discipline and the teaching of self-respect, but each has its focus and limitations."

On this evening, BMAA features six classes in as many disciplines, two for children and four for adults. The grown-up classes are more specialized, including two relatively new disciplines -- kickboxing aerobics and Brazilian jiujitsu. Aikido, traditional kung fu and tai chi are available the following night.

Kickboxing aerobics blends martial-arts striking and a tae-bo style workout: Eighteen men and women pair off, bouncing, circling each other and delivering martial-arts-style punches and kicks into thick, hand-held pads. "It's more a purely physical workout than an education in ... technique," says Carden Snider, a Catonsville mother who has also studied karate.

In Brazilian jiujitsu , a dozen students, all men, run and stretch, then break into pairs and hit the mat. Instructor Matt Handsman circles the room, offering comments on grips and joint locks meant to immobilize a foe on the ground.

"Everything's gotta be tight," he tells a combatant whose legs enwrap his partner's neck. "It's like tightening a bolt."

Experts say potential students, young or old, should consider several variables before choosing a school. There is no central governing body for martial arts -- there are too many overlapping traditions for that -- and that means, in effect, that it's "buyer beware," says Ernest McPeek, general secretary of the U.S. Jiu-Jitsu Federation, which oversees certification only within that discipline.

"There's nothing stopping a guy from saying 'I have a black belt' and opening up a school," McPeek says. But consumers can call the organizations through which instructors claim to be certified; visit schools and ask questions of teachers, students and parents; check in with the Better Business Bureau and the local police department, whose members often take classes, and see if Web sites are thorough and informative.

Call or visit a school to see whether it stresses exercise or technique, kids or adults, or some combination. McPeek and Berger agree that no school should rush potential clients to sign contracts.

Keep in mind, however, that most legitimate schools require a contract of between six months and a year. Under Maryland law, though, schools collecting fees more than three months in advance must be bonded with the state Consumer Protection Division.

jonathan.pitts@baltsun.com

From aikido to judo: Defining the disciplines

Gary Berger, founder of the Baltimore Martial Arts Academy, says nothing's more crucial than finding the right martial-arts teacher, whatever his or her specialty. Go to a martial-arts school and ask questions.

It's also important to know the basics of the major disciplines. Here's a primer:

Aikido --Japanese martial artist Morihei Ueshiba developed this grappling art ("the way of harmonious spirit") in the 1920s. Practitioners blend with the motion of the attacker, then redirect his or her momentum without directly opposing it, using throws and joint locks.

Brazilian jiujitsu --The Gracie family of Brazil developed this grappling art. The goal is to get the opponent on the ground and apply a sophisticated array of torques and joint locks. In the mid-1990s, Royce Gracie popularized the art when he won three Ultimate Fighting Championships (then "no-holds-barred" competitions) by defeating vastly larger foes. Brazilian jiujitsu is America's fastest-growing martial art.

Judo --Jigoro Kano created judo ("gentle way") in late-1800s Japan in reaction to jiujitsu, whose techniques were so lethal it couldn't be used in competition. The goal is to throw one's foe to the ground and immobilize him or her with grips or locks. (The colored-belt system originated in this tradition.)

Jiujitsu --A grappling art, it gave feudal Japanese warriors a way to face armed opponents when weapons were unavailable. Its joint locks, throws and pins are based on the principle of using a foe's energy against him.

Karate --Developed in 19th- and 20th-century Japan and China, it's a striking art. Though the word "karate" (empty hand") is used as an umbrella term for "martial arts," true karate spotlights punching, kicking and open-handed striking.

Kickboxing --This is a modern blend of martial-arts kicking and Western boxing, sometimes in competitions. "Cardio kickboxing" and "kickboxing aerobics," both growing in popularity in the U.S., stress kickboxing's striking and movements mainly for physical fitness. Paired partners take turns kicking and punching hand-held pads.

Kung fu --The term can mean Chinese martial arts in general, but properly used, it describes a system of kicking, punching and throwing based on reverence for nature. It draws on the movements of nature's most adaptive creatures, including the shrimp, the praying mantis, the snake and the tiger.

Tae kwon do --The national sport of South Korea, it stresses kicks, using the leg's reach and force to disable an opponent from afar. Sparring in tae kwon do ("the way of the foot and fist") is an Olympic sport. It's the most widely practiced martial art among U.S. kids.

Tai chi --Westerners know tai chi as a form of meditative, slow-motion exercise practiced in groups. This Chinese art is easy on the joints and good for conditioning and combating stress. Some teachers apply its principles to self-defense, preparing practitioners for tournaments that stress sumo-wrestling-style pushing and pulling.

[Jonathan Pitts]