Dennis Nackord, a six-foot, 205-pound, ninth-degree black belt who has practiced martial arts for 50 of his 70 years, exudes devastating power even when he's standing still.

Teaching an advanced class of 21 black belts at his Nackord Karate System school in a Wayne shopping center, he stared solemnly at his sparring partner, not moving a muscle, preparing to demonstrate the oneness of defense and attack.

As his partner attempted to punch him, Nackord said, "This is an inward block," suddenly bringing an arm up vertically in front of his face to ward off the blow. "But if my opponent's head is there, I hit him - bam! - and it's a punch. Defense becomes offense. See?"

His students saw. Some have trained with Nackord for several years, some for decades, learning the lesson it took their teacher a lifetime to absorb: Once a martial-arts fighter knows how to break an opponent's face, instantly, unstoppably, it's less stressful to walk away from a potential fight without striking a crippling blow.

At 1 p.m. Saturday, dozens of the 250 black-belt students Nackord has promoted over the years, many of them well into middle age, will gather at his Gateway Shopping Center school for an open-to-the-public celebration of his 50 years as a fighter and mentor - and to spar using his Nackord Karate System, which combines ju-jitsu, kenpo, boxing, and weaponry.

"It's a martial-arts demonstration, not a carnival event," Nackord said, with obvious distaste for the Hollywood version of his lifelong passion. "Guys jumping around and breaking boards? That's a bunch of baloney. Boards don't attack you, so you don't need to break boards."

On Saturday night, Nackord, who trained for several years to earn each of his nine black-belt degrees, will be awarded karate's highest honor: a 10th-degree black belt.

Nackord was an athletic young student, growing up in Belmont, Calif., in the '60s, when he squared off to help out a buddy in a fight over a girl and suddenly realized, "I didn't know what to do."

So he took up martial arts and became a karate fighter. "It was supposed to be medium-contact point karate, where you got points for landing light punches to the head and body," he said. "But guys got fired up, and it was all blood and guts back then. We fought bare-handed. We had a cup and a mouthpiece and no other gear, and we were banging pretty good. I knocked a ton of guys out in those years with two knuckles to the head. I got disqualified in those fights but, OK, fine."

Nackord flashed back to his early years. "Just before a match, I get into my stance," he said, crouching. "I inhale through my nose, I touch my tongue to the top of my mouth, and that gets my adrenaline going." In an instant, and with minimal motion, Nackord physically transformed himself into a bare-knuckle kickboxer.

Then he relaxed. "I had the skill back then, but not the temperament," he said. "Today, I have a calm inner core. It only took me 50 years."

Nackord came here from California to manage American Karate Studios in the 1970s, then opened his own King of Prussia school in 1984, before moving it to Wayne 10 years ago.

"I started off teaching fighting, and I ended up teaching people," he said. "There is a saying, 'When the student is ready, the teacher will appear.' At some point, I realized, 'Wow, these guys are getting so much more out of this than just the martial-arts part.' It's not about, 'I can kick your butt.' It's about, 'Who am I?' "

He has trained thousands and continues to have a profound effect on his longtime students.

Beth Van Cleve, who has trained with him for 16 years and teaches kickboxing at his school, said martial arts has made her more patient with people - even when one guy rushed her in a parking lot, seemingly out of control.

"I held my hands up and told him, 'You can stop right there,' " she said. "My eyes were on him, not looking away. I thought, 'If you go past this line, you've been warned.' " He stopped about six inches from her boundary and ran off.

"We don't need to prove ourselves," she said. "On the other hand, if you're going to go primal, we're going to go primal."

Irv Rosenzweig, a Malvern investment counselor, said he came to Nackord 10 years ago after training in a much more aggressive martial-arts system.

Rosenzweig had an epiphany during a business meeting when one of his clients appeared ready to physically attack him.

"I pulled my chair out and suddenly realized that all I knew was the maiming and killing type of stuff," he said. "I realized my inventory of martial-arts skills was limited."

Nackord, he said, "is like a chess player. You ramp up the degree of what you do based on the degree of the attack. In the heat of battle, when your blood starts to boil a little bit, you try to calm yourself down and decipher the situation."

Nackord has no thoughts of retiring.

"When you throw about two million punches, putting all your energy into that explosive movement compresses the joints, so after 50 years, you probably will have sore joints," he said. "My head and neck get stiff, too."

Then the old martial-arts warrior smiled. "But my heart rate is perfect."