Immortal combat: This martial artist's in it for the fight

Shan-Yuan Ho still remembers how good it felt to break another woman's nose. Even years later, Ho, 42, says it is among her proudest moments, watching the woman, a Hungarian national team member, walk away bloodied as Ho advanced in the US Open Taekwondo Championships.

''I did an ax kick and just busted her nose," Ho recalls. ''She was a formidable opponent. She was good. She won the bronze medal the following year at national championships."

On this day, though, she was no match for Ho, who at 5-foot-3 and about 100 pounds spent a decade competing at the highest levels of her sport. There were disappointments along the way, missed opportunities. Ho's attempts to make the US Olympic team came up short again and again. Her mother died and Ho nearly did, too. A bicycle accident on Mass Ave. in 1998 left her unconscious in the middle of the road.

But Ho, who earned a doctorate in electrical engineering at the Massachusetts Institute of Technology, bounced back off the pavement the same way she did so many other times in her life. She may be small, but she is a fighter. She may be slight, but she is strong. She may not be the Olympic champion she once longed to be, but two nights a week inside a gym in Cambridge she asks MIT students to give her everything they have. To sweat. To kick. To jab. To fight.

The woman known as Ho Ho doesn't know how to live any other way.

''Follow me," she barks at her students.

''Let's go, let's go, let's go."

''Faster, faster, faster."

Born in Taiwan, the oldest of three children, Ho was raised just outside San Francisco on the tough streets of Daly City. There, Ho recalls, she was teased for her Asian heritage, mocked for speaking her native Mandarin, and, every once in awhile, jumped by knife-wielding neighborhood thugs.

One time, she says, one of those thugs slashed her leg. More often, she was simply punched, kicked, knocked down, or bashed about the face. ''I have been knocked unconscious," she says. ''I've been unconscious before. That was really bad." But Ho, sufficiently scared, did not run. She decided to train instead. At age 11, she took up taekwondo.

''Keep those hands up," she shouts at her students.

''Watch, watch."

''Move."

''Don't turn your back."

What Ho learned was no match for the street fighters who ran in groups and almost always had the element of surprise on their side. But it made Ho more aware, she says, and more confident. By the time she was in high school, Ho realized she was actually quite good at the sport she had chosen to protect herself. And she was smart, too. The girl from Daly City applied to MIT, got accepted, came to Boston, and graduated with degrees in mathematics and electrical engineering in 1986.

Ho, who remembers being sickly and weak as a child, was now strong. Her intensity, her trademark. When Noel Bennett first met her at a gym in Dorchester in 1993, he couldn't get over her agility, how she not only moved fast, but talked fast. Like a bumblebee in hyper-speed, Ho barely pauses long enough for a breath in conversation, then she's on to the next thought, the next challenge, and it's much the same in competition.

In a sport that's all about timing and quickness, knowing when to strike and when to wait, Ho's speed made her hard to beat, says Bennett, and her confidence, once rattled, was rock-solid. ''She knows," says Bennett, ''that she can't be beaten." But the 1990s proved disappointing for Ho.

''I'm not successful," says Ho, ''not in my opinion. I feel like a big, total failure. I really do. I tried out for the Olympic team -- didn't make it. I tried out for the national team -- came very close."

There was that bicycle accident in 1998, just three weeks before the Olympic team trials, and, worst of all, her mother's death. But Ho pushed on, retiring from her sport, yet not giving it up. Now two days a week at MIT she works as a mathematics instructor, teaching differential equations, and two nights a week she ties a black belt around her pencil-thin waist and shouts at a room of wannabe kickboxers.

''Some people," Ho says, ''think I'm nuts to be doing what I'm doing."

They say she should be focusing more on her research or on her sport, that life is only about gold medals and Nobel Prizes and everything in between doesn't matter. She knows. She still feels the pressure. It's all around her, she says.

But looking out at the class standing before her, Ho sees life differently these days.

The kids, as she calls them, are computer science majors and synthetic biology graduate students.

They are not the best athletes perhaps, not Olympians by any measure, but they are trying. They are focused. They are here to fight, and so is Ho.

''Follow me," she tells them, and they do.

Heart of the City is a series profiling people around our neighborhoods. Got a subject to suggest? E-mail Keith O'Brien at kobrien@globe.com.