Exercise combining aerobics and self-defense skills is the latest craze among young women in Tokyo, where the number of reported stalking cases is also on the rise.

"Suppose your offender comes from that way. You guard yourself with the left forearm this way, kick the person roundhouse with your right knee, then quickly get back in one step," instructor Kazue Higashiyama tells students in one exercise class.

A group of young women repeat the karatelike motion to the sound of up-beat background music, while Higashiyama goes around with a kick shield, letting each of them punch and kick the shield in turn.

"Don't be meek! Kick with a shout! Shout, shout, shout!" Higashiyama yells.

The class becomes animated, chanting "Ha! Ha! Ha!" at each motion, in the manner of martial arts practitioners.

Soon, the the studio's glass windows steam up on the inside as the women work up a sweat.

The women participating in the class are mostly students and office workers in their 20s and 30s. They gather at the studio after work to learn self-defense skills, get some exercise and burn off some stress.

AXIS.K studio in downtown Tokyo launched the special exercise courses in 1997.

Higashiyama, a high-level master in various martial arts, including karate and aikido, devised the courses and is one of the chief instructors at the studio.

"I had the experience of being confronted by a few men on a street late at night, but I was able to dodge them," Higashiyama said, by using a technique she now teaches.

The experience inspired her to teach self-defense skills to other women, she said. "All we need to know is how to dodge at an initial stage of attack so we can run."

Higashiyama and her colleagues believed that many women might feel self-conscious going to a dojo to learn fighting techniques, and they also decided that the training had to be fun.

They arrived, therefore, at the notion of combining a number of fighting skills with aerobics motions and launched their programs in ordinary gyms.

They call this new approach to fitness "goshinbics," a word that fuses "goshinjutsu" (self-defense skills) and aerobics.

The novelty of this name grabbed the attention of young women right away, and word about the new exercise programs spread quickly.

The number of students for the courses has quadrupled in the past three years, with classes taking place at the studio and at various gyms and local community centers.

Similar courses that place emphasis on self-defense skills have also been set up in fitness clubs run by other operators. One of these is called Bodycombat.

The increasing number of stalking cases reported in Japan has led to a growing awareness among women of the need to protect themselves, and has thus added momentum to the rise of goshinbics.

A particularly gruesome case in October 1999, in which a college student was stabbed to death on the outskirts of Tokyo by a man hired by her former boyfriend, has heightened society's sensitivity toward the issue.

The victim had sought police intervention after being persistently stalked for nearly 10 months by the former boyfriend, who also circulated defamatory leaflets about the victim among her neighbors.

The police, who have traditionally kept their distance from what appear to be lovers' quarrels, have been criticized for not taking her pleas seriously and for failing to protect her.

The case spurred people to take precautionary measures and more than 11,000 stalking complaints were submitted to police nationwide during the first six months of 2000 -- 1.8 times more than in all of 1999, according to a National Police Agency report.

Mounting public disquiet over the issue moved lawmakers to enact a law in November that stipulates swift police action.

Various businesses, meanwhile, have benefited from the heightened social awareness surrounding the stalking issue.

There has been a steady increase in the sales of self-defense items such as personal alarms and detectors for wiretaps. Private security providers are also currently receiving more inquiries about their services.

But for the students in Higashiyama's class, goshinbics is, above all else, a fun pastime.

Mika Okuma, 24, has been coming to the gym for 18 months because, she says, "It's cool." She added that she likes learning new and unusual things.

Kaori Tagami, 26, said she feels she has realized her childhood dream of becoming a ninja, although she admitted she is not sure she would actually be able to use her skills if she were attacked.

However well prepared, no one, of course, ever wants to have to learn the answer to that question.