Few things can make a working mother adopt a fitness routine that almost makes her puke, but an insult tossed by a teenage son must surely top the list.

Marie Imanaka, a competitive tennis player in Hawai'i adult leagues, vividly recalls the verbal ace delivered by her oldest son.

"He said I could hit the ball but I was too slow," she said. "It really stung. I was kind of insulted, but I knew he was right."

Imanaka didn't get mad. Instead, she got a personal trainer.

Now after 18 months of tailored supervision at the Honolulu Club, she's faster, more fit and training smarter on less than half the time.

Not bad for 49.

"I never believed in personal trainers before," said Imanaka, who juggles training with her job as president of Wells Fargo Home Mortgage of Hawai'i. "But when I hit my mid-40s, I started looking like a 50-year-old woman. I was looking like a dumpy woman."

And that from someone who had finished marathons and triathlons, who jogged three times a week and lifted weights just as often, who dabbled in yoga and entered tennis tournaments on weekends.

Her trainer, Brad Krzykowski, owner of Beyond Fitness Hawaii, designed routines to increase strength, balance, power and endurance. Imanaka does exercises familiar to many gym rats, including lunges, chest presses, pull-ups and sprinting up stairwells.

But other Krzykowski exercises border on the bizarre, Imanaka said. Picture this one: One-legged squats while standing on the rounded side of a hemispheric ball. With your eyes closed.

Imanaka's transformation also included plyometric exercises. These target the muscles used to create explosive, powerful movement. Krzykowski will have her hop repeatedly atop a two-foot-tall box or back and forth across a line 90 times in 20 seconds.

"He has actually increased the muscles which help me with speed and agility," Imanaka said. "We do a lot of hip flexor work so I can be a faster sprinter. And we do a lot of speed work and stairs."

She works so hard that club members tell Imanaka she's suicidal. But she knows where to draw the line.

"I haven't thrown up yet," she said. "I have gone to a point where I am breathing so hard that my chest is literally burning. I have to really use zone techniques to just get through some things. I struggle to push myself that hard."

The health benefits that came with all this left Imanaka feeling better. Her body composition has changed, she said.

Her overall cholesterol dropped from 245 to 199 in six months, her body fat dropped 5 percent and even though Imanaka wasn't trying to lose weight, she lost about four pounds.

"Women get stuck on how much they weigh," she said. "I go by how my clothes feel. Weight isn't a factor for me anymore. If I didn't know what my weight was, I would feel like I lost eight pounds."

But what about her tennis game?

"I really believe that thanks to training I am a lot faster on the court," she said. "But it took a year and a half. The first year I didn't see as good a result as I hoped for. Now I see them."

This silenced the only critic that mattered, the teen with top spin — the oldest of Imanaka's two sons.

"If you ask him, he will admit that my speed really improved," she said.

Imanaka still can't beat him, but she'll give him a game. Her son's tennis-playing friends find that as bizarre as hopping up stairs.

"They say, 'You play with your mom?' " she said. "But he says: 'You don't know my mom. My mom is a very determined person. Don't underestimate her.' "