By Dorene Internicola
NEW YORK, Jan 20 (Reuters) - As Jillian Michaels, the tough-love trainer on NBC's hit reality show "The Biggest Loser," lunges towards her middle years she infuses her fitness routine with the same take-no-prisoners mindset that impels her TV contestants to shape up.
The Los Angeles-based trainer, who turns 40 next month, is determined to fight, rather than embrace, that milestone.
"I'm trying to get into the best shape of my life for 40," Michaels said in an interview in New York while demonstrating a workout designed for Curves, the global chain of women's fitness centers.
Her own fitness path began as an overweight 13-year-old whose mother enrolled her in a martial arts class. She has spun her TV role improving the fitness of people who are 100 pounds (45 kilos) or more overweight into an empire of exercise DVDs, equipment, best-selling books and clothing.
These days, she said, her fitness credo is all about variety and gradually ratcheting up the intensity of her workouts.
"I don't lock into one type of exercise," said Michaels, adding the workouts she creates focus on flexibility, balance, core stabilization, power, speed and agility.
"I change the workout every month, so you never adapt and never plateau."
She also advises upping the ante of a regimen at a 10 percent rate every two weeks, by increasing something, be it weight, repetitions or speed.
"The more you change and stress the body the quicker it's going to adapt and change," she explained.
Dr. Michele Olson, of the American College of Sports Medicine, agrees with the 10 percent rule as a general means of adjusting exercise intensity or length in order to gain improvements at a reasonable rate.
"It can help you progress but is not such a leap that you might risk over-exertion or injury," the exercise physiologist said.
She said periodization, or varying the type, intensity and duration of an exercise can prevent staleness, reduce fatigue and injury and produce power changes.
Michaels's weekly routine is nothing if not varied.
"Usually I'll do one boxing session, one yoga session, two resistance sessions a week," said Michaels. "I'll also work out with friends and then once a week I'll go for a jog."
For inspiration she cites her fitness idols Jack LaLanne and actress Jane Fonda, even as she stresses the importance of knowing your limitations.
"For example I've never been flexible so I'm not able to just pop into splits," she said. "But the more I take care of my body the more I progress."
Michaels is quick to label her tough reputation "a television persona created to market a television show" even as she concedes that it resonates.
"The reality is I'm not a sympathetic person. Sympathy to me is an agreement that you are sad and sorry and (can't do it)," she said.
"I'm empathetic. I get it. It's hard. It sucks. But I also know that you can do it."
Michaels see fitness as transformative and knows from experience that it can improve confidence and empower people.
"I could take somebody that is a second away from having a heart attack and in four months I can have them running a marathon," she said. "That's amazing. I would never have thought that was possible 10 years ago." (Editing by Patricia Reaney and Stephen Powell)