Stretching it

A digital clock on the wall in a Main Street garage blinks down the final seconds of Kristin Bell's lunch break.

She and others working out at Chattanooga Crossfit sometimes do a workout her trainers call the Murph, named for a Navy SEAL who was killed in Afghanistan.

It includes a one-mile run, 100 pull-ups, 200 push-ups and 300 squats, capped with another one-mile run. And it's all done as fast as possible.

Ms. Bell is one of 20 people on a recent weekday at Chattanooga Crossfit completing a high-intensity workout before returning to work. Crossfit is part of an emerging trend in the fitness business toward timed, intense workouts.

"The elliptical (machine) can get pretty boring," Ms. Bell said. "Crossfit is never boring."

Crossfit trainers use basic workout equipment to stage a workout with "a sense of urgency that comes from trying to complete a given amount of work as fast as you can," said trainer Mike Alley.

Mr. Alley said his goal is to give clients an enjoyable workout in about 20 minutes. Hence, the ticking clock.

"We've got a group of people who are all kind of pushing themselves," he said. "When you want to take a break and you look over beside you and that person is really going for it, it motivates you to continue to push yourself hard."

Participants said "extreme" workouts that could lead to overexertion are discouraged at Chattanooga Crossfit.

"You just have to listen to yourself," said Marc Mayes, a physician's assistant. "If you think that your heart rate's too high, then you need to stop. The trainers here are very tuned in to people's capacity and what you can do."

According to participants and trainers, no one expects new Crossfit clients to dig right into something as intense as the Murph.

"If you have a teachable spirit and you're willing to be humble at first, you can really make a lot of progress," said Ms. Bell. The first month of membership costs $200, and includes 12 one-on-one workouts. On Saturdays, the club hosts a free beginners workout.

"What you need is the willingness to push yourself hard and the willingness to live with being uncomfortable," said Mr. Alley. "Then you're used to being a little uncomfortable day to day, so when you're confronted with climbing five flights of stairs, that's easy."

OTHER EXTREME WORKOUTS

* HOT YOGA -- At North Shore Yoga, the hot yoga class consists of a series of 26 postures performed in precise order in a room heated to 105 degrees. It is designed to impact every part of the body during a 90-minute class. One trainer called it "super detoxifying."

* RUSH POWER -- Included in the price of membership at any Rush Fitness Complex location, this workout corresponds songs -- everything from AC/DC to Madonna -- to different muscle groups for resistance training. Bench press, bicep curls and abdominal work could be used in an hourlong workout, but the workout is different every day, along with the music.