Gym Takes Step Aerobics to the Great Outdoors With Hill Hikes : Exercise: Class participants head out of a Thousand Oaks health club to the Los Robles trails for 5-mile workout.

It all started with paint fumes, and soon became an exercise trend.

Five years ago, aerobics instructor Jami Way, pregnant with her third child, walked into a freshly painted aerobics room and was hit by a wave of nausea.

“I said to everyone, ‘I can’t stand it in here. Let’s go outside,’ ” Way said. “We headed up to the hills on a hike, and that was the beginning of this class.”

Every Thursday since then, Way has led a class of about 20 women on a five-mile hike along the Los Robles trails above Thousand Oaks.

Her gym, the Body Focus Health Club, also has moved its conditioning class outdoors and now holds six running and walking classes per week. Other Ventura County clubs such as the Westlake Sporthouse and Extreme Fitness in Westlake also have begun offering outdoor classes ranging from intense running clubs to hikes in the hills.

During a recent hiking class, the Body Focus group wound like a slow snake up the hills of Los Robles.

Starting off at 8:15 a.m., some members jogged up the switchbacks while others hiked at a brisk pace, swapping stories and admiring the wildflowers along the routes.

“It’s not an easy walk,” said Tracy Ford, 31, of Moorpark, one of many mothers who drop their children at the gym’s child-care center and head up the hill each week.

“One time I was with a group who was lagging behind. Some mountain bikers who were riding down the hill told us that Jami had a message for us, to get our butts moving,” Ford said.

Longtime hikers have given their own nicknames to the hills and trails in the Los Robles area. The group dubbed one Hell Hill and another Baby Hell Hill, reflecting their difficulty. Then there’s Bikini Hill.

“If you can hike Bikini, you can wear one,” Ford said.

Body Focus General Manager Glenda Metler said holding classes outdoors allows the club to provide a wide variety of exercise courses.

“We only have one aerobics studio, and it’s maxed out,” she said. “Bringing some classes outdoors allows us to hold them when there’s no inside room available.”

Kathy McNeil, a spokeswoman for the International Health Racquet and Sports Club Assn., said outdoor walking classes have been popping up at health clubs throughout the country, with one out of every five clubs offering such a class.

She said she would like to see clubs move more of their classes outdoors. “It’s a great idea,” McNeil said. “I was watching this TV show the other day, and they showed Venice Beach and the people working on the weight equipment outside, and I thought, ‘Why don’t we promote more outdoor training?’ ”

Many of the 20 regulars who attend Way’s class said exercising outdoors clears their heads and puts them in touch with nature. But hikers said one disadvantage of exercising outdoors is the changes in weather. And, of course, there’s always the danger of animals. “Wait, what’s that?” Way said, stopping as a growl rose above the women’s chatter on a recent hike. “Oh good, it’s just a plane. I think a group this large would scare mountain lions away, but I like to be alert.”

Way said the group has come across rattlesnakes and coyotes, but has not encountered any mountain lions.

Most of the women in Way’s group say hiking in a group forces them to hike more quickly than when they walk alone. Many are stay-at-home moms who use the hiking class as a break from their children.

“When I first stopped working, I didn’t feel connected to anyone,” said Lisa Creps, who quit her job as a financial analyst at Rocketdyne to raise her two sons. “This class allows me to connect with other women and share parenting issues.”

The women hiked in groups of three or four, discussing day-care centers, recipes and the latest Little League game.

“We discuss the construction of the Arts Plaza, hysterectomies, the pros and cons of hormone replacement, silicone versus saline and, of course, O. J.,” said Way.