JACKSON, Wyo. (AP) - Every year ski fitness classes become more popular. The horror stories about the people who blow out a knee or pull a muscle send locals to the fall training classes to prepare for winter.

This year the trend continues: The thought of spending a winter stuck indoors watching the latest Warren Miller film has people rushing to get in shape.

"Nobody wants to get injured," said Carey Clark, fitness instructor for Core Changes with Carey. "Really the only thing that gets you in shape to ski is skiing. But what we try to do at Core Changes with Carey is build the bigger muscle groups such as the core and legs to provide the base needed to prevent injury."

Trainers all over the Jackson Hole valley are busy getting pro and amateur athletes in shape for winter. Many trainers have devised ski fitness classes that develop muscles you didn't even know you had until your first day on the slopes.

Beyond the core and legs, Clark's class works on developing the "stabilizer muscles."

"My class is core the entire time, but I try to focus on deep-position exercises and single-leg exercises." Carey said. "These provide the strength and stability needed while skiing."

Many people believe the way to get in shape for the ski season is to just hammer the quad muscles and get them as big and strong as possible.

"I'm off work for the offseason, so I save my money and work out at home," said Chip Land, an avid snowboarder who's heading into his fourth winter in Jackson Hole. "I sometimes work my abs, but I try to do weighted lunges as much as possible. My legs are actually starting to get kind of big."

Pro skier Jess McMillan, who teaches her own class at Core Pilates, said big quads aren't necessarily the answer.

"My class isn't about weight lifting," McMillan said. "My class focuses more on all of the other muscles. The goal is to make you fit. You don't need huge quads to be fit."

McMillan said muscle imbalances and a weak core can cause back pain during ski season. Her class teaches balance and core conditioning to make her students less susceptible to injury.

Ski fitness sessions train the body in a variety of ways, and any two classes can differ widely in how they get people ready to ski.

Francine Bartlett has been an athletic trainer for 15 years, primarily focusing on injury prevention. She opened Studio X a year ago and offers two styles of ski fitness.

The class Bartlett teaches is more neurologically based, concentrating on visual training as well as alignment and how to jump or land.

Amy Truitt teaches ski fitness yoga at Studio X. The former college ski racer conducts the 45-minute sessions in a relaxing manner.

Bartlett said Truitt's class is about promoting flexibility and length through yoga. Truitt has her students ending each session in restorative poses that promote balance.

Studio X also sees many people who were injured in training and need rehabilitation. Bartlett considers her studio to be as much a physical therapy center as a fitness studio.

"I like to promote physical therapy while at the same time getting a kick-ass workout." Bartlett said.

Staying healthy is the main idea behind all of the ski fitness classes. Every class is different, which allows students to choose the class they want based on fitness goals.

But whatever the method or philosophy, the trainers all agree it's a bad idea not to prepare for the slopes. And with so many great options around the valley, there is little excuse to not be in decent shape come ski season.