It's opening day on the ski slopes, the snow is cold and fast, and your legs feel like rubber after two quick runs.

It's opening day on the ski slopes, the snow is cold and fast, and your legs feel like rubber after two quick runs.

When you're back in the lodge, wishing you'd gotten in shape to ski, Gene Wolf will still be skiing. At 76, he knows the hours he spends in the gym in October and November mean more time on the snow at Mount Ashland when winter finally comes.

The retired Medford teacher exercises with the same energy he brought to the classroom, but these days his goal is to build strength and endurance, especially in the big leg muscles that do yeoman work on the slopes.

Wolf works out three times a week on exercise machines that target specific muscle groups. One of his favorite machines simulates the movements of roller skating on a stationary platform. Turns out, those same muscles are the ones that steer his skis through long effortless turns.

"The first time I tried it I could barely go five minutes," he recalls. "I could hardly walk and my legs were so rubbery."

Now he routinely does 20 minutes on the machine as part of his regular 90-minute workout.

Exercise machines can help you get in shape, but you don't have to join a gym to get ready for winter sports. One of the best exercises for building thigh strength is the "wall sit," which requires nothing more than a blank wall surface to sit against without the benefit of a chair. In the chairless position, the big muscles of the thigh (quadriceps) are forced to work to hold the body upright.

It's harder than it looks. Many people feel the burn in their thighs within 30 seconds or less when they first start out.

Tanya Dadaos, an Ashland personal trainer, recommends gradually increasing the "sitting" time to several minutes and then gradually making the exercise more difficult to gain strength.

"You have to make it just a little bit harder," she says. "Pretty soon that becomes your baseline."

There are several ways to raise the ante. First, lift one foot off the ground for five or 10 seconds, then the other. Sitting on one leg forces the body to work harder to maintain balance, another critical element of successful skiing and snowboarding. Each foot needs to be off the floor for the same amount of time to make sure both sides of the body get an equal workout.

Placing a large exercise ball behind the back while doing the wall sit also adds difficulty to the exercise, Dadaos says. The big ball creates instability, which forces the body to make countless tiny corrective movements to stay in balance.

Dadaos says these movements help increase "dynamic" balance, the ability to stay centered and upright while the body is in motion. She also encourages her clients to do some of their exercises with their eyes closed to feel the body in balance without the visual feedback.

She encourages clients to use any of the many kinds of balance boards (also known as wobble boards or rocker boards) now on the market. They're relatively inexpensive (about $30 to $70) and many can be adjusted to different angles to make them more difficult as the user gains control.