The reader: Katie Lowran, 35, Michigan business owner and mother of three tore cartilage in her knees while participating in a boot camp class.

The expert: Nicholas DiNubile, M.D., orthopedic consultant for the Pennsylvania Ballet and the Philadelphia 76ers and author of FrameWork: Your 7-Step Program for Healthy Muscles, Bones, and Joints.

Before: Always involved in a variety of activities, Lowran, has successfully juggled work, family, and exercising three to four times a week for seven years. Since her knee injury, she's had to reduce the length and intensity of her workouts. "I still play tennis twice a week, but my knees ache the next morning," she says.

The knees are the most frequently injured joints in the body, says DiNubile. He says women are more likely than men to injure their knees because the muscles supporting the joints there tend to be weaker. So even if yours are healthy now, care for them to provide long-term benefits. "Keeping your knees strong can prevent you from having to limit your fitness options later," DiNubile says.

The workout: To help Lowran exercise with ease again, DiNubile created a Knee-friendly Fitness Plan. The first stage includes classic stretches, plus a gentle strength move. "The combination helps loosen and strengthen the muscles that support the knees," DiNubile says. The second stage is a full-body workout that's easy on the joints, so Lowran can tone her muscles and burn fat without pain.

After: After only one week of trying the workout, Katie Lowran regained lost mobility and had a better range of motion. "I haven't really bent my knees since the day I hurt them, so they were stiff," she says. "The stretching was difficult at first, but after just a few days, I could do all the moves. And the further along I was in the program, the more my legs loosened up."

Lowran also loved the workout's versatility. "I am on the go for most of the day, so I really liked the way the whole plan was easy to fit into my schedule," she says. "Because it required no equipment, I could do the stretching routine anywhere, and my kids could do it with me."

Myatt Murphy has written more than 300 exercise and health articles and the book, The Body You Want in the Time You Have.