ST. PETERSBURG — The day before her 38th birthday, Michele Forte had total knee replacement surgery, a last-resort procedure more common for patients twice her age when arthritis or other ailments have destroyed the joint.
It wasn't a lifetime of wear and tear, but too much of a good thing that made Forte's knee give out. The fitness enthusiast sustained sports injuries competing in more than 20 triathlons in five years, plus a grueling, 13.5-hour Ironman, a marathon run plus intense bike and swim legs.
She pushed through pain and injury to cross that finish line, permanently damaging her right knee. Still, Forte has no regrets.
"It's better than sitting on the couch and eating cookies and smoking cigarettes," she said. "But you know, I know people who do that, and their bodies are in better shape."
Today, several thousand people from around the bay area and beyond will run, swim and bike through the annual St. Anthony's Triathlon in St. Petersburg, in which Forte once competed. Most will emerge with sore muscles and a sense of achievement, not a severe sports injury.
But some doctors say they are seeing more patients like Forte, whose enthusiasm drives them into orthopedic problems normally not seen until long after they're eligible for Medicare.
Where weekend warriors and daily joggers once were content to pound out 5K races, now the half-marathon — 13.1 miles — has become the fastest growing road race distance in popularity.
Experts say that as good as regular exercise is for you, the average body can only take so much pounding.
In the next few years, the under-65 set is projected to surpass the number of seniors getting joint-replacement surgery, according to a recent study presented to the American Academy of Orthopaedic Surgeons. High-impact exercise is a contributing factor.
Among 45- to 54-year-olds, the demand for total knee replacement is projected to reach nearly 1 million by 2030, if current trends continue. Not a huge number relatively speaking, but consider that there were around 60,000 in 2006.
This scenario poses long-term financial implications, given that joint replacements may only last 10-15 years, and cost thousands of dollars.
Despite the physical and financial implications, many prospective patients have no intention of slowing down.
"I wouldn't want to send the message that an active lifestyle is bad. An active lifestyle is good for a number of reasons," said Dr. Kevin Bozic, a study author and an associate professor at the University of California at San Francisco. "If there's a detrimental impact on your joints, we have a very good treatment for that."
But he would prefer that 30-something and 40-something athletes take steps to preserve their bodies from overuse injuries, rather than undertake a lifetime of doctor's visits and even joint replacements.
Ouch, ouch, ouch
Sports activities resulted in more than 6.2 million injuries serious enough to receive medical attention in 2007, according to the National Health Interview Survey.
That beats the number of injuries sustained working in the yard or house, or attending school. Athletics was responsible for more injuries than any other activity among families making $50,000 or more.
Athletic injuries come in two types: acute and overuse. You'll feel an acute injury when it happens, such as a sprained ankle, fractured wrist or dislocated joint.
Casual joggers aren't likely to do traumatic damage on a morning run. It's the accumulated distance logged by the fervent that can cause overuse injuries.
"There's no question that when you get the patients that are getting into the half-marathons and marathons, the risk of injury gets higher because they are pushing their bodies harder," said Dr. George Canizares, a sports medicine specialist at All Florida Orthopaedic Associates in St. Petersburg who treated Forte.
"Eventually, your body is going to break down. It's unavoidable. Your body wasn't meant to do that."
Still, many people push on, figuring the farther and faster they go, the better their bodies will be.
"Performance does not equal health," said William Kraemer, a professor of kinesiology at the Human Performance Laboratory at the University of Connecticut. "You have to ask yourself, is your body type and your body mass and all your mechanics properly matched for such an event?"
Women, who are prone to athletic injury for a variety of reasons, in particular need to train carefully. At the same time, they are a driving force behind the nation's so-called "second running boom," often spurred by a desire to lose weight by training with supportive friends.
Kraemer hasn't always practiced what he preaches. A former football player, he ran three half-marathons a decade ago, seeking a challenge. He concedes that his body wasn't suited for them. People who are heavier, whether because of muscle or fat, need to consider the level of stress they are placing on their joints.
But he wanted to do it. That kind of desire has the sports medicine community focused on fixing people, so they can continue to do what they love, rather than telling them to quit.
"We'll encourage people to do what they like, and if running a marathon is what you like, you'll do it for as long as you can tolerate it," said Jeff Konin, executive director of the University of South Florida's Sports Medicine and Athletic Related Trauma Institute.
"We could only wish that we had an epidemic of people running triathlons and dealing with stress fractures, versus the trends in obesity and diabetes right now."
An ounce of prevention
There is, however, a lot of room between obesity-related diabetes and exercise-induced joint replacements.
Bayfront Medical Center's director of sports medicine, Dr. Arnold Ramirez, compares human joints to the tread on car tires. How long they will last "depends on how often you use it."
Genetics matter too. Experts say some of us are blessed with sturdier frames than others. They point out that the population of middle-aged adults reaching the point of joint replacement remains small, and younger cases are rare.
But it is growing at a rapid clip. People under 65 could become the majority of knee and hip replacement patients as soon as 2016, researchers reported this winter at a conference of the American Academy of Orthopaedic Surgeons.
The University of California's Bozic said he is seeing as an orthopaedic surgeon that higher activity levels are contributing to much of the rise, as younger people used to rigorous exercise develop arthritis or otherwise injure their joints at earlier ages — and seek treatment to stay active.
But researchers haven't quantified all of the possible reasons for the higher demand. Other factors may include joint damage from obesity, trauma, better technologies and increasing acceptance of the procedures.
Given the pain and expense — joint replacements cost tens of thousands of dollars — what's the alternative for adults who want to be active?
Try cross-training, experts say. Runners, for example, could mix things up on an elliptical machine or a bike. Hiking, rigorous walking and swimming are joint-friendly alternatives to running. Resistance training and light weight-lifting also help to strength the body and improve performance.
These days, Forte, the triathlete who had her knee replaced almost three years ago, does a lot of biking and walking. She is trying to spare her new joint, which she has been told should last 10 to 15 years, if she's careful.
Lately, though, she has been thinking about her triathlon, the adrenaline rush before she hit the water, the self-esteem boost that lingered long past the finish line.
She's missing today's St. Anthony's Triathlon. But she has her eye on another in late August.
Times researcher Shirl Kennedy contributed to this report. Letitia Stein can be reached at firstname.lastname@example.org or (813) 226-3322. For more health news, visit www.tampabay.com/health.