|So you've swapped your running shoes for swim goggles and a life membership at the pool, thinking that no-impact sports mean no physical wear and tear. Not so fast. Contrary to popular fitness wisdom, such a move might undermine your health down the road. A recent study clinched what a few researchers already guessed: Since bone tissue breaks down and rebuilds itself not unlike muscle tissue, stress from high-impact sports involving running, and load-bearing activities like backpacking and weight-lifting, can actually strengthen bones.
In the broadest study yet of bone density, conducted at Australia's Edith Cowan University, doctors surveyed 60 female athletes and found that those who had engaged in high-impact sports for 20 years had much stronger bones than those who swam. "This should alert men and women in their twenties and thirties to start now," says Barbara Drinkwater, a Seattle-based physiologist and one of the country's leading bone density experts. "A lifetime of running and jumping exercises is crucial to bone strength."
That doesn't mean enter a marathon tomorrow. While stronger bones guard against injury, repetitive impact can predispose athletes to stress fractures. So it's wise to ease into any new high-impact sport. Start off slowly and increase your duration and intensity by no more than 10 percent each week. "If you tend to overdo everything, running 80 miles a week, you'll have problems," Drinkwater says. "Run three miles a day and you'll be fine."