When it comes to building healthy bones, exercise plays an important role. Children and teens who exercise regularly and consume a variety of healthy foods have the best chance of building strong bones and reducing the risk of osteoporosis, a disease that causes brittle bones, in adulthood. But, according to researchers from Children's Hospital and Harvard Medical School, both in Boston, Massachusetts, exercising a lot may actually increase the risk for stress fractures, especially in teen girls.
Stress fractures are tiny cracks in the bone that usually occur when a person increases the amount or intensity of an activity too quickly. According to the American Academy of Orthopaedic Surgeons, female athletes are more likely to develop stress fractures. In 1998, researchers surveyed 5,461 11- to 17-year-old girls and their moms about the girls':
- physical activity (the number of hours the girls exercised each week)
- nutrition, eating, and weight control habits (what and how much they ate and whether they ever dieted, exercised, or vomited/used laxatives to control weight)
- periods (when they started their periods and whether they had regular menstrual cycles)
The moms also noted whether their daughters had ever had stress fractures.
Overall, about 3% of the girls had experienced stress fractures. Also, about 3% of the girls had disordered eating habits - they fasted, vomited, or used diet pills or laxatives to control their weight. And 16% of the girls in the study exercised moderately to vigorously for 16 or more hours each week, whether in sports or on their own.
The girls who exercised 16 or more hours each week had almost twice the risk of having stress fractures, compared to girls who exercised less than 4 hours each week. The heavy exercisers also had a greater risk of having disordered eating habits. The type of activity a girl did was also associated with the risk of stress fractures: Activities that place a high impact on the bones and joints - like running, cheerleading, and gymnastics - were associated with a higher risk of stress fractures.
What This Means to You: Teen girls who participate in moderate to vigorous exercise many hours each week could be at increased risk for stress fractures and disordered eating habits. If your daughter loves sports, make sure she follows the team's training schedule, and check with your child's doctor if she wants to add extra practices on her own. You may also want to discuss her diet with a doctor or registered dietitian to make sure she's getting enough calories for growth and development while she's doing all that physical activity. Finally, keep an eye out for symptoms of stress fractures, which often occur in the lower legs and feet and may include swelling, pain, a dull ache after physical activity, and a spot that feels tender when you touch it.
Source: Keith J. Loud, MDCM, MSc; Catherine M. Gordon, MD, MSc; Lyle J. Micheli, MD; Alison E. Field, ScD; Pediatrics, April 2004
Reviewed by: Steven Dowshen, MD
Date reviewed: April 2005