Stress fractures are tiny cracks in a bone. They're caused by repetitive force, often from overuse — such as repeatedly jumping up and down or running long distances. Stress fractures can also develop from normal use of a bone that's weakened by a condition such as osteoporosis.

Stress fractures are most common in the weight-bearing bones of the lower leg and foot. Track and field athletes and military recruits who carry heavy packs over long distances are at highest risk, but anyone can sustain a stress fracture. If you start a new exercise program, for example, you might develop stress fractures if you do too much too soon.

At first, you might barely notice the pain associated with a stress fracture, but it tends to worsen with time. The tenderness usually starts at a specific spot and decreases during rest. You might have swelling around the painful area.

When to see a doctor

Contact your doctor if your pain becomes severe or if you feel pain even when resting or at night.

Stress fractures often result from increasing the amount or intensity of an activity too quickly.

Bone adapts gradually to increased loads through remodeling, a normal process that speeds up when the load on the bone increases. During remodeling, bone tissue is destroyed (resorption), then rebuilt.

Bones subjected to unaccustomed force without enough time for recovery resorb cells faster than your body can replace them, which makes you more susceptible to stress fractures.

Factors that can increase your risk of stress fractures include:

• Certain sports. Stress fractures are more common in people who engage in high-impact sports, such as track and field, basketball, tennis, dance or gymnastics.
• Increased activity. Stress fractures often occur in people who suddenly shift from a sedentary lifestyle to an active training regimen or who rapidly increase the intensity, duration or frequency of training sessions.
• Sex. Women, especially those who have abnormal or absent menstrual periods, are at higher risk of developing stress fractures.
• Foot problems. People who have flat feet or high, rigid arches are more likely to develop stress fractures. Worn footwear contributes to the problem.
• Weakened bones. Conditions such as osteoporosis can weaken your bones and make it easier for stress fractures to occur.
• Previous stress fractures. Having had one or more stress fractures puts you at higher risk of having more.
• Lack of nutrients. Eating disorders and lack of vitamin D and calcium can make bones more likely to develop stress fractures.

Some stress fractures don't heal properly, which can cause chronic problems. If underlying causes are not taken care of, you may be at higher risk of additional stress fractures.

Simple steps can help you prevent stress fractures.

• Make changes slowly. Start any new exercise program slowly and progress gradually. Avoid increasing the amount you exercise by more than 10% a week.
• Use proper footwear. Make sure your shoes fit well and are appropriate for your activity. If you have flat feet, ask your doctor about arch supports for your shoes.
• Cross-train. Add low-impact activities to your exercise regimen to avoid repetitively stressing a particular part of your body.
• Get proper nutrition. To keep your bones strong, make sure your diet includes enough calcium, vitamin D and other nutrients.

Doctors can sometimes diagnose a stress fracture from a medical history and a physical exam, but imaging tests are often needed.

• X-rays. Stress fractures often can't be seen on regular X-rays taken shortly after your pain begins. It can take several weeks — and sometimes longer than a month — for evidence of stress fractures to show on X-rays.
• Bone scan. A few hours before a bone scan, you'll receive a small dose of radioactive material through an intravenous line. The radioactive substance is heavily absorbed by areas where bones are being repaired — showing up on the scan image as a bright white spot. However, many types of bone problems look alike on bone scans, so the test isn't specific for stress fractures.
• Magnetic resonance imaging (MRI). An MRI uses radio waves and a strong magnetic field to create detailed images of your bones and soft tissues. An MRI is considered the best way to diagnose stress fractures. It can visualize lower grade stress injuries (stress reactions) before an X-ray shows changes. This type of test is also better able to distinguish between stress fractures and soft tissue injuries.

To reduce the bone's weight-bearing load until healing occurs, you might need to wear a walking boot or brace or use crutches.

Although unusual, surgery is sometimes necessary to ensure complete healing of some types of stress fractures, especially those that occur in areas with a poor blood supply. Surgery also might be an option to help healing in elite athletes who want to return to their sport more quickly or laborers whose work involves the stress fracture site.

It's important to give the bone time to heal. This may take several months or even longer. In the meantime:

• Rest. Stay off the affected limb as directed by your doctor until you are cleared to bear normal weight.
• Ice. To reduce swelling and relieve pain, your doctor might recommend applying ice packs to the injured area as needed — 15 minutes every three hours.
• Resume activity slowly. When your doctor gives the OK, slowly progress from non-weight-bearing activities — such as swimming — to your usual activities. Resume running or other high-impact activities gradually, increasing time and distance slowly.

You're likely to start by seeing your primary care provider. If you are a competitive athlete, you might go directly to a doctor who specializes in musculoskeletal problems.

What you can do

Before the appointment, make a list of:

• Your symptoms, including any that seem unrelated to the reason for your appointment
• Key personal information, including your level and type of physical activity and whether you've increased training recently
• All medications, vitamins or other supplements you take, including doses
• Questions to ask your doctor

Take a family member or friend along, if possible, to help you remember the information you're given.

For stress fractures, basic questions to ask your doctor include:

• What is the likely cause of my symptoms?
• What tests do I need?
• Do I need to stop my activity? For how long?
• Should I see a specialist?

Don't hesitate to ask other questions.