Ask the Expert: What is a stress fracture?


Q: To celebrate Canada 150, I decided to participate in the Nijmegen Marches. After a relatively inactive winter I tried to make up for lost time by training harder. I quickly increased the length of my rucksack marches and after four weeks was comfortably marching 80 kilometres a week. Seven weeks into my training, my left foot suddenly became sore and eventually I was unable to walk around the block. Despite having normal X-rays, I was diagnosed with a stress fracture and told to stop all impact activities for at least eight weeks. What exactly is a stress fracture and how did this happen to me?

— Discouraged

A: Dear Discouraged:

Your story is classic for a stress fracture. Stress fractures are often referred to as a hair line or march fracture and are basically an overuse injury of the bone.

Bones are dynamic living tissues that constantly repair and remodel themselves in response to the stresses they experience. They do this using two unique cells—osteoclasts (bone digesters) and osteoblasts (bone builders)—that work hard to remove damaged bone and replace it with new bone.

When bones are subjected to more repetitive stress than they are used to, osteoclasts are stimulated to clean up the damage faster than the osteoblasts can repair it. The net result is that microtrauma accumulates and the architecture of the bone is weakened. If the stress continues, the bone can be weakened to the point it fails and you develop a stress fracture.

Stress fracture symptoms include pain, especially with weight-bearing activity. The more active you are, the more pain you will experience. There may be swelling and tenderness to the touch over the fracture site. Stress fractures are usually too small to be seen with X-rays. To confirm the diagnosis, you often need an MRI or bone scan. The best strategy to prevent stress fractures is to avoid sudden, large increases in your training workload by limiting the increases in your training volume to five to 10 per cent a week. When stress fractures occur, the best treatment is to avoid all high impact activity for a minimum of four to eight weeks.

The bottom line: Stress fractures almost always result from failing to allow bones adequate time to repair and remodel after they have been stressed, and this is exactly how you sustained your injury. The good news is that once you are completely healed, you can begin to slowly build up for next year’s Nijmegen Marches.

Exercise is medicine!


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