Keys To Treating Stress Fractures In The Endurance Athlete

John Mozena, DPM

Stress fractures represent 4 to 16 percent of running injuries.1 Fractures occur in 8 percent of the males and 13 percent of the females.1 The cause of stress fractures is repetitive and sub-maximal loading of the bone. The bone eventually fatigues and a stress fracture occurs. Prolonged stress can lead to a complete fracture. A regular fracture differs from a stress fracture in that no acute trauma has taken place.

   Endurance events, like marathons and Ironman triathlons, expose the bones in the foot to increased stress and strains in these endurance events. When training for these endurance events, the ground reaction forces can approach 3½ to 12 times body weight. Bone geometry and bone density influence how we respond to these ground reaction forces. When it comes to endurance athletics, certain bones react differently to the stress placed upon them. For example, long bones are more resistant to compression forces but seem to have more problems with torsional or bending forces.2,3

   Approximately 500,000 marathon times were recorded in 2010.4 This represents a 6.4 percent increase for males and a 10 percent increase for females. Women represent an increasing number of marathon finishers. Forty-two percent of all marathon finishers were female.4

   There was an even larger increase in half marathons in 2011. The constant influx of amateur athletes means that sports injuries are on the rise as well. Another endurance event has shown recent growth. The Ironman triathlon consists of a 2.4-mile swim, an 112-mile bike ride and a 26.2-mile run. It is an elite endurance event differing from other triathlons by its extreme distance.

   Training for these extreme athletic events exposes the endurance athlete to repetitive lower extremity trauma due to ground reactive forces. The many hours required to be prepared for such events set up the athlete for a multitude of possible problems with injuries.

A Guide To Physiological Changes In The Endurance Athlete

High-level physical activity can cause well-documented hormonal changes in females. Consider the female athlete triad of eating disorders, amenorrhea and osteoporosis. Osteoporosis is related to a decreased rate of estrogen, which may lead to lower mineral absorption in bone and possible stress fractures due to poor bone density.Women who have zero to five menses a year have a 49 percent higher risk of stress fracture.6 Those with more menses demonstrated a lower rate.

   Testosterone may have a direct effect on bone formation by influencing the osteoblasts.6 Long-term exercise may suppress baseline levels, thus affecting bone structure. Several studies have reported lower bone density in male long-distance runners. Male triathletes have also shown significantly lower levels of testosterone.6

   The relationship of prolonged exercise on the male athlete causing stress fractures is not well understood. It may be related to hormonal control but may not be as significant as it is to female athletes.6

What You Should Know About The Effects Of Vitamin D

Vitamin D is a fat soluble vitamin. When our dermal layers absorb ultraviolet rays from sunlight, this triggers the synthesis of vitamin D. The vitamin is inert and must undergo hydroxylation in the body. Vitamin D promotes calcium absorption in the gut and maintains serum calcium and phosphate concentration to enable normal mineralization of the bone.

   In one study, female military recruits who took calcium and vitamin D had a 20 percent lower incidence of stress fracture.7 Stress fractures are one of the most common injuries in female recruits.


Stress fractures can also arise in recreational runners, especially over a long weekend with nice weather. Speaking from experience, I was one of five runners who presented to a single office a few summers ago after a long 4th of July weekend with lot of daylight and cool temperatures. We all forgot the rule not to increase distance by more than 10% a week. After five days of continuous long runs, our first marathon training was derailed.

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