Stress fractures in sport: When stressed bones fight back

"Competitive and amateur sports are equally affected. It's about relative overload," Karsten Hollander explains to DW.

"For example, you sign up for a spring marathon on New Year's Eve and go from doing nothing to training 20, 40 or 60 kilometres per week — these are high-risk moments. The same thing can happen to a competitive runner after a four week break — for example, a college runner who gets back into high intensity training very quickly after the semester break."

Hollander is a professor of sports medicine at the Medical School Hamburg and since January 2024, has also been the head doctor for the German Athletics Association (DLV).

"In my own career as a middle-distance runner, I got away with only one low grade stress fracture," reveals the sports physician, who has been researching this type of injury since his studies.

Gradual process

A classic fracture occurs when a force, for example from a blow or kick, suddenly impacts on the bone from the outside. In contrast, a stress fracture, often referred to as a fatigue fracture, occurs at the end of a gradual process. Scientists also speak of "bone stress injuries", ranging from oedema — a painful accumulation of fluid in the bone — to actual fracture.

"The pain is usually already there at the start of the run and tends to get worse so that you can't run to the end of your route," says Hollander, describing the alarm signals that indicate a possible stress fracture. "This is different from tendon injuries, for example, which may not be as painful after the warmup phase as they were at the beginning."

If you experience dull or pulling bone pain while running, you should consult a doctor. The main areas at risk when running are the shin and foot.

Most cases in running sports

Stress fractures can occur in any type of sport, and bones that are subject to high stress are at particularly high risk. For example, fatigue fractures occur more frequently in the ribs of rowers or golfers, in tennis in the elbow or forearm bone near the wrist, and in jumping sports such as basketball, the foot bones as well as the foot and knee joints are often affected. In weightlifting and gymnastics, the vertebral arch is particularly at risk.

However, most stress fractures are reported in running sports. "On the one hand, running is a very popular sport in Germany, with 18 to 20 million people taking part. This results in a high number of cases. On the other hand, the impact forces that occur when landing are an important factor for bone stress injuries," explains Hollander.

Female athletes at more risk

According to studies, the risk of women suffering a stress fracture is around twice as high as that of men. There are several reasons for this. Firstly, women often have lower bone density and secondly, hormone levels.

"Oestrogen [female sex hormones] is important for bone metabolism," explains sports physician Hollander. "The type of contraception can also play a role: To what extent do the preparations interfere with the metabolism?"

This is why sports gynaecologists are now also part of the DLV's medical network. In addition, eating disorders are more common in female athletes than in male athletes and such disorders also increase the risk of stress fractures. "Too little relative energy intake must be avoided at all costs," says Hollander.

Sufficient calcium, but not too much

To prevent stress fractures, athletes should make sure their body is sufficiently supplied with calcium and vitamin D. Calcium stabilizes the bones, while vitamin D ensures that calcium is better absorbed by the body and incorporated into the bones.

While you are normally sufficiently supplied with the "sun hormone" vitamin D during the summer months when doing sport, calcium must be added to the body. As a rule, the daily requirement of around 1000 milligrams of calcium can be easily covered with a healthy diet, for example with dairy products, vegetables or mineral water containing calcium.

"Vegetarians or vegans who use milk substitutes should be careful. There are some with calcium and others without," Hollander points out. Even if calcium is excreted through sweat during intensive training, you should not thoughtlessly reach for calcium tablets to compensate for the deficit, warns the scientist.

"It can also be dangerous to take too much calcium. Among other things, this can increase the risk of kidney stones."

Gradually increase training

As stress fractures are a result of overloaded bones, Hollander recommends sensible training management.

"You shouldn't increase your workload by more than 20% from week to week. This applies to the total distance covered per week, the length of the longest run, but also to the intensity and scope of the individual running intervals."

Fitness apps on your smartphone or smartwatch can help monitor your exertion. A biomechanical analysis can also help. After all, your personal running style also determines how much strain is placed on your bones.

"A high frequency, like smaller steps, is preventative. The load per step is then lower," says Hollander.

And if a fatigue fracture does occur? Then the top priority is to protect the affected bone. In contrast to "classic" fractures, the broken bone parts rarely move in stress fractures. It is therefore usually not necessary to immobilise the bone completely with a plaster cast. Even playing sport remains possible, albeit in a different way.

"For passionate runners, taking a break from sport is usually the last thing they want to do," says Hollander. "They are more likely to switch to cycling or aqua jogging."

This article was originally written in German.