Rhabdomyolysis (often abbreviated to “rhabdo”) is a condition that causes our muscles to break down or leak, releasing the muscle cells’ contents into the bloodstream. Those contents contain a protein, myoglobin, which can cause injury to the kidneys.

If there is pre-existing kidney disease, this can result in kidney failure and death. Other problems include those caused by changes to blood chemicals (electrolytes), which can affect muscles, the heart and the brain. An additional consequence is compartment syndrome, where the pressure from swollen muscles can cut the blood supply, depriving tissues of their nourishment.

The three major symptoms of rhabdo are pain, weakness and tea-coloured urine owing to filtered myoglobin. Patients may also experience nausea and lethargy.

What causes it?

There are two main ways enough cells can be damaged to cause systemic problems. The first way is crush injuries from direct rupture of the cell walls. This is often associated with motor vehicle accidents and blunt trauma such as building collapse.

The second principal cause is from depleted energy levels in the cells. If the cells lack the energy to perform necessary functions such as maintaining the electrolyte balance, the cell walls are injured and leak. This is the type of muscle breakdown seen in elderly people who have a fall and are not found for some time, and in people following major surgery and after extreme exercise. This last cause is referred to as “exercise-induced” and “exertional” rhabdo.

A little more than a decade ago exertional rhabdo was rarely reported and was mostly associated with marathon runners and army training camps. However, with the popularity of high-intensity resistance training, increasing numbers of these patients are presenting to doctors and hospital emergency departments.

One form of high-intensity resistance training, CrossFit, seems to have a particularly strong association with exertional rhabdo online and in the popular press. Studies have shown the association is similar to that of other forms of high intensity training. This association was acknowledged by the program’s founder, his blog on the topic also included the creepy clown motif “Uncle Rhabdo” associated with CrossFit.

There is a lively online community posting selfies from hospital and who consider a rhabdo diagnosis as a badge of honour, showing their dedication to exercise.

How is it diagnosed?

Diagnosis is usually based on the levels of an enzyme called creatine kinase (CK) in the blood, which is released when cells are damaged.

CK, which is involved in energy production and cell transport, is itself not harmful, but is a useful marker of cell destruction.

There is no consensus as to what level of creatine qualifies as a diagnosis. But it ranges from five times to more than 400 times the upper normal limit.

It’s not uncommon for those with exertional rhabdo to share stories and even boast about their CK values on social media.

Studies suggest younger males are more likely to develop exertional rhabdo. One suggested reason for this is the higher male muscle mass. Another is that female hormones have a protective effect.

Our ongoing review of a decade of exertional rhabdo presentations to a leading Brisbane emergency department also noted more males than females.

The top three activities causing the rhabdo were gym workouts, long-distance running, and manual labour.

But if we take out the manual labourers, the male versus female statistics are almost equal.

How dangerous is it?

While rhabdo due to other causes can be fatal, exertional rhabdo without pre-existing disease normally follows quite a benign course.

Most people recover from exertional rhabdo relatively quickly. They require intravenous fluids and rest, and only suffer from a setback in their training.

However, as reported in a recent review of exertional rhabdo, there are rare and extreme cases where exertional rhabdo has caused kidney failure, irregular heart rhythm, and death.

How is it treated?

Usual treatment is by oral or IV fluids. These help the kidneys flush the myoglobin into the urine. Creatine levels are monitored until they go back to normal.

When there is co-existing kidney disease or the patient is otherwise unwell, dialysis (where a machine does the work of the kidneys) may be required to remove the toxic products from the blood and re-establish normal electrolytes.

Is it on the rise?

In our review of cases presenting to our emergency department, the number of people with exertional rhabdo each year has risen steadily since 2005. In the past five years there has been a 20-fold increase in cases compared to the previous five years.

We think this is a result of both changing exercise habits and increased awareness by patients and GPs. It could be that people engaging in activities that lead to exertional rhabdo are often aware of the symptoms – leading them to present to an emergency department where previously they would have recovered at home without medical intervention.

Doctors are also more aware of exertional rhabdo due to the increased presentations and diagnosis. The scientific literature has contributed to this with two recent literature reviews.

Some contributory factors may make someone more likely to get exertional rhabdo. These include use of amphetamines and alcohol, extreme temperatures, dehydration and infections.

An appreciation of the condition, knowledge of one’s limits, avoidance of the factors above, and using common sense when performing high-intensity resistance training will go a long way towards reducing your chance of seeing us in emergency.

Update: amendments were made to the article to reflect the association between CrossFit and exertional rhabdomyolysis compared to other forms of high intensity resistance training.