"Why am I so sore?" Recognizing Exercise Induced Rhabdomyolysis

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New England is wild. I can get messages that both warn of the dangers of extreme heat and read about a hypothermia rescue within a few days. 

I've written about heat illness and hypothermia in the past, but after reading my current issue of Emergency Medicine Practice I decided that I wanted to add some info about another condition that's also more likely in higher temps: rhabdomyolysis.

The cool kids just call it "rhabdo," and it can mild to severe to potentially life threatening. 

Rhabdo has been in the news here and there, and seems to be most commonly associated with spin classes or cross-fit type activities. A couple of years ago, 12 Tufts college students were treated for rhabdo after a 45 min Navy Seal workout. 

I couldn't find much describing the incidence in trail users, but studies have looked at the effect of long distance running and another study posted by the NIH showed that Ultra-runners tended to develop rhabdomyolysis more frequently than mountain bikers. Either way anyone who is exercising in heat, and may be pushing harder than normal, is at risk.

So what is it? Rhabdomyolysis is breakdown of muscle tissue. The Cleveland Clinic describes it as muscle "disintegrating," which is a bit dramatic, but indeed the muscle breakdown is serious.

When the muscle tissue is damaged to this degree, the cells leak enzymes (creatine kinase), proteins (myoglobin) and electrolytes (potassium) into the blood stream, and these can overwhelm the kidneys. That strain on the kidneys can lead to kidney failure and death. 


Exercising in high temps increases the risk of developing rhabdo for a couple of reasons:

  • increased body temp can inherently lead to cellular damage
  • increased sweating can lead to dehydration which will effectively increase the proportion of circulating components of muscle breakdown
  • dehydration can tell the kidneys to send signals to the blood vessels to constrict (to maintain a good blood pressure), and those constricted blood vessels will slow the body's ability to manage ongoing muscle damage
  • dehydration can exacerbate any developing electrolyte imbalance
Other risk factors include a person's fitness level, the intensity of the exercise, trauma, alcohol, and some supplements. Some medications themselves can cause rhabdomyolysis (statins like Lipitor), and some medications can worsen the effects on the kidneys (NSAIDs like ibuprofen/Motrin/Advil). Eccentric muscle contractions seem to be more likely to cause rhabdo than concentric. So, we've all had those days where we've hit the trails harder, faster, or longer than normal. How can you tell if you've got rhabdo?

One key would be unusually painful muscles. Not just *sore,* but real pain. This may be associated with  muscle swelling and cramping. The key thing to look for will be dark urine. When the myoglobin leaks out of the muscles it gets into the urine, making it look like tea. Myoglobin will fool urine dipstick tests into turning positive for blood, but when the urine is looked at under a microscope, no red blood cells are seen. 

In the hospital setting, we check the creatinine kinase level in the blood along with kidney function, electrolytes, liver enzymes, and urine tests. Intravenous fluids are typically started as well. 

If you *think* you're on the fence and *may* have rhabdo, you could try resting and staying well hydrated at home, but be sure to use Tylenol (acetaminophen) rather than NSAIDs. If you've got continued dark urine or decreased urine output, you do need to be checked.

Rhabdo is preventable.

Pace yourself, stay well hydrated, avoid NSAIDs, and listen to your body.

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