When 'No Pain, No Gain' Goes Too Far
After your next workout, take a peek in the toilet bowl...
Namely, I want you to check your urine.
That probably sounds strange. But if it's suddenly the color of iced tea or cola after an especially grueling workout, don't ignore it.
Dark urine can be one warning sign of rhabdomyolysis, or "rhabdo" for short.
Rhabdomyolysis is a type of muscle injury where your muscle tissue starts breaking down. It's a serious condition (more on that in a moment).
Other signs of rhabdomyolysis include experiencing muscle pain or cramping that's a lot worse than you'd expect after exercise, feeling unusually weak or fatigued, and sometimes swelling of the muscles.
Here's what's tricky... Those symptoms don't always show up right away. They could appear hours – or even days – after the muscle damage occurs.
Besides occurring after an injury, rhabdomyolysis can also result from an infection, certain medications, or other health problems. But I want to focus on the cause you can largely control...
That's doing too much exercise before your body is ready for it.
A new review from the April issue of the Journal of Human Kinetics warns that overly strenuous workouts – including high-intensity interval training, CrossFit, and strength training – can damage your muscles enough to trigger rhabdomyolysis and, in severe cases, injure your kidneys.
I'm not trying to scare you away from exercising.
It's just that there's a big difference between challenging your muscles and overwhelming them. So today, I'll show you what happens when a workout pushes your muscles past their breaking point, why two common mistakes can make kidney trouble more likely, and how to exercise hard without landing yourself in the hospital.
What Happens When Your Muscles Spring a Leak
Exercise damages your muscles.
That's not as bad as it sounds. Let me explain...
When you challenge your muscles, you create tiny amounts of damage. Your body repairs that damage and adapts, which helps those muscles become stronger.
Rhabdomyolysis takes this process to a dangerous extreme. With this condition, large numbers of skeletal-muscle cells break down and spill their contents into your bloodstream.
One of those substances is myoglobin, a muscle-cell protein that helps store oxygen.
When a large amount of myoglobin gets dumped into your bloodstream, your kidneys have to filter it out. When the filtering process goes wrong, myoglobin can damage your kidney cells and contribute to blockages inside of the tiny tubules in the organ.
This can result in acute kidney injury ("AKI"), which is a sudden decline in the blood-filtering ability of your kidneys.
Another of the substances that spills into your bloodstream is an enzyme called creatine kinase ("CK"), which doctors measure to help diagnose rhabdomyolysis. Now, you might assume that more CK spilling from your damaged muscles increases the danger to your kidneys. But according to a 2024 JAMA Network Open study, it's not as simple as that...
Researchers examined 200 patients hospitalized with exertional rhabdomyolysis brought on by strenuous exercise. Seventeen patients developed AKI. Yet their CK levels weren't significantly higher than those of patients who hadn't developed AKI – and in some cases, they were even lower.
What did stand out were two factors: dehydration and use of nonsteroidal anti-inflammatory drugs, or NSAIDs.
Nearly 65% of the AKI patients had used an NSAID before arriving at the hospital. Among patients without AKI, that figure was about 22%. Likewise, roughly 53% of the AKI patients showed evidence of dehydration, compared with just 5% of those without AKI.
Altogether, researchers estimated that eliminating those two factors could have prevented about 93% of the AKI cases in this study. And that brings me to some of my top tips for working out safely...
Three Tips for Healthy Workouts
- Think twice before reaching for that Advil or Aleve. NSAIDs include drugs like ibuprofen and naproxen, which work by inhibiting the production of compounds called prostaglandins. These compounds also help regulate kidney blood flow... which is especially important if dehydration is already reducing your blood volume. If you routinely need to pop NSAIDs just to push through that post-exercise pain, take that as a sign to back off and figure out why you're hurting.
- Start off your workout well-hydrated instead of with an empty tank. Make sure you're also replacing the fluid you're losing, especially during hot weather. Dehydration is a major risk factor for your kidneys.
- And finally, don't go from zero to 100 in your workout. In other words, don't subject your muscles to an intensity they're not accustomed to.
If you haven't exercised in, say, six months, your first day back isn't the best time to see how many squats you can do... sign up for the toughest boot-camp class... or try to keep pace with a more seasoned gym buddy. Start at a manageable intensity and go from there. Pay attention to your body... While muscle soreness after a new workout is normal, severe muscle pain that keeps getting worse or comes with major weakness or swelling is a cause for concern.
Although rhabdomyolysis is dangerous, don't use the fear of this condition as an excuse to stop exercising. Exercise is still the best way to prevent cancer, heart disease, diabetes, and even back pain and arthritis.
If you have a history of kidney problems, make sure to consult your doctor before starting any new exercise. An excellent way to get started is to build up a good foundation of low-intensity workouts before adding in short periods of intensity. In fact, we recommend interval training to help build up endurance. This can be as simple as adding in a minute or two of jogging during your usual walk.
As I mentioned earlier, some medications can put you at risk for rhabdomyolysis. But sometimes the biggest risk with medications isn't just one "bad" drug... It's when you have perfectly reasonable prescriptions that start piling up.
I took a closer look at the problem of polypharmacy in my recent Retirement Millionaire issue, along with how taking multiple meds can become more complicated as we age, how side effects can cause prescriptions to build up, and simple tips on how to protect yourself or an elderly loved one. (You can claim a risk-free trial subscription to my flagship newsletter here.)
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Here's to our health, wealth, and a great retirement,
Dr. David Eifrig and the Health & Wealth Bulletin Research Team
September 3, 2026