Dr. James Lilly is a competitive CrossFitter. He is also an emergency physician at Surepoint Emergency Centers. So when he talks about the line between a hard workout and a dangerous one, he is speaking from both sides of it.
Most people who train hard are familiar with soreness. The stiffness that settles in a day or two after a tough session, known clinically as delayed onset muscle soreness, is a normal part of how muscles adapt. But there is a point where muscle damage goes beyond soreness and becomes a medical condition called rhabdomyolysis, and most people outside of medicine have never heard of it.
“There is a difference between being sore and being in trouble,” Dr. Lilly says. “Soreness shows up when you move. Rhabdo shows up when you stop. If you are sitting still and the pain is getting worse, not better, that is your body telling you something has gone wrong.”
What Rhabdomyolysis Actually Is
Rhabdomyolysis occurs when muscle fibers break down and release their contents into the bloodstream. The proteins that spill out, particularly one called myoglobin, can overwhelm the kidneys. In severe cases, this leads to acute kidney injury, dangerous electrolyte imbalances, and hospitalization. In rare cases, it can be fatal.
The condition is not new. It was first documented in crush injury victims during World War II. But over the past 15 years, emergency departments have seen a significant rise in cases tied to exercise. Research published in Apunts Sports Medicine found that the incidence of exertional rhabdomyolysis has been linked to the growing popularity of high-intensity functional training programs, with the condition likely underreported because many people do not recognize the symptoms. A study in the Sports Health journal noted that about 75% of exertional rhabdomyolysis cases occur in people under 40, and males are disproportionately affected.
The Symptoms That Should Stop You
The challenge with rhabdomyolysis is that early symptoms can feel like a really bad case of post-workout soreness. The difference is in the severity and what comes with it.
Normal soreness shows up when you move the affected muscle. Rhabdomyolysis pain is intense even at rest. The muscle may swell noticeably, and the most distinctive warning sign is urine that turns dark brown or cola-colored. That discoloration comes from myoglobin being filtered through the kidneys, and it means the condition is already serious enough to need medical attention.
Other signs include extreme fatigue or weakness that feels disproportionate to the workout, nausea, and a general sense that something is significantly wrong. If any combination of these shows up in the hours or days after intense exercise, it is not something to push through.
Who Is Most at Risk
Rhabdomyolysis does not only happen to beginners. It can affect well-conditioned athletes who suddenly change their routine, increase volume or intensity too quickly, or train in heat and humidity without adequate hydration. Research has consistently identified dehydration, high ambient temperatures, and eccentric loading (the lowering phase of movements like squats or pull-ups) as contributing factors.
That Texas heat matters here. Exercising in high temperature and humidity is one of the most well-documented triggers. Military data from the Armed Forces Health Surveillance Branch shows that the majority of exertional rhabdomyolysis cases among service members occur between June and August.
“It’s more common than you think,” Dr. Lilly says. “Someone goes back to the gym after a couple weeks off, it is 100 degrees outside, they push hard, and two days later they are in our emergency room with brown urine and sky-high labs. Hydration and a slower ramp-up are the name of the game.”
Certain medications also raise the risk, including statins, some antipsychotics, and stimulants. Anyone starting a new high-intensity program, returning to training after a break, or exercising in summer heat should be aware.
When to Come In
Rhabdomyolysis is diagnosed with a blood test that measures creatine kinase, a marker of muscle damage. Treatment typically involves aggressive IV fluid hydration to protect the kidneys, along with monitoring of electrolytes and kidney function. Most patients recover fully with prompt treatment, but the key word is prompt. Delaying care when symptoms are present increases the risk of kidney damage.
At Surepoint Emergency Centers, the team can run labs and begin IV hydration on the spot, 24 hours a day. There is no need to wait for a primary care appointment or wonder whether this is “bad enough” for the ER. If the pain is severe at rest, if the swelling is significant, or if the urine has changed color, those are reasons to be evaluated now.
Dr. Lilly would be the first to say that hard training is worth it. But knowing when your body is sending a different kind of signal is what keeps you training for the long run.
If you are experiencing a medical emergency, call 911 or visit your nearest emergency room immediately. This post is for informational purposes only and does not replace guidance from your healthcare provider. Clinical information referenced from the Cleveland Clinic (clevelandclinic.org), Apunts Sports Medicine, Sports Health journal, and the Armed Forces Health Surveillance Branch. Current as of April 2026.