What is rhabdo? The workout warning sign every woman should know

You finally signed up for the class everyone’s been talking about. The music was loud, the instructor was electric and you pushed harder than you have in years. The next day your legs ache. By day two you can barely sit down, your thighs look puffy and your pee is the color of iced tea. That last part is the one to pay attention to.

That combination can be a sign of rhabdomyolysis, which most people shorten to “rhabdo.” It’s rare, and the vast majority of tough workouts end in nothing more than ordinary soreness. But rhabdo is serious, it’s very treatable when caught early, and it tends to show up in exactly the people who are excited about getting stronger: new exercisers, people returning after a break and people trying a brand new class.

We love a good sweat. We also want every woman in our community to know the difference between “that was hard” and “something is wrong.” This post walks through what rhabdo is, what the research says about who gets it and why, and how to start any new routine in a way that keeps you training for the long run.

The short answer

• 💪
  What it isMuscle that breaks down

  Damaged muscle cells spill their contents into your blood, which can strain your kidneys.

• 🍵
  Big warning signTea or cola colored pee

  Dark brown, red or cola colored urine after a workout needs medical care the same day.

• 🚲
  Common triggerToo much, too soon

  Intense exercise your body isn’t used to, especially in heat or when dehydrated.

• 🌱
  The good newsTreatable and preventable

  Early care usually leads to a full recovery, and gradual training lowers your risk.

What rhabdo is

Rhabdomyolysis is pronounced “rab-doe-my-AH-luh-sis.” The word breaks down into pieces that tell the story: rhabdo refers to striated (skeletal) muscle, myo means muscle and lysis means breaking apart. Put together, it describes skeletal muscle, the kind you use to walk, lift, pedal and squat, breaking down.

Cleveland Clinic describes rhabdo as a rare but life-threatening condition that can happen after an injury or after excessive exercise without enough rest. They estimate that about 26,000 people in the United States develop it each year. That makes it uncommon, but not so rare that you’ll never hear of it, especially in fitness circles.

There are many causes of rhabdo, from car accidents to certain medications. When it’s caused by physical effort, doctors call it exertional rhabdomyolysis. That’s the type this post focuses on, because it’s the one most connected to workouts, classes and training plans.

What happens inside your body

Every time you work out, you create tiny amounts of stress in your muscle fibers. That’s normal, and it’s part of how muscles adapt and get stronger. Your body repairs the small damage, and you come back a little more capable next time.

Rhabdo is what happens when the damage goes far beyond what your muscles can handle. The cells are injured so badly that their walls break open, and what’s inside leaks into your bloodstream. According to the Merck Manual, that includes:

• Myoglobin. A protein that stores oxygen in muscle. In large amounts it’s hard on the kidneys, and it’s what turns urine dark brown or red.
• Creatine kinase (CK). An enzyme that lives inside muscle. A high CK level in the blood is the main lab sign doctors use to diagnose rhabdo.
• Electrolytes like potassium and phosphate. When too much potassium floods the blood, it can disturb your heart rhythm.

Your kidneys are the filters that have to deal with all of this. When they’re overloaded, especially if you’re also dehydrated, they can be injured. That’s why rhabdo is treated as a medical issue and not just a “really bad soreness” issue.

Most people who get exertional rhabdo have perfectly healthy muscles. A 2015 Korean case report on spin-related rhabdo explains it simply: in exertional cases, the muscle demands more energy than can be supplied, and the cells start to fail. Think of it as asking your muscles to write a check your training hasn’t funded yet.

Symptoms to know

Doctors often talk about a “classic triad” of rhabdo symptoms:

1. Muscle pain. Often in the big muscles you worked hardest, like the thighs, shoulders, lower back or calves. It can be intense and out of proportion to what you’d expect.
2. Muscle weakness. Trouble lifting your arms, climbing stairs, standing up from a chair or moving your legs normally.
3. Dark urine. Brown, red, tea colored or cola colored pee.

Here’s the tricky part. Very few people have all three. The MSD Manual notes that the full triad shows up in fewer than 10% of cases, and WebMD points out that as many as half of people with rhabdo may have no muscle symptoms at all. So you can’t rule it out just because one piece is missing.

Other symptoms people may notice include:

• Swelling or tightness in the worked muscles. Some people describe thighs or arms that look puffy or feel hard.
• Tenderness when you press on the muscle.
• Nausea or vomiting.
• Feeling unusually tired, unwell or feverish.
• A fast heart rate.
• Confusion in more serious cases.
• Peeing less than usual, which can be a sign your kidneys are struggling.

Timing matters too. Cleveland Clinic says symptoms usually develop one to three days after the muscle injury. That’s the same window when normal post-workout soreness peaks, which is one reason rhabdo can be easy to brush off.

Normal soreness or rhabdo?

If you’ve ever felt stiff and achy a day or two after a new workout, that’s delayed onset muscle soreness, or DOMS. It’s uncomfortable, it’s common and it usually means you did something new. Rhabdo is a different thing entirely. Nationwide Children’s Hospital puts it well: rhabdo symptoms are out of proportion to normal post-exercise soreness, and they don’t get better quickly after you stop exercising.

Here’s a side-by-side to help you think it through. It’s not a diagnostic tool, so when in doubt, get checked.

One helpful tip comes from an Air Force aerospace medicine consultant: dark urine from dehydration is still yellow. If your pee looks brown, reddish or like tea or cola, that’s a different signal, and it’s a reason to call a provider rather than just drink more water and wait.

When to get help right away

Rhabdo is one of those conditions where early care makes a real difference. WebMD notes that early treatment often brings a good outcome. Don’t worry about overreacting. Healthcare teams would much rather check you and send you home than meet you after your kidneys are in trouble.

When you go in, tell them what you did and when. “I took my first spin class two days ago” or “I did a hundred push-ups yesterday after months off” is exactly the kind of history that helps them think of rhabdo quickly. Bring a list of any medications and supplements you take, too.

What causes rhabdo

The Merck Manual notes that any form of muscle damage can, in theory, lead to rhabdo. The causes fall into a few big groups:

• Trauma or crush injuries. Car accidents, serious falls, being trapped under something heavy, electrical injuries or severe burns.
• Extreme or unaccustomed exercise. Especially when the intensity or volume is far beyond what you’re used to.
• Heat. Heatstroke and exercising hard in hot, humid conditions.
• Medications. Including statins (cholesterol medications) and some antibiotics, antipsychotics and anxiety medications, especially in combination with other risk factors.
• Alcohol and drugs. Including cocaine and amphetamines.
• Infections. Such as influenza A and B, and COVID has also been linked to rhabdo.
• Lying still for a very long time, such as after a fall where someone couldn’t get up.
• Electrolyte and metabolic problems, like very low potassium or phosphate, and some endocrine conditions.
• Genetic muscle conditions, such as certain muscular dystrophies or metabolic muscle disorders.

Often it isn’t just one thing. Barbell Medicine points out that dehydration, heat and humidity, or an underlying muscle condition can mean rhabdo shows up after less intense exercise than it otherwise would. It’s usually a stack of factors, not a single bad workout in perfect conditions.

The first class problem

If there’s one workout that keeps coming up in the rhabdo research, it’s indoor cycling. WebMD notes that some doctors have seen more rhabdo cases and connect the rise to extreme exercise like HIIT, spinning, CrossFit and ultrarunning. Spin, in particular, has been written about again and again.

• Korea, 2015A hospital in Korea reported 11 spinning-related rhabdo cases in about nine months. Patients had typically gone to a spin class for the very first time two to three days before they came in.
• United States, 2017Doctors writing in The American Journal of Medicine called spin rhabdo a public health concern, nicknaming it “freebie rhabdomyolysis” because cases followed free trial classes.
• Singapore, 2021A Cureus case series described five hospital admissions after spin. The authors noted the pattern often involved previously fit adults after their first spin session, with symptoms appearing within a week.
• Canada, 2026CBC reported that Newfoundland and Labrador Health Services raised concerns about a rise in cases among young women in the St. John’s area. One woman shared that she spent about six days in hospital at age 24 after her very first spin class.

Notice a theme? “First class.” “Free trial.” “Previously fit.” Being generally active doesn’t automatically protect you from a new kind of stress. Spin works the thigh muscles hard and repeatedly, often for 45 minutes or more, in a warm room, with a whole crowd and an instructor cheering you to go faster and add resistance. It’s a recipe for doing far more than your legs are ready for, especially if you’re a runner or a lifter who assumes you’re conditioned for anything.

One of the patients in the Singapore series had two pints of beer right after his spin session. Alcohol is listed among rhabdo’s possible contributors, and it doesn’t help with hydration either, so it’s worth skipping the celebratory drinks right after a punishing first workout.

None of this means spin is dangerous or that you should avoid it. Indoor cycling is a fantastic, joint-friendly workout and a lot of women love it. It means the first few rides should be about learning the bike, not proving something.

Who’s more at risk

Some of the clearest data on exertional rhabdo comes from the U.S. military, where training is intense and every case is tracked. The Armed Forces Health Surveillance Division found 464 cases among active duty service members in 2024, a rate of 35.9 per 100,000 person-years. Recruits in basic training had rates more than 13 times higher than officers and enlisted members. Earlier reports note that exertional rhabdo shows up most often in the first 90 days of basic training.

Why does that matter for the rest of us? Because recruits are the clearest example of the pattern: people suddenly doing a lot more, a lot harder, often in the heat. The military reports name starting high-intensity exercise at an unfamiliar intensity or duration, particularly under heat stress, as a key trigger. The Air Force puts it even more plainly: risk is highest for people with lower fitness who suddenly and significantly ramp up their activity.

A U.S. Customs and Border Protection information sheet sums up the risk and protective factors well:

A few other things are worth knowing:

• Eccentric movements. These are movements where the muscle lengthens under load, like lowering into a squat, running downhill or slowly lowering a weight. The Air Force notes that high-volume eccentric work is a known risk.
• Sickle cell trait. People with sickle cell trait carry a higher risk with intense exercise. Nationwide Children’s Hospital is clear that athletes with the trait can safely play sports, and may benefit from a personalized plan to build intensity. If you know you carry the trait, talk with your provider before starting an intense program.
• Medications and supplements. Statins, some weight-loss medications, stimulants and certain other drugs can play a role. If you take anything regularly, ask your provider or pharmacist whether it affects your training.
• Being sick. Infections like the flu can affect muscle on their own. Training hard while you’re ill is not the move.
• A previous episode. Military reports note that people who have had exertional rhabdo may be at risk of it happening again, which is why a careful return matters so much.

How doctors diagnose it

Rhabdo is diagnosed with your history plus lab tests. The main ones are:

• Creatine kinase (CK) blood test. This is the big one. The Merck Manual says diagnosis is typically confirmed by a CK level greater than five times the upper limit of normal, which many references round to roughly 1,000 U/L. In serious cases it can be many times higher.
• Urine tests. A urine dipstick may show “blood” even when there are no red blood cells under the microscope. That’s often a sign of myoglobin.
• Kidney function and electrolytes. Blood tests like creatinine and potassium show how your kidneys and heart rhythm are being affected.

CK doesn’t peak right away. Clinical references describe it rising within the first 12 hours, peaking around two to three days after the injury and returning toward normal within about 10 days. That’s why your care team may want repeat blood tests to make sure the numbers are heading in the right direction.

How it’s treated

The main treatment is surprisingly simple: fluids, usually through an IV. The Merck Manual describes treatment as supportive, with IV fluids plus treating whatever caused the rhabdo and any complications. The fluids help flush myoglobin through the kidneys and protect them.

Depending on how serious things are, treatment may also include:

• Monitoring and correcting electrolytes, especially potassium, to protect your heart.
• Watching urine output and kidney function with repeat tests.
• Stopping or adjusting medications that may have contributed.
• Dialysis, in a small number of severe cases where the kidneys need temporary support.
• Surgery for compartment syndrome, a rare complication where swelling inside a muscle compartment builds up dangerous pressure.

Some mild cases can be managed with close follow-up, while others need a hospital stay. That decision belongs to your medical team.

The complications, honestly

The biggest worry with rhabdo is the kidneys. The MSD Manual reports that acute kidney injury happens in somewhere between 15% and 55% of rhabdo cases overall, and is more likely with dehydration, infection or very high CK levels. Other possible complications include dangerous electrolyte imbalances, heart rhythm problems and compartment syndrome.

Here’s the reassuring part: exertional rhabdo tends to carry a lower risk of kidney injury than rhabdo caused by trauma or serious illness, according to clinical references. Most people who get prompt care recover fully. The key word is prompt.

Recovery and getting back to exercise

After rhabdo, it’s natural to want to get back to your routine quickly, or to swear off exercise forever. Neither extreme is the answer. Nationwide Children’s Hospital notes that even after symptoms and blood tests improve, people need a gradual return to activity to stay safe and reduce the risk of another episode.

A clinical review on exertional rhabdo in athletes says return to activity should be based on each person’s individual risk. Your provider may want to look at things like how high your CK went, how quickly you recovered, whether this has happened before and whether there could be an underlying condition worth testing for.

In general, a return usually looks something like this. It’s an example of the shape of a plan, not a prescription, and the real timeline comes from your care team:

1. Rest and recover. Follow your provider’s guidance on fluids, rest and follow-up labs until symptoms are gone and numbers are back toward normal.
2. Get clearance. Ask directly when and how you can start moving again, and whether you should avoid anything specific.
3. Start with easy movement. Gentle walking and light activity, with no intense intervals or heavy eccentric work.
4. Build slowly. Add a little time or effort at a time, watching how you feel the next day.
5. Bring back intensity last. Hard intervals, heavy lifting and high-volume classes come back only once lighter work feels easy.
6. Keep watching. Any return of severe pain, swelling or dark urine is a reason to stop and check in with your provider.

Many people go on to train happily and safely after rhabdo. It often becomes the moment they learn to train smarter, not just harder.

How to prevent rhabdo

The research on exertional rhabdo points again and again to the same few things. Here’s how to put them into practice.

• Ramp up gradually. Increase intensity, duration or volume a little at a time. A new class, a new sport and a big jump in mileage are all “new” to your muscles, even if you’re fit in other ways.
• Respect the first session. Treat the first one or two times you try anything as an introduction. Leave something in the tank.
• Hydrate well, without overdoing it. Drink before, during and after exercise, especially in the heat. More isn’t always better, though. Our post on how much water you need when working out breaks down how to find your balance.
• Be careful in the heat. Let your body adjust to warm weather over a couple of weeks, and dial things back on very hot or humid days or in hot rooms.
• Go easy on eccentric-heavy work. Lots of slow lowering, downhill running or high-rep squats and lunges can be especially taxing when they’re new.
• Skip the booze right after a punishing workout. Give your body time to rehydrate and recover first.
• Don’t train hard while sick. If you have a fever or the flu, rest.
• Know your medications and supplements. Ask your provider or pharmacist if anything you take affects your muscles, especially statins, stimulants or pre-workout products.
• Listen to warning signs. Stopping when something feels wrong isn’t weakness. It’s good training.

Your first class plan

Trying a new class is one of our favorite ways to shake up a routine. Here’s an example of how to approach a first spin, HIIT, boot camp or strength class so you leave energized instead of in trouble.

1. Tell the instructor it’s your first time. Good instructors will help you set up the bike or equipment and remind you to go at your own pace.
2. Arrive hydrated. Drink normally through the day and bring water into class.
3. Aim for about half effort. Turn the resistance lower than the instructor calls, skip a few sprints and sit out a round if you need to. Your goal is to learn the format.
4. Ignore the leaderboard. Comparison has no place in your first week. Everyone around you started somewhere too.
5. Plan an easy next day. A gentle walk is great. A second hard class is not.
6. Check in 24 to 72 hours later. Normal soreness is fine. Extreme pain, swelling, weakness or dark urine means calling your provider.
7. Build week by week. Add a bit more effort each class instead of chasing the hardest version on day one.

If you’re new to running, the same idea applies. Our 5K walk to run plan for moms builds slowly on purpose.

Coming back after baby or a long break

Many of the women in our community are coming back to exercise after pregnancy, a long illness, a tough season of life or simply a few years of putting everyone else first. That’s worth celebrating. It’s also exactly the situation where it’s easy to accidentally do too much, too soon.

Your body after a break isn’t the same as your body at your last peak. Muscles that haven’t worked hard in a while need time to rebuild their capacity, no matter how strong you used to be. The urge to “get back to where I was” can push you into the very pattern the research warns about: a big, sudden jump in intensity.

If you’re postpartum, wait for clearance from your provider before starting exercise, and consider a pelvic floor physical therapist if you have any leaking, heaviness or pain. Our guide to postpartum exercise and where to start walks through gentle first steps. Interrupted sleep, feeding and lower fluid intake can all make a hard workout feel tougher, so be patient with yourself.

Your goal right now isn’t to prove anything. It’s to build a body that feels strong and capable for years.

A coach’s view: no pain, no gain is a myth

Fitness culture loves a good story about pushing through. The puke bucket in the corner. The class that “destroyed” you. The post-workout selfie lying flat on the floor. It’s easy to start believing that the harder a workout hurts, the better it was.

That isn’t how bodies actually get stronger. Progress comes from steady, repeatable work with enough recovery for your muscles to adapt. A workout that leaves you unable to walk for three days doesn’t make you fitter faster. It just takes you out of training.

Here’s how we like to think about it as coaches:

• Consistency beats intensity. Three moderate workouts a week for a year will change your life more than one heroic session.
• Effort should be scalable. Every good class and program has easier and harder options. Choosing the easier one is smart, not lazy.
• You don’t have to keep up. The person next to you may have been doing this class for five years.
• Recovery is training. Rest days, sleep, fluids and enough food are when your body rebuilds.
• Your body is giving you information. Pain that stops you in your tracks is a signal, not a challenge.

Working with a coach or a training buddy can make all of this easier, because someone is there to say “that’s enough for today.” Our post on why working out with friends works has more on that.

Myths

1. Myth #1
   What you’ve heard

   “Only out of shape people get rhabdo.”

   The truth

   Fit people get it too, especially when they try a new type of exercise or jump in intensity.

2. Myth #2
   What you’ve heard

   “If I’m that sore, it was a great workout.”

   The truth

   Extreme soreness doesn’t mean better results, and it can be a warning sign.

3. Myth #3
   What you’ve heard

   “Dark pee just means I need more water.”

   The truth

   Dehydrated pee is still yellow. Brown, red or cola colored pee needs medical care.

4. Myth #4
   What you’ve heard

   “I can treat rhabdo at home by drinking lots of water.”

   The truth

   Rhabdo needs medical testing and often IV fluids. Don’t wait it out alone.

5. Myth #5
   What you’ve heard

   “After rhabdo, I can never work out hard again.”

   The truth

   Many people return to full training with a gradual, provider-guided plan.

The bottom line

Rhabdo is rare, serious and very treatable when it’s caught early. It happens when muscle breaks down faster than your body can handle, often after a brand new or much harder workout, especially in heat or when you’re dehydrated. The warning signs to remember are severe muscle pain, real weakness, swelling and, above all, dark brown, red or cola colored urine.

The best protection is the least glamorous advice in fitness: start easier than you think you need to, build gradually, drink enough, rest well and listen to your body. You don’t have to earn your place in any class by suffering through it. Show up, go at your own pace and come back next week. That’s how strong is built.

• Rhabdo
• Exercise safety
• Spin class
• Recovery
• Hydration