It takes an iron will and balls of steel to break out of your comfort zone and seriously strive to attain a new level of fitness, athleticism, and GAINS!
Related: 5 Weight Lifting Injuries That Are Far Too Common
There comes a time when pushing the boundaries goes a bit too far, and athletes, especially lifters, stay in the red too long and set themselves for a nasty encounter with rhabdomyolysis.
It's extremely rare, but can bear fatal consequences for those who get too aggressive with their fitness.
What Is It?
Rhabdomyolysis, or "rhabdo" for short, is the rapid breakdown of skeletal muscle tissue.  When this rapid breakdown occurs, myoglobin (protein that stores oxygen in muscle) is released into the bloodstream, and when too much accumulates in the blood, it is harmful to the kidneys and may lead to kidney failure.
Rhabdo can occur from a number of conditions, including severe (i.e. 3rd degree) burns, car accident, crushing injury, ischemic limb injury, heat stroke and even certain infection, but the form of rhabdo we are most interested in related to this article is exertional rhabdomyolysis, or rhabo brought on by intense physical exercise.
In severe cases, rhabdomyolysis can lead to acute renal failure (ARF), liver dysfunction, heart failure, arrhythmias, compartment syndrome (excess pressure buildup in muscle tissue), electrolyte imbalance, and, in the most severe cases, death. 
It's extremely rare to experience exertional rhabdo, though, as it only has an incident rate of roughly 29.9 per 100,000 patient-years. 
How Does Rhabdomyolysis Occur?To understand exactly how one develops rhabdomyolysis, requires a little understanding of human physiology. Don't worry, we'll keep this as easy-to-understand as possible!
Exertional rhabdomyolysis results from damage to the intercellular proteins inside the cell membrane of skeletal muscle cells. Myosin and actin break down when ATP is no longer available due to injury to the sarcoplasmic reticulum. 
Damage to the sarcolemma and sarcoplasmic reticulum causes a surge of calcium into the muscle leading to calcium buildup in the mitochondria, which restrict cellular respiration.  The mitochondria thus aren't able to produce adequate ATP which then prevents the cell from removing calcium.
This calcium imbalance causes certain enzymes to facilitate further muscle breakdown even more , and, on top of that, the high levels of calcium also prevent the muscle from relaxing, keeping it constantly in a contracted state.
From here, things only get worse, as oxygen and ATP depletion ensues and with it the cell membrane "pump" gets damaged resulting in myoglobin seeping into the bloodstream (which can lead to kidney damage). Furthermore, the body notes the dysfunction occurring in the muscle, so it increases intracellular swelling at the injury site, which means that creatine kinase (CK) and myoglobin are flushed from the damaged muscle and travel in the bloodstream until they arrive at the kidneys.
The closing act of this horror show ends with vast amounts of potassium, sodium, and chloride ions entering the circulatory system where they can affect the heartbeat and renal function, leading to cardiac arrhythmias and kidney failure!
Suffice it to say, this is a recipe for disaster on a grand scale, and not something that you can deal with by "popping a couple aspirin." Rhabdomyolysis is serious stuff, and needs to be handled and assessed by professionals.
But, how do you know what to look for?
Symptoms of RhabdomyolysisThe onset of rhabdomyolysis may be subtle and can be a combination of any of the following symptoms:
- Muscle weakness
- Excessive soreness
- Low urine output
- Dark, tea-colored urine
- Infrequent urination
- Sense of malaise
Testing for RhabdomyolysisLet's say you think you've given yourself rhabdo, or worse yet, induced it on some other poor soul who was trying to keep pace with you during your workouts. How can you actually determine if you have it?
Well, there are several blood markers doctors can test for to verify if indeed you do have rhabdo. Elevated levels of these are indicative of muscle damage and may point to rhabdomyolysis:
- Creatine kinase (enzyme found in the skeletal muscles, the brain, and the heart)
- Myoglobin in blood and urine
- Potassium (essential mineral that may leak from injured bone and muscles)
- Creatinine in blood and urine (by-product created by muscle typically removed from the body by the kidneys)
Recovery ProtocolSo, how does one exactly recover and get back to training after dealing with rhabdomyolysis?
In a word SLOWLY!
A review in the Journal of Sport and Health Science analyzed all the current exercise-induced rhabdomyolysis research to date and outlined a periodized recovery protocol specifically for athletes , which consisted of:
- Phase 1: CK and urinalysis are monitored during moderate resting
- Phase 2: Initiation of physical activity (i.e. low level movement to restore joint function and mobility)
- Phase 3: Gradual return to activity
So an example rehab protocol may look something like this:
LOTS of rest for the first month!
No workouts, no staying late at work, no working weekends; get 8 hours of sleep each night and take naps, you need to recharge after putting your body through hell.
Blood work to monitor creatine kinase levels.
Only after levels return to normal or below should you even consider mild physical activity.
Easing into it.
Go for a walk or do some light bodyweight exercises -- basically "going through the motions" in gym speak. You're trying to acclimate your body to exercise after a traumatic experience, so GO SLOW!
Return to normal activity.
Assuming you're feeling no fatigue, soreness, or pain and have been cleared by your doctor you can gradually (i.e. slowly) increase the intensity of your workouts.
Preventing RhabdomyolysisBefore we go, let's give you a handful of tips on how to avoid ever having to deal with this disastrous condition:
- Plan your peak efforts accordingly and ensure your training is supporting your climb to the top.
- Don't go "balls to the wall" in a workout if you haven't exercised in a long time.
- Avoid trying any zany "cross-fugly" workouts that look like a recipe for overexertion and an injury weighting to happen (i.e. max rep clean & press for time followed by 100 box jumps followed by 200 burpees).
- Don't engage in any "extreme" workouts if you're not currently working out and haven't been cleared by a physician.
- Check your ego at the door -- if you're not feeling 100% on a given day, back off and don't push it.
- Adequately hydrate -- dehydration is a key factor in many rhabdo cases.
- Be wary of your surroundings -- exercising outdoors is great, but if it's 110 degrees outside, maybe trying to set a world record isn't the best idea.
- Eat a well-balanced diet -- diets deficient in protein may potentially develop rhabdomyolysis. 
- Consume a carbohydrate and protein-rich meal after training to restore muscle glycogen and support the repair and rebuilding process
TakeawayRhabdomyolysis isn't something that you'll easily encounter, but just the same, it's not something to toy with either. Know your own physical limits, and if you're going to push them, do so methodically and judiciously.
The body is a powerful, amazing machine, just don't try to wreck it!