You might have spotted pro triathlete Sam Pictor chatting to Andy about his ‘Everesting’ challenge on our YouTube channel. He felt like he’d taken a "sledgehammer to the quads" after the event, which got us talking in the office about all the times we’d experienced a similar feeling after tough races.

In most cases it's a classic case of DOMS taking effect, but there's also situations where a more serious condition called rhabdomyolysis could come into play... 

Most serious athletes are familiar with the feeling of sore, achy muscles. You might have even contemplated taking the stairs backwards the day after a hard workout or race (and, to avoid embarrassment, probably settled on taking them very, very slowly...). But why does this happen? And is it ever something more serious?

Three Oregon Ducks American Football players would answer ‘yes’ to that question. After days of gruelling, ‘military-style’ workouts that involved hundreds of push-ups and up-downs, they were each left with life-long kidney damage after being hospitalised with ‘rhabdomyolysis'.

Player, Doug Brenner, described his arms afterwards as being so swollen that he couldn’t open a car door, take his shirt off or lift a fork to his face to eat (watch the interview here).

Whilst this is obviously on the extreme end of the spectrum, it’s illustrative that sore, painful muscles aren’t always just a harmless side-effect of hard training…

Image credit: StockSnap (copyright free)

What is DOMS?

DOMS is an acronym for ‘Delayed-Onset Muscle Soreness’ (i.e. muscle pain experienced 24-72 hours after exercise).

It occurs as a result of small microscopic tears in the muscle fibres. This triggers the body’s inflammatory response and muscles can feel swollen and sore as the body heals.

High-intensity, repetitive or eccentric-loading (a contraction of the muscle whilst it’s lengthening under load) exercise are common causes of DOMS. Downhill running - an eccentric contraction - is classically used to induce DOMS in scientific research.

‘Unaccustomed exercise’, like starting a new exercise programme, switching up your routine or changing the intensity or duration, can also have the same effect.

Usually DOMS isn’t a serious problem. Whilst uncomfortable, it can be a ‘nice’ (and I use that term lightly) reminder that you did something tough and pushed the body beyond its limit.

Active recovery, getting a sports massage, staying hydrated and getting some decent sleep are all valid ways of reducing muscle soreness. But, it’s fair to say there's no ‘cure’ for DOMS because when the damage is done, it’s done, and (just like for a broken heart) time is the only real healer. 

What is Rhabdomyolysis?

Rhabdomyolysis (‘rhabdo’ for short) is on the same continuum as DOMS but involves far, far more severe damage to the muscle.

The condition involves extensive muscle breakdown which causes the muscles' cells’ internal contents (proteins (e.g. myoglobin) and electrolytes) to leak into the bloodstream.

It’s considered a rare condition but if serious enough can lead to life-long damage, especially to the kidneys, and in the worst cases, can cause the heart to stop (due to a build-up of calcium and potassium in the blood).

‘Rhabdo’ was initially known as “crush syndrome” as it was seen as a consequence of traumatic natural or artificial disasters like earthquakes or bombings which crushed people and caused blunt trauma (e.g. if someone had a limb trapped beneath fallen debris).

During the ‘London Blitz’ of World War II, there were people who survived being crushed but then died several days later of kidney failure or cardiac arrest because releasing their trapped limbs allowed ‘contaminated’ blood to flow out and circulate around the rest of the body.

Should athletes be worried about 'rhabdo'? 

Beyond severe trauma, rhabdo may occur as a result of taking certain drugs, temperature extremes, muscle enzyme deficiencies, electrolyte abnormalities, or exercise that is longer and/or more intense than a person is accustomed to (e.g. an ultramarathon). The latter is referred to as 'exertional rhabdomyolysis' and, up until around a decade ago, was rarely reported. If it was, it was in the military or long-distance runners.

This is changing though and exertional rhabdomyolysis has been documented in various exercise populations.

Cases in CrossFit are becoming increasingly regular and are a concern to the medical community. It seems that CrossFit’s emphasis on rapid, heavy lifting and high-intensity repetitions lends itself to an especially high injury risk. Worryingly in the unique culture of Crossfit, to suffer from rhabdo seems to have become a badge of honour in some fringe groups and a sign of your commitment and determination to the sport.

Image credit: Pexels (copyright free)

It can be difficult to know when an athlete crosses the line from a normal adaptive, physiological response to exercise (like acute muscle soreness/DOMS) to rhabdomyolysis.

The major indicators of rhabdo during or after a competition/workout are:

  • Generalised muscle pain or weakness out of proportion to the effort
  • Cola-coloured urine (caused by the high-presence of myoglobin)
  • The inability to pee for 12 to 24 hours post-race
  • Or swelling

The latter two especially are suggestive of kidney damage.

Why are the kidneys so affected?

The kidneys are responsible for filtering the blood, removing waste products and maintaining a balance of water, salt and minerals. Under normal circumstances, myoglobin is a small molecule which passes through the kidneys easily and appears in our urine.

But, in extreme instances when overloaded with the muscle protein, the kidneys can become blocked, their function impeded, and acute kidney injury (AKI) can ensue.

Creatine kinase

Clinically, rhabdomyolysis is identified by measuring blood creatine kinase (CK) levels. Creatine kinase is an enzyme that - like the molecule, myoglobin - is released into the blood following muscle breakdown.

Normal CK levels are somewhere between 45 and 260 units per litre (U/L). Outside of exercise, a CK measure greater than 1,000 U/L is concerning because elevated muscle breakdown shouldn’t happen at rest. There’s no consensus on a threshold level of CK that should cause concern following exercise.

After the Western States ultramarathon, a blood CK level >100,000 U/L without any apparent health consequences wasn’t a rare finding (no reports of acute kidney injury were reported that year). A certain amount of skeletal muscle breakdown is expected following an event like an ultramarathon, and very rarely leads to clinically significant exertional rhabdomyolysis.

Because of this, in order to diagnose exertional rhabdomyolysis, it’s generally agreed that a person must have both a CK value reflective of excessive muscle breakdown and be presenting with the appropriate symptoms (dark or no urine, extreme or disproportionate muscle pain or stiffness).

How is rhabdomyolysis associated with hyponatremia?

When muscles break down they release myoglobin, muscle enzymes and electrolytes into the bloodstream. The latter may cause dangerous electrolyte abnormalities in the body.

Certainly, exercise-induced rhabdomyolysis is often associated with hyponatremia (low blood sodium concentration). Their concurrent development has two possible explanations:

  1. One causes the other. For example, rhabdo may be a factor in the development of hyponatremia but low blood sodium levels may also cause easier breakdown of muscle
  2. Or, they occur independently but interact to complicate the treatment of the problem

The number of case reports (see examples here and here) suggests a causative link but occurrence is uncommon and so the underlying mechanism remains unknown.

How to treat rhabdo

The best course of action for treating rhabdomyolysis is unclear. The limited evidence suggests that increasing urinary output by administering fluids may protect the kidneys. This keeps the myoglobin soluble and therefore allows easier passage out of the body. Somewhere between 1-2L per hour is the suggested administration rate.

But, this advice must be followed carefully. The danger is that athletes or patients are overtreated and are exposed to overhydration. This could be particularly detrimental if the person is already suffering from acute hyponatremia, so this interplay adds complexity to the correct treatment protocol.

In very severe cases, rehydration and fluid management would be best met by the use of intravenous fluids and proper medical care which allows for renal function to be monitored.

How to avoid suffering from rhabdo

The aim is not to avoid ever suffering from DOMS. At times, DOMS is not only inevitable but also necessary in athletes looking to improve their performance, make progression and drive to the next level.

Some acute muscle damage is a natural consequence of pushing hard and stimulating adaptation to the training stimulus.

What is important though is keeping to ‘the right side of the line’ and not damaging the muscles so severely that rhabdo occurs and other possible serious complications. This is a sure sign of having gone too far.

Fortunately, the primary ways to avoid or minimise rhabdo are relatively simple:

1. Specific, properly progressive management of training overload

2. Appropriate hydration

3. Avoid taking anti-inflammatory drugs before, during or after!

Image credit: Dale Travers ©

Specific training

It’s well-known that you’re more susceptible to rhabdo when using your muscles in a new way. Repetitive, unfamiliar stress to any muscle group can set you up for rhabdomyolysis.

Therefore, if you’re starting a new workout or a different type of training, you should build up the intensity and gradually ease yourself in. Once you’re accustomed to it after a couple of weeks, then you can step it up a gear.

If you’re planning an endurance event, you should do at least some of your training on the terrain you plan to race for the same reason that it will help the key muscles become accustomed to working on the terrain. This is particularly true if you’re doing lots of downhill running (e.g. a mountain race or fell run) because it’s almost always the descending part that will cause the most damage to poorly conditioned muscles.


Maintaining a good flow rate through the kidneys by maintaining an appropriate hydration level will ensure that myoglobin is excreted easily in our urine, reducing the likelihood of acute kidney injury.

But, this is not encouragement to overhydrate.

Surprisingly enough, we’ve covered hydration during exercise in a few other blogs -including here and here - if you want to learn more.

Rhabdo and the danger of NSAIDs

Non-steroidal anti-inflammatory drugs (NSAIDs, pronounced ‘n-sads’) are sometimes used by athletes to relieve pain and soreness before or after exercise. In the late 1990s to early 2000s, NSAID use in endurance sports was extremely common.

Whilst they can effectively reduce the sensation of pain, NSAIDs also increase the risk of kidney injury by impairing the excretion of water and other waste products (like myoglobin) from the blood. For this reason, NSAIDs are one of the bigger accelerants of rhabdo and their use is becoming increasingly frowned upon in athletic events.

With this in mind, I touched base with ultra-running coach, author and host of the KoopCast podcast, Jason Koop, who’s previously spoken out about the use of NSAIDs in sport. Here’s what he had to say:

I’ve seen rhabdo range from benign to being actually scary and I would say that we’ve been pretty good at educating ourselves, particularly on the use of NSAIDs in competition.

It wasn’t that long ago that NSAID use was rampant, in all endurance sports. They’d take two Advil right before the race or during the race - for some people it was almost part of their nutrition plan. I would say that in the ultra-running world that was very common.

That’s now not only starting to change, that already has changed. Athletes are more educated.

If I do find an athlete who has Ibuprofen in their race kit, I’ll just take it out of there, throw it away and let them be mad at me.

Debunking a cool myth: Ice baths

Let’s take a quick dip into ice baths...

A cold plunge has long been touted as an alleviator of sore, achy, DOMS-suffering muscles. The rationale behind their use is that cool water constricts the blood vessels, which in turn reduces inflammation and swelling.

But, the most recent evidence suggests that the inflammatory response is necessary for proper recovery and that by delaying the process you’re only slowing healing and adaptations from occurring. Therefore, icing may reduce the perception of pain when suffering from DOMS, but it may be unhelpful - even detrimental - to the recovery process.

Image credit: Unsplash (copyright free)

Key takeaways

Occasionally, DOMS is a necessary side-effect to heavy training. Using a healthy amount of initiative in finding your ‘sweet spot’ in your training load and intensity will prevent DOMS from being a regular nuisance.

Much more severe muscle damage lends us to rhabdomyolysis which can have serious consequences, especially for the kidneys.

Though exercise-induced rhabdomyolysis rarely leads to dangerous complications, you can mitigate the damage you cause by using some common sense.

So, undertake suitable progressive training, maintain appropriate hydration and avoid the use of NSAIDs during intense, prolonged or repetitive activities. It’s in your best interest!

Further reading

The content of this blog is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Users should not disregard, or delay in obtaining, medical advice for any medical condition they may have, and should seek the assistance of their health care professionals for any such conditions.