The Scientific Rebuttal to an Anecdotal Claim about CrossFit’s “Dirty Little Secret”

In a recent controversial article entitled, “CrossFit’s dirty little secret,” [1] Eric Robertson reports a case of Rhabdomyolysis (Rhabdo) and makes the claim that the medically serious condition experienced by his colleague was induced by a CrossFit workout. The story is simple: The patient is the protagonist; CrossFit is the clear antagonist. The setting is a “warm Texas evening,” and the plot is a potentially fatal condition known as Rhabdomyolysis. There is no denying that the medical condition endured by the patient is extremely unfortunate and any reader would and should empathize with her circumstance.

We recognize that CrossFit-associated bloggers have raised emotional skepticism about Robertson’s article [2]. However, we argue against Robertson’s claims by using an objective, evidence-based approach from the perspective of a non-CrossFit affiliate. ScientiFIT, a registered 501(c)(3) non-profit organization with the explicit goal of evidence-based public education in areas of health and fitness, has carefully evaluated the premises of Robertson’s story. It is precisely this type of anecdotal claim about which we strive to raise awareness and we could not ignore the severe need for an accurate rebuttal.

The overarching problem with the story presented in Robertson’s article is that it is a story. While intriguing, a story is diametrically opposed to evidence-based information. A story, at best (i.e. when peer-reviewed by a group of scientists), represents a case-study; but a meaningful case-study requires the support of at least some scientific data which is generally reviewed and vetted by a panel of peer-reviewers prior to publication. Unfortunately, this story is incomplete and devoid of supporting data.

Let’s investigate the article:

Sample Size
The article is comprised of what the scientific jargon refers to as: “an n of 1,” meaning the sample size=1 individual. Though we are not, in any way, dismissing the seriousness of Rhabdo experienced by this individual, it is important to remember that making reliable and meaningful associations between two variables (in this case, CrossFit and Rhabdo), especially in the human population, generally requires a much larger sample size- generally numbering in the hundreds!

Correlation ≠ Causation
Although never explicitly stated, the article implies CrossFit-induced Rhabdo, suggesting a causative relationship between the two variables. However, in the absence of a sufficiently large sample size and due to the presence of a multitude of other confounding variables (see item 3 below), even strong correlations are difficult to achieve, let alone causative ones.

More Questions than Answers
Rhabdo is associated with a number of risk factors, including heatstroke, genetic muscle diseases, and drug use [3]. So, let’s ask some additional questions that were not addressed in the published article and could have played a significant role in inducing Rhabdo:

• What exactly was the temperature of this “warm Texas evening” [1]?
• Were other possible risk factors ruled out?
• What was the medical history of the patient?
• Did she have any genetic predispositions that made her susceptible to Rhabdo?
• Was she fully hydrated prior to and during exercise?
• Had she been involved in any other forms of activity that could have potentially exerted her muscles?
• What did she eat before the workout?

How Many People Does Rhabdo Affect
The article acknowledges the extremely low incidence of Rhabdo (“0.06%”) and claims that the condition is “normally reserved for the elite military trainee, ultra-endurance monsters, and for victims of the occasional psychotic football coach.” For one, the un-referenced number calls into question its accuracy (i.e. 0.06% of what? The entire population? The number of individuals reporting to the hospital?). To confirm the stated figure, we performed an extensive search for reported Rhabdo incidences. These results revealed a single Wikipedia result of 26,000 annual cases per year in the US in 1997, which, when adjusted for the population size of that year, would result in 0.009% of the US population. We searched the reference associated with the Wiki stats [4], and traced it back to the original reference from the CDC [5]. We were unable to find the rate of incidence in that reference. Furthermore, a general search on the CDC website revealed no figures and statistics related to the condition. This led us to conclude that the CDC has not released any clear data on incidence of Rhabdo, suggesting that the condition is either extremely rare or poorly documented.

What is Known About Rhabdo in Other Forms of Exercise
A search of the National Library of Medicine (PubMed) using the keywords “exercise-induced rhabdomyolysis,” revealed over 146 hits dating back to 1970, long before the days of CrossFit, which of course confirms that Rhabdo can be the result of a variety of exercises (not to mention the non-exercise induced factors). The populations affected by exercise-induced Rhabdo and reported in peer-reviewed journal articles and case-studies range anywhere from teenage athletes [6, 7] to professional football players [8], fire-fighters [9, 10], army and air-force personnel [11, 12], body-builders [13], and swimmers [14]. Therefore, it appears that exercise-induced Rhabdo can afflict individuals in almost any form of intense exercise. This phenomenon is not exclusive to CrossFitters.

How Many Cases of Rhabdo in CrossFit
At least until 2006, CrossFit was relatively transparent about the documented cases of Rhabdo in its affiliate boxes. According to a 2006 report [15], there were 6 known cases of Rhabdo in individuals who participated in a CrossFit workout (again, this does not imply that Rhabdo was directly “caused” by the CrossFit workout). One of these cases subsequently led to a lawsuit [16] in which CrossFit, though implied to be responsible, was not documented as the legal defendant. Now, let’s do the math: The first CrossFit-affiliated box was opened in 1995. That equates to less than 1 case per year, accounting for 0.00000036% of the US population averaged over those 10 years. Of course, the most salient percentage to report would be that which calculates the 1 case per year figure against the number of CrossFit members- an estimate we were unable to find. It is expected that with the increase in the number of CrossFit members, both within the US and world-wide, the potential number of Rhabdo cases will also increase. However, these numbers are still far fewer than suspected national averages.

The “Uncle Rhabdo” Controversy
The article paints CrossFit as an entity that pokes fun at a very serious and potentially fatal condition like Rhabdo by displaying images of the cartoon character, “Uncle Rhabdo.” However, an extensive search of the CrossFit Journal (dating back to 2005) reveals a number of publications [15, 17, 18, 19] warning of the serious and potentially damaging effects of Rhabdo. This suggests that CrossFit at least recognizes the negative consequences of overexertion and does not make a mockery of the condition. Albeit, CrossFit’s depiction using the Uncle Rhabdo imagery may be inappropriate and misleading.

So, Can CrossFit “Kill” You?
Sure! But so can running, swimming, playing football, or any other form of physical activity. The key is to recognize the potential risk of overexertion regardless of the type of exercise and to ignore one’s inner competitive voice that may say things like, “I didn’t want to not match my partner. Normally I may have rested a little, but the partner workout kept me going [1],” or even the overly motivating trainer who thinks he/she is doing his/her job by motivating the participant to keep going. Learning to walk the line between mindful athleticism and competitive overexertion is critical in any form of exercise.

Is There Scientific Evidence For or Against CrossFit?
While there is one published article on the beneficial effect of CrossFit on aerobic fitness and fat percentage [20], the bottom line is that the CrossFit culture is still at a very scientifically premature stage and requires extensive investigation into both its potential beneficial and potential detrimental effects. Until that point where there is sufficient evidence in support of or against CrossFit WODs (workout of the day), it is the responsibility of every participant to tread with caution and never push to the point of overexertion.

To conclude, the purpose of the present article is not to question or dismiss the seriousness of the patient’s condition (which goes without saying). Our response letter addresses a far broader concern, especially in the fitness industry, about the use of anecdotal claims in place of scientific evidence to support or reject ideas. Do all of our beliefs have evidential support? Unlikely! But when it comes to the selection of our health habits, we must at least assess the relative acceptability of ideas on the basis of evidence.

Disclosures:

Dr. Hooshmand is not and has never been a CrossFit member. She does not have any affiliations with CrossFit Headquarters. She has occasionally participated in CrossFit workouts. Her company, Mixx Yoga, LLC, provides yoga classes to several CrossFit boxes in Southern California.