Postexercise Physical Dysfunction in CrossFit® & ACSM Training

Several months ago a research study was published by Drum and others comparing CrossFit® training to an American College of Sports Medicine (ACSM)-based training session. The paper begins by discussing CrossFit as an extreme/high intensity conditioning program and notes how people have been concerned about its safety, in particular, to what extent it contributes to Exertional Rhabdomyolysis (ER), a condition where muscle damage causes the bloodstream to fill with proteins and other cellular material. The authors’ rationale for the study is that “ongoing high rates of perceived exertion (RPE) could cause a higher risk to suffer from ER. However there is lack of information on RPE levels during CrossFit classes in comparison to health related fitness courses meeting the ACSM prescriptive guidelines.” So the paper intends to compare RPE between the programs and also see if those values correlate with medical complications like ER.

The Takehome: I was disappointed in this study for a number of reasons. First, this study doesn’t tell us anything we don’t already know from casual observation: CrossFitters (who are not beginners) work at higher levels of exertion, train with more hard days each week, and have more fatigue and soreness after training. We know this already; it’s part of the process. A closer examination of medical complications (as this study tried to perform) might have yielded novel results, but previous studies on injury rates in CrossFit compared to other activities suggested this would be a fruitless endeavor. Indeed, aside form the symptoms just listed, no differences were found (and this includes no statistical difference in ER occurence). I should also note that the authors tried to examine their chosen medical complications by using survey responses. I understand that sometimes this is a necessary tool, but when nearly half of the questions revolve around the participant’s ability to recognize symptoms without a medical professional (e.g., muscle weakness, shortness of breath, excessive fatigue etc.) there are bound to be inconsistencies across participants. Sitting as a cloud over the entire study is also the statistically significant observation, that the CrossFit participant group had a greater history of exercise training than the ACSM group. In this respect the study is comparing apples to oranges. Those with more experience will be able to perform at a higher level and also generate more fatigue. This is the heart of the stress-recovery response (and the General Adaptation Syndrome as it applies to training). Finally, as detailed in the Limitations section below, the authors make comments in the Discussion section that 1) try to link high levels of exertion in CrossFit to ER and 2) suggest that beginner CrossFitters should seek training under a ACSM or NSCA training (instead of a CrossFit coach). Neither of these claims is supported by their data, leaving the reader to wonder if there was an inherent bias against CrossFit that gave rise to this study.

Experimental Design:

  • A questionnaire was used for participants to record rate of perceived exertion values, medical complication occurrences (i.e., ER), and occurrences of risk factors for medical complications.
  • The study was conducted over 5 weeks.
  • 101 participants were in the CrossFit group and 56 in the ACSM group.
  • Questionnaires were sent to 25 randomly selected states in the USA. 35 States and Canada returned questionnaires as those initially receiving the questionnaires were allowed to pass them on to others they knew.
  • Independent t-test analyses were performed to compare descriptive means from CrossFit and ACSM groups.
  • Chi-square analyses were used to determine if a difference existed between symptoms of post-exercise dysfunction.


  • CrossFitters completed more weeks of the program than ACSM participants.
  • Average self-reported RPE was significantly higher in CrossFit workouts than ACSM workouts.
  • CrossFitters completed more “hard” days of training than ACSM participants.
  • CrossFitters had more prior exercise experience than ACSM participants.
  • CrossFitters reported more excessive fatigue after workouts, more muscle pain to light touch, and more limited movement in muscles during exercise.
  • No other symptoms or medical complications (i.e., ER) were significantly different between CrossFit and ACSM training groups.


  • Conducting a study to see if perceived exertion in CrossFit workouts is greater than ACSM workouts is not a good use of time and resources. Anyone watching the two modalities can see that CrossFit workouts will entail greater exertion from those with experience in the training modality.
  • The final two study groups had unequal participants, such that the CrossFit group had nearly twice as many as the ACSM group. The authors did not note if they had proper statistical power given this very large difference.
  • CrossFit participants completed more of the 5 week program than ACSM participants and it is not clear if those who completed only part of the program were still used in the analyses.
  • Although their data did not support a connection between ER and CrossFit, the authors still push for a connection in the discussion by saying that “muscle soreness, swelling, and pain to light touch have been reported in literature as common signs of ER.” All of these can also occur, and frequently do, when ER is not present, so making such a statement is not meaningful.
  • The study appears to be agenda-driven as the authors end by saying “…individual exercisers should make efforts to understand their individualized response to exercise with the suggestion they also consider working with a certified (e.g., ACSM-CPT, NSCA-CPT) exercise professional as a beginner CrossFit® participant.” No results from this study suggest that beginner CrossFitters need to work with a specific type of trainer.
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