Anther survey-based study of CrossFit has surfaced on the internet, this time in the Open Access Journal for Orthopedic Sports Medicine. The study, titled Injury Rate and Patterns Among CrossFit Athletes, reports a near 20% injury rate among CrossFit participants, but then compares this to the “incidence rate” of injury in running, cited to be between 19.4% to 79.3%. This obviously puts CrossFit on the lower end of the calculated range.
But there is a problem with this study. What the authors call an “injury rate” is simply not an injury rate. The 20% figure represents the percentage of respondents to the study who claimed to have an injury from CrossFit. By definition, an injury rate is a calculation of how many injuries occur during a given span of time. The authors seem to conflate the calculation of an injury rate with the calculation of incidence. For a detailed description of the differences between these terms, read Dr. Feito’s blog post on the subject.
Why is this a problem? Consider that dozens of news sources have already misquoted or misinterpreted the injury survey study by Paul Hak, which clearly distinguishes between the percentage of injured survey respondents and the rate of injury. If the media gets it wrong that easily, then it’s just going to cause more problems for CrossFit when the academics get it wrong for them.
In order to address this, I emailed the corresponding author, Dr. Brian Giordano, who was more than happy to schedule a phone interview with me. That is, until he mysteriously backed out and requested I follow the formal process of sending a letter to the editor if I had questions or critiques of his work. In other words, Dr. Giordano must have googled me and discovered what can happen during my interviews. He did, however, consent to answering a few questions via email. Below is a copy of the email I sent him on June 3rd, 2014. So far I have received no response:
For the sake of simplicity, I will only ask three questions. I’ll also keep the focus of these questions confined to a single topic, your study’s use of the term “injury rate.”
1. How did you define the term “injury rate” for the purposes of your study? How did you calculate this?
2. It appears that you calculated “injury rate” as the percentage of respondents to your survey that reported injuries, yet none of the studies you cite for comparison calculate injury rate this way:
– (11) Handball injuries during major international tournaments. This study uses the terms “incidence of injury” and “injury rate” interchangeably, and calculates “The incidence of injury was expressed as (a) number of injuries/match and (b) number of injuries/1000 player hours.”
– (13) Risk factors for lower extremity injuries in elite female soccer players. This study calculates injury rates as “Individual exposure data were calculated as the total number of hours of training and match play during the season, and injury rates are reported as the number of injuries per 1000 player hours”
– (10) Prevalence of Musculoskeletal Injuries in Swedish Elite Track and Field Athletes. This study calculates injury “prevalence” as “…an indicator of morbidity, accounting for the number of individuals with an existing disease or injury in a given time interval.” You acknowledge this study when your paper compares the 42.8% “1-year retrospective injury prevalence” from this study with your “20%” calculated “Injury rate” for CrossFit. This comparison implies that these calculations are the same, and yet no explanation of the difference in terminology is given. Is your 20% figure an “injury rate”, as claimed, or a measure of injury prevalence among your respondents?
– (3) Gymnastics injuries. You use this study to compare your “injury rate” data to the injury rate of gymnasts, yet this study also calculates injury rates as “number of injuries/1,000 h.”
Can you explain your justification for comparing your measure of “injury rate” with these apparently different injury rate calculations?
3. I can find no basis in scholarly literature for defining “injury rate” as the percentage of solicited survey respondents who report injuries. The most authoritative documents on the subject repeatedly define injury rate as a ratio of the number of injuries per unit of exposure time.
Given this information, how do you justify referring to your calculation as an “injury rate?”
Thank you for your time.