Lopes et al1 collected incidence and prevalence rates of running-related musculoskeletal injuries (RRMIs). Incidence of injury is defined as the number of new injuries occurring during a specified time frame and represents an estimate of the risk of developing the injury during that time frame.2 For instance, if a group of runners is followed for 1 year in regard to training and injury, one can calculate the number of injuries per a certain amount of training hours (eg, 7.4 injuries per 1000 hours of training). Lopes et al1 extracted data regarding injury incidence from prospective studies of uninjured runners who were tracked for injury over a 12-month period. Prevalence of injury is the number of existing injuries in the total population being studied at a given point in time and represents an estimate of the probability that an individual will have a particular injury at that time.2 For instance, if 46 runners in a retrospective survey of 100 participants reported an injury in the previous year, there is a 46% probability that any randomly selected runner from that population would have had an injury. Lopes et al1 extracted data regarding injury prevalence from retrospective, cross-sectional studies that surveyed runners about their injuries in the past 12 or 24 months or prospective, cross-sectional studies that tracked runners for injury during a 5- to 8.5-day ultramarathon event.
When reading a systematic review article such as that by Lopes et al,1 it is important to do so with an understanding of the quality of the incidence and prevalence data presented. The most accurate reporting of incidence and prevalence of injury occurs when consistent definitions and methodology exist. Clearly defining the research question assists other authors who are preparing a systematic review to report studies with consistent definitions and methods. Often, the acronym PICOS (Participants, Intervention, Comparators, Outcomes, Study design)3 is used to help authors develop their precise research question. It is unclear whether Lopes et al1 used PICOS when writing their systematic review, as their definitions of a runner and the ways their outcome (injury) was measured were rather broad. However, the authors may have deliberately chosen these broad definitions because little data exist on incidence and prevalence rates of RRMIs, and their review highlights the need for further research on this topic.
Another important consideration when reading a systematic review is to evaluate the risk of bias within the studies included in the review. Table 5 in the Lopes et al1 article outlines the risk of bias assessment and points to the heterogeneity of the definitions and methods in the included studies. For example, 2 of the ultramarathon studies did not provide a clear definition of an RRMI, one of the general RRMI studies rated injuries on a scale of 1 to 4 (with 4 being the highest) on the basis of symptoms, and others simply broadly defined an RRMI as affecting or impairing training or racing performance. How a diagnosis was made also varied, with 2 studies using self-report and the remainder of studies used health care providers’ diagnoses. In addition, 2 studies reported the overall injury rate as a ratio of RRMI to hours of exposure to running, but no studies reported individual injury rates in this manner. Varying modes of data collection of RRMIs were also used both across studies and within 3 of the included studies. Finally, there were a total of 3482 runners in the 8 studies reviewed, and, although all articles in the systematic review provided a description of the runners studied, the participants ranged from sprinters to ultramarathon runners. These are populations with disparate training, racing, and physical demands, and their distinct biomechanical loads may influence injury rates. The lack of consistency among the studies in regard to definitions and methods precluded Lopes et al1 from performing a meta-analysis, which would have provided readers with more detailed information regarding injury rates in specific populations of runners. As those authors acknowledge, the lack of consistency also points to the need for more research utilizing a standardized RRMI definition and tracking process within similar running populations.
Despite inconsistencies among the studies reviewed by Lopes et al,1 there was consistency in the frequency of injury types reported. Medial tibial stress syndrome, Achilles tendinopathy, and plantar fasciitis were the most frequently reported general RRMIs, with incidence rates ranging from 4.5% to 20% (n = 98) and prevalence rates ranging from 5.2% to 17.5% (n = 3276). Achilles tendinopathy and patellofemoral pain were the most frequently reported ultramarathon racing injuries, with prevalence rates ranging from 2% to 18.5% (n = 126). Interestingly, it appears that runners participating in a variety of distances incur similar injuries, such as medial stress syndrome, Achilles tendinopathy, plantar fasciitis, and patellofemoral pain.
Although not the focus of the systematic review reported by Lopes et al,1 as health care providers, it is valuable to note that common RRMIs share an overuse mechanism of injury and thus may also share a general prevention strategy. Preventing RRMIs involves finding the zone whereby runners train at an optimal level to meet their performance goals, while not surpassing their individual limit of running volume (distance, intensity, or frequency).4 This allows for positive remodeling to occur between bouts of training, without the repetitive loads that result in accrued tissue microdamage and tissue failure (injury).4 To find this optimal zone, many clinicians, coaches, and runners follow the anecdotal “10% rule” and increase training volume no more than 10% per week, which may be too high for some runners4 and perhaps too low for others. The amount and type of running is likely unique and specific to each runner based on his or her health and running history. Randomized controlled trials are needed on individualized, progressive, and periodized training and racing programs for the prevention of RRMIs.
More prospective investigations, with a standard RRMI definition and consistent methodology, of various running populations are needed. This will help to obtain a better understanding of primary risk factors for RRMIs, which may guide preventive and treatment strategies. However, prospective research investigations require time; in the more immediate term, clinicians can assist runners by educating them about the importance of individualized, progressive, and periodized training and racing programs, as well as the importance of a strong and symmetrical foundation of alignment, biomechanics, and strength. Although more research is needed in these areas, theoretically, the more balanced one’s anatomy, biomechanics, and strength are, the more forces his or her body can withstand and the higher the magnitude of training that can be obtained injury free.
- Lopes AD, Hespanhol Júnior LC, Yeung SS, Costa LO. What are the main running-related musculoskeletal injuries? A systematic review. Sports Med. 2012; 42(10):891–905.
- Portney LG, Watkins MP. Foundations of Clinical Research: Applications to Practice. 2nd ed. Upper Saddle, NJ: Prentice-Hill: 2000.
- Liberati A, Altman DG, Tetzlaff J, et al. The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate health care interventions: explanation and elaboration. J Clin Epidemiol. 2009;62(10):e1–e34. doi:10.1016/j.jclinepi.2009.06.006 [CrossRef]
- Edwards BW, Derrick TR. Preventing overuse injuries in running: a perspective based on tissue damage, repair, and adaptation. Track & Cross Country Journal. 2011;1(1):17–22.