…or is it? The media are lapping up the press release associated with this study: Researchers explode the myth about running injuries. The title above is the title of the study as it appears in the British Journal of Sports Medicine. I added the question mark at the end for a reason. Does the study live up to the hype that it is generating in the media? Lets start with the abstract:
Foot pronation is not associated with increased injury risk in novice runners wearing a neutral shoe: a 1-year prospective cohort study
Rasmus Oestergaard Nielsen, Ida Buist, Erik Thorlund Parner, Ellen Aagaard Nohr, Henrik Sørensen, Martin Lind, Sten Rasmussen
Objective: To investigate if running distance to first running-related injury varies between foot postures in novice runners wearing neutral shoes.
Design: A 1-year epidemiological observational prospective cohort study.
Participants: A total of 927 novice runners equivalent to 1854 feet were included. At baseline, foot posture on each foot was evaluated using the foot-posture index and categorised into highly supinated (n=53), supinated (n=369), neutral (n=1292), pronated (n=122) or highly pronated (n=18). Participants then had to start running in a neutral running shoe and to use global positioning system watch to quantify the running distance in every training session.
Main outcome measure A running-related injury was defined as any musculoskeletal complaint of the lower extremity or back caused by running, which restricted the amount of running for at least 1 week.
Results: During 1 year of follow-up, the 1854 feet included in the analyses ran a total of 326 803 km until injury or censoring. A total of 252 participants sustained a running-related injury. Of these, 63 were bilateral injuries. Compared with a neutral foot posture, no significant body mass index-adjusted cumulative risk differences (RD) were found after 250 km of running for highly supinated feet (RD=11.0% (−10% to 32.1%), p=0.30), supinated feet (RD=−1.4% (−8.4% to 5.5%), p=0.69), pronated feet (RD=−8.1% (−17.6% to 1.3%), p=0.09) and highly pronated feet (RD=9.8% (−19.3% to 38.8%), p=0.51). In addition, the incidence-rate difference/1000 km of running, revealed that pronators had a significantly lower number of injuries/1000 km of running of −0.37 (−0.03 to −0.70), p=0.03 than neutrals.
Conclusions: The results of the present study contradict the widespread belief that moderate foot pronation is associated with an increased risk of injury among novice runners taking up running in a neutral running shoe. More work is needed to ascertain if highly pronated feet face a higher risk of injury than neutral feet.
This is a really impressive, and generally, well done and analysed large prospective study that classified the feet of 927 runners into different foot types using the Foot Posture Index; gave them all the same running shoe (Supernova Glide 3) and then followed them for a year and 252 of them got an injury.
The reported incidence of injury in each of the groups that they used to classify the feet were:
As you can see from the table, the incidence of injury was lower in the pronated group (p=0.03) and appeared highest in the highly pronated group, but that was not statistically significant, though it was trending that way. This was relative to the neutral group which they defined as a Foot Posture Index (FPI) between 0 and 7. The pronated group was defined as an FPI of 7 to 10 and highly pronated as greater than 10.
Does the study support all the media hype of “Researchers explode the myth about running injuries“?
Anyone familiar with the FPI, knows that any FPI value above 0 is pronated, so almost all the feet in their ‘neutral’ group (except those with an FPI of 0) will be pronated!! So no, the study does not explode the myth as most of the neutral group had a pronated foot!! (personally, and anecdotally, I and all the people I know who have worked with the FPI and have discussed this, generally consider 0-4 to be a reasonable normal range and anything above 4 to be pronated. The study used anything above 7 to be pronated ).
Even if the results were correct, it does not support the hype in the press release. The evidence from the most recent meta-analysis of all the available studies show that there is a small, but statistically significant risk from a pronated foot for overuse injury. If another meta-analysis was done to include the above study claiming to show no relationship between pronation and injury and the other recent new study that found there was, then the overall results of the meta-analysis is probably unlikely to change from the small, but statistically significant risk from ‘overpronation’.
Additionally, they eliminated all those wearing inserts or foot orthotics from the study. It would be reasonable to assume that those wearing these would probably have been in the pronated group and probably be at greater risk of developing an injury (hence they needed the foot orthotics!). This presumably left the group of pronated feet that were included in the study at less risk for injury in the study (as they did not need foot orthotics). Can you see how this might have introduced some sort of bias into the results?
Furthermore, no data was presented on the reliability of the 4 testers in their assessment of the FPI. We have no idea what the intratester or intertester reliability was or if there was consistency between those doing the testing.
Moreover, was it reasonable to give the pronated feet a neutral shoe and then determine the injury rate? Surely if the prevailing paradigm (flawed as it may be!) is to give a pronated foot a motion control shoe, would it not have been more reasonable to do that? In the real retail world, that is probably what would have happened. (However, I not sure this would actually make any difference).
As an aside, the 252 injuries that the study found is a prevalence of 27%; certainly a lot less than than the 70% figure you read so often in the crankosphere blogosphere and at the lower end of 20 to 70% you read in the scientific literature.
As always, I go where the evidence takes me until convinced otherwise and I will stick to the higher level of evidence from a meta-analysis and not the over-hyped media release.
Nielsen, R., Buist, I., Parner, E., Nohr, E., Sorensen, H., Lind, M., & Rasmussen, S. (2013). Foot pronation is not associated with increased injury risk in novice runners wearing a neutral shoe: a 1-year prospective cohort study British Journal of Sports Medicine DOI: 10.1136/bjsports-2013-092202