Throwback Thursday: No, expensive running shoes do not lead to 123% increase in injuries

Well, its really only Tuesday, but I did start writing this on a Thursday. In my alerts a while back, there was an exchange between Robbins and the authors on this study. I may or may not weigh in on that debate later, but a comment by Robbins caught my eye:

Marti reported that runners participating in an event wearing expensive shoes sustained 123% percent more injuries than wearers of cheaper ones

This study was also a favorite of Chris McDougal’s when trying to promote barefoot running. You also see a lot of fan boys promoting that figure. I can only assume that they did not actually read the study that it was based on, or if they did they had an epic fail in how you interpret results from such a study design and in their critical thinking skills.

Here is the actual study in question:

On the epidemiology of running injuries. The 1984 Bern Grand-Prix study.
Marti B, Vader JP, Minder CE, Abelin T.
Am J Sports Med. 1988 May-Jun;16(3):285-94.
Using a survey questionnaire design, we investigated the incidence, site, and nature of jogging injuries among all participants of a popular 16 km race. The response rate was 83.6%. Of 4,358 male joggers, 45.8% had sustained jogging injuries during the 1 year study period, 14.2% had required medical care, and 2.3% had missed work because of jogging injuries. Occurrence of jogging injuries was independently associated with higher weekly mileage (P less than 0.001), history of previous running injuries (P less than 0.001), and competitive training motivation (P = 0.03). Higher mileage was also associated with more frequent medical consultations due entirely to jogging-related injuries. In 33 to 44 year olds (N = 1,757), the number of years of running was inversely related to incidence of injuries (P = 0.02). Injuries were not significantly related to race running speed, training surface, characteristics of running shoes, or relative weight. Achillodynia and calf muscle symptoms were the two most common overuse injuries and occurred significantly more often among older runners with increased weekly mileage. We conclude that jogging injuries are frequent, that the number of firmly established etiologic factors is low, and that, in recommending jogging, moderation should be the watchword.

First, notice nothing about running shoes in the abstract, so the authors obviously did not think the “123%” was important.
Secondly, notice that this was a cross-sectional design, so you can not infer causation from a cross-sectional design.
Thirdly, it relied on the self-reporting of injuries, which is problematic
Fourthly, it was done in 1984. The makeup and characteristics of runners have changed a lot since then; so have running shoe design features.

Delving into the study, what did they actually find on running shoes? In the results section they reported:

Inexpensive running shoes (less than 60 Swiss francs) did not appear to be involved more frequently in running injuries, although only a small minority (3%) of GP runners wore such shoes. Expensive shoes (more than 140 Swiss francs) were actually associated with a higher incidence of running injuries. A likely explanation would be that injury-prone runners or high-mileage runners choose to wear expensive shoes.

Early in the results they did report a high correlation between the history of injury and a higher running mileage. It is entirely plausible that those who run higher mileage also wore expensive shoes and the injury risk is due to the mileage and nothing to do with the shoes.

Where did the “123%” come from? Nowhere in the study is that mentioned. Nowhere in the study do they report the numbers on running shoes that that number can be calculated from.

Further information was provided on the study here by Marti:
Marti B. Relationship between running injuries and running shoes – Results of a study of 5000 participants of a 16-km run – The May 1984 Berne “Grand Prix”. In: Segesser B, Pforringer W, eds. The shoe in sport. Chicago: Year Book Medical Publishers, 1989: 256-65.

In this presentation of the results, yes there were more injuries in the group that wore the more expensive running shoes compared to the cheaper shoes (based on 1984 prices and 1984 design features in the running shoes), which may be where the 123% figure might have come from (though the authors did not state it). However, the group wearing the expensive shoes ran twice as far as the group wearing the cheaper shoes. It could also be that those with the more expensive shoes had a history of injury which is why they went for those shoes. This is known as ‘confounding by indication‘.

The authors even said “It is probably incorrect, however, to interpret this surprising finding to mean that more expensive running shoes cause more running injuries and running related problems” and “The relationship should not be taken at face value“, so despite this and the confounding by indication, it still did not stop the fanboys sensationalizing the findings and engaging in a bit of intellectual dishonesty to suit their narrative.

As always, I go where the evidence takes me until convinced otherwise …. and expensive running shoes do not lead to 123% increase in injuries. #alternativefacts

Marti, B., Vader, J., Minder, C., & Abelin, T. (1988). On the epidemiology of running injuries: The 1984 Bern Grand-Prix study The American Journal of Sports Medicine, 16 (3), 285-294 DOI: 10.1177/036354658801600316

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