Predictors of multiple injuries in distance runners

Physical activity is universally promoted for its health benefits, and it is encouraging to see an increase in
participation by recreational runners in mass- participation community-based events. However, running
does have a high risk of injury, with 20% – 80% of runners reporting a running related injury in a 12-
month period. There are very few research studies that have reported on multiple injuries per individual
runner per year and over more than 1 season, and none that have identified risk factors predictive of
runners with multiple injuries. Researchers from the University of Pretoria’s Sport, Exercise Medicine
and Lifestyle Institute (SEMLI) and the SA Medical Research Council (SA MRC) recently published their
investigations into this question.

An online medical screening questionnaire was completed by runners prior to the 2012 to 2015 Two
Oceans 21.1 km and 56.0 km races. The average number of injuries for each runner each year was
calculated and runners were categorized into 4 “multiple injury risk” (MIR) categories – i.e. high,
intermediate, low, and very low. The research team then determined whether demographics, training
and racing, a history of chronic disease, or a history of allergies were predictive of a high MIR (defined as
an average of more than 1 injury per year). Of all the entrants that completed the questionnaire, 9.2%
reported at least 1 injury, and 0.4% of the entrants were in the high MIR category. The researchers
found that 2.5 injuries occurred per 10 runner-years.

The researchers concluded that runners who have been running recreationally for more than 20 years
and those with multiple chronic diseases or a history of allergies were at higher risk of experiencing
multiple running-related injuries. One of the novel findings of this study was that a history of chronic
disease is predictive of runners with high MIRs. Almost 19% of all study entrants reported at least 1
chronic disease; however, among entrants with high MIRs, 26% had 1 chronic disease, 9.7% had 2
chronic diseases and 3.2% had 3 chronic diseases. Another novel finding was that runners with histories
of any form of allergy have significantly higher odds than those with no histories of allergies of being
high MIR runners as opposed to very low MIR runners. Another interesting result related to training load
was that neither weekly running mileage nor any of the other training-related risk factors were
predictors of a high MIR, however the number of years running recreationally was. It was specifically
those runners who had been running for more than 20 years, irrespective of age or gender, who had
significantly higher odds of being high-MIR runners as opposed to very low-MIR runners, when
compared to those who had been running for less than 10 years.
The researchers acknowledge that there may be other intrinsic factors (e.g. medication use) that could
possibly contribute to being a high-MIR runner, and they recommend that this should be explored
further in future research studies.

Reference for this summary:
Swanevelder S, Sewry N, Schwellnus M, Jordaan E. Predictors of multiple injuries in individual distance
runners: A retrospective study of 75,401 entrants in 4 annual races – SAFER XX. J Sport Health Sci
2022;11:339-46
https://pubmed.ncbi.nlm.nih.gov/34801747/