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Study: watch out for these predictors of multiple injuries

Despite how common injuries are among runners, we still know relatively little about what specific factors cause them, or how to prevent them. We know even less about why some runners suffer multiple injuries in a season, while others seem to be able to run forever with next to no issues. Recently, researchers in South Africa tried to understand what causes some runners to experience multiple injuries, and their findings may surprise you.

The study

The study, which was published in the Journal of Sport and Health Science, collected running-related injury data from 75,401 race entrants across four years (2012-2015) at the annual Two Oceans 21.1 km and 56.0 km races in South Africa. The average number of injuries for each runner every year was calculated by taking a runner’s race entry history and injury history into account and categorizing entrants into four multiple injury risk (MIR) categories — high, intermediate, low and very low.

The researchers used odds ratios (multiple logistic regression modeling) to determine which factors predicted a high risk of multiple injuries. The factors they considered included demographics, training and racing, chronic-disease history and history of allergies.

The results

Interestingly, the results showed that less than 10 per cent of the runners surveyed experienced an injury over the four years, and only 0.4 per cent of them experienced multiple injuries during that time. This, the researchers admitted, is relatively low compared to other studies, which have previously reported between 19.4 per cent and 79.3 per cent of runners experiencing at least one injury every year, and warrants further investigation.

The study determined three independent risk factors that seemed to predict a higher instance of multiple injuries. These included older age (more than 40 years old), a longer history of recreational running (more than 20 years) and running longer distances, like ultramarathons. Counter to what you may think, neither weekly running mileage nor any other training-related risk factors were predictors of a high rate of multiple injuries.

Chronic disease and injuries

The researchers also identified two novel risk factors for multiple injuries: a history of chronic disease or a history of allergies. Nearly 19 per cent of all runners involved in the study reported at least one chronic disease, and these people accounted for 26 per cent of runners with multiple injuries. If the number of chronic diseases in a runner increased from one to two, their odds for having multiple injuries increased by a factor of 2.2 per cent. If they went from two to three, those odds went up another by a factor of 4.7.

The authors of the study note previous studies have shown that chronic diseases are common among endurance runners. They also point out that other studies have reported a link between chronic diseases like diabetes mellitus and hypercholesterolemia are associated with injury. They believe that one reason for this association is that runners with chronic diseases are likely on a number of medications, which could influence their risk for injuries. “There is also evidence that medications used to treat chronic diseases can be associated with increased risk of tendinopathies, ligament injuries and bone-stress injuries,” the researchers say.

Allergies and injuries

The study also found that runners with a history of any form of allergies had significantly higher odds of experiencing multiple injuries than those who didn’t. “Runners with allergies are likely to be taking antihistamines, especially because endurance running is an outdoor activity,” the researchers concluded. “One of the oral sedating H1 antihistamines, Promethazine, has been associated with severe tissue injury.”

The bottom line

Injuries are complicated and often multi-faceted, and scientists are still learning what causes some people to become injured more than others. This study has a few specific limitations, including the self-reported nature of the data, and the fact that none of the injuries were confirmed by healthcare professionals.

The results of this study were also correlations, not causations, and cause-effect relationships between the risk factors couldn’t be confirmed due to the cross-sectional design of the study. The researchers also didn’t address risk factors that could potentially play roles in multiple injuries among runners, like body mass index, specific medications, type of training/surface or biomechanics, among others, and they did not account for recurrent injuries in their data.

Still, runners with allergies or chronic diseases should take note of this study, and take extra precautions with their training. Particularly if you’re taking medications for your condition, you should talk to your doctor about the potential side effects and how you can lower your risk for injuries and train safely.