The epidemiology and associated risk factors for Achilles tendon overuse running injuries in the Two Oceans Marathon

Abstract

Distance running is an effective, low-cost training modality known to improve endurance capacity and cardiovascular health that is accessible to both the competitive and the novice athlete. The accessibility of running has led to an increase in participation around the world. South Africa has various running events taking place year-round. The Two Oceans Marathon is one of the more predominant running events in the country, with around 26000 runners participating each year. It is pertinent to note that running related musculoskeletal injury (RRMI) is a common side effect of running, particularly to the novice runner. RRMIs can be defined as any injury acquired to the musculoskeletal system whilst running resulting in a loss in training time or prevention of participation in competition. The aetiology of such injuries is complex and multifactorial in nature and predisposing factors from extrinsic factors such as footwear to intrinsic factors such as biomechanical abnormalities. The most common anatomical sites of RRMIs are in the lower limb, most of which can be attributed to overuse. Gradual onset Achilles tendon injury (GoATI) is of the more synonymous RRMI when it comes to lost training and racing time. A plethora of risk factors have been associated with the development of GoATI with an increasing body of evidence linking metabolic disorders and tendon degeneration, however, there remains an uncertainty on majority of the effects and an understanding of the causation remains unclear. Additionally, it is unclear if these risk factors differ in ultramarathon runners when compared to marathon runners, as this research is limited. Over four years 106743 runners entered the Two Oceans Marathon races, of which 61374 gave written informed consent for pre-race medical screening data, including injury data in the last 12 months, to be used for research purposes. Seven hundred and thirty-nine runners reported a GoATI in the 12 months before race entry. We found an annual incidence of 1.2% of GoATIs. 52.1% of the injuries were severe enough to affect or even prevented running adversely. Over half (>50%) of the injured population reported symptoms lasting for > 7 months, but only 50% were treated using strengthening exercises, which is the most successful treatment for GoATIs. Apart from age, longer race distance and male sex, novel independent factors predicting distance runners are at risk of GoATI were: increased years of being a recreational runner, a higher chronic disease composite score and a history of allergies. The study’s limitations are that data was self-reported, which may have introduced the possibility of a recall bias. When comparing the study population to all race entrants, there was an over- representation of females, younger age groups, and 21.1km race entrants. This needs to be considered when generalising results across all entrants. Injuries were not diagnosed by a trained clinician and injury severity data also relied on the participant’s subjective experience of pain to determine severity grade. Due to our study’s cross-sectional nature, we could not infer a cause-effect relationship between identified risk factors and GoATIs. We believe our study’s main strengths are the large sample size and a good response rate. To our knowledge, the largest study to date investigating risk factors predictive of GoATIs in distance runners. 57.5% of total entrants consented to the use of their data for the sake of this study. This study explored associations between novel independent risk factors, including a chronic disease composite score, and GoATIs. This is the first study to report on such associations. We suggest that athletes’ and clinicians; education is important so that GoATIs are correctly diagnosed and treated earlier and appropriately. Runners at risk for sustaining GoATIs could be targeted for future injury prevention interventions. Future studies should focus on establishing a causal relationship.