Everything we thought about running injury development was wrong, study shows
Study with over 5,200 runners shows that running injuries do not develop gradually over time – but most often occur during a single running session. Millions of runners are therefore receiving incorrect guidance from sports watches, researcher warns.
Facts about the study
- The Garmin-Runsafe Running Health Study followed 5,205 runners from 87 countries over 18 months.
- Participants recorded 588,071 running sessions, and 35 percent of participants sustained a running-related injury during the study.
- The study documents concrete risk increases with increased running distances compared to the longest run in the past 30 days:
- 10-30 percent increase: 64 percent increased injury risk
- 30-100 percent increase: 52 percent increased injury risk
- Over 100 percent increase: 128 percent increased injury risk
- The study also shows that injury risk increases with progressions over 1 percent (in the interval between 1 and 10 percent), which questions whether the frequently used 10% rule for safe training progression is accurate.
A new study from Aarhus University turns our understanding of how running injuries occur upside down.
The research project, which is the largest of its kind ever conducted, shows that running-related overuse injuries do not develop gradually over time, as previously assumed, but rather suddenly – often during a single training session.
"Our study marks a paradigm shift in understanding the causes of running-related overuse injuries. We previously believed that injuries develop gradually over time, but it turns out that many injuries occur because runners make training errors in a single training session," explains Associate Professor Rasmus Ø. Nielsen from the Department of Public Health at Aarhus University, who is the lead author of the study.
The study followed 5,205 runners from 87 countries over 18 months and shows that injury risk increases exponentially when runners increase their distance in a single training session compared to their longest run in the past 30 days. The longer the run becomes, the higher the injury risk.
Incorrect guidance for millions of runners
According to Rasmus Ø. Nielsen, the results cast critical light on how the tech industry has implemented so-called "evidence." Millions of sports watches worldwide are equipped with software that guides runners about their training – both for training optimization and injury prevention.
However, the algorithm used for injury prevention is built on very thin scientific grounds, according to Rasmus Ø. Nielsen.
"This concretely means that millions of runners receive incorrect guidance from their sports watches every day. They think they are following a scientific method to avoid injuries, but in reality they are using an algorithm that cannot predict injury risk at all," he says.
Non-existing evidence behind guidance
The current algorithm, called "Acute:Chronic Workload Ratio" (ACWR), was introduced in 2016 and is now implemented in equipment from companies that produce sports watches, while organizations and clinicians, such as physiotherapists, also use the algorithm.
The ACWR algorithm calculates the ratio between acute load (last week's training) and chronic load (average of the past 3 weeks). The algorithm recommends a maximum 20% increase in training load to minimize injury risk.
According to Rasmus Ø. Nielsen, the algorithm was originally developed for team sports and was based on a study with 28 participants. Due to the few participants in the study combined with data manipulation, the evidence base for using the algorithm to prevent running injuries is therefore "non-existent."
Realtime guidance
The research team has therefore worked for the past eight years to develop a new algorithm that will be much better at preventing injuries for runners.
Rasmus Ø. Nielsen emphasizes that he and the other researchers behind the study have no commercial interests in launching a new algorithm as a potential replacement for a method he himself criticizes.
The algorithm will be made freely available to runners, companies, clinicians and organizations who can use it actively to guide training and injury prevention.
Rasmus Ø. Nielsen hopes that the new insights will be implemented in existing technology.
"I imagine, for example, that sports watches with our algorithm will be able to guide runners in real-time during a run and give an alarm if they run a distance where injury risk is high. Like a traffic light that gives green light if injury risk is low; yellow light if injury risk increases and red light when injury risk becomes high," explains Rasmus Ø. Nielsen.
About the research results
Study type: Cohort study with 18 months follow-up period
Collaborators: Garmin International (participant recruitment) and researchers from Denmark, Sweden, Luxembourg and Australia.
External funding: The study received external funding from Aarhus University Research Foundation and the Danish Rheumatism Association. Garmin and external funders had no influence on study design, research questions, data collection, data processing and statistical analysis and/or interpretation of data as well as the writing and publication process.
Conflict of interest: None
Link to scientific article: How much running is too much? Identifying high-risk running sessions in a 5200-person cohort study | British Journal of Sports Medicine
Contact
Associate Professor Rasmus Ø. Nielsen
Aarhus University, Department of Public Health
Phone: +45 61 18 15 99
Email: roen@ph.au.dk