Could Knee Stiffness Be Our Best Bet in Predicting Injury in Recreational Runners?

A 2-Year Prospective Cohort Study of Overuse Running Injuries
The Runners and Injury Longitudinal Study (TRAILS)

American Journal of Sports Medicine, May 23rd, 2018

Messier Et.Al  

 J.B. Snow Biomechanics Laboratory, Department of Health and Exercise Science, Wake Forest University, Winston-Salem, North Carolina, USA

Everyone loves running. Okay, maybe not everyone…. but at least 20 million people in America engage in regular running each year! Combine this with the fact that up to 65% of runners sustain an injury within a 2-year time span and that’s a serious amount of injuries and a massive demand from people like to us to help out.

Down the road from me in Winston-Salem, NC, the researchers of this study looked into what risk factors differentiated runners who would go onto becoming injured vs. those that escaped injury free in a cohort of 300 recreational runners over a 2-year time span.  The study looked at all kinds of baseline data including anthropometrics, strength, running gait biomechanics, arch height, q-angle, flexibility, footwear, and psychosocial variables.

Surely, many of these variables were correlated with the runners who went on to develop injuries such as inflexibility, weakness, type of shoe, flat feet, and so-on as we have been telling our patients for years, right?


In a George R.R. Martin-style-plot-twist, there were shockingly few variables that were associated with injury asides from knee stiffness, gender (females) and psychosocial factors.

Increased Knee Stiffness in Injured Runners

Knee stiffness was the only predictor of injury in the cohort. The study describes knee stiffness in regards to the knee’s ability to dissipate force upon impact while running; not in the arthrokinematic-hypomobility-Maitland sense. To help paint a clear picture, imagine the change of force that occurs in the quads along with the concurrent change in knee flexion when the foot strikes the ground. For example, a runner with a heavy, stiff-legged impact while running would have higher knee stiffness and possibly a higher risk of injury.

  • Increased knee stiffness is more likely to be found in runners with higher BMI
  • For every 1 degree of N * M / Deg increase in knee stiffness, the odds for injury increased by 18%

How We Can Help Our Runners

With the results of this study, the authors suggest that perhaps instructing runners to shorten their step length and/or run on a soft, but stable, running surface could help reduce knee stiffness and injury. Don’t forget to help encourage positive psychosocial outcomes as this was another area that was associated with increased injury risk in the study.

The average individual in the study was as an 11-year running veteran with a training volume of 20 miles per week and at 9-minute mile pace. Perhaps the results would change if excessive loading with heavy milage were to occur in a repeated study. The heavier mileage and intensity could stress our bodily tissues beyond their resilience. However, with the cohort under examination, mileage, albeit fairly mild milage, was not predictive of injury.

Let’s keep our runners happy and treading lightly.

Tyler Cope

Forever Disclaimers:

1): Readers –  If any of these articles peak your interest, please click the link to the original source to read the full text! It’s important to interpret research for yourself and as it pertains to you and your practice. Not to mention, we should support our journals and authors that provide this content.
2): Journals and authors – I do my best job to help promote the message from the research you provide to help clinicians improve. This is not a platform to try and promote my own individual views. I can promise you that I will not always have everything right, so please, if you have any feedback for me or if I misinterpreted anything then let me know!

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