Coordination Variability in injured vs healthy runners, green oranges, and focusing on things in our control

📝 Weekly paper summary

Bilateral Differences in Coordination Variability among Injured and Uninjured Runners: A Prospective Study (Desai and Gruber, 2021)

Category

Prospective Study

Context

Most research assessing running-related injury mechanisms historically explored the relationship between discrete traditional biomechanical metrics (e.g., average or peak forces, joint angles, etc.). Recently, researchers have placed relatively more emphasis on dynamical systems-based analyses that assess the relative motions of segments and the variability of these motions.

The variability-overuse injury hypothesis posits that coordination variability (either its magnitude or structure) can influence the risk of lower extremity overuse injury. However, there is currently limited data assessing whether coordination variability within the injured limb or asymmetries in coordination variability between limbs is related to lower extremity injury risk.

Therefore, the study's purpose was to explore whether differences in coordination variability or the degree of asymmetry in coordination variability between limbs was associated with lower extremity injury risk.

Correctness

The study recruited fifty-five recreational runners without any previous injury, at least two years of running experience, and ran at least 10 miles (~16km) per week. The researchers conducted the follow-up assessment six months later, and participants all performed their usual running program during this time. Therefore, I'd argue the sample reasonably represents the type of people most trainers or therapists may be working with in their practice.

However, running speed was standardized for all participants at 4m/s (about a 4:10/km pace), slightly faster than their preferred speed of 3.71m/s (about a 4:30/km pace). Although this isn't a massive discrepancy when running over an 18m runway, given the sample's running experience and how far they reportedly run every week, this seems more likely to be a "tempo run" pace than a pace they would maintain for a longer-duration run. Since movement velocity can influence coordination variability, this decision made by the researchers is essential to consider when extrapolating how people moved during the study versus how they might run outside the lab during their actual training.

Also, as highlighted in the October 26, 2021 newsletter, coordination variability was quantified using circular statistics, which can result in statistical artifacts (Stock et al., 2019). Therefore, it is also essential to consider this potential limitation when interpreting the researchers' data.

Contributions

• An increase in knee-ankle coordination variability during the mid-stance phase decreased the odds of developing a repetitive running injury (Odds Ratio=0.8).
• An increase in shank-ankle coordination variability during initial-stance increased the odds of developing a repetitive running injury (Odds Ratio=1.2).
• The degree of asymmetry in coordination variability was not associated with an increased risk of developing a repetitive running injury.
• These findings demonstrate that the relationship between the magnitude of movement variability and injury risk is perhaps not as simple as "more variability = more movement solutions = reduced injury risk." The authors suggest that at initial stance, higher variability may indicate that these individuals could not accommodate the demands imposed from the high impact forces during heel strike. Conversely, increased variability during mid-stance between the knee and ankle would represent increased coordinative flexibility (i.e., movement solutions) to accommodate the weight-bearing demands during this phase of running.

🧠 Fun fact of the week

I ate a lot of fruit over the holidays, so here's a fun fruit-related fact. Did you know that the first oranges weren't orange? The original fruit was a tangerine-pomelo hybrid from Southeast Asia and was green!

🎙 Podcast recommendation

Although he's somewhat of a controversial figure nowadays, I do think there's value in listening to how Elon thinks in this interview!

🗣 Quote of the week

"The chief task in life is simply this: to identify and separate matters so that I can say clearly to myself which are externals not under my control, and which have to do with the choices I actually control. Where then do I look for good and evil? Not to uncontrollable externals, but within myself to the choices that are my own..."

- Epictetus, Discourses, 2.5.4-5