I recently read an article (read it here) by Chris Bishop on asymmetry in Sportsmith. I thought he did a great job summarizing the research on asymmetry testing.
I often get asked about hip and groin strength testing. Things like how much asymmetry is acceptable, when do you intervene and what do I do with asymmetry to enhance performance or reduce injury risk.
Obviously all of this depends on the context of testing and the athletes situation. But I wanted to share my 4 key takeaways from Chris’ article which might help answer some of your questions around hip and groin strength asymmetry.
Now, let’s dive in.
#1 Asymmetry alone tells us little about performance and injury risk:
Most sports require some degree of asymmetry. Some will require more asymmetry to excel than others.
The magnitude of “acceptable” asymmetry will vary depending on the task and the chosen metric. The standard 10%-15% that is often used is likely not generalizable for all tests and metrics.
This means that when we look at asymmetry values, we need to take into consideration the sport, the task and the metrics. Because asymmetry is task specific, if the test does not replicate the sport, the asymmetry found may not be a great indicator of performance or injury risk.
#2 Interpreting noise in asymmetry:
All testing and data collection consists of noise. Noise is the expected variability between tests. This variability can be from testing device error and day to day human variability (think of it like day to day fluctuations in weight). In short, noise is normal variation in testing results.
So how do we determine the noise from actual asymmetry? The coefficient of variability (CV) is a helpful value in determining true asymmetry. CV represents the average difference between each athlete’s test score from the mean group score. We can use the CV to represent the noise, where an asymmetry value below the CV is considered to be from device error or human variability.
#3 Direction of asymmetry:
Similar to the magnitude of asymmetry, the direction of asymmetry has been shown to also be highly variable.
This means that changes of asymmetry from one limb to the other are a normal occurrence. Interestingly, this also means that consistent asymmetry in one direction may be more concerning. This may be normal from playing asymmetrical sport, but may also be an indication of compensation and injury risk.
#4 Asymmetry monitoring:
A big mistake I often see is practitioners relying on single data points to make decisions.
Single data points are a snapshot of here and now. Particularly with variability of asymmetry, this can be grossly misleading. My biggest takeaway from this article is the need to monitor asymmetry over time and look for consistency in patterns in the data. Only once patterns are identified should we intervene if needed.