Did you know there are at least ten different equations for calculating athlete asymmetries? In this post, we explore the asymmetry 'Calculation Conundrum' and discuss which may provide the best approach.
Have you ever wondered how a single test could yield multiple outcomes regarding athlete asymmetries? It might seem straightforward, but the methods of calculating such asymmetries are quite diverse and intricate. Crucially, they output different results for the same data so understanding which you're using and why is critical.
What Are Asymmetries?
Asymmetries refer to differences in performance or function within an athlete's body. There are two primary types:
Intra-limb Asymmetries: These occur when comparing different muscles within the same limb.
Inter-limb Asymmetries: These involve comparing the same function or performance between the left and right limbs.
Intra-limb Asymmetries
Intra-limb asymmetries entail examining the strength and capacity of different muscles within a single joint. For example:
Hip and Groin Area: The Adductor-Abductor ratio is frequently analysed using instruments like VALD's ForceFrame. This is particularly relevant for athletes prone to groin injuries, such as those in ice hockey or kicking sports.
Shoulder Strength: The external-to-internal rotation (ER:IR) strength ratio can be assessed, especially useful for overhead athletes like those engaging in throwing sports.
Inter-limb Asymmetries
More commonly referenced, inter-limb asymmetries involve comparing the left and right sides of the body. These can be examined through:
Bilateral Movements: For instance, using dual force plates like VALD's ForceDecks during a countermovement jump.
Unilateral Movements: Evaluating performance in single-leg tests to pinpoint discrepancies between limbs.
The Asymmetry Calculation Conundrum
Calculating asymmetries is not as straightforward as it might seem. There are numerous methods, each with its specific application and limitations. As Dr Chris Bishop previously discussed for Global Performance Insights, we face a 'Calculation Conundrum' when trying to quantify an asymmetry from athlete performance testing in sports science.
In the video below, I discuss asymmetries in more detail, including all the 'Calculation Conundrum' equations and why it matters whether you're conducting a bilateral or unilateral test with your athletes. Further below, try out our Asymmetry Calculator.
An Athlete Asymmetry Calculation
Use the calculator below to see how your asymmetry outcomes differ based on which equation you use. You can find the detail of each of these calculations, along with their citations, in the video above.
A massive thank you to Ash Anand who wrote the HTML code for our asymmetry calculator. You can learn more about how he developed his own data science skills in his guest post for the blog.
The Right Equation for the Right Task
So which asymmetry calculation is 'correct'? Well, as discussed in the video further above, it depends! Dr. Chris Bishop's work highlights that the choice of equation should depend on the nature of the test:
Bilateral Tests: It is suggested to use equations like the Bilateral Asymmetry Index 1 or Symmetry Index, as they consider the total output generated by both limbs together.
Unilateral Tests: For isolated limb capacity, equations like the Bilateral Strength Asymmetry or Standard Percentage Difference are recommended.
Visualising Asymmetries
Interpreting asymmetries visually can be guided by various methods:
Directional Accounting: Dominant side values should always be positive, and non-dominant values negative to maintain context.
Graphical Representation: Using graphs to plot and track asymmetries over time can aid in more intuitive understanding and monitoring.
For more on visualising asymmetries and the critical importance of adding direction to these visualisations, read the guest post by Dr Chris Bishop.
Final Thoughts
Recognising and calculating athlete asymmetries are pivotal in optimising performance and understanding injury risks. The Calculation Conundrum brings to light the nuances in selecting the right method based on the test's constraints and goals. As sport scientists, comprehending these methods helps in accurate assessment and ultimately, in tailoring interventions for athletes.
FAQs on Athlete Testing Asymmetries
What are asymmetries in athletes?
Asymmetries refer to functional or performance differences between or within the limbs of an athlete.
What is the difference between inter-limb and intra-limb asymmetries?
Intra-limb asymmetries concern differences within a single limb, such as the hip adductor: abductor ratio, while inter-limb asymmetries compare performance between the left and right limbs, such as maximum force in each side during the Nordic hamstring test.
Why is it important to calculate asymmetries differently for different tests?
Bilateral tests involve both limbs working together, thereby necessitating a total output measure. Unilateral tests assess each limb in isolation, requiring direct side-by-side comparison.
What are the recommended methods for calculating asymmetry?
For bilateral tests, use the Bilateral Asymmetry Index 1 or Symmetry Index.
For unilateral tests, use the Bilateral Strength Asymmetry or Standard Percentage Difference.
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This article is support by VALD Performance. For more information, about their technology, visit their website.
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