Is There A Secret Sauce - Part IV - Continued

Importance of Single Limb Testing – Cont.

Last week we started to discuss the importance of single limb testing.  This week, we will continue this discussion.  We will start off with a further examine of this concept of single limb testing versus bilateral, by looking at Myers work in 2012.  Myer et al published a paper in 2012 in the American Journal of Sports Medicine looked at asymmetries in single limb performance in vertical jump and associated force attenuation in athletes that were released to return to sport following ACL reconstruction.  What they found was that these asymmetries continue to be present and concluded that if they do persist, then this may increase the risk of either contralateral (opposite side) or ipsilateral (same side) injury.  So clearly, we have to be able to measure these deficits in a single limb fashion to even know they exist. 

So based on all this information, then it make sense that we should test single limb.  We also know from Stearns et al work in 2014, that adduction in the frontal plane is directly correlated to the adduction moment.  We also know from previous work that the larger the adduction moment then the greater the risk is for ACL injury.  Considering this, then when we look at single limb testing, we need to quantify adduction in the frontal plane.  Besides just the injury perspective, why is this important?  Consider this case in point.  If this athlete pictured here was a DI soccer athlete being recruited under a scholarship, do you think she would be at risk for injury?  If you say yes, what would make you say that?  If you say no, do you think this would impact her performance?  Considering both of these factors, would you want to know these conditions exist if you are spending your limited scholarship dollars on this athlete?  According to Rugg et al in AJSM 2014, athletes who have had a previous knee injury or ACL injury prior to their DI career are at an 8 to 800 fold increase risk of injury.  But outside a reported previous injury, how would you ever know that the conditions exist?  Although there are methods to test these things, current methods limit us from measuring this clinically or in mass pre-participation physicals with any degree of sensitivity. 

What is sensitivity?  The sensitivity of the test in this case is the ability of the test to demonstrate minor improvements or decreases in performance with a high degree of reliability.  Although some tests use the eyeball to quantify, some of the more sophisticated used 2D technology to quantify.  But, even if we use 2D technology to quantify performance on single limb testing, the ability to do it with any high degree of sensitivity is limited.  For example, with most tests, if you do one rep, three reps or 10 reps, the score is based off the worst rep observed during the sequence.  This makes sense using this methodology since it is the largest magnitude of the deviation that puts you at highest risk.  We also know that if you scored every rep, then this would not be a very efficient test and impractical for adopting as a standard of practice for mass physicals.  

But is scoring off one rep really sensitive?  What if you compared two athletes, one that did 10 reps and with each rep he/she had a large degree of adduction in the frontal plane versus an athlete that did 10 reps and only had one rep with a large degree of adduction in the frontal plane.  Which one of the athletes would you say is at greater risk? Obviously, we would all say the one in the first scenario since it is the same degree but occurs multiple times.  But if you were scoring only the worst rep, then on paper they would appear to be at the same level of risk.  So, how truly helpful is that information?  How can we account for that?  There is a couple of different ways to accomplish this.  One is to perform multiple single limb tests and to score every rep.  In this example, the three single limb tests consists of 10 reps per limb on each of the tests or a total of 30 reps.  With a recently introduced 3D technology, we are now able to score every repetition performed during each for the tests based on the degree of adduction in the frontal plane present.  Previously, performance on these three tests would give you a cumulative score of 9 points on the right and 9 points on the left.  But, by performing in this fashion with this technology, you now have a score of 90 points for the right and 90 points for the left.  By doing it in this fashion, this allows you to see minor improvements in movement on as little as one rep. 

By performing three tests in sequence, we can also put the easiest test first and the harder test at the conclusion.  It would make sense, in this sequence that those that fall apart on the earlier test verses the later would be at higher risk.   In this example then, we have two ways of capturing risk.  One is with a more sensitive test and one is through where the athlete falls apart in the sequence of tests.  Collectively, both methods bring to light ways in which we can apply the current research with methods and technology which can provide us with a much clearer picture of risk.

As much as we have talked in this SL testing portion, several key things for everyone to understand.   First is that if we can prevent injuries, we preserve the future joint health and opportunities for our athletes.   For many young athletes, their only opportunity for a higher education and life opportunities is a college scholarship.  If we can prevent injuries, we give them a better opportunity to do that.  The additional benefit of this approach is the impact that it has on performance as well.  It does not take a biomechanist to look at the athlete pictured above to see potential opportunities for improvement in performance.  Movement like this that is noted above results in loss of kinetic energy and decreased power output.  This means decreased sprint speed and decreased vertical jump.  If we have the opportunity to improve their future opportunities and their future performance, why would we not?

We hope that you found this blog insightful and useful.  Next week we wrapping up this series with a discussion on gradients of gluteus medius weakness and how do we indentify.  As we stated previously, stay tuned and if you like what you see, SHARE THE PASSION!  It is the biggest compliment you can give.  Follow us on Twitter @ACL_prevention and tweet about it.  #ACLPlayItSafe and help us spread the passion.

Dr. Nessler is a practicing physical therapist with over 20 years sports medicine clinical experience and a nationally recognized expert in the area of athletic movement assessment.  He is the developer of an athletic biomechanical analysis, is an author of a college textbook on this subject  and has performed >5000 athletic movement assessments.  He serves as the National Director of Sports Medicine Innovation for Select Medical, is Chairman of Medical Services for the International Obstacle Racing Federation and associate editor of the International Journal of Athletic Therapy and Training.