Article Overview: 757 words on assessing functional asymmetries using dual force plate methodology.
About 3 weeks ago I gave an hour presentation at a local ski shop to discuss my PhD research, which focused on functional neuromuscular assessments throughout the late phase rehabilitation to improve outcome for ACL injured elite ski racers.
Like most applied strength and conditioning research projects, this one evolved out of ongoing efforts to track and monitor my athletes. In addition to tracking training loads and athlete readiness using subjective questionnaires, I was using a dual force plate system to assess explosive strength, mechanical muscle power and jumping ability in my athletes.
As time went on, I started to see that the lower limb force asymmetry obtained during vertical jumping was sensitive to MSK functional status throughout the return to sport phase after an ACL injury.
This is not a new finding but I took a unique perspective as a strength coach and began looking at specific movement phases that we often address in our programming. Specifically, I broke the asymmetry in the countermovement jump down into the eccentric deceleration phase and the concentric phase, and looked at the early phase asymmetry in an unloaded and loaded squat jump along with the late phase asymmetry. More recently, I began evaluating the landing asymmetry as well. I coined the term kinetic impulse asymmetry index (KIAI) and published a paper on how I go about doing this in case you’re interested (Jordan et al., 2015. SJMSS).
The functional asymmetry assessment along with a few other specific neuromuscular diagnostic tests have now become integral to my approach for evaluating uninjured and ACL-reconstructed athletes alike. In fact, as a part of our monitoring system, we began evaluating functional asymmetry in many of our uninjured athletes and we are now finding the kinetic impulse asymmetry index in the eccentric deceleration phase to be predictive of lower body injury in previously uninjured athletes.
In terms of assessment time, the two tests take about 10 minutes to perform and are easily administered in a high performance weight room. You can also obtain a dual force plate system for around $2500-$3000. This is still expensive but it is far cheaper than the typical price tag of $15,000 / force plate. I’ll tell you, this is the best money I’ve spent in a long time but you’re talking to a strength coach that sticks to the basics.
I often get asked by strength coaches if it is adequate to simply look at vertical jump height or jump distance. The short answer is that it does provide some insight into functional asymmetry. However, using a dual force plate system and looking at the kinetic impulse asymmetry index allows me to obtain a much better picture of where the deficits lie and how I will program to fix them. Remember, that athletes can often shift their jumping strategy so that jump performance remains the same but in the case of the ACL-reconstructed athlete, deficits may still remain.
Your uninjured athletes will also find crafty ways of maintaining performance in the presence of an impending injury or fatigue. This is why how an athlete performs the movement is more important than the performance in the context of identifying athletes who may be around the corner from a injury.
Using this approach along with the information I obtain from my MSK assessment, I’m able to zero in on deficits and barriers that are limiting an athlete’s return to sport after an ACL injury.
I’m also able to evaluate when my programming is out of whack and when it has led an athlete into a state of maladaptation.
Together, having these metrics have really shaped how I program for the ACL-reconstructed athlete.
On that note, you can click the link below to get a PDF of the presentation I gave a few weeks ago. There is some background information on ACL injuries and I also provided some thoughts on how I program for ACL injury prevention.
By no means is this exhaustive but it gives an idea of the approach I take. I also recognize there is some amazing expertise out there so I would encourage you to read up from others if you are interested in how to manage this extremely challenging and multi-factorial injury.
I think the important take home message is that you never know where simple monitoring will get you as a strength coach. The key is to start evaluating what you think is important and then keeping an open mind to the possibilities.
As always, I look forward to comments and feedback so send them along.