Last week we concluded with a
study by Howell et al that
looked at the impact that concussion has on gait balance deficits in youth
athletics. We concluded with the
question, what does this mean? First and
foremost this demonstrates that the impact of a concussion has on a young
athlete can last for several months. We
need to manage these better! This is
critical since most are returned to sport way too early and, from what this study
indicates, you may be putting them at greater risk for additional
injuries. Why? The ability of an athlete to control COM medial/lateral
displacement is critical. Not only is this an indication of control of
balance, but it also has a huge impact on injury risk and performance. We know from the research that if you have
bad balance, that you are at increased risk for non-contact ankle sprains. But looking further at injury risk, the
larger the displacement that occurs medial to lateral, the greater the load is
to the medial and lateral structures of the body (spine, hip, knee and ankle). This means that tissues and joints are being
loaded in a suboptimal way and often will create shearing stresses to the
articular cartilage. In this diagram, we
can see how this motion would stress the SI joint in the back, the hip
joint/labrum of the hip, the meniscus and ankle. In most cases, the athlete will also be
unable to control the knee which will result in valgus and internal rotation
stress at the knee in combination with the lateral displacement. It is this suboptimal loading and shearing stresses
that cause tissue breakdown and injury.
Looking at performance, think
about your athlete. If you had an
athlete that was running and had an excessive amount of medial to lateral
movement of their upper body during a run, would you expect them to have
optimal performance? What we do know is the
larger the magnitude of medial to lateral displacement means loss of kinetic
energy and decreased force production.
This medial and lateral displacement also results in decreased
efficiency of movement. This loss of maximal
force production, loss of kinetic energy transfer across the system and
decreased efficiency of movement will result in decreased power output and
decreased endurance over time.
Keep in mind that this study looked at athletes “walking”. So, the question becomes does this get worse
with running and what does single limb performance look like? Well first look at running. We know for a
fact that what we see in walking gait will be magnified when observed in
running due to the increased force demands.
So, if you are seeing this in walking, you can be assured that this will
be even worse in running gait.
But what about single limb
performance. Well, that is where we get
back to the previous study I mentioned that is ongoing. Ironically, they are seeing very similar
results with the post concussed athlete.
Not only are they seeing a much higher percentage of non-contact lower
kinetic chain injuries being reported post concussion, they are also seeing
dramatic changes in single limb performance.
Specifically, when concussed athletes’ single limb performance is compared
to controls, you see a significant difference in ability to control medial/lateral
displacement of the lower limb (adduction toward midline) in athletes with a
concussion history. Knowing that single
limb performance has a better predictive value for what performance will be
like in sport and that single limb performance has a better predictive value
for non-contact ACL injury risk, then what we are seeing is an increased risk
for non-contact ACL injuries post concussion.
Concussion and ACL risk. Now that is new. But only the beginning of what we can and
will learn if we use technology to its fullest capability. Because, through all the assessments in sports
and military, there are some common themes.
Whether you label it COM medial to lateral displacement, lateral trunk
lean or retro-trendelenbury (all which mean essentially the same), the ability
to control the core is essential to prevent injuries to the upper and lower
extremity. Upper extremity? Yes, upper extremity.
To examine this point, let’s look at a recent paper from the March
2015 issue of the American Journal of
Sports Medicine by Solomito et al. In this study, the authors looked at the
impact of lateral trunk lean on ball velocity and upper extremity joint
moments.
Methods: 99 Division I and Division III pitchers underwent a pitching
analysis using 3 dimensional motion analysis techniques and 12 camera vicon motion
system. Each player was assessed for contralateral
trunk lean, ball velocity as well as elbow varus and glenohumeral internal
rotation moments.
Results: What the study found was that the greatest magnitude of lateral
trunk lean occurred around the time of the peak elbow varus moment. The results also indicate for every 10°
increase in contralateral trunk lean, there was a corresponding increase of .5
m/s in ball velocity. The results also
showed that for every 10° increase in contralateral lean, there was a
corresponding elbow varus moment of 3.7 Nm and a glenohumeral internal rotation
moment increase of 2.5 Nm.
Unfortunately what some will
take away from this is that to increase ball velocity, we should instruct in
contralateral trunk lean. But that could
be the furthest thing from the truth.
Contralateral trunk lean is a compensatory strategy for poor mechanics
and poor throwing velocity. The lateral
trunk lean is a way to compensate to increase the velocity and maximize
velocity on already bad throwing mechanics.
Because one thing that is clear from this study is that pitchers who
throw with contralateral trunk lean have a limited athletic career ahead of
them. With the increased varus moment at
the elbow and the increased internal rotation moment, this means that, if
continued, this will eventually lead to a ulnar collateral ligament tear (Tommy
John), labral tear or rotator cuff tear.
If you look further in the results section of this study what you find
is that the Division I pitchers had less contralateral trunk lean when compared
to the Division III athletes and an overall higher pitching velocity than the
Division III athletes.
In looking at that, it makes
sense that the Division I athlete would have better throwing mechanics and
better velocity and hence why they are Division I athletes. One thing that comes abundantly apparent when
assessing Division I and III athletes is that you see a signficant difference
in skill acquisition and athleticism between these two levels of athletes. That considered, it makes sense they would
have better throwing mechanics and increased throwing velocity.
One thing that movement
analysis has taught us is that you can see this contralateral trunk lean in
pitch but also in single limb performance.
So whether you call it retrotrendelenburg or contralateral trunk lean,
it has an impact on upper extremity injury risk as well as lower extremity
injury risk. 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. #MovingToChangeMovement
and help us spread the passion.
Trent Nessler, PT, MPT, DPT: Physical Therapist | Author | Educator |Innovator in Movement
Science and Technology. Dr. Nessler is a physical therapist and owner
of Athletic Therapy Services. He serves as a practicing clinician
and movement change consultant for practices and organizations looking to develop
injury prevention initiatives and strategies.
He has been researching and developing movement assessments and
technologies for >10 years is the author of the textbook Dynamic
Movement Assessment: Enhance Performance and Prevent Injury, and
associate editor for International Journal of Athletic Therapy &
Training. You can contact him
directly at drtrent.nessler@gmail.com
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