Balance and Lower Extremity Control
Balance is physical equilibrium or the ability to maintain stability produced by even distribution of weight on each side of a vertical axis. In humans, there are three factors that influence balance. These are:
·
The Vestibular
System: complex mechanism in the inner ear that controls
balance by monitoring the position of your head.
·
The Visual
System: uses input from your eyes to detect changes in the
floor surface.
·
The Somatosensory/Proprioception
System: Uses sensory input from your lower extremities to give
your brain feedback about the body’s relationship to the floor.
Some authors argue that there is a fourth component that influences balance which is a psychological component: the fear of falling. For our purposes and for the athletic population, we will address only the three factors listed above. Of those factors, pathokinematics has the largest influence on the somatosensory system or proprioception. So prior to talking about the impact pathokinematics has on the somatosensory system or proprioception, we must first define proprioception.
Proprioception is the sense of the
relative position of neighboring parts of the body, joint position and the strength
of effort being employed during movement.
This complex sense is provided by multiple systems (Neuroscience,
2nd edition, by Purves et al. 2001) including the inner
ear (bony labyrinth) and sensory receptors in the joint
capsule, in the musculotendinous junction (golgi tendon organ) and within the
muscle (muscle spindle). Stimulation of
these systems contributes to our sense of awareness of where our body is in
space. Several factors that can
negatively impact this input are injury, pain and/or abnormal movements (bad
technique) performed over time. With
regard to this last factor, we need to remember that poor movement patterns
repeated over time result in repetitive stimulation of these systems in these
altered positions. This, in a sense, “teaches”
the fibers that this is the “correct movement or posture” when in fact, it is
not. The same is true with pathokinematics over time. The body becomes accustomed to moving in this way, and the athlete senses that this is normal movement---it “feels” right. Again, let’s use the example of the athlete above who squats with the obvious lateral shift. Because he has trained his body over the span of months to squat in this way (or he has allowed himself, knowingly or unknowingly, to squat in this way) his body perceives this as “normal.” When moved into a more anatomically correct movement pattern, he feels awkward, weak and perceives the positions and motions as abnormal. This is due in part to the proprioceptors in his lower extremity. They must be re-trained to sense this “new” position as correct relative to space.
So, let’s examine this concept in
more depth as it relates to performance by looking at proprioception or balance
in the core and hip (marked in red in the photograph). A decrease in proprioception and balance in
the core and hip can lead to many performance limitations, and we see this especially
in many of our female athletes. Such a
deficiency in proprioception can present itself in the form of an inability of
the athlete to disassociate lumbar spine motion from hip motion, as in the
example of lumbopelvic disassociation.
Also if one has weak hips, particularly in the stabilizing muscles of
the hip such as the gluteus medius and other smaller and/or deeper stabilizers,
(gluteus minimus, gemelli, obturators, tensor fasciae latae, quadratus femoris),
we might expect to see a reduction in the ability of the athlete to balance,
especially during single limb activities. In an unpublished 2009 study, a group of examiners assessed 3 different movement screens commonly used in sports medicine and implemented these during collegiate and high school physicals over the span of 3 years. Subjects consisted of 600 male and female athletes ranging in age of 15 years old to 20 years old. One of screens used during this study was the Star Excursion Balance Test. One of the key movements being assessed during this test by examiners was posterior medial movement (shown above). This motion requires a significant amount of proprioception in the hip as well as gluteus medius strength in order to stabilize the knee in a closed kinetic chain situation like this one. Male athletes performed favorably on this movement with 80% of subjects able to perform the test to within 10 cm of the contralateral limb. Female athletes performed less favorably, with less than 55% of subjects able to perform the test to within 10 cm of the contralateral limb. Most examiners noted that females would first lose control at the hip and fall into a trendelenburg (versus pronating at the foot first) which would be followed by loss of control at the knee which would lead to the knee moving into a valgus position.
One of the questions one might ask at this point is whether or not it is the pathokinematics that lead to significant reductions in balance and lower extremity control over time or is it the reductions in balance and lower extremity control that lead to pathokinematics? Again, it is the question of the egg before the chicken or the chicken before the egg. Although we don’t know the answer to this question, we do know is that both present together in a majority of cases and if we improve proprioception, then we also see a corresponding improvement in pathokinematics. And, of course improved balance, body control and movement all lead to athletic performance improvement and reduction in injuries.
Reaction Time
The last performance related area we would like to address that is directly affected by pathokinematics is reaction time. Before we discuss the impact of pathokinematics on reaction time, let’s review some basic concepts on reaction time. Reaction time, in the most simplistic terms, is a combination of:
1. Perception
time – time from which the athlete senses the need for movement (my opponent is
moving to the right) to the time the athlete chooses the appropriate response
(response selection – I need to cut to the left). This is often referred to as processing time
as it is the time that it takes for the person to sense a stimulus, the brain
to process it and then select the appropriate movement. This requires visual input, the processing of
that input in the higher centers of the brain, and then a selection of the
appropriate motor program (in the primary motor cortex). There are a lot of factors that impact
perception time or processing time[vii]. These include but are not limited to:
a.
Mental alertness
b.
Mental rehearsal
c.
Age
d.
Vision
e.
Distraction level
f.
Fatigue
2. Movement
time – once the response is selected, movement time is the time that it takes
the athlete to execute the required movement.
There are a lot of factors that impact movement time. These include but are not limited to:
a.
Age
b.
Gender
c.
Fatigue
d.
Exercise
e.
Stimulus drugs
f.
Illness
Understanding the components of reaction time and the factors which positively or negatively impact reaction time gives us a better understanding of how pathokinematics can play a role in limiting performance by increasing reaction time. For example, if an athlete demonstrates significant pathokinematics resulting in altered length tension relationships, decreased efficiency of movement, poor proprioception, and decreased endurance, then one can easily see how reaction time would be negatively impacted. This is especially true and more evident in later phases of the game when an athlete’s pathokinematics may become more pronounced and the efficiency of the system becomes compromised to an even greater degree due to fatigue and other contributing factors.
Reaction time, like all of the other sports performance fundamentals discussed in this chapter, including pain and pain prevention, efficiency, energy conservation, endurance, power, speed, flexibility, balance and lower extremity control, has a direct correlation to pathokinematics. In addition, it’s important to note that each of these performance considerations is affected by the others. This results in a powerful compounding effect when any one or more is present. In other words, when pathokinematics lead to a deficit in any one of these or any other sports performance area, all other areas are affected as well.
I hope you found this information valuable. As always, I appreciate all our followers and hope you find the information we provide useful in your practice with your athletes. If you do, please follow me on instragram @bjjpt_acl_guy and Twitter @acl_prevention. I also just launched a new website, www.drtrentnessler.com. My vision is to create a movement revolution in the world of ACL rehab. Check it out, hear more about my story and where we are headed. Train hard and stay well. #ViPerformAMI #ACLPlayItSafe
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 and ACL injury prevention. He is the founder | developer of the ViPerform AMI, ViPerform AMI RTPlay, the ACL Play It Safe Program, Run Safe Program and author of a college textbook on this subject. Trent has performed >5000 athletic movement assessments in the US and abroad. He serves as the National Director of Sports Medicine Innovation for Select Medical and movement consultant for numerous colleges and professional teams. Trent also a Brazilian Jiu Jitsu purple belt and complete BJJ/MMA junkie.
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