A Bit Of Science
During a squat, researchers observed increased neuromuscular activity of the adductors (the muscles on the inside of the thighs), the tibialis anterior (shin muscles) and gastrocnemius (one of the big calf muscles) in subjects with MKD. Conceptually, the increased activity in these muscles makes them stiff, resulting in limited dorsiflexion. This in turn leads to increased tibial internal rotation, talar adduction and calcaneal eversion. (These are discussed in more detail in this article.)
Note the lack of control in the knee. There is significant deviation of the knee medially as the client descends into the lunge.
Why You Should Care
Injury Potential
Although most commonly around the ACL (review that here), the three points above are all potential areas of injury, particularly when high forces are involved. Tibial internal rotation describes rotation of the bigger of the 2 shin bones. Grab a skeleton and you will see how little rotation you can coax out of it without popping it out of alignment. It is such a minuscule amount that the articulation of the bones forming the knee joint is very often describes simply as flexion and extension. So imagine a wringing movement- in Valgus, the femur (thigh bone) falls inward, and the tibia rotates outward. Now imagine that happening at speed, with a 100+ pounds. That's what the knee goes through when players compete for an aerial ball and return to the ground.
Power
Joint centration is an important concept. The body has an incredible capacity to create and distribute force, and the higher the force, the greater the demand for proper alignment. Ask anybody to jump as high as they can and the first thing you see is that they get 'shorter.' By going down, we tap into the power of the hips. The movement itself loads the muscles (potentiation) and the elastic energy thus created allows the explosive spring that gives us the vertical jump. To a degree, the lower you go, the greater the amount of energy stored in the muscles, and the greater the height. This is because there is an optimum level of muscle contraction for maximal force production. Either side of that point, whatever you are doing, you're leaving some of your potential on the table.
Not only can an athlete who displays MKD not reach that optimal range for force production, more often than not, the forward movement of the knees pulls the athlete forward. Introducing load to this type of movement pattern would be disastrous. And trust me, you want to add load.
According to a classic paper by Stolen, et al, (2005), "Physiology of Soccer" players sprint approximately every 75 to 90 seconds, with each sprint lasting 2-4 seconds. That's equivalent to about 40 meters or less. This means that when it comes to ASSESSMENT, knowing how fast you can dash 40 meters is nice but knowing if you can do it repeatedly is even better. The 40m dash provides valuable information about the athlete's power, acceleration, reaction time and anaerobic system. For it to be even more meaningful for coaches and players alike, it must be repeated. Several trials will give an indication of the athlete's capacity to sustain those qualities. How well do they recover? How many sprints can they run before there is a significant decrease in performance? These questions and others like them become a wellspring of data coaches can use to decide who is going to struggle if they are trying to employ strategies that rely on the hard graft of wing back; who would be most impactful as a substitute; when to make that substitution. Of course this too can be used as you observe the opposition- see a player struggling to recover? Play in that area. A lot. Chances are, you'll find plenty of success there. But what do repeated sprints have to do with knee Valgus?
In THIS study, researchers wanted to find out how lower body power variables would impact repeated sprint performance. Nineteen players were tested through several sessions. The first of these included the countermovement jump (CMJL) and the progressive full squat (FSL), both with external loads. Power in the CMJL and FSL was measured with each load that was lifted. In the second session, the repeated sprint index or RSI was calculated. The players had to sprint a timed 40m distance. They were allowed as much as 2 minutes rest before going again and continued until a 3% decrement in performance was noted. The results suggested repeated sprint performance was moderately correlated with power relative to body mass in the CMJ and Full squat demonstrated by differences in the RSI (9.1 ± 4.2 vs. 6.5 ± 1.6) and 10 m sprint time (p ± 0.01). That means the most powerful players ran up to 13 times before that 3% decrement was noted compared to just 7 in their weaker counterparts. Moreover, the more powerful players were 0.01 seconds faster in getting to the 10m.
The correlation between the performances in the repeated sprint test and the CMJ and squat are clear. Both the squat and countermovement jump are performed poorly with increased risk in an athlete with knee valgus. So why should you care? Speed. Power. Sprint ability. Because, unless your players are excellent compensators, this simple deviation in knee tracking can tell you who is likely to be added risk for injury; and, based on the study discussed here, who is likely to prove a weaker player during the course of a match. It is important to note that as a bio-marker, medial knee collapse is a predictor, not a given. On the other hand, strength, when all else is equal, pretty much guarantees who will be the better performer.
Brent Brookbush has a wonderful review about MKD as well as exercises you can do to address so you can get back to training hard and winning game.
Remember, injury prevention and performance enhancement are rooted in the same work.
Related Articles:
Reducing ACL Injury Risk
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