The knee is a hinge joint. It’s designed to flex and extend with the thigh bone (femor) and the shin bone (tibia) in the same plane. A healthy joint can tolerate a certain amount of torquing or poor distribution of the body’s weight on occasion, but repetitive movements of that nature and /or severe uncontrolled movements can lead to permanent damage. Healthy knees are stable when straight (extended), but become slack when bent (flexed.)
Knee damage among martial artists is all too common, and the causes may or may not be self-evident. Martial artists whose practice includes kicks that require pivoting on a support leg or which involve landing leaping maneuvers may be intimately aware of the risks. However, the first martial art that I ever trained in had no twisting / pivoting kicks and few leaps (that were rarely practiced), but knee injuries were epidemic. The culprit in this case was low postures which required the thigh to be turned out (externally rotated and abducted) with the knee deeply flexed.
Well, I should say those postures were the culprit in conjunction with lack of flexibility and/or strength in all the right places. This isn’t to say that the individuals who developed knee problems weren’t strong or flexible, but the areas that needed work weren’t necessarily the big muscle groups that leap to mind when workout time comes around. Emphasis on the big muscle groups (quadriceps and hamstrings) with neglect of the muscles involved with adduction, abduction, external rotation, internal rotation and stabilization can create some problems. If you’re a runner or a weightlifter (with good form) you may be able to get away with such a stretching and strengthening emphasis. [Note: I’m not advocating such an approach for anyone. What I’m saying is that if your knee is only worked with the knee straight below the hip and pointed forward in a hinge fashion, your risks are not the same as someone who works with a flexed knee with the thigh turned out. The likely injuries are different.]
To do a posture like the one above, one needs the flexibility to keep the knee wide enough so that it points the same direction as the toes. The joint shouldn’t be wrenched or torqued with load on it. The four ligaments (Anterior Cruciate Ligament [ACL], Posterior Cruciate Ligament [PCL], Medial Collateral Ligament [MCL], and the Lateral Collateral Ligament [LCL]) and the surrounding musculature keep the joint snug during movements. And, as mentioned earlier, when the knee is deeply flexed it’s more sloppy than when extended.
-Increase flexibility in the muscles that internally rotate and adduct the thigh: When one goes into a wide-legged stance, one’s thigh is pulled away from the body’s center-line (abducted) and the thigh externally rotates. If the muscles that act in the opposite direction (pulling the thigh back on center and rolling the thigh inward) are too tight to allow the knee to move into proper position, then the load of the body weight will be going into the ground through a kinked joint. Furthermore, one will end up torquing through the joint as one moves. Below are a few hip openers that will help one achieve the requisite range of motion.
-Strengthen the muscles that stabilize the knee-joint. One begins this process with the usual suspects of leg exercise. One just needs to focus intently upon alignment. Here are a few of the exercises you may already be doing.
As one needs more challenge, one can achieve it in the usual ways (single-legged, unstable surface, add weight, or combinations thereof.) Below are a couple of variations that combine single-limbed work with an unstable surface.
-Save static stretching for after the joint has warmed up. It used to be common to begin a workout with static stretching. While few do this anymore, it’s a practice that needs to be replaced. Stretch warm.
-Don’t neglect the opposing muscle groups: When I said that one needs to increase flexibility in adductors and internal rotators, that doesn’t mean to ignore the opposing muscles. Nothing good comes of stretching or strengthening in an unbalanced fashion. Your musculature works as a team with agonists, antagonists, and stabilizers all working in conjunction to produce effective movement.
-Don’t go overboard with stretching: If your aim is to be a contortionist, then by all means go ahead. However, highly flexible martial artists need to be concerned about joint laxity. Laxity is when the joint gets so loose that it’s vulnerable to popping out-of-place. A martial artist needs a balanced style of fitness. Extreme flexibility results in weakness and lack of joint robustness, just like extreme strength training produces a body that lacks range of motion and stamina.
Most importantly, don’t ignore pain when it’s still at the minor twinge point. If you have knee pain you’re doing something that joint doesn’t like. One should reevaluate your movement and, if necessary, considering stepping back from your current practice to work on capacity building exercises.