The knee, like the foot, is a beautiful, well engineered piece of biological machinery.
And also like the foot, the knee is very easy to injure.
When a person is standing, their weight is pushing down through their entire leg, and the bones of the leg are supporting most of the force. The knee is in no danger in this position, and we’ll use this as our starting point.
The knee pain comes when we load the knee, do so improperly, and then end up placing far more stress on the knee than it can recover from.
Loading the Knee
In order to forcefully drive off the ground, an athlete must load the knee. Our goal, though, is to load the entire supportive structure of lower body, specifically the strong muscles of the posterior chain, rather than just the knee itself. The more load the glutes, hamstrings, and lower back take, the less load on the knee, and vice versa.
Forward Knee Shear
Shear force occurs at the knee when an athlete’s weight is far over their toes, and the knee is being forced to support that weight with little help from the strong muscles of the legs and back.
The exact biomechanical explanation of this force is beyond the scope of this article, but you can feel it yourself. We’ll examine two distinct, different loading positions and their effects on the knee – exaggerate them, and you’ll be able to feel the stress on your knee (or lack there of) yourself.
The Typical Untrained Person
The typical 21st century human being is quad dominant – there’s a proportional strength imbalance between the quads and the hamstrings, and the quads are proportionally stronger. This is primarily due to sitting, during which the quadriceps is contracted, while the hamstring is elongated.
The result is that most recreational athletes attempt to use their stronger quads, rather than their weaker hamstrings, to generate ground force when they have to push off. This takes the form of bending the knees forward, then using the quadriceps to explosively extend them.
The position shown here is the beginning of that process – the forward knee bend. When in this position, you’ll feel stress on the front of your knee. The athlete’s center of mass isn’t balanced over the foot, and, due to that, more force is on the patella tendon and accompanying knee structure, and less force is on the hamstrings and glutes.
The result is typically the somewhat inappropriately named “overuse” injury. More stress is placed on the knee during each training session than it can recover from before the next, and due to that, tissue damage accumulates. The cause of the injury here is not so much overuse as it is misuse. By preparing to explode in a different way, we can significantly decrease the stress on the knee during each session, down to a point where it can easily recover before the next. The term “overuse” is misleading, because the problem isn’t that we’re using a tissue too much, it’s that we’re using it wrong.
The Proper Athletic Position
In order to protect the knee during explosive athletic movement, we want to load the strong muscles of the posterior chain – the hamstrings, glutes, and lower back. Loading these muscles reduces the load on the knee.
Effective athletes are not quad dominant, but instead have well trained posterior chain strength as well. When an athlete like this attempts to generate ground force, they sit back, rather than just bend their knees forward. When they explode off the ground, though the quadriceps certainly do participate, the hamstrings and glutes also play a large roll:
- When the hamstrings contract, the shin is pulled towards the femur – think of it as pulling the ground behind you, thereby driving you forward.
- The glutes fire to further straighten the hip-torso angle, driving the athlete even further forward.
This extra muscle recruitment leads to position #2 being more balanced and more explosive than position #1.
And, most importantly, it’s safer.
In position #2, the start of a biomechanically friendly explosive motion, the posterior chain is loaded far more, and the knee, far less. Adopt the two positions back to back, and you’ll be able to feel the difference.
- In #1, you’ll feel the load at the front of your knees.
- In #2, you’ll feel the load on your glutes and hamstrings.
Note that position #2 still possesses the triple flexion necessary for athletic movement – the ankle, knee, and hips are all flexed. The knee is still being loaded, and used to drive off the ground, it’s just being loaded less due to the greater hip flexion, which moves stress onto the upper leg muscles instead.
Without a solid proprioceptive understanding of how to properly balance using the muscles of the posterior chain (or natural, athletic talent), you’re likely putting this shear force on your knee unintentionally.
Due to the quad dominance discussed above, most recreational athletes will not move correctly without training. Instead, they’ll use position #1, and variations of it, all around the court, neglecting the critical hip flexion that moves stress off of the knees, and onto the strong, blood-flow rich, quick recovering muscles of the thighs.
Strength training provides two critical benefits that protect the knee (as well as the rest of your connective tissue).
1. Strength (duh)
The stronger your muscles, the more load they can take, and the less load your tendons and ligaments needs to support.
Often, your brain has a great intuitive understanding of how to do something strenuous, but that technique starts to break down under fatigue. As the muscles fatigue, your brain subconsciously alters your technique to move some of the load from the fatiguing muscles to the connective tissue (so that the movement still succeeds). The stronger you are, the less you fatigue, and the less your brain feels the need to do this.
Also, competitively, strength provides significant benefit as well, granting you the ability to hit harder without increasing your level of effort.
2. Proprioceptive Awareness
The underrated, but perhaps even more important benefit of strength training is that it teaches you to feel the muscles you’re supposed to be loading.
Most untrained athletes cannot feel a contraction in their hamstrings. They don’t understand how to flex their glutes, and them to straighten their lower back is like asking them to do advanced calculus.
Adult males get injured every day carrying tiny amounts of weight improperly. We’re talking about 40-50lb (20kg) loads here, and people are throwing out their backs. The problem isn’t strength, but rather the lack of athletic understanding of how to recruit the lifting muscles properly.
Strength training trains not only the muscles, but the nervous system. It teaches an athlete to use and load these muscles, and allows them to move in a safer, faster, more explosive manner.