Alright, What's really going on here? ACL's are popping all across the nation.
The ACL is the Anterior Cruciate Ligament and what it does is keep the femur (thigh bone) from sliding opposite of the tibia (larger lower leg bone). This is the reason you see most injuries to this area during deceleration, like landing after jumping or slowing down when sprinting. These are the most common factors I see leading to this injury epidemic. (for now I'm not going to differentiate between male and females, but there is a definite difference and is obvious in the rate of injuries in each.)
1) Weak or inhibited glutes, either way its bad. If the hip flexors are too tight, they will pull the hips into anterior pelvic tilt and inhibit the glutes from firing. The glutes are quite possibly the most important muscle in the whole body, if they are not firing you've got some MAJOR problems.
This is most often the most missed and under appreciated area I've had to deal with coaches on. If this muscle is weak or inhibited you are asking for all kinds of injuries and a huge decrease in potential for performance.
Following the striations gives you a good clue as to which way the muscle pulls.
2) To go along with #1 is a weak posterior chain. I already briefly hit the glutes, so lets go to the hamstrings. Your hamstrings perform an action on the knee very similar to the ACL. It is also a major stabilizer for the knee.
3) Bracing. Somethings gotta give and if its not where the brace is it'll happen somewhere else. Ever wonder why all those basketball players where pateller wraps?
How much dorsiflexion do you think this athlete will be able to get with this wrap??
If you are wearing an ankle brace, taping your ankles, or wearing high top shoes you are decreasing the mobility and range of motion of the ankle. Now, like I said before, something has to give. If the ankle is not able to move enough, then the knee or the foot is going to have to make up for that deficiency. So the reason many basketball players need to wear the patellar wraps is because their patella has had to take over for the lack of mobility of the ankle, especially when landing or absorbing force.
4) Footwear. Basketball (in the case of high tops) shoes are heavy, decrease mobility of the ankle joint to extremes and are usually accompanied by athletes that wear nothing but all year long. Same problem as above. Something is going to give and this is why many times you see basketball players with dropped arches or even flat feet and tons of ankle and knee problems.
The feet are not supported in a fashion that promotes health or performance. Most athletes would be better going barefoot everywhere.
5) Quad dominance. I forgot to mention this before. I thought it would be self explanatory but to make sure everyone knows, quad dominance is a huge problem as well. If you move everywhere with your quads you will not perform well and will dramatically increase your risk of injury. Not like the quads are not a great muscle but they can be a problem when the dominate the post chain. So, pretty much I'm saying that do nothing but TKE's to work on the VMO is pretty pointless, actually is pretty dumb, but I'll get more into that next time.
6) Programming. The last, most preventative, and sad to say but quite possibly the most common one I see is absolutely terrible programming. Now this is a whole topic in itself. I'm gonna save it for tomorrow.