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==Excessive stress==
[[File:Knee Stress.png|right|thumb|300px|The stress on the knee can be a single heavy overload, or it can be a lighter stress applied many times. The green area is the area of safe functioning, and its upper limit is the blue line. The yellow area is where damage will occur to the knee, and the red area is where the damage becomes catastrophic. Note the gray area in the lower left where inactivity also causes knee damage.]]
The kneecap is an amazing structure, but like all body parts, it has limits in the load it can take. This [[Overload|overload ]] may be due to a number of factors.
* '''Low [[Cadence]]'''. Having a low [[Cadence]] results in more vertical movement, and thus higher landing forces.
* '''Highly cushioned shoes'''. Counterintuitively, the more cushioned your shoes are, the greater the loading force on your knees<ref name="ref9"/><ref name="ref10"/>.
==Maltracking/malalignment==
[[File:Kneecap.png|right|thumb|200px|A cross section of the kneecap and femor (thigh bone) showing how the kneecap fits in a groove.]] The kneecap moves in a groove in the thigh bone (femur), and it is widely believed<ref name="KneeRW"/> that if the kneecap does not track in this grove it will rub on the sides and cause knee pain. While this belief is not well supported by the evidence<ref name="patellaralignment"/>, the following underlying problems may still cause knee pain through other mechanisms.
* '''Weak [[VMO]].''' The alignment of the kneecap is not related to the overall strength of the quads, but rather an imbalance of the muscles that make up the quads. The quads consist of four muscles, and a relative weakness in a subdivision of one [[Muscle|muscle]], the Vastus Medialis Obliquus or [[VMO]], has been linked to kneecap alignment<ref name="KneeLinTomo"/> and knee pain<ref name="KneeVMOAtrophy"/>.
* '''[[VMO]] Delay.''' There is some evidence that people suffering from knee pain (PFPS) have a delay in the activation of the [[VMO]] compared with the main quad muscles<ref name="KneeVMODelay"/><ref name="KneeVMODelayMeta"/>, which reduced the lateral force by 25%<ref name="KneeVMODelayPower"/>. Detecting this timing difference is normally requires sophisticated clinical equipment, but there is some suggestion that the delay can be felt directly by placing fingers on the belly of the [[VMO]] and the VL<ref name="PFClinical"/>.
* '''Weak Hips.''' A weakness in the hip muscles has been linked to knee pain<ref name="KneeHip"/>. Weak hip muscles result in the leg rotating so the foot points towards the midline of the body (internal rotation), so when the leg bends extra stress is placed on the knee.
* '''Running form'''. Good running form has many benefits, but changing form tends to be difficult and can easily result in new injuries if done [[Too Much Too Soon|too quickly]]. I would recommend looking at [http://www.chirunning.com/ Chi Running] or the [http://posetech.com/ Pose Method], though personally I don't agree with their approach of pure forefoot running (your heal not touching the ground) and prefer a midfoot strike.
* '''Check for ITBS'''. ITBS produces pain to the outside of the knee, rather than under the kneecap. It's possible to have both kneecap pain and ITBS, so read [[Iliotibial band syndrome]].
* '''[[Taping]]'''. The use of tape has been shown to be effective at reducing knee pain<ref name="KneeLongTerm"/><ref name="KneeTapeBrock"/><ref name="KneeTapeMcConnel"/>, by over 90% in one study<ref name="KneeTapeEMG"/>. One study used tape to pull the knee cap towards the midline of the body<ref name="KneeTapeMedial"/>, others relied on evaluation to define the correct direction<ref name="KneeTapeBrock"/>. The most common method mentioned is 'McConnell taping'<ref name="KneeTapeMcConnel"/><ref name="KneeTapeBrock"/>, and instructions can be found by Googling 'McConnell taping'.
* '''[[VMO]] Re-timing.''' If the firing of your [[VMO]] is delayed, it may be possible to correct this. Ideally, the correction uses a combination of training and down in EMG biofeedback device. These devices can be quite expensive, but it may be possible to detect the difference in timing between the [[VMO]] and the VL using your fingertips<ref name="PFClinical"/>. The goal should be retraining control rather than strengthening, with 200 repetitions per day (20x 10 reps) being required<ref name="PFClinical"/>. (I did find instructions for a [http://www.instructables.com/id/EMG-Biofeedback/ DIY EMG].)In addition, it may be possible to mitigate the [[VMO]] timing problem with taping<ref name="KneeLongTerm"/><ref name="KneeTapeMcConnel"/> (see below).
* '''[[Joint Supplements]]'''. The joint supplements glucosamine and chondroitin provide marginal benefit, but are considered safe, so they may be worth considering if you can justify the expense. Other supplements such as [[Omega 3 ]] oils and Vitamin C/E may be worth considering. For more details, see [[Joint Supplements]].
* '''Knee brace/sleeve/strap'''. A knee sleeve is a simple elastic wrap that goes around the knee, sometimes with a hole to avoid pressure on the kneecap. A knee brace usually provides hard plastic support in addition to the sleeve. The evidence supporting knee braces is limited<ref name="KneeBracingBrouwer2005"/><ref name="KneeBracing"/>, with many of the studies having poor quality<ref name="KneeBracing"/>. One reasonable study showed improvement with a brace<ref name="KneeBracingPowers2004"/>, but better quality studies showed no benefit<ref name="KneeBracingMiller1997"/><ref name="KneeBracingLun2005"/><ref name="KneeBracingHunder2011"/>. There are even fewer studies for knee sleeves<ref name="KneeSleeveBea09"/>. The only study on knee straps showed no benefit<ref name="KneeBracingMiller1997"/>. I found no indications of the long term effects or safety of knee braces, sleeves or straps. Based on the available evidence, the use of these approaches does not seem justified. I found no studies that looked at [[A review of graduated compression wear|Compression Tights]] but they may act in a similar way to a knee sleeve and they have [[Why compression clothes|other benefits]].
=Anti-treatments=