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From Fellrnr.com, Running tips
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There are a number of possible root causes of knee pain.
==Excessive stress==
* '''Low [[Cadence]]'''. Having a low [[Cadence]] results in more vertical movement, and thus higher landing forces.
* '''Obesity'''. Obviously being overweight puts more stress on the knees and is linked to knee pain<ref name="KneeObesity"/>.
* '''Bad [[Running Form]]'''. Problems with [[Running Form]] can increase the landing forces and cause injury.
** '''Overstriding'''. [[Overstriding]] is''' '''landing with the foot ahead of the hip, can increase the landing forces and cause injury<ref name="KneeOverstride"/>.
** '''Heel strike. '''Landing with the weight on the heel of the foot creates a greater peak force than landing so the weight is taken by the midfoot or forefoot<ref name="KneeForefoot"/>. See [[Foot Strike]] for more details.<br style="clear: both" />
* '''Highly cushioned shoes'''. Counterintuitively, the more cushioned your shoes are, the greater the loading force on your knees<ref name="ref9"/><ref name="ref10"/>.
* '''Motion control shoes'''. There is evidence that motion control shoes cause more pain for all runners, regardless of their arch height<ref name="RyanValiant2010"/>.
[[File:Knee Stress.png|none|thumb|400px|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.]]
==Inactivity==
The human body needs activity to remain healthy, and the knee is a prime example of this. Animal studies have shown than complete immobilization of the knee can result in a 50% reduction in the cartilage thickness within weeks<ref name="KneeInactivity"/>. Thankfully this damage appears to be reversible.<br style="clear: both" />
It is common for people with knee pain to have weak quads<ref name="PFClinical"/>. However, I have found no research to suggest that weak quads are a cause of knee pain, a rather than a result of knee pain. I believe that it is more reasonable to conclude that knee pain results in less exercise as the patient avoids activities that cause pain, and thus the quads become weaker through inactivity.
==Maltracking/malalignment==
* '''[[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.
* '''[[Q Angle]]'''. The thigh bone and lower leg are not in a straight line, but form an angle at the knee called the '[[Q Angle]]'. A large [[Q Angle]] is often thought to cause or contribute to knee pain, but a high [[Q Angle]] was only seen in 6% of knee pain (PFPS) cases<ref name="RunningInjuries"/> and a high Q angle is not associated with biomechanical knee stress<ref name="KneeQAngle"/>.
* '''Over Pronation'''. Pronation is the natural movement of the foot where the arch flattens to absorb landing forces. If the foot pronates too much, the foot will lean towards the midline of the body and the lower leg and knee will follow this motion, moving towards the midline. Like weak hips, the movement of the knee towards the midline creates extra stress on the knee.
[[File:Kneecap.png|none|thumb|200px|A cross section of the kneecap and femor (thigh bone) showing how the kneecap fits in a groove.]]
==Arthritis==
Arthritis is an inflammation of the joints and can affect the knee. There are various types of arthritis, and diagnosis requires X-Ray, testing the fluid around the joint or inserting a viewing scope into the joint. Arthritis is outside of the scope of this article.
* '''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=
<ref name="KneeBracing">Patellar taping and bracing for the treatment of chronic knee pain: A systematic review and meta-analysis - Warden - 2007 - Arthritis Care & Research - Wiley Online Library http://onlinelibrary.wiley.com/doi/10.1002/art.23242/full </ref>
<ref name="KneeRunnersKnee">Runner's Knee (Patellofemoral Pain) - OrthoInfo - AAOS http://orthoinfo.aaos.org/topic.cfm?topic=a00382 </ref>
<ref name="RyanValiant2010">M. B. Ryan, G. A. Valiant, K. McDonald, J. E. Taunton, The effect of three different levels of footwear stability on pain outcomes in women runners: a randomised control trial, British Journal of Sports Medicine, volume 45, issue 9, 2010, pages 715–721, ISSN [http://www.worldcat.org/issn/0306-3674 0306-3674], doi [http://dx.doi.org/10.1136/bjsm.2009.069849 10.1136/bjsm.2009.069849]</ref>
</references>
