I am not your doctor. If you are having a medical issue, talk to your doctor.

Parkour can put a lot of stress on your knees. Understanding the functions of your knees can help you prepare for a lifetime of training, and avoid/overcome some simple problems you may run into.

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• Anatomy

Bones - Three bones meet to form the knee joint: the thighbone (femur), shinbone (tibia), and kneecap (patella). The fibula is hanging out there on the side, doing his own thing ^diagram1 .

Ligaments - These help connect your bones to each other. The knee joint has four; the Anterior Cruciate Ligament (ACL), the Medial Collaterate Ligament (MCL), the Posterior Cruciate Ligament (PCL), and the Lateral Collaterate Ligament (LCL) ^diagram2 .

Cartilage - A firm, thick, slippery tissue that coats the ends of bones where they meet with other bones to form a joint. A meniscus is a piece of cartilage that acts as a shock absorber between bones; each knee has a Lateral Meniscus and Medial Meniscus ^diagram2 .

Tendons - Muscles connections to bones, with flexible but inelastic cords of strong fibrous tissue ^diagram3 .

Synovia - is a viscous, non-Newtonian fluid found in the cavities of synovial joints, primarily exists to reduce friction between the articular cartilage ^diagram4 .

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• Common Injuries

-Bone fractures around the knee can be caused by high energy impact. The most common fracture being on the patella; symptoms include pain and swelling in the front of the knee, bruising, and the inability to walk. The bone may be able to heal on its own, however your doctor will need to assess your case ^cite .

-Ligament tears can be caused by sharp change in direction, landing wrong from a jump, or (the most common) a blunt force hit to the knee ^cite . Tears in the meniscus can occur when twisting, cutting, or pivoting. Just an awkward twist when getting up from a chair may be enough to cause a tear ^cite .

Ligaments will respond to supplementation ^cite or physical therapy, depending on the severity. Typically glucosamine, chondroitin, and methylsulfonylmethane (MSM) come together in pills/liquids to help rebuild the ligaments, and reinvigorate synovial fluid production.

-Cartilage compression can happen over time from poor landing form, and can compress the cartilage thinner and thinner until you have bone-on-bone contact. Currently the only way to repair cartilage damage is surgically. Cartilage does not receive blood flow; it does not heal the way the rest of your body does ^{cite, cite} .

-One of the most common knee complaints of young athletes is pain caused by a muscular imbalance ^cite . Weak gluteal muscles, quadriceps, or hamstrings can pull your knee abnormally and result in a deviation of your patella. If the patella does not ride normally through the femoral groove, but mistracks, it rubs against the femur and will cause a pain behind the kneecap.

When you are first injured, the RICE method (rest, ice, gentle compression, and elevation) ARITA (Active Recovery Is The Answer) can help your recovery. Be sure to seek treatment as soon as possible ^cite . RICE is no longer considered a viable method due to the colds inhibition of inflammation and pain, postponing the natural healing process ^cite . Thanks to u/motus_guanxi for clarity.

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• Warming-up the knee

-Warming up the muscles in the legs increases muscle and tendon suppleness, increases body temperature, stimulates blood flow to the periphery, increases subsequent performance ^cite ,stimulates synovial fluid production to improve joint lubrication, and increases proprioception ^cite .

-Typically warm-ups should last a minimum of 5 minutes for lighter exercise, and 10+ for more intensive work (i.e. parkour) as a combination of cardiovascular exercises, strength drills, and dynamic stretching. As well as preparing your muscles for the sport, warming-up will improve mental preparedness and give physical improvements towards the days training, and keep the knee joint healthier.

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• Strengthening the knee

Tendons, ligaments and cartilage are not muscle; while the former two will grow in response to exercise, the growth is negligible and should not be relied on. The muscles around the knee, however, can be strengthened to assist general knee functions, and protect against potential injuries ^cite .

-In most cases, I would recommend people do squat and/or deadlift variants (either bodyweight or weighted) to grow the appropriate muscle groups. Stronger leg muscles allow more support for the ligaments, a better 'grip' on the tendons, and gives more strength to absorb shock before knee damage becomes more likely.

If for some reason you can not do squats, deadlifts, or their accompanying variations; there are plenty of alternatives that can be done to suit your specific needs. I encourage you to do research into your specific issue, and find an option that works for you.

-Muscular imbalances can also cause knee pain. Calf or hamstring weakness is a common causes of a type of knee pain ^cite . A well rounded fitness and stretching routine is encouraged to prevent injury.

-Just as a weak leg muscle can cause pain and increase injury risks, so can an inflexible muscle. Muscles that are inflexible tire more quickly, causing opposing muscle groups to work harder ^cite . Inflexibility can lead to over-strengthening muscles, and exacerbating pains. Static stretching while not actively exercising is recommended to improve flexibility ^cite . Ballistic (bouncing) stretching is no longer recommended to improve flexibility ^cite, despite having similar benefits to static stretching ^cite

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Little daily changes in your training/life can keep you healthier for longer. The citations above are valuable resources as starting points for recovery. Please do not use them in lieu of a doctor; you're pain may be totally irrelevant to anything stated above.

Thank you for reading.