Knee injuries, especially those involving the ligaments of the knee, can be career ending for many athletes, however, for those who remain physically active yet do not regularly participate in sports knee injuries are often due to overuse.

Common overuse knee injuries:

Patellofemoral pain syndrome (PFPS) - this is a broad term for injuries causing pain around the knee cap. During the deep squat position a lot of tension is put on the patella by the quadriceps tendons, a straight and stable knee alignment means that the patella during this will remain in the patellofemoral groove, but misalignment of the knees, causes large amounts of stress on the patella as well as the surrounding tissue, grinding of the underside of the patella on the femur can cause erosion of the smooth cartilage on the underside of the patella leading to a condition known as chondromalacia.

IT band syndrome (ITBS) - the IT band is a thick piece of fascia which runs from the top of the hip down to the outside of the knee, certain movements, most commonly the knees caving in causes large amounts of tension to be placed on the distal part of the IT band, this will apply pressure to a layer of fat underneath the IT band on the lateral part of the distal femur, just above the knee, this layer of fat is highly innervated with nerves and can cause large amounts of pain.

Patellar/Quad tendinopathy - the patella tendon runs from the patella to the ischial tuberosity of the tibia, while the quadricep tendon attaches the quadricep to the top of the patella. These tendons are placed under very large amounts of stress during many sporting movements, such as those which involve jumping, this can cause damage of the tendon which usually will heal in a couple of days, however, if stress on the tendon continues it will become inflamed and start to cause large amounts of pain, allowed to continue even further from this stage and the collagen fibres can begin to degrade and lose their ability to withstand load, in this phase pain is often reduced however the risk of more serious injury greatly increases.

Knowing what type of knee issue you are experiencing is only the first step in the process of getting over the injury, the next step is finding the cause of the injury, this can be categorised into mobility, stability or load intolerance.

Performing a basic body weight squat and recording from different angles then reviewing the footage. Look for asymmetries in either side of your body, such as whether your body weight shifts more to one side on the ascent of the squat or if one foot is more angled inwards than the other, this often points to mobility restrictions.

Assessing hip internal rotation in order to find any mobility asymmetries is recommended, do this by laying on a flat surface with your knees facing the ceiling and your knee flexed to 90 degrees, have a partner rotate your leg outwards, if there were significant mobility differences in internal rotation perform mobilisation exercises than retake the test, such exercises include:

Banded stretch - loop a band around your upper thigh pulling your leg laterally, now kneel on the opposing leg, use your hand to help pull your knee across your body and pause here before bringing it back and pausing in the start position, perform this for several repetitions to free up impingements in the hip.

Squat rack stretch - set a bar up in a squat rack at shoulder level, take a big step back and lean over at your hips to grip the bar with both hands at shoulder width, on the target leg lift it off the ground behind you while keeping it straight, turn in the direction of the raised leg exposing your chest outwards, make sure to also point your toes of the target leg outwards, pause here for a bit before bringing your whole body inwards and slightly in the direction of the other foot, pause here, perform about 10 repetitions of this exercise.

Basic piriformis stretch - a common cause of poor internal rotation is a tight piriformis muscle, a good stretch for this is to sit on the edge of a chair and place the foot of the target leg on top of the thigh of the other leg, from here lean your chest forward to stretch the piriformis, do this for about 3 sets of 30 seconds.

General kettlebell stretch - hold a kettlebell with both hands in front of your body, drop down onto one knee and the other leg can remain on the foot but angled more outwards, rock back and forth so your knee passes the toes of this leg and then back, make sure to hold each position, this can be a great hip stretch on both sides.

A single leg squat of a box is great at revealing stability issues, if of a box a bodyweight single leg squat to parallel can not be performed, at least without much instability this may be a cause of knee issues, especially for athletes who often move and land on one leg. The knee caving in during the single leg squat often points towards a lack of coordination in the glute muscles to keep the knees in a stable position.

Tight gastrocnemius and soleus muscles are often a cause of knee pain, if these muscles are tight than less dorsi flexion of the ankle can be performed when landing on the foot, this means that more force is transferred to the knee. A test for ankle mobility is to stand facing a wall with your tested foot 5 inches away from the wall, drop down onto your other knee, lean forward, if you can not get your knee to touch the wall without your heel coming off the ground you likely have poor ankle mobility. To deal with poor ankle mobility several exercises can be performed:

Wall calf stretch - stand by a wall with your legs straight, step the target leg forward so that the toes are on the wall but your heel is still planted on the ground, lean forward to get a good stretch, do this for about 3 sets of 30 seconds.

Deep goblet squat - take a light plate and go into a deep squat with your elbow positioned inside of your knee, rock side to side pushing your knees over your toes on each leg to get a good stretch.

Box stretch - stand away from a raised surface of about knee height, step your target leg onto the object, lean your body weight forward so that the knee of your target leg passes your toes, do this for about 3 sets of 30 seconds.

A common cause of knee pain is poor coordination or weak glutes causing the knee joints to overwork and the hip joint to underwork, to test for this the best exercise is the single leg bridge, lay on your back with one knee flexed to 90 degrees and planted on the floor and the other leg extended out straight, push off the ground performing hip extension and pause in the top position for about 5 seconds making sure to squeeze the glutes, make sure to perform this on both legs, if you felt your hamstrings performing this movement your glutes are likely underperforming and exercises must be done to address this issue, if you felt your quads performing this movement your posterior chain is likely underperforming. To address glute and other lateral hip muscle issues there are certain exercises which can be performed:

Single leg bridge -  you can perform the single leg bridge as an exercise for about 15 repetitions on each leg with a 5 second pause.

Lateral band walk - put a band around your ankles pulling them together and drop into a very slight squat, step your trail leg in then your lead leg out to just beyond shoulder width, side walk for about 20 feet and than stop and move in the other direction.

Single leg banded abduction - put a band around your ankles, drop into a slight squat and balance on one leg, with the other leg perform abductions for about 15 reps and 3 sets on each side, this is a great exercise to build stability around the knee and hips, and also to strengthen the lateral hips on each side.

Banded body weight squat - put a band around your knees pulling them inwards and performing 3 sets of 10 reps at a slow tempo. This is a great exercise to build coordination in the lateral hip muscles during the squat to stop the knees from caving in and thus reducing injury risk.

Banded lunge - tie a band around the leg just above the knee pulling it inwards and lunge down onto the opposing leg, this is another great exercise to build coordination in the lateral hip muscles, do about 2 sets of 20 reps on each leg.

Another common cause of knee pain is due to poor coordination in or a weak vastus medialis muscle which should work in sync with the vastus lateralis to keep the patella in a stable alignment, closed chain exercises are best at dealing with this, this is because they are more similar to everyday movements, but also because during open chain exercises of the knee, such as leg extensions, when the knee bends the patella comes into greater and greater contact with the femur, this means that at peak extension there is little surface area between the patella and femur, but there is much force going through it from the quads, this can cause large amounts of pain and further inflammation of the injured area. In closed chain exercises, such as the body weight squat, the patella will remain with a greater surface area of contact with the femur and thus the injury is less likely to become irritated. When introducing the squat to your rehab plan, make sure not to squat too deep into knee flexion as this will likely cause irritation, instead go to a pain free depth before adding a barbell and increasing the load. 

Once pain of the knee has gone it is important to add in exercises which will ensure that the injury will not reappear, such exercises include:

Single leg squat - perform the single leg squat of a box, slow and controlled lower your body till the leg not on the box touches the ground, this should be in a position where the other leg femur is parallel with the ground, perform this exercise for about 3 sets of 10 on each leg. This is a great exercise to build knee stability and strength of the lower body.

Balance star exercise - on the floor tape a straight line, tape another line at a 90 degree angle from this line and another 2 lines at a 45 degree angle of the others. Stand barefoot on a single leg in the intersection of these pieces of tape, with the free leg extend the leg to touch the furthest point along each piece of tape while keeping balanced, perform this exercise for about 5 sets on each leg. This is a great exercise to build balance and proprioception, this is important to keep the knees in a stable position.

Once performing the exercises to help with your knee issues, foam rolling the muscles around the knee can be a good option to reduce muscle stiffness, however, avoid foam rolling the actual knee which may irritate the area further due to inflammation in this region.

A load intolerance in the knee is usually due to tendinopathy, a test for load intolerance is to perform several jump tucks, you can perform this on both legs or as a single leg jump, if this caused greater pain than the normal squat you likely have a load intolerance due to tendinopathy as this exercise will place more stress on the tendons surrounding the knee. If you experience knee pain when squatting in one area consistently this further indicates a load intolerance, while if it moves around the patella this points to more of a biomechanical dysfunction. 

Deal with a load intolerance by dropping volume and/or intensity of training, it is important not to eliminate all exercise as this will simply weaken the tendon that is already experiencing symptoms meaning that reinjury is more likely to occur when returning to training. Isometric exercises are a great option for those dealing with knee pain due to a load intolerance. Cortical inhibition often causes muscles surrounding the knee to decrease in activity, isometric exercises allow for large activation of these muscles without cortical inhibition as they place little stress on the actual joints, they have also been shown to be highly effective for reducing pain, which may come in particularly useful prior to exercise. The wall squat is a great isometric exercise to start, if this is not challenging enough to the point where you can barley hold the squat for 60 seconds, try the wall squat but with one leg extended out in front of the body but make sure to do this on both sides, still if this is not challenging enough try the spanish squat, tie a band around a pole and the back of your knees, step backwards till there is tension in the band and sit backwards performing a squat. Once isometric exercises have been used for some time to reduce knee pain it is time to start performing isotonic exercises in conjunction with isometric exercises, this will place more stress on the tendons around the knee and if done properly will make them stronger, such exercises include:

Squat - Squatting with a loaded barbell is a classic and realistic exercise to build strength surrounding the knee.

Box squat - The box squat requires you to stand with a barbell on your back and sit down onto the box with a brief pause before performing the ascent of the lift. This squat means the knees can not pass the toes as much in the deep position, there is less spring of the tendon during the transition from the eccentric to concentric phase of the lift, and you can easily choose the depth of which you squat too by adjusting the block height, all of this will place less stress of the tendons of the knee. 

Front squat - The front squat is a great exercise on the transition from box squat to regular squat, this is because it requires you to squat with a much more upright chest position to keep a stable center of gravity, this stops the toes from trailing too far over the feet and thus exacerbating any existing knee pain.

Bulgarian split squat - Stand in front of an object at about knee height facing away from it while holding a dumbbell, put the toes of one leg back and onto the object, lunge putting 90% of your weight into the front leg while using the other for stability. This is a great exercise for building strength and stability on each leg.

A load greater than 70% 1 rep max is needed for the best development of tendon strength, however, jumping straight into these sort of loads can be more damaging than helpful, instead start with a load which is challenging for about 4 sets of 15 reps, and slowly drop from 15 reps per set, to 12, 10, 8 and then 6. Regardless of weight on the bar these exercises should be done with a slow and controlled tempo at first, over time the concentric phase can gradually be sped up which will place more stress on the tendons.

Isotonic exercises are great at strengthening the muscles and tendons surrounding the knee but plyometric exercises are needed to help tendons regain the ability to store and release energy in a spring like fashion, such exercises include:

Box drops - stand on a box raised about 8 inches off the ground, drop off the box and land on both legs, use this energy from the box to propel you into another jump upwards, perform this exercise for about 30 jumps. If this is too intensive to start with you can simply just perform the landing portion of the exercise, eventually working your way up to the normal exercise, then a higher and higher box or performing it on one leg instead of two.

Jumping - a simple yet effective exercise is too jump up and down on the spot, you can make this exercise more intense by jumping higher and tucking your knees, or by performing this exercise on one leg as a hop.

Forward jumps - jump forwards as far as possible and without a break perform another jump forward using the momentum of the previous jump and the spring of the knees.

For athletes whose sports require sudden acceleration and deceleration or change in direction exercises which include this type of movement may also be beneficial in the late stages of knee rehab.