The knees are one of the most susceptible body parts in terms of injuries whether you’re an athlete or a weekend warrior, so it only made sense for me to post this as the first thread of the new year in order to help you bulletproof your lower body.
The knee joint is one of the largest and most complex joints of the human body. It is constructed by 4 bones and an extensive network of ligaments and muscles.
The thigh bone (femur), the shin bone (tibia) and the kneecap (patella) articulate through tibiofemoral and patellofemoral joints. These three bones are covered in articular cartilage which is an extremely hard, smooth substance designed to decrease the friction forces. The patella lies in an indentation of the femur known as the intercondylar groove.
Although the fibula runs alongside the tibia and is attached via the superior tibiofibular joint, it is not directly involved in the knee joint, it does however provide a surface for important muscles and ligaments to attach to.
There are two menisci in the space between the femoral and tibial condyles. They are crescent-shaped lamellae, each with anterior and posterior horn, and are triangular in cross-section.
The surface of each meniscus is concave superiorly, providing a congruous surface to the femoral condyles and is flat inferiorly to accompany the relatively flat tibial plateau.
The horns of the medial meniscus are further apart and meniscus appears ‘C’ shaped, than those of the lateral one where meniscus appears more ‘O’ shaped. This is due to the increased size of the medial meniscus, which unfortunately leaves a large exposed area that in turn can be prone to injury.
The ligaments of the knee maintain the stability of the knee. Each ligament has a particular function in helping to maintain optimal knee stability.
• Medial Collateral Ligament (MCL) – This ligament can be divided into two sets of fibres – the superficial and the deep fibres.
The MCL primarily resists forces acting from the outer surface of the knee, valgus forces, but also resists the lateral rotation of the tibia on the femur.
The MCL is also able to resist a valgus stress more effectively in the closed pack position (extension) due to the laxity of the ligament in the open packed position (flexed). The MCL has another role in restraining anterior translation of the tibia on the femur. Therefore when someone has an MCL injury the protection of the anterior cruciate ligament needs to be considered.
• Lateral Collateral Ligament (LCL) – this cord like ligament begins on the lateral epicondyle of the femur and joins with the tendon of the biceps femoris (hamstring muscle) to form the conjoined tendon. This ligament is different to the MCL and is considered to be an extracapsular ligament.
Its main role is resisting varus forces on the knee, and similarly to the MCL is most effective in full extension. Another similarity of the MCL and the LCL is the ability of the LCL to also resist lateral rotation of the tibia on the femur.
• Anterior Cruciate Ligament (ACL) – The ACL is an important structure in the knee for resisting anterior translation of the tibia on the femur. This ligament is a very well known ligament due to the high injury rate of athletes, which has resulted in a lot of research being done in the field of the ACL.
The cruciate ligaments are so called because they form a cross in the middle of the knee joint. The ACL twists medially as it travels proximally. There are thought to be 2 bundles of fibres that form the ACL – the anteromedial bundle (AMB) and the posterolateral bundel (PLB).
The ACL is responsible for resisting anterior sheering forces on the knee. Dependant on the position of the knee, will depend on which bundle of the ACL fibres will be taut.
So when the knee close to full extension the PLB will be taut and resisting the force, but as the knee moves into a flexed position the PLB become lax and the AMB becomes taut, taking over the role of resisting the anterior sheering forces.
At approximately 30° of flexion neither of the bundles of the ligament are taut leading to the most anterior translation available at this range. It is most commonly injured in twisting movements. The ACL is also an accessory ligament in resisting rotary forces medially and laterally as well as valgus and varus forces.
• Posterior Cruciate Ligament (PCL) – This ligament runs from the posterior surface of the tibia between the two posterior horns of the menisci it then runs superiorly and anteriorly and attaches to the lateral aspect of the medial femoral condyle. It is much shorted and less oblique with a much larger cross sectional area in comparison to the ACL.
The PCL blends with the posterior capsule as it crosses to the tibial attachment. Factors such as the size, shape and location possibly contribute to the increased strength of the PCL in comparison to the ACL and is much less frequently injured.
The PCL similarly has 2 bundles of fibres the posteromedial (PMB) and the anterolateral bundle (ALB). When the knee is in near full extension the ALB which is much larger and stronger are lax and the PMB are taut whereas in 80-90° of flexion the PMB are lax and the ALB are taut.
The PCL is more adept for resisting posterior translation / sheering forces in knee when it is flexed despite there being the most posterior translation available at 75-90° flexion. The secondary stabilisers at this point in the range are ineffective and relay upon the PCL. The PCL also plays an important role in resisting rotation and valgus / varus forces on the knee.
It best resists medial tibial rotation at 90o flexion rather than extension, but is not very good at resisting lateral tibial rotation. If the PCL becomes damaged the popliteus muscle plays an important role in stabilising the knee from posterior sheering forces.
In the PCL deficient person hamstring contraction can destabilise the knee joint alongside a gastrocnemius contractions (at angles greater than 40° knee flexion), whereas quadriceps contractions degrees the strain on the PCL between angles of 20 and 60° flexion.
The muscles surrounding the knee are the following:
• Rectus Femoris (Strong extensor of the knee, The only muscle of the quadriceps to cross both the hip and knee joints. It flexes the thigh at the hip joint, and extends at the knee joint)
• Vastus Lateralis (Extends the knee joint and stabilises the patella)
• Vastus Intermedius (Extends the knee joint and stabilises the patella)
• Vastus Medialis Obliquus (VMO) (Extends the knee joint and stabilizes the patella, particularly due to its horizontal fibers at the distal end)
• Semitendinosus (Flexor and internal rotator of the knee)
• Semimembranosus (Flexor and internal rotator of the knee)
• Gracilis (Flexor and internal rotator of the knee)
• Sartorius (Flexor and internal rotator of the knee)
• Popliteus (Flexor and internal rotator of the knee,
Prevents the femur from slipping forwards on the tibia during squatting)
• Tensor fasciae latae (Weak extensor when knee is extended, Weak flexor and external rotator of the knee in flexion greater than 30°)
• Gastrocnemius (Weak flexor of the knee,
Weak internal and external rotator of the knee,
Strong plantiflexor and inventor of the heel)
• Biceps femoris (Strong flexor and external rotator of the knee)
The main movement of the knee is flexion – extension. The secondary movement is internal – external rotation of the tibia in relation to the femur, but it is possible only when the knee is flexed.
Research & Knee Health
A large number of studies had already established that stronger quads = less knee pain [1, 2]. A stronger quad will also help control the speed at which the knee experiences “impulsive forces” (or sudden large impacts) such as when the heel strikes the ground when walking or running. Interestingly, it is the rate at which the impulse happens that is the driver of knee cartilage damage and not the amount of the load.
The VMO is also a primary player in helping to protect medial knee cartilage volume, and therefore joint space as well. Patients with knee osteoarthritis that increased the size of their VMOs over a two year period had significantly less knee pain and cartilage loss than those whose VMOs had gotten smaller. The same study also found that this increased VMO size also reduced the risk of knee replacement over a four year period.
Additionally, a stronger VMO improves patellar tracking.
The problem with research however, besides the fact that it’s more often than not sponsored by Big Pharma, is that it takes decades to come up with scientific evidence that supports anecdotal evidence and empirical data that derive from strength coaches that actually know what they’re talking about.
Such is the case with VMO isolation. All the studies that tried to find if the VMO can be isolated in training, experimented with various squat types and hip positions to isolate the VMO but to no avail. What all these studies had in common was that they only trained knee extension from a maximum of 90 degrees knee bend.
Research in 2016 appears to suggest that when the knee is taken to around 140 degrees of flexion, the VMO is proportionally activated to a greater degree than other parts of the quadriceps.
Contrary to early research and popular belief, deep squats are actually protective for the knees.
To no ones surprise, the bigger your VMOs are, the better your deep squat performance is.
So if you want less knee pain, you must squat deeper and develop bigger VMOs.
Last but not least, backward walking reduces knee pain and acts as a shock absorber, helping to decrease the forces your knee joint experiences with every step and is therefore protective against knee pain and deterioration.
For decades coaches like Charles Poliquin and Louie Simmons among others, had been saying that not only the VMO is key for knee health and that you can isolate it if you squat deep enough, but that using a sled and walking backwards strengthens the quads and protects the knees.
Of course not everybody will be able to achieve full knee flexion right away (or perhaps ever — if they’ve had a knee replacement), and that’s okay. The key is to keep working progressively until you can squat as deep as your biomechanics allow you to.
As previously mentioned, training the VMO along with the muscles of the posterior chain, is going to be key in order to bulletproof your knees and avoid injuries, especially if you’re an athlete.
During a sprint you don’t simply extend your hips back, but you flex the knee as well. Therefore, training both functions of the hamstrings (hip extension and knee flexion) is crucial for injury prevention, as well as makes sense from an arthrokinematic standpoint.
Hip extension exercises like Good Morning variations, RDLs, Sumo, Zercher and Conventional Deadlifts, along with 45° hypers and reverse hypers should be a staple in any Strength & Conditioning program, as should all leg curl and nordic curl variations as well.
Eccentric strength is also of huge importance in order to prevent hamstring injuries. Some of the best and most underrated eccentric strength exercises are Nordic curls. When combined with leg curl variations they will build strong hamstrings and decrease the chances of sport injury. Nordic curls build extreme eccentric strength and reduce hamstring injuries by 51%.
The majority of the leg curl variations should be performed with heavier weights in the 4-8 rep range, along with the frequent addition of lighter weight, ultra high rep sets.
Remember that you have more leg curl variations than you think. Say you have a lying, a standing and a seated leg curl machine, by simply pointing your toes inward, outward and keeping them neutral you just added 3 variations per machine. That’s 9 different exercises to progress.
Additionally, leg curl variations with the toes pointing in, out or kept neutral target different areas of the hamstrings. When you point your feet inwards you target the semimembranosus muscle, when you point your toes straight ahead you target more of the semitendinosus muscle, and when you point your toes outwards you target more of the biceps femoris.
Performing frequent high volume leg curls will drive blood in the tendons and thicken the soft tissue, increasing kinetic energy and help with reversal strength in the process. These can be easily implemented at the end of the workout for prehab purposes.
Another pro tip that I learned from the late Charles Poliquin is to perform leg curls with the feet plantar flexed. Most people usually perform the exercise with a dorsiflexion (toes pointing towards the shins) and when you do so you actually use your hamstrings and your gastrocnemius to flex the knees.
When you have your feet plantar flexed the gastrocnemius is out of the equation. That means that if you want to overload/isolate your hamstrings you have to do your leg curls with your feet plantar flexed.
For even better results you can perform leg curls with your feet dorsiflexed (toes pointed towards your shins) on the lifting phase and your toes plantar flexed (toes pointed away from your shins) on the lowering phase. This lets you eccentrically overload your hamstrings on leg curls.
Incorporating power walking with a sled is a game changer for knee health. Walking with the straps between the legs, performing sumo sled pulls, bent over sled pulls and pull throughs are only a few possible exercises with a sled.
Another exercise that is often neglected is the box squat. When performed correctly it’s a supreme method to develop the posterior chain. You can check my article on box squats on how to properly perform them.
When it comes to quad training like previously mentioned the key is to primarily strengthen the VMO. Some of the best exercises include but can’t be limited to backwards sled drags, cyclist squats, cyclist 1½ squats, single leg and close stance leg presses, bulgarian split squats, reverse/walking lunges, Poliquin step ups, hindu squats, front squats, hack squats, pendulum squats, sissy squats and occasionally leg extensions.
Something that’s also extremely important yet often neglected is to strengthen the foot arch. Collapsed arches are a greater risk for ACL tears. There are even teams that won’t draft an athlete that has fallen arches, since the there’s a higher probability of an ACL tear due to valgus knees.
Stronger quads = less knee pain.
A stronger quad will also help control the speed at which the knee experiences “impulsive forces” (or sudden large impacts) such as when the heel strikes the ground when walking or running. Interestingly, it is the rate at which the impulse happens that is the driver of knee cartilage damage and not the amount of the load.
The VMO is also a primary player in helping to protect medial knee cartilage volume, and therefore joint space as well.
A stronger and a bigger VMO leads to significantly less knee pain, decreased cartilage loss and reduced risk of knee replacement to patients with osteoarthritis.
A stronger VMO improves patellar tracking.
To isolate the VMO the knee has to be taken to around 140 degrees of flexion, aka squat deep.
Deep squats are protective for the knees.
Athletes who regularly perform deep squats have demonstrated increased ACL and PCL thickness.
Contrary to early research and popular belief, deep squats are actually protective for the knees.
Moderate loading of knee cartilage has also been shown to elicit improvements in cartilage volume.
if you want less knee pain, you must squat deeper and develop bigger VMOs.
Backward walking reduces knee pain and acts as a shock absorber, helping to decrease the forces your knee joint experiences with every step and is therefore protective against knee pain and deterioration.
Hamstring eccentric strength is crucial for knee injuries. Both functions of the hamstrings must be trained for structural balance as well as from an arthrokinematic standpoint.
You have more exercises to your disposal than you think.
Don’t neglect your foot arch health as it also plays a role to knee injuries.