Lot of fitness trainers are concerned or should I say confused about locking knees during a concentric movement while performing a full range squat. Every now and then you will find those self proclaimed fitness gurus telling you that you will have knee problem when you get older or your knee would get weak if you lock them in full extension and if you ask them why it would happen, they would be clue less about it. Indeed I am not asking for hyper extending or hyper flexing your knee joint BUT a full range of motion. There are conditions like RUNNER’S KNEES( It may refer to conditions like Chondromalacia patellae, Patellofemoral pain,Iliotibial band syndrome or Plica syndrome) or OSTEOARTHRITIS(cartilage gradually deteriorates and joint fluid loses its shock-absorbing qualities) in older age. These conditions are direct result of weak knee joints and an overuse injury from repetitive overloading of the extensor mechanism of the knee but no co relation between locking your knees in full extension. If we gather the Statistics from orthopedic surgeons of all the knee replacement performed or the clients who have been treated of knees ailments, you will be surprised to find that 70% of them never would have engaged in resistance training as compared to only 30% who have working on strengthening their knee joints.
Before we go into technical aspect and anatomy of knee joint, let’s get back to basics. Try climbing stairs of your house twice once with your knees locked and second time without locking your knees or try standing for 30 minutes once with your knees locked and in second time without locking your knees. How would you feel in both the activities? You will feel more stress on your knees if they are not locked rather them keeping them locked in full extension. Take an another example, whenever you lift anything heavy from the floor or put anything heavy on upper shelf of a almirah, your body automatically performs full extension of both hip and knee joint to transfer the kinetic energy to potential energy to that object. It is how our knee joints are designed during the evolution of homosepians when they become biped from quadruped. Our muscles can’t differentiate between motion or they can differentiate if you are working out in a gym or simply doing daily chores. They can only contract or relax during a movement. Their only job is to either flex or extend or abduct or adduct the joints of human body. It is our body’s natural mechanism to perform full extension in knee joint while lifting from squatting position to generate maximum force irrespective of if you are doing a heavy squat. Body is just acting against a resistance and gravity to perform maximum work.
Now let’s talk about anatomy of knee joint. The knee joint joins the thigh with the leg and consists of two articulations one between the femur and tibia, and one between the femur and patella. It is the largest joint in the human body. The knee is a mobile a hinge joint which permits flexion and extension as well as slight internal and external rotation. The knee is a hinge synovial joint, which is composed of three functional compartments, the femoropatellar articulation, consisting of the patella, or “kneecap”, and the patellar groove on the front of the femur through which it slides; and the medial and lateral femorotibial articulations linking the femur, or thigh bone, with the tibia, the main bone of the lower leg. The joint is bathed in synovial fluid which is contained inside the synovial membrane called the joint capsule. The ligaments surrounding the knee joint offer stability by limiting movements and, together with several menisci and bursae, protect the articular capsule. Knee has two washers like substance called menisci, the menisci fulfils two vital functions. They transfer the load from the upper leg to the lower leg and stabilize the knee during flexion, extension and during circular movements. The menisci move during the backward flexion and the forward extension of the knee in order to balance the change of the articular surfaces.
Loss of bone density and weakening of joint in SPACE- Effect of Prolonged Space Flight on Human Skeletal Muscle – The National Aeronautics and Space Administration (NASA) in there long space exploration found that astronauts lose a significant amount of bone density and often experience muscle atrophy and joint weakening in their long stay in zero gravity. It was later found out that if no resistance is applied on joints and connective tissues( like on earth gravity does) they becomes weaker with time. To solve this problem NASA designed specific resistance training equipment for the astronauts to keep their joints and connective tissues stronger for longer duration. So increasing resistance is very important to keep our joints stronger.
Role of torsion force on knee- A lot of fitness enthusiastic prefers leg extension over squats and leg press as according to them it puts less stress on knee. In fact leg extension put more stress on knee joint. During Leg Extensions, the resistance is located at the shins, just above the feet. This causes shearing forces on the knees, which means the force is experienced horizontally across the joint. Your body does not like this. In most serious injuries, there’s some form of horizontal force whether from a collision or momentum that causes the injury. In the case of the Leg Extension, the ACL is the primary concern. The ACL prevents your lower leg from sliding forward relative to your thigh. The Leg Extension directs its forces on the ACL. According to a study published in the Journal of Biomechanics, peak ACL tension was experienced during the Leg Extension when compared to the Squat and Leg Press.
The weight used may be light compared to an exercise like a Squat, but that doesn’t necessarily matter. A study in The American Journal of Sports Medicine found that increasing the resistance during the Squat did not increase strain on the ACL, whereas increasing the resistance during the Leg Extension did add strain to the ligament. The force is applied far from your knee, so if you’re using 100 pounds, your knee will experience a much greater weight. Also, your body is designed to handle the compressive force of a Squat, so lifting hundreds of pounds is not a problem. A study published in the Journal of Bone and Joint Surgery confirmed this. The researchers found that movements like the Squat and Deadlift cause greater compression force and muscular activation, while movements like the Leg Extension produce greater shear force and minimum muscular activation.
As a responsible fitness instructor it is the duty of a trainer to provide actual knowledge to the client rather than just spreading the unproven theories about exercise. After reading the article don’t just tell every client of yours to lock their knees. Observe their past workouts and gradually put them in right bio mechanics of workouts. Remember all the connective tissues(Tendon,ligament,bones,muscles)of our body gets stronger with time but IT has to be a gradual process. Increase the resistance slowly to reach the maximum potential in each workout. PRAVESHH GAUR.