My Least Favorite Exercise Part 2 – The Quadricep Knee Extension
Continuing with the theme of our last blog post My Least Favorite Exercise – The Clamshell, I’d like to highlight another popular exercise that should be avoided at all costs. This week, my least favorite exercise is the quadricep knee extension exercise. I regularly see people at the gym using the quadricep knee extension machine, and I truly worry about their orthopedic health when I’m watching them. To perform the machine based knee extension exercise, people sit in a chair with a pad on their shins. Next, they kick their legs straight against the resistance of the machine, contracting the quadriceps muscle. People perform this exercise because they want to improve the strength and size of their quadriceps muscle – some may even think it’s healthy for their knees; however, the biomechanical consequences of this exercise can be highly detrimental to the health of your knees.
Open vs. closed chain exercises
The machine based knee extension is a single joint, open chain exercise. Open chain exercises refer to movements where the distal extremity (hand or foot) is not fixed and is freely moving in space with or without external resistance. Examples of open chain exercises include a bicep curl, hamstring leg curl, and shoulder fly. Open chain exercises cause an isolated muscle contraction over a single joint of movement, which some believe to be beneficial in the early stages of an injury rehabilitation program. Open chain exercises are in contrast to ‘closed chain exercises’ where the hand or foot is fixed to the floor. Examples of closed chain exercises include the squat, deadlift, or push up. Closed chain exercises involve multiple muscle groups and require coordinated muscle contractions to complete the compound (multi-joint) movement.
The forces imparted on the joints differ between open and closed chain exercises. For open chain exercises (quadricep knee extension) the force imparted by the weighted resistance is transmitted back up the leg and into the knee joint. This force can cause compression in the knee joint, putting increased pressure on the meniscus, ACL, PCL, and patella-femoral joint. In contrast, with closed chain exercises (deadlift) the force imparted by the external resistance is transmitted into the ground. For instance, in a deadlift, the force from the load is pressed through the feet into the ground rather than up the body into the knees and hips.
The second problem with the exercise is that it is a repetitive concentric exercise. Remember from my last post, concentric muscle contractions occur when the muscle is shortening and repetitive contractions over time can cause a shortening and tightening of the muscle fibers even while at rest. Ignoring the eccentric (muscle lengthening) component of a muscle’s function can be detrimental to movement patterns and ultimately put you at an increased risk of injury. Additionally, a short and tight quadriceps muscle can pull upwards on the patella, altering the mechanics of the patella-femoral joint and cause conditions such as patellar tendinitis which is also known as Jumper’s knee.
What to do instead – deadlifts, squats, single leg squats, reverse lunges
If you want to strengthen your quads and the rest of the muscles in your leg, the best exercises are closed chain, compound movements that integrate the feet, hips, and core to create a functional and stable lower body. My favorites are deadlifts and lunges because you can add a lot of weight without placing much force on the knee joint (when performed properly). 
As I said previously, closed chain exercises like the squat and lunge transmit force down into the ground, which is why they are popular for building speed and explosiveness in strength and conditioning programs.
Post written by Dr. Riley Kulm, DC.
Check out his bio here.
Train like a pro
Elite athletes understand they need to build durable and resilient muscles, joints, ligaments, and tendons. The best way to do this, aside from a healthy diet (nutrition blog post) and adequate recovery practices (sleep blog post), is resistance weight training. When we lift weights, we place an external load on the body, mimicking the forces encountered in sports. Forces placed against the body are present in both contact and non-contact sports. When participating in non-contact sports such as running, throwing, and golf, forces are still exerted from contact with the ground or from internal forces the body places on itself during movement. This week we will dive into the key principles of strength and conditioning that will help you train like a pro.
Keep it simple
Most people would be surprised by the simplistic workouts of the world’s top athletes. There is a misconception professional athletes are using state of the art equipment unavailable to the average person. While elite athletes do have access to incredible facilities and equipment, most pros are still using simple squat racks, barbells, dumbbells, pull-up bars, and kettlebells – equipment we almost all have access to.
Traditional bodybuilding training focuses on single joint, single muscle group exercises. While effective for improving aesthetics, these movements do not increase functionality in the athlete or mimic the demands encountered in sports. The key is to focus on compound, multi-joint exercises like the deadlift, squat, pull-up, bench press, and weighted rows. These exercises will stress multiple muscle groups, requiring they work together to move the load.
Focus on closed chain exercises
Closed chain exercises are when the body part being moved is anchored to the ground or an immovable object, like a pull-up bar. The direction of muscle pull is towards the ground or immovable object. Force is being transmitted through the ground, not through the air when you perform exercises such as deadlifts, squats, push-ups, pull-ups, or lunges. These exercises recruit larger muscle groups and require they work together to move the load. Closed chain exercises also require greater stabilization of the spine, which is essential for protecting the lower back during sports.
Contrarily, open chain exercises are when the arm or foot is free to move and is not anchored to the ground or an immovable object. The direction of muscle pull is inwards toward the body when you perform exercises such as bicep curls, bench press, hamstring leg curls, or quad knee extensions. The muscle is mainly recruited in the concentric (shortening) phase of muscle action. As such, open chain exercises are less functional to the athlete and should not be the focus of a strength and conditioning program.
Control the eccentric portion of the lift
Many injuries in sports occur when the muscle is asked to contract while it is in the process of lengthening. Bicep tendon tears, hamstring tears, and achilles ruptures are common injuries that often occur in the eccentric phase of muscle action. This type of contraction causes the most tearing of muscle fibers, whether injury occurs or not. A simple example of eccentric muscle action is during the bicep curl. As the weight is lifted, the bicep is acting concentrically, meaning it is shortening while it is contracting. As you slowly lower the weight, the bicep is eccentrically contracting, meaning you are putting it under load as the muscle lengthens.
By focusing on slow lowering in movements like the squat (descent), deadlift (lowering the bar to the ground), and pull-up, you can target the eccentric muscle actions, making your body more durable and resilient to injury. As an added bonus, muscle growth is stimulated most by eccentric exercises.
Adopt a pull to push ratio of 2:1 or 3:1
This ratio will maintain the balance of your posterior (back) and anterior (front) muscle chains. Proper balance and upright posture depends on balance between these two chains of muscles. Most people are insufficient in their posterior chain (calves, hamstrings, glutes, triceps, upper back muscles) and overly sufficient in their anterior chain (quads, upper abdominals, pecs, and biceps). A reason for this pattern is the anterior chain muscles are the ones typically associated with an aesthetic body and are trained more often than the posterior chain muscles. When it comes to function, a strong posterior chain in balance with the anterior chain is key. A strong posterior chain will help you develop more force in your running stride, take and receive hits in contact sports, and stick a landing after a vault in gymnastics.
Pulling exercises include pull-ups, deadlifts, seated rows, dumbbell rows, and lat-pull downs.
Pushing exercises include push-ups, bench press, incline DB press, landmine press, and strict press.
SAID principle
Finally, it is important your gym training closely mimics demands encountered by your sport. The Specific Adaptation to Imposed Demands (SAID) principle states the biomechanical and neural adaptations your body makes to training will be specific to the movements being trained. For example, if you want to get better at running, you should not bench press every time you go to the gym. Conversely, if you are an offensive lineman in football, obtaining a strong bench press will be essential to success in your sport. Choosing exercises that either recruit the muscle groups you plan to use or movements that look similar to the ones you perform in your sport is crucial to training like a pro.
Have questions? feel free to reach out to Dr. Riley at [email protected].
Post written by Dr. Riley Kulm, DC. Check out his bio here.
