Strengthening the Knee: What Type of Exercise is Best?

Strengthening the Knee: What Type of Exercise is Best?

Written by Stacy Ciarleglio, a licensed athletic trainer and ultra runner.

Do you have knee pain? Or do your knees sometimes get achy after a run? I often hear this complaint from runners and one of the questions I ask them is, besides running, what do you do to strengthen your knees?

The answers vary from nothing at all, isn’t running good enough? To biking, squats, boot camp, yoga, machines at the gym and cross fit. What type of strength training is good for the knees? There is a lot of info out there that can be confusing when you are trying to decide which exercises to do to strengthen your knees. Are squats bad? Should I use machines? What about lunges?

Today, I am going to discuss two different types of exercises; closed kinetic chain (CKC) and open kinetic chain (OKC) and the benefits of each. Before I get to the exercises, let’s take a brief look at the basic anatomy of the knee so it is easier to understand why certain exercises are good and others may not be.

The kneecap (patella) sits within a groove on the femur (upper leg bone). The underside of the patella and the surface of the femur and tibia (shin bone) are covered in cartilage that helps to make joint motions smooth. Collectively, the patella, femur, and tibia make up what is known as the patellofemoral joint (PFJ), or, the knee! The patella is embedded within the quadriceps tendon, which is the large muscle group on the front of the leg that helps to extend the leg. The quadriceps tendon engulfs the patella and extends down to the shin where it attaches and is known as the patella tendon.

At different points in the range of motion of the knee (deep bend to hyperextension), varying amounts of force are generated within the PFJ. Studies have shown that the greatest amount of pressure occurs in deep bends (greater than 90 degrees) and in full extension. The forces in full extension are even greater if the quadriceps muscle is loaded with an outside force (a weight). Keep that in mind as we talk about different types of exercises.

Strengthening the muscles around the knee, the quadriceps and hamstrings, can help to reduce the risk of injury and knee pain from running. Running alone is not enough to properly strengthen the knee. There are a lot of exercises out there to choose from. Let’s look at the two major types of exercise.

Open Kinetic Chain versus Closed Kinetic Chain

The first type of exercise is the open kinetic chain exercise. In an OKC exercise, the distal (farthest from the body) segment of the limb is free to move in space. For example, the machine at the gym where you sit down and put a bar over your shins and extend your knees is an open chain exercise. Your feet are not on the ground and your limb is moving through a range of motion. A bicep curl in which you hold the weight in your hand and bend your elbow is an example of an OKC exercise for the upper extremity.

A closed kinetic chain exercise involves the distal segment of the limb being fixed and the body moving over it. For example, a body squat is a closed chain exercise for the lower extremity. A push up is an example of a CKC exercise for the upper body.

OKC exercises can be helpful in isolating a body part to target a specific area of weakness. They are often used in early stages of rehabilitation after an injury. One drawback to OKC exercise is that it is not very functional, meaning that the motions performed are rarely used in daily activities or sporting activities. CKC exercise mimics functional activity and strengthens larger muscle groups and movement patterns.

Knee Extension Machine?

Now that we know that the forces generated in the knee joint are greater when the knee is in full extension, and even greater when there is a weight placed on our feet, why would we do the leg extension machine at the gym if we are experiencing knee pain? The quadriceps muscle has to contract to move the leg into full extension, this contraction increases the compressive forces within the joint, and, the act of straightening the leg while in a seated position is not very functional, especially for running!

Performing a weighted, seated, leg extension is a common mistake that I hear runners making in an effort to strengthen their knee. For the motion of running, a closed kinetic chain exercise is much more functional. That means that the strength gained from doing a CKC exercise will turn over into strength that can be used while running. If performed within a range of motion that does not exceed 90 degrees of knee bend, the forces that a CKC exercise places on the knee joint are relatively low.

Examples of CKC exercises that can benefit runners are split stance lunges and regular lunges. These motions are very functional for running as they isolate a single leg at a time, and they strengthen all of the large muscle groups used in running. Start with split stance lunges and progress to regular lunges. To perform a split stance lunge, step forward with one foot and keep the other foot on the floor. Bend your knee to just less than 90 degrees and then come back up into the split stance position. Do not come back fully to a standing position. Repeat the motion 10 times. In a regular lunge, you will step into position, bend your knee, but then you come back up into a full standing position before stepping again. An important point to note here is that the larger your lunge step, the less force will be placed on your knee. So don’t step too close to your body.

Which exercise is right for me?

Both OKC and CKC exercises have benefits and can be helpful depending on what the goal of the exercise is. Strengthening exercises should never be painful. It’s important to make sure that you are performing the exercise within the proper range of motion. A general rule of thumb is that the extremes of motion are usually not good, so don’t lock your knee out while straightening, and don’t bend too far into a squat. If you are recovering from an injury, you should be supervised while performing knee exercises. Even if you haven’t been injured, it’s still a good idea to have a qualified professional show you how to properly perform exercises for your knee.