Primary Distance Runners Knee Muscles


By Rick Morris


The muscles acting on your knee joint will extend, flex and rotate your knee and lower leg. Here are the primary running muscles that act on your knee joint.


Rectus femoris


This is a two joint muscle, meaning it passes over and acts on two of your joints. The rectus femoris originates on the outside of your pelvis just above your hip socket. It attaches to your upper patella and patella tendon. The rectus femoris flexes your hip and extends your knee. This muscle is part of the quadriceps muscle group and is easily felt in the middle of your thigh.


Vastus lateralis


This is one of three vasti muscles in your quadriceps muscle group. The vastus lateralis is a large muscle that originates on the lateral surface of your upper femur and attaches to the upper/outside portion of your patella and patellar tendon. You can easily feel and see this muscle on the front/outside portion of your thigh. The main duty of this muscle is to extend your knee. An overdeveloped or tight vastus lateralis muscles can cause knee problems because of the slightly lateral pull on your patella. This is a more common problem among women runners due to their wider hips structure.




























Vastus intermedius


The second of the three vasti muscles is the vastus intermedius. This muscle cannot be felt because it’s located directly under your rectus femoris. The vastus intermedius originates on the upper two thirds of the front of your femur and attaches to the top of your patella and patellar tendon. This muscle extends your knee.


Vastus medialis


The final vasti muscle is the vastus medialis. This muscle originates on the upper/inside portion of your femur and attaches to the upper/inside part of your patella and patellar tendon. This is another large thigh muscle that you can see and feel on the front/inside part of your thigh. Just as the other vasti muscles, this one extends your knee.


Biceps femoris


This “two headed” muscle is one of three muscles that make up your hamstrings muscle group. The long head of the biceps femoris originates on the lower part of your pelvis while the short head originates on the front of your femur. This muscle attaches to the lateral side of the top of your tibia and the top of your fibula. This muscle extends your hip, flexes your knee, and externally rotates both your hip and knee.




The second of three hamstring muscles, this one originates on your lower pelvis and attaches to your upper tibia. This muscle extends your hip and flexes your knee. It also internally rotates both your hip and knee.




This is the final muscle in your hamstring group. This muscle originates on your lower pelvis and attaches to your upper tibia. This muscle performs the same action as the semitendinosus. Both the semitendinosus and semimembranosus are important muscles for maintaining knee stability.




Of all of the muscles that flex your knee, this is the only one that is a dedicated knee flexor. All other knee flexors are two joint muscles that perform additional duties. The popliteus only flexes and internally rotates your knee. This is a relatively small muscle that originates on your femur near your knee joint. It attaches to the rear/upper part of your tibia. This is a deep muscle that you can’t see or feel.


Hamstring Muscle Group


Some muscle are more well known by there muscle group names. You are probably very familiar with your hamstring muscle group. There are very few runners that haven’t has the occasional pulled “hammy”.  The three muscles in the hamstring group are the biceps femoris, semitendinosus and semimembranosus. The hamstring muscle group is commonly called the “running muscle” because of their importance in accelerating, pushing off and hill running. The hamstrings are primarily knee flexor muscles but are powerful hip extensor muscles.


Quadriceps Muscle Group


The second major muscle group that acts on your knee is your quadriceps muscles. Just as the name suggests, there are four muscles in this group – rectus femoris, vastus lateralis, vastus intermedius and vastus medialis. The rectus femoris is a two joint muscle that also acts as a hip flexor. The three vasti muscles are one joint muscles that extend your knee. These muscles are used strongly when decelerating, running down hill, jumping and pushing off.


Primary Knee Extensors


The primary muscles that extend your knee are the quadriceps muscles - rectus femoris, vastus lateralis, vastus intermedius and vastus medialis.


Primarily Knee Flexors


The most important knee flexors are the biceps femoris, semitendinosus, semimembranosus and popliteus.





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