Knee Joint Muscles

The knee joint consists of the femur (thigh bone), tibia and fibula with the patella or kneecap. Muscles producing joint actions at the knee joint are the quadriceps muscles (vastus medialis, vastus lateralis, vastus intermedius and rectus femoris at the front, with the hamstring muscles (semitendinosis, semimembranosus and biceps femoris) at the back along with the popliteus muscle.

The Hamstring muscles

The hamstring muscles at the back of the thigh consist of the biceps femoris, semitendinosus and semimembranosus.

Semitendinosus

Semitendinosus muscleWhen running the hamstrings act eccentrically to slow down the knee extension motion. Hamstring strains are common in individuals with chronically tight hamstrings or who do not warm-up thoroughly.

Origin : Ischial tuberosity.

Insertion : Upper medial surface of the tibia.

Actions : Hip extension.
Knee flexion.
Internal rotation of the hip when the knee is flexed.

Innervation : Tibial part of the sciatic nerve.

Daily uses : Bending the knee to step over something.

Example strengthening exercises : Knee curl with resistance band.
Nordic curl.

Example stretches : Sitting hamstring stretch.
Standing hamstring stretch.

Semimembranosus

Semimembranosus muscleSemimembranosus is the most medial of the three hamstring muscles. Chronically tight hamstrings are often a contributory factor to lower back pain and knee pain.

Origin : Ischial tuberosity.

Insertion : Posterior part of the medial condyle of the tibia.

Actions : Hip extension.
Knee flexion.
Internal rotation of the hip when the knee is flexed.

Innervation : Tibial part of the sciatic nerve.

Daily uses : Bending the knee to step over something.

Example strengthening exercises : Knee curl with resistance band.
Nordic curl eccentric exercise

Example stretches : Sitting hamstring stretch.
Standing hamstring stretch.

Biceps Femoris

Biceps Femoris muscleBiceps Femoris is one of the three muscles which form the hamstring group forming the back of the thigh. The muscle is often described as having a long head (the attachment from the ischium) and a short head (attached to the femur).

The Quadriceps muscles

Vastus Medialis

Vastus Medialis Muscle

Vastus Medialis is the most medially (inner) located of the quadricep muscles. The portion of the muscle just above the knee is known as VMO (vastus medialis oblique). This is important in stabilising the knee joint and often becomes inhibited following injury.

Origin : Intertrochanteric line (between the greater and lesser trochanters of the femur).
Medial lip of the linea aspera of the femur.

Insertion : Patella via the quadriceps tendon and then the tibial tuberosity via the patella tendon.

Actions : Knee extension.

Innervation : Femoral nerve.

Daily uses : Cycling.
Walking up stairs.

Example strengthening exercises : Knee extension with a rehab band.
Squats.

Example stretches : Standing quad stretch.
Laying quad stretch.

Vastus Lateralis

Vastus Lateralis Muscle

Vastus Lateralis is the most lateral (outer) of the four quadriceps muscles and is felt on the outside top of the thigh.

Origin : Outer surface of the greater trochanter of the femur.
Upper half of the linea aspera.

Insertion : Patella via the quadriceps tendon and then the tibial tuberosity via the patella tendon.

Actions : Knee extension.

Innervation : Femoral nerve.

Daily uses : Cycling.
Walking up stairs.

Example strengthening exercises : Knee extension.
Squats.

Example stretches : Standing quad stretch.
Laying quad stretch.

Vastus Intermedius

Vastus Intermedius Muscle

Vastus Intermedius is one of four quadricep muscles, located deep in the thigh underneath the Rectus Femoris muscle.

Origin : Anterior and lateral surfaces of the shaft of the femur.

Insertion : Patella via the quadriceps tendon and then the tibial tuberosity via the patella tendon.

Actions : Knee extension.

Innervation : Femoral nerve.

Daily uses : Cycling.
Walking up stairs.

Example exercises : Knee extension with a band.
Squats.

Example stretches : Standing quadriceps stretch.
Laying quadricep stretch.

Rectus Femoris

Rectus Femoris Muscle

The Rectus Femoris muscle is part of the Quadriceps muscle group. It is the only muscle of the group which crosses the hip joint and is a powerful knee extensor when the hip is extended, but is weak when the hip is flexed.

Origin : Anterior Inferior Iliac Spine (AIIS).

Insertion : Top of the patella and the patella tendon to the tibial tuberosity.

Actions : Flexion of the hip.
Extension of the knee.

Innervation : Femoral nerve.

Daily uses : Kicking a football.

Example strengthening exercises : Standing hip flexion using resistance band.
Sitting hip flexion - isometric.

Example stretches : Hip flexor stretch.
Laying quadricep stretch.
Standing quadricep stretch.