muscles of knee flexion

Hamstring Group - Location & Function

Located at the back of the upper leg. All cross the hip except the short head of the biceps femoris. Function: Knee flexion, assists in hip extension.

Why is it hard to touch your toes without bending your knees?

Most hamstring muscles cross both the hip and knee, so stretching them pulls at both joints.

Biceps Femoris - Origin (Long & Short Head)

• Long Head: Ischial tuberosity (superficial to short head)

• Short Head: Posterior femur, distal half (deep to long head)

Biceps Femoris - Insertion & Action

• Insertion: Lateral aspect of head of fibula

• Action: Knee flexion, hip extension

Semitendinosus vs. Semimembranosus

• Semitendinosus: Thin & on Top of semimembranosus

• Semimembranosus: More Meaty, Deep to semitendinosus

Gastrocnemius - Origin, Insertion, Action

• Origin: Medial & lateral epicondyles of femur (posterior)

• Insertion: Calcaneus via Achilles tendon

• Action: Knee flexion & plantar flexion (important for walking, running, jumping)

Quadriceps Group - Overview

• Four heads

• Only rectus femoris crosses the hip

• Vastus group originates on the femur

• Common insertion: Tibial tuberosity via patellar ligament (distal to patella) & quadriceps tendon (proximal to patella)

Rectus Femoris - Origin, Insertion, Action

• Origin: Anterior inferior iliac spine

• Insertion: Tibial tuberosity

• Action: Extends knee

Vastus Lateralis - Origin, Insertion, Action

• Origin: Greater trochanter of femur

• Insertion: Tibial tuberosity

• Action: Extends knee

Vastus Medialis - Origin, Insertion, Action

• Origin: Linea aspera of femur (not lesser trochanter)

• Insertion: Tibial tuberosity

• Action: Extends knee

Vastus Intermedius - Origin, Insertion, Action

• Origin: Distal half of anterior femur (deep to rectus femoris)

• Insertion: Tibial tuberosity

• Action: Extends knee

Semitendinosus - Origin, Insertion, Action

• Origin: Ischial tuberosity

• Insertion: Medial condyle of tibia

• Action: Knee flexion, hip extension

• Mnemonic: "Thin and on top of semimembranosus"

Semimembranosus

• Origin: Ischial tuberosity

• Insertion: Medial condyle of tibia

• Action: Knee flexion, hip extension

• Mnemonic: "More meaty than semitendinosus"