Knee Flexion and Extension

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Quick‑Reference Table

| Action | Plane/Axis | Main Muscles | Typical ROM | |----------------|------------------------|---------------------------------------------------|------------------| | Flexion | Sagittal / medial–lateral | Hamstrings, gastrocnemius, 💪 Sartorius, popliteus | 0 → 135° | | Extension | Sagittal / medial–lateral | Quadriceps | 135° → 0° (→5° hyperextension) |

Knee Flexion

• Definition: Bending the knee so the heel moves toward the buttock, decreasing the angle between the femur and tibia.
• Range of Motion (ROM): ~0° (full extension) → 135° (deep flexion)
• Prime Movers:
  • Hamstrings:
    • Biceps femoris (long & short heads)
    • Semitendinosus
    • Semimembranosus
  • Assistants:
    • Gastrocnemius (crosses knee)
    • Gracilis
    • Popliteus
• Functional Role:
  • Swing phase of gait (foot clearance)
  • Sitting, squatting, climbing

Knee Extension

• Definition: Straightening the knee, increasing the angle between femur and tibia toward 180°.
• Range of Motion (ROM): ~135° (full flexion) → 0° (full extension); some individuals permit 5–10° hyperextension.
• Prime Movers:
  • Quadriceps group:
    • Rectus femoris
    • Vastus lateralis
    • Vastus medialis
    • Vastus intermedius
• Functional Role:
  • Stance phase of gait (support)
  • Rising from a chair, jumping, kicking