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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
- Hamstrings:
- 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
- Quadriceps group:
- Functional Role:
- Stance phase of gait (support)
- Rising from a chair, jumping, kicking