Extension

Extension: A sagittal plane joint action that results in an increase in the angle between two bones.

• Opposing Joint Action: Flexion
• Plane of Motion: Sagittal
• Direction Bias: Backward
• Note: Joint actions may be referred to as "osteokinematic motions" or "osteokinematic joint actions" to differentiate them from "arthrokinematic motions " (e.g., spin, glide, roll, compression, and distraction).

For more (including a video lecture), check out:

• Lesson 3: Joint Actions
• Lesson 18: The Spine and Trunk Muscles

Joints that Perform Extension (and Sample Exercises):

1. Shoulder joint (Glenohumeral joint): Extension involves moving the arm backward (posteriorly) from a flexed position, as observed during a row or crunch and catch (during the concentric phase of throwing).
2. Elbow joint: Extension involves straightening the elbow and moving the forearm away from the upper arm, as observed during a triceps extension or dumbbell chest press .
3. Wrist joint: Extension occurs when the hand moves backward in the direction of the back (dorsal ) side of the hand. The wrists are extended in exercises like push-ups .
4. Hip joint : Extension occurs when the thigh moves backward, away from the abdomen, as observed during squats or lunges (during the concentric phase on the way up).
5. Knee joint : Extension involves straightening the knee and moving the lower leg away from the thigh. as observed during knee extensions, squats , or lunges (during the concentric phase on the way up).
6. Ankle joint (Talocrural joint) : Plantar flexion is a specific form of extension at the ankle, where the foot moves up away from the shin, as observed during a calf raise, squat , or tibialis posterior activation .
7. Interphalangeal joints (fingers and toes): Extension occurs when the fingers or toes straighten, as observed when opening the hand from gripping.
8. Spine (Intervertebral joints) : Extension occurs when the spine bends backward, as observed during lumbar extension exercises.