Muscle Actions: Extension

Extension refers to a movement that increases the angle between two body parts or the straightening of a joint.

The opposite movement of extension is flexion.

Extension Exercise Examples:

Extension of the knee.

Picture a person sitting on a chair. As they flex their leg straighten it, their heel moves further away from their hip.

The leg extension machine pictured below is a perfect example.

Leg Extension

In the first picture above, the lower leg makes about a 90º angle with the upper leg. In the second the leg extends and makes a straight line. The angle between the lower leg and upper leg increases form 90º to 180º.

Extension at the elbow occurs via the triceps resulting in an increase in the angle between the ulna and the humerus. Your wrist moves away from your shoulder.

When it comes to the foot, we don’t use the term extension. Instead the extension and flexion of the foot is referred to as plantar flexion and dorsiflexion. I don’t know why. It’s just the way it is.

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