Origin and Insertion
Most skeletal muscle is attached to bone on its ends by way of what we call tendons. As the muscles contract, they exert force on the bones, which help to support and move our body along with its appendages.
In most cases, one end of the muscle is fixed in its position, while the other end moves during contraction. The origin is the attachment site that doesn't move during contraction, while the insertion is the attachment site that does move when the muscle contracts.
The insertion is usually distal, or further away, while the origin is proximal, or closer to the body, relative to the insertion. For example, one could say the wrist is distal to the elbow. Conversely, you can say the elbow is proximal to the wrist.
Muscular contraction produces an action, or a movement of the appendage. We will use examples to describe how the origin and insertion affect the action of a skeletal muscle.