Angle of pull By Dr M Abbas Jamil

Angle of pull By: Dr. M. Abbas Jamil

� Angle between muscle insertion and bone on which it inserts is angle of pull. � Components: � Rotary component = 90 � Stabilizing component < 90 � Dislocating component > 90

� Several factors determine the role that a muscle will play in a particular joint motion. Determining whether a muscle has a major role (prime mover), a minor role (assisting mover), or no role at all will depend on its: � Size � Angle of pull � Joint motions possible � Location of the muscle in relation to the joint axis � For example, compare the size of the triceps with that of the anconeus. It is easy to see that the anconeus will have little effect on joint motion compared to the triceps. In the case of the elbow, the motions possible are flexion and extension. The triceps and anconeus cross the joint posterior to the joint axis. Because the triceps is much larger than the anconeus, it crosses the elbow posteriorly, and extensors must cross the elbow posteriorly, it is logical that the triceps is a prime mover in elbow extension.

� Angle of pull is usually a major factor. Most muscles pull at a diagonal. That diagonal line of pull is the resultant force of a vertical force and a horizontal force. � In the case of the shoulder girdle, muscles with a greater vertical angle of pull will be effective in pulling the scapula up or down (elevating or depressing the scapula). Muscles with a greater horizontal pull will be more effective in pulling the scapula in or out (protracting or retracting). Muscles with a more equal horizontal and vertical pull will have a role in both motions.

� Force may be resolved into x (horizontal) and y (vertical) components. � The y component is perpendicular to the lever, called rotary component. � The x component is parallel to the lever and is the non-rotary component.

Rotary component Nonrotary component

� Angle of pull < 90º � Non-rotary force is directed toward fulcrum. � Helps maintain integrity of the joint (stabilizes) Rotary component Non-rotary component

� Angle of pull > 90º � Dislocating force is directed away fulcrum. � Does not occur often. � Muscle is at limit of shortening range and not exerting much force.

� Angle of pull = 90º § Force is all rotary. � Angle of pull = 45º § Rotary & non-rotary components are equal. � Muscular force functions: § Movement § Stabilization