WHAT'S YOUR ANGLE ON THE MATTER?
While movement is initiated neurally by the nervous system, and physically by the skeletal muscle, which exact movement will actually result depends completely on how the tendon of the skeletal muscle connects onto the bone. Thus, the rule of simplified motion analysis is "follow the tendon" as it will reveal everything needed in order to know the movement to happen.
Since the skeletal muscle pulls on the tendon, that in turn pulls on the bone, it is how the bone is pulled that will determine the movement that will result. Three optional movements exist: 1) Linear movement such as flexion, extension, adduction and abduction; 2) Diagonal movement resulting from a combination of linear movement and mild rotation; 3) Rotational movement such as pronation, supination, horizontal rotation, medial (internal) and lateral (external) rotation.
Advertisement
Linear movement is the outcome of the skeletal muscle's tendon connecting down the longitudinal midline of the bone. The skeletal muscle's tendon does not cross over the longitudinal midline of the bone nor loops around it. Diagonal movement is the outcome of the skeletal muscle's tendon diagonally crossing over the longitudinal midline of the bone. Rotation is the outcome of the skeletal muscle's tendon looping around the bone from its medial side (inward) to its lateral side (outwards) or vice versa.
A skeletal muscle's tendon that goes from the inner aspect of the bone and connects on to the outer aspect of the bone, will cause internal rotation, while a skeletal muscle's tendon that goes from the outer aspect of the bone and connects on to the inner aspect of the bone, will cause external rotation. The tendon will pull in the opposite direction of which it connected onto the bone.
Every skeletal muscle's head (cep) is analyzed differently with it own tendon, and its specific connection to the bone. This allows us to understand how one muscle can create more than one movement. The more heads the skeletal muscle has, the more possible influence it can have on a certain bone and joint. In theory, depending on how each muscle head's tendon connects onto the bone, it could also create diverse movements.
This image shows a long bone and its longitudinal midline with a dotted line on it.
Each yellow dot represents a possible insertion point of a muscle's tendon onto the longitudinal midline of the bone, causing linear movement (flexion, extension, adduction, or abduction).
Each yellow dot represents a possible insertion point of a muscle's tendon after it diagonally crosses the longitudinal midline of the bone, causing diagonal movement (flexion/extension with mild rotation OR adduction/abduction with mild rotation).
Advertisement
The straight line represents the muscle's tendon as it connects to the bone from the medial (inner) aspect onto the bone on its lateral (external) aspect. As the muscle pulls on the tendon, and in turn on the bone, internal rotation is created. The more the tendon loops around the bone before connecting physically, the greater the rotation created.
The straight line represents the muscle's tendon as it connects to the bone from the lateral (external) aspect onto the bone on its medial (inner) aspect. As the muscle pulls on the tendon, and in turn on the bone, external rotation is created. The more the tendon loops around the bone before connecting physically, the greater the rotation created.
Comentários