[Mathew]

The right arm is always in a state of extending or trying to become straight which is a non accelerating thrust hence not moving the left arm. You can probably guess this is called extensor action.

The left arm is connected to the left shoulder and can move around this point with its range of motion being spherical. The right forefinger or pp3 traces back this line and then lifts the primary lever assembly upwards on the vertical hinge action plane. Because this plane is inside a sphere and goes through a center point (left shoulder) this means that the upwards motion is circular and because of such, the structure of the right arm has to collapse as this tracing occurs inorder to lift the left arm on this plane. This is the primary cause of loading acc no.1.