For example, in the image below the joint angle is 60° and the reference position is a nearly horizontal forearm creating a 90° between the bicep muscle and the bones of the forearm. (This is not nece...For example, in the image below the joint angle is 60° and the reference position is a nearly horizontal forearm creating a 90° between the bicep muscle and the bones of the forearm. (This is not necessarily how the reference angle is defined for measuring elbow range of motion by health professionals) The distance we are trying to calculate is known as the arc length, and to find it we multiply the angle in units of radians by the distance from the rotation point (also known as the radius).
