Some of the forces that influence human movement:
|wind / water
The rules by which we draw a vector DEPEND ON THE TYPE OF FORCE THE VECTOR DEPICTS.
Point of application
Muscle's point of attachment to moving bone
Line of application
follows muscle or tendon fibers local to the joint being analyzed
toward center of muscle
Other important forces we'll need to depict using vectors are reaction forces.
Time out: a dose of common sense about forces from Fred Gram, Cuyahoga Community College.
Determine the vector's moment arm and determine the moment that gravity produces around the joint's axis in the plane depicted.
Decide which muscle forces act in a direction that produces moments that oppose gravity's moment.
Follow the rules for muscle forces to depict these muscle forces as vectors.
Determine each muscle vector's moment arm with respect to the joint axis.