Kinetics - Pt 1 Continued

line of action: internal moment

parallel to the direction of the muscle fibers

point of application: internal moment

at the attachment of the muscle on the moving segment

direction: internal moments

toward the stabilizing segment

angle of application: internal moment

angle between the line of action of the muscle (tendon) and the long axis of the bone onto which the tendon inserts

moment arm

perpendicular distance from the linear force to the axis (makes 90 degree angle with the line of action)

force vector

attaches on the segment → line of action can be extended past the segment

line of action: external moment

• gravity and added resistance (extra weight): vertical

• added resistance: in line of directed force

point of application: external force

• gravity and added resistance - free weight: at the weight CoM

• added resistance - manual: at the point of contact

moment arm: external moment

line that is perpendicular to the line of action of external force to the joint axis of rotation

if line of action of muscle passes anterior to coronal axis, what will happen?

muscle will flex the joint (exception → the knee)

if line of action passes posteriorly to the frontal axis, what will happen?

muscle will extend

if line of action of a muscle passes superiorly to the A/P axis, what will happen?

muscle will abduct

if line of action of muscle passes inferiorly to the sagittal plane or A/P axis, what will happen?

muscle will adduct