Apply the principles of resolution of forces, composition of forces, and trigonometry to calculate the magnitude and direction of muscle and joint forces acting on the human body.
 

1. Rarely linear, parallel, or perpendicular
2. Usually applied at angles

1. Allows visualization of effect of angular forces
2. Breaks resultant force into parallel and perpendicular components
3. Facilitates determination of torque and calculation of muscle and joint forces

1. Rotary perpendicular to the long axis of the lever arm (bone)
2. Rotary components are used to calculate torque
3. Compressive or Distractive parallel to the long axis of the lever arm (bone), perpendicular to the rotary component

1. Make the resultant force the hypotenuse of a right triangle
2. Make the rotary and compressive/distractive component forces the
3. sides of the right triangle
4. Use trigonometric functions to calculate magnitudes and directions of the unknown forces

1. Sine = opp / hyp
2. Cosine = adj / hyp
3. Tangent = opp / adj