Figure 1.9 Linear movement occurs in a straight line along a coordinate of the Cartesian coordinate system.
Figure 1.10 A sagittal view of the wrist in flexion. Linear movement (arrows) occurs between carpal bones during wrist movement.
x y
Figure 1.11 During the gait cycle, the entire body moves in a linear motion, whereas the center of gravity of the body moves in a curvilinear motion. The highest point of the curve occurs during mid-stance of the limb; the lowest point occurs during heel strike.
ROTARY MOTION
Rotation or rotary motion (also called angular motion) describes the arc of motion of a body around an axis. Joints in which the body part moves in a circular path around a pivot point represent this axis of rotation. An example of rotary motion is when the lower leg rotates around the knee joint axis during fl exion. Rotary motion also occurs in the frontal plane as the arm or leg moves
in abduction and adduction in the frontal plane around a sagittal axis. During rotary motion, each point on the limb moves in the same direction, time, and angle but through different distances. The movement is measured using the polar coordinate system, which documents the angle in one dimension between two fi xed points and is measured in degrees. In Figure 1.12, the lower leg is rotating around the knee joint axis from 0° to 90° of motion.
