Chapter 2

After completing this chapter, you will be able to:

• Provide examples of linear, angular, and general forms of motion.
• Identify and describe the reference positions, planes, and axes associated with the human body.
• Define and appropriately use directional terms and joint movement terminology.
• Explain how to plan and conduct an effective qualitative human movement analysis.
• Identify and describe the uses of available instrumentation for measuring kinematic quantities.

Is it best to observe walking gait from a side view, front view, or back view? From what distance can a coach best observe a pitcher’s throwing style? What are the advantages and disadvantages of analyzing a movement captured on video? To the untrained observer, there may be no differences in the forms displayed by an elite hurdler and a novice hurdler or in the functioning of a normal knee and an injured, partially rehabilitated knee. What skills are necessary and what procedures are used for effective analysis of human movement kinematics?

One of the most important steps in learning a new subject is mastering the associated terminology. Likewise, learning a general analysis protocol that can be adapted to specific questions or problems within a field of study is invaluable. In this chapter, human movement terminology is introduced, and the problem-solving approach is adapted to provide a template for qualitative solving of human movement analysis problems.

Most human movement is general motion, a complex combination of linear and angular motion components. Since linear and angular motion are “pure” forms of motion, it is sometimes useful to break complex movements down into their linear and angular components when performing an analysis.

### Linear Motion

Pure linear motion involves uniform motion of the system of interest, with all system parts moving in the same direction at the same speed. Linear motion is also referred to as translatory motion, or translation. When a body experiences translation, it moves as a unit, and portions of the body do not move relative to each other. For example, a sleeping passenger on a smooth airplane flight is being translated through the air. If the passenger awakens and reaches for a magazine, however, pure translation is no longer occurring because the position of the arm relative to the body has changed.

Linear motion may also be thought of as motion along a line. If the line is straight, the motion is rectilinear; if the line is curved, the motion is curvilinear. A motorcyclist maintaining a motionless posture as the bike moves along a straight path is moving rectilinearly. If the motorcyclist jumps the bike and the frame of the bike does not rotate, both rider and bike (with the exception of the spinning wheels) are moving curvilinearly while airborne. Likewise, a Nordic skier coasting in a locked static position down a short hill is in rectilinear motion. If the skier jumps over a ...

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