Chapter 21

### Outline

• Meaning of Impact and Its Reception

Problems and Concepts

Falls and Landings

Protective Equipment

Catching

• Principles in Receiving Impact

Related to Avoiding Injury

Related to Maintaining and Regaining Equilibrium

Related to Accuracy and Control

• Laboratory Experiences

### Objectives

At the conclusion of this chapter, the student should be able to:

1. Name the common problems associated with the diverse forms of receiving impact.

2. Explain how the work–energy, impulse–momentum, and pressure–area relationships apply to receiving the impact either of one's own body or of external objects.

3. State the principles related to avoiding injury while receiving impact, and furnish an application for each.

4. State the principles related to maintaining and regaining equilibrium while receiving impact, and furnish an application for each.

5. State the principles related to accuracy and control while receiving impact, and furnish an application for each.

### Meaning of Impact and Its Reception

The word impact is derived from the Latin word impingere, “to press together.” Impact is further defined as force of contact, violent collision, striking together. Receiving impact is opposing or resisting in some manner the force with which a moving body tends to maintain its speed and direction. Impact may be from one's own body, as in landing from a jump or fall, or imparted by external objects, as in catching or spotting.

Impact of one's own body is experienced following any fall through space. Such falling motion, which occurs subsequent to a jump, a dive, or an accidental fall, has a rapidly increasing velocity because of the uniform acceleration effect of gravitational force. When the body lands on a supporting surface, impact has been said to occur. The impact is felt as the force of contact. Likewise, impact is experienced in a horizontally moving body when the motion is stopped as a result of contact with a resisting surface, such as a wall or another obstacle.

Examples of receiving impact from external objects are commonly seen in sports. Baseballs are caught or fielded with the hands, hockey balls and pucks are received with a stick, soccer balls are trapped with the feet, and blows from an opponent's fist are received by various parts of the body. Examples of receiving impact are also seen in industry and in daily life. Cartons and tools are tossed from one person to another, red-hot rivets are caught in tongs, and victims from a fire are caught in nets or air bags.

Impact generally has a negative connotation, but there are benefits to controlled impacts, such as mechanical loading of bone during walking. Specifically, it is widely accepted that bone will adapt to the mechanical stresses placed upon it. Intuitively, it is apparent that the bones of adults and adolescents will not adapt in the same manner, yet the bones of both groups are altered by mechanical loading (Ruff ...

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