Chapter 6

### INTRODUCTION

After completing this chapter, you will be able to:

• Identify the basic behavioral properties of the musculotendinous unit.

• Explain the relationships of fiber types and fiber architecture to muscle function.

• Explain how skeletal muscles function to produce coordinated movement of the human body.

• Discuss the effects of the force–velocity and length–tension relationships and electromechanical delay on muscle function.

• Discuss the concepts of strength, power, and endurance from a biomechanical perspective.

What enables some athletes to excel at endurance events such as the marathon and others to dominate in power events such as the shot put or sprinting? What characteristics of the neuromuscular system contribute to quickness of movement? What exercises tend to cause muscular soreness? From a biomechanical perspective, what is muscular strength?

Muscle is the only tissue capable of actively developing tension. This characteristic enables skeletal, or striated, muscle to perform the important functions of maintaining upright body posture, moving the body limbs, and absorbing shock. Because muscle can only perform these functions when appropriately stimulated, the human nervous system and the muscular system are often referred to collectively as the neuromuscular system. This chapter discusses the behavioral properties of muscle tissue, the functional organization of skeletal muscle, and the biomechanical aspects of muscle function.

### BEHAVIORAL PROPERTIES OF THE MUSCULOTENDINOUS UNIT

The four behavioral properties of muscle tissue are extensibility, elasticity, irritability, and the ability to develop tension. These properties are common to all muscle, including the cardiac, smooth, and skeletal muscle of human beings, as well as the muscles of other mammals, reptiles, amphibians, birds, and insects.

The characteristic behavioral properties of muscle are extensibility, elasticity, irritability, and the ability to develop tension.

#### Extensibility and Elasticity

The properties of extensibility and elasticity are common to many biological tissues. As shown in Figure 6-1, extensibility is the ability to be stretched or to increase in length, and elasticity is the ability to return to normal length after a stretch. Muscle's elasticity returns it to normal resting length following a stretch and provides for the smooth transmission of tension from muscle to bone.

###### FIGURE 6-1

The characteristic properties of muscle tissue enable it to extend, recoil, and contract.

The elastic behavior of muscle has been described as consisting of two major components. The parallel elastic component (PEC), provided by the muscle membranes, supplies resistance when a muscle is passively stretched. The series elastic component (SEC), residing in the tendons, acts as a spring to store elastic energy when a tensed muscle is stretched. These components of muscle elasticity are so named because the membranes and tendons are respectively parallel to and in series (or in line) with the muscle fibers, which provide the contractile component (Figure 6-2...

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