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After completing this chapter, you will
be able to:
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- 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.
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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?
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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.
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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.
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Extensibility
and Elasticity
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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.
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The elastic behavior of muscle has been described as consisting
of two major components (41, 65). 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). The elasticity of human skeletal muscle is believed to be
due primarily to the SEC. Modeling studies show that the height
of a jump increases when ...