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Greatness lies not in being strong, but in the right use of strength.

—Henry Ward Beecher, 1813–1887 Congregationalist, clergyman, social reformer, abolitionist, and orator



This chapter discusses muscle structure and activity and factors that produce or affect muscle strength. By the end of this chapter, you should be able to:

  • Explain the differences in various muscle activation methods;

  • Identify the differences in muscle fiber types and their significance in muscle function;

  • Discuss the differences between the types of muscle functions;

  • Provide an explanation of the stress-strain curve and its relevance to stretching tissue;

  • Create two examples of active and passive muscle insufficiency;

  • List and explain the components that determine muscle force;

  • Outline the importance of lever arm length and muscle length in terms of muscle force production;

  • Discuss eccentric muscle force and how it impacts muscle injury.



Two promising track athletes on scholarships at Rochester State University have been in this country for only a couple of weeks. They are both from Ireland and have never experienced workouts as extensive as those that their new coach has been having them perform since they arrived on campus. Both athletes, Owain and Xavier, reported to the injury clinic this morning. They each suffered the same complaints. They had a lot of pain in their hamstrings and calf muscles after their long hill workouts yesterday. They both complained that it was difficult to get out of bed, and the pain in their hamstrings was especially uncomfortable. The clinician who examined each of them found it curious that they both suffered the same symptoms, but she suspected that she knew what the problem was.


In the last chapter, we explored the microscopic elements involved in muscle structure and the neural elements that provided muscle activity and responses. This chapter explores the muscles at a macroscopic level. Now that you have an appreciation of the physiological function of the neuromuscular system, we can move on to realize what happens when the factors you learned in the last chapter are put to functional use. This chapter will help you understand how muscles move joints and limbs to produce daily activity and functions without a thought given to their effort. Whereas the last chapter dealt with physiology, this chapter deals with mechanics.

To make muscle mechanics easier to understand, muscle forces are depicted as acting at a single point on the body. This simplification is helpful in demonstrating principles of biomechanics, but it is important to keep in mind that many complex forces impact function. Muscles are not the only force producers affecting motion. Other soft tissues may also transmit forces of muscles through their attachments to fascia, ligaments, cartilage, joint capsules, and tendons of other muscles, as well as to bones. Active and passive structures affecting motion are ...

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