6 Copyright Goodheart-Willcox Co., Inc. 166 The Muscular System Chapter 6 Outline Section 6.1 Types and Functions of Muscle Tissue • Muscle Categories • Functions of Muscles Section 6.2 Skeletal Muscle Physiology • Motor Units • Types of Skeletal Fibers • Strength, Power, and Endurance • Directional Motions Section 6.3 Major Skeletal Muscles • Muscles of the Head and Neck • Muscles of the Trunk • Muscles of the Upper Limb • Muscles of the Lower Limb Section 6.4 Development of Muscles • Development and Growth of Muscles • Aging and Sarcopenia Section 6.5 Common Muscle Injuries and Disorders • Muscle Injuries • Muscle Disorders M uscle is the only human tissue capable of shortening, or contracting. This unique ability is what makes purposeful body movements possible. Without muscle, the powerful movements required in athletic performances would be impossible, as would the finely tuned movements needed to thread a needle, send a text message, or play a musical instrument. Muscles also control the movements of the eyes, the movement of food through the digestive system, and the beating of the heart. What enables muscle to be so versatile? This chapter describes the different types, properties, and structures of muscle and examines the effects of different kinds of physical training on skeletal muscle. It also discusses some of the common muscle injuries and disorders, how these problems tend to occur, and how their likelihood, in some cases, can be reduced. Clinical Case Study Mike played varsity basketball in high school and now, in his second year of college, he still enjoys an occasional pick-up game with his friends. In a friendly game just yesterday he had an opening to break around two defenders and sprinted to make a layup shot. But he did not make it to the basket because in mid-stride he suddenly felt a sharp pain on the mid-posterior aspect of his right thigh. Today Mike cannot walk without limping, although he does not have any swelling in his thigh. He decides to head over to the student health center to find out what to do. Based on the description of his situation and symptoms, what diagnoses are possible, and which seems most likely? Given the description, what grade is his injury? Chad Zuber/Shutterstock.com