By studying this chapter, you should be able to do the following:
Draw and label the microstructure of a skeletal muscle fiber.
Define satellite cells. What role do satellite cells play in muscle repair from injury?
List and explain the chain of events that occur during muscular contraction.
Define both dynamic and static exercise. What types of muscle action occur during each form of exercise?
Describe the three factors that determine the amount of force produced during muscular contraction.
Compare and contrast the major biochemical and mechanical properties of the three primary types of muscle fibers found in human skeletal muscle.
Describe how skeletal muscle fiber types influence athletic performance.
Graph and describe the relationship between movement velocity and the amount of force exerted during muscular contraction.
Structure of Skeletal Muscle
Energy for Contraction 184 Regulation of Excitation-Contraction Coupling
Exercise and Muscle Fatigue
Exercise-Associated Muscle Cramps
Exercise-Associated Muscle Cramps Are Not Caused by Dehydration or Electrolyte Imbalance
Exercise-Associated Muscle Cramps Are Likely Due to Changes in the Central Nervous System
Exercise-Associated Muscle Cramps: Conclusions
Muscle Fiber Types
Overview of Biochemical and Contractile Characteristics of Skeletal Muscle
Functional Characteristics of Muscle Fiber Types
Fiber Types and Performance
Speed of Muscle Action and Relaxation
Force Regulation in Muscle
end-plate potential (EPP)
neuromuscular junction (NMJ)
sliding filament model
swinging lever-arm model
type I fibers
type IIa fibers
type IIx fibers
The human body contains more than 600 skeletal muscles, which constitute 40% to 50% of the total body weight (61). Skeletal muscle performs three important functions: (1) force generation for locomotion and breathing, (2) force generation for postural support, and (3) heat production during cold stress. The most obvious function of skeletal muscle is to enable an individual to move freely and breathe. New evidence also suggests that skeletal muscles are endocrine organs and play an important role in the regulation of a variety of organ systems in the body. This concept was introduced in Chap. 5 and will be mentioned again in this chapter.
Skeletal muscles are attached to bones by connective tissue called tendons. One end of the muscle is attached to a bone that does not move (origin), and the opposite end is fixed to a bone (insertion) that is moved during muscular contraction. A variety of different movements are possible, depending on the type of joint and muscles involved. Muscles that decrease joint angles are called flexors, and muscles that increase joint angles are called extensors.