Series Preface

ix

Preface

xi

Acknowledgments

xiv

Credits

xv

Chapter 1

Muscle Fibers, Motor Units, and Motoneurons

1

Muscle Heterogeneity

2

Orderly Motor Unit Recruitment

7

Smaller Motoneurons Are More Excitable

9

Membrane Resistivity and Motoneuron Size

9

Other Factors Determining Action Potential Generation

11

Minimal Firing Rates and Afterhyperpolarization Durations

12

Motoneuron Current-Frequency Relationship and Excitability

15

Late Adaptation

17

Motoneuron PICs

20

Summary

23

Chapter 2

Motor Unit Recruitment During Different Types of Movements

25

Measuring Human Motor Unit Recruitment

25

Influence of Task

27

Slow-Ramp Isometric Contractions

28

Maintained Isometric Contractions

32

Isometric Contractions in Various Directions

34

Isometric Contractions Versus Movements

35

Lengthening Contractions

38

Cocontraction of Agonists and Antagonists

40

Unilateral Versus Bilateral Contractions

40

Rhythmic Complex Contractions

41

Maximal Voluntary Contractions

42

Summary

44

Chapter 3

Muscle Blood Flow and Metabolism

46

Muscle Blood Flow

46

Muscle Metabolism

53

Summary

60

Chapter 4

Peripheral Factors in Neuromuscular Fatigue

63

Intramuscular Factors and Muscle Force

64

Involvement of Structures Other Than Muscle

67

Research From Animal Experiments

77

Summary

80

Chapter 5

Central Factors in Neuromuscular Fatigue

83

Motoneuron Activity During Sustained Contractions

83

Isometric Versus Anisometric Tasks

98

Rotation of Motor Units?

99

Summary

99

Chapter 6

Muscular Mechanisms in Aerobic Endurance Training

101

Chronic Muscle Stimulation

102

Coordination of Muscle Protein Systems

104

Pretranslational Control

106

Translational Control

109

Posttranslational Modifications

110

Simultaneous Expression of Isoforms

112

Adaptations Can Occur Ex Vivo

112

Adaptations Appear in a Specific Sequence

112

Thresholds of Activity for Adaptation

114

Chronic Stimulation and Atrophy

115

Metabolic Signals and the Adaptive Response

117

Degenerative and Regenerative Processes

122

Summary

122

Chapter 7

Neural Mechanisms in Aerobic Endurance Training

125

Adaptation of the Neuromuscular Junction

125

Responses of Motoneurons

130

Adaptations of Spinal Cord Circuits

134

Summary

139

Chapter 8

Muscle Molecular Mechanisms in Strength Training

141

Acute Responses in Protein Synthesis and Degradation

142

Connective Tissue Responses

155

Role of Muscle Damage

156

Role of Dietary Supplements

157

Summary

158

Chapter 9

Muscle Property Changes in Strength Training

161

Increased Muscle Fiber Cross-Sectional Area

161

Fiber Type Composition

162

Muscle Fiber Number

163

Muscle Composition

165

Muscle Architecture

166

Muscle Fiber Ultrastructure

166

Evoked Isometric Contractile Properties

167

Changes in Muscle Force, Velocity, and Power

169

Fatigue Resistance

171

Role of Eccentric Contractions

171

Summary

173

Chapter 10

Neural Mechanisms in Strength Training

175

Gains in Strength Versus Muscle Girth

175

Strength Gains Show Task Specificity

176

Surface EMG Response During MVC

178

Imaginary Strength Training

179

Reflex Adaptations

179

Cross Education

181

Decreased Activation of Antagonists

183

Changes in Motor Unit Recruitment

183

Changes in Motor Cortex

186

Summary

186

References

189

Index

225

About the Author

229