UNIVERSITY OF OKLAHOMA GRADUATE COLLEGE AN EXAMINATION OF AGONIST AND ANTAGONIST MOTOR UNIT FIRING PROPERTIES A DISSERTATION SUBMITTED TO THE GRADUATE FACULTY in partial fulfillment of the requirements for the Degree of DOCTOR OF PHILOSOPHY By JASON DEFREITAS Norman, Oklahoma 2013 AN EXAMINATION OF AGONIST AND ANTAGONIST MOTOR UNIT FIRING PROPERTIES A DISSERTATION APPROVED FOR THE DEPARTMENT OF HEALTH AND EXERCISE SCIENCE BY ___________________________ Dr. Travis W. Beck, Chair ___________________________ Dr. Michael G. Bemben ___________________________ Dr. E.Laurette Taylor ___________________________ Dr. Paul W. Branscum ___________________________ Dr. Howard M. Crowson © Copyright by JASON M. DEFREITAS 2013 All Rights Reserved. ACKNOWLEDGEMENTS “If I have seen further it is only by standing on the shoulders of giants” – Isaac Newton, Feb. 15 1676 This particular quote is dear to me, as it so honestly and succinctly sums up how I feel. There are several individuals who have assisted me in pursuing and achieving the completion of this research and hence my doctoral degree. For all that I may have seen or accomplished, none of it would have been possible without having their many shoulders to stand on. First, my sincere appreciation goes to my mentor, Dr. Travis Beck. His expertise, guidance, and belief in me helped me develop into not only a better researcher, but a better person as well. His teachings go well beyond what can be learned from textbooks. I would also like to thank the other members of my committee, Drs. Bemben, Crowson, Taylor, and Branscum for their time, support, and invaluable input throughout the process. My sincere gratitude goes to my colleagues who have assisted me throughout the many stages of my research; especially the assistance and support provided by Matt Stock. Finally, I would like to give my deepest appreciation to my wife, Leigh DeFreitas. Her continuous patience, support, understanding, encouragement, and unwavering belief in me have allowed me to pursue my dreams. iv TABLE OF CONTENTS ABSTRACT .................................................................................................................. X CHAPTER 1 - INTRODUCTION ......................................................................................1 1.1. Introduction ..........................................................................................................1 1.2. Purpose of the Study .............................................................................................7 1.3. Research Questions ..............................................................................................7 1.4. Hypotheses ...........................................................................................................8 1.5. Significance of the Study ....................................................................................10 1.6. Delimitations ......................................................................................................11 1.7. Limitations ..........................................................................................................11 1.8. Assumptions .......................................................................................................12 1.9. Threats to Validity ..............................................................................................13 CHAPTER 2 - REVIEW OF LITERATURE ....................................................................14 2.1. Agonist/Antagonist Interaction and Peripheral Feedback ..................................14 Summary ............................................................................................ 45 2.2. Motor Unit Firing Properties ..............................................................................47 Summary ............................................................................................ 76 2.3. Motor Unit Synchronization ...............................................................................79 Summary .......................................................................................... 117 2.4. Effects of Fatigue on Neuromuscular Function ................................................119 Summary .......................................................................................... 136 2.5. Effects of Stretching on Neuromuscular Function ...........................................137 Summary .......................................................................................... 146 v CHAPTER 3 - METHODS ..........................................................................................148 3.1. Participants .......................................................................................................148 3.2. Research Design ...............................................................................................148 3.3. Instrumentation and Procedures .......................................................................151 3.3.1. Isometric Strength Assessment .............................................. 151 3.3.2. Submaximal Muscle Actions ................................................. 152 3.3.3. Fatiguing Protocol .................................................................. 153 3.3.4. Stretching Protocol ................................................................. 154 3.3.5. Electromyography .................................................................. 155 3.3.6. Signal Processing ................................................................... 157 3.3.7. EMG Decomposition ............................................................. 157 3.3.8. Motor Unit Synchronization .................................................. 158 3.3.9. Estimation of Net Post-Synaptic Potentials ........................... 162 3.4. Statistical Analyses ...........................................................................................165 CHAPTER 4 - RESULTS ............................................................................................166 4.1. Descriptives ......................................................................................................166 4.2. Effects of Agonist Fatigue on Neuromuscular Function ..................................167 4.3. Effects of Antagonist Fatigue on Neuromuscular Function .............................172 4.4. Effects of Prolonged Agonist Stretching on Neuromuscular Function ............177 4.5. Effects of Prolonged Antagonist Stretching on Neuromuscular Function .......182 CHAPTER 5 - DISCUSSION .......................................................................................187 5.1. Implications and Significance ..........................................................................187 5.2. Limitations ........................................................................................................192 5.3. Future Research Needs .....................................................................................194 CONCLUSIONS .........................................................................................................195 vi REFERENCES ...........................................................................................................197 APPENDICES ............................................................................................................217 A. Abbreviations ......................................................................................................217 B. Glossary/Operational Definitions .......................................................................218 C. Data Collection Form .........................................................................................223 D. Informed Consent ...............................................................................................228 E. Pre-Exercise Health Questionnaire .....................................................................229 F. Recruitment Flyer ...............................................................................................230 vii LIST OF TABLES TABLES 1. Stretches for the Biceps Brachii muscle ................................................154 2. Stretches for the Triceps Brachii muscle ...............................................155 viii LIST OF FIGURES FIGURES 1. Summary of agonist and antagonist inputs ................................................4 2. Testing setup for isometric strength assessment ....................................151 3. Trapezoidal template for force-tracking ................................................152 4. Fatigue Protocol .....................................................................................153 5. Example of decomposition output .........................................................161 6. Example of synchronization and nPSP output .......................................164 7. Agonist Fatigue results: Force and EMG ...............................................168 8. Agonist Fatigue results: Averaged Motor Unit Variables .....................169 9. Agonist Fatigue results: MFR/RT relationships ....................................170 10. Agonist Fatigue results: Sync Index/Mean RT relationships...............171 11. Antagonist Fatigue results: Force and EMG ........................................173 12. Antagonist Fatigue results: Averaged Motor Unit Variables ..............174 13. Antagonist Fatigue results: MFR/RT relationships .............................175 14. Antagonist Fatigue results: Sync Index/Mean RT relationships ..........176