STUDIES IN SPORT, PHYSICAL EDUCATION AND HEALTH 242 JenniLauri Kulmala Stenroth Structure and Function of Human triceps surae Muscle and Tendon in Aging STUDIES IN SPORT, PHYSICAL EDUCATION AND HEALTH 242 Lauri Stenroth Structure and Function of Human triceps surae Muscle and Tendon in Aging Esitetään Jyväskylän yliopiston liikuntatieteellisen tiedekunnan suostumuksella julkisesti tarkastettavaksi yliopiston vanhassa juhlasalissa S212 syyskuun 2. päivänä 2016 kello 12. Academic dissertation to be publicly discussed, by permission of the Faculty of Sport and Health Sciences of the University of Jyväskylä, in building Seminarium, auditorium S212, on Sebtember 2, 2016 at 12 o’clock. UNIVERSITY OF JYVÄSKYLÄ JYVÄSKYLÄ 2016 Structure and Function of Human triceps surae Muscle and Tendon in Aging STUDIES IN SPORT, PHYSICAL EDUCATION AND HEALTH 242 Lauri Stenroth Structure and Function of Human triceps surae Muscle and Tendon in Aging UNIVERSITY OF JYVÄSKYLÄ JYVÄSKYLÄ 2016 Editors Taija Juutinen Faculty of Sport and Health Sciences, University of Jyväskylä Pekka Olsbo Publishing Unit, University Library of Jyväskylä URN:ISBN:978-951-39-6715-4 ISBN 978-951-39-6715-4 (PDF) ISBN 978-951-39-6714-7 (nid.) ISSN 0356-1070 Copyright © 2016, by University of Jyväskylä Jyväskylä University Printing House, Jyväskylä 2016 ABSTRACT Stenroth, Lauri Structure and function of human triceps surae muscle and tendon in aging Jyväskylä: University of Jyväskylä, 2016, 87 p. (Studies in Sport, Physical Education and Health ISSN 0356-1070; 242) ISBN 978-951-39-6714-7 (nid.) ISBN 978-951-39-6715-4 (PDF) Aging is associated with loss of muscle mass leading to impairments in muscle function, such as loss of muscle strength or power. These impairments may eventually lead to physical disabilities. Although loss of muscle mass has a major role in age-related loss of muscle function, there is a disproportionate loss of muscle strength and power with aging suggesting that other factors are also involved. These other factors may include age-related modifications in muscle architecture and tendon mechanical properties, factors that have a significant effect on muscle function. Currently there is no consensus about age-related changes in muscle architecture or tendon mechanical properties, or their role in age-related impairments of physical function. Therefore, the aim of this thesis was to examine associations between aging and muscle architecture, tendon mechanical properties and muscle-tendon function during walking in the human triceps surae muscle by comparing healthy young and older adults. Associations between tests of physical function and triceps surae muscle- tendon properties were also investigated in older adults. The results suggested only modest effects of aging on triceps surae muscle architecture and Achilles tendon mechanical properties. However, inter-individual differences in triceps surae muscle architecture and Achilles tendon stiffness explained variance in 6- minute walk test and in timed “up-and-go” –test in older adults. Muscle-tendon function was found to be dependent on walking speed in older adults, with no significant differences between young and older adults when compared at matched walking speed. These results suggest that the commonly observed age-related slowing of preferred walking speed may represent an attempt to compensate for loss of muscle strength in triceps surae muscle. In conclusion, the results of the current thesis suggest that aging may be related to changes in triceps surae muscle architecture and Achilles tendon mechanical properties. However, these changes seem to be part of an adaptation process that helps to maintain muscle function despite declines in muscle mass and strength with aging. Keywords: triceps surae, Achilles tendon, muscle architecture, stiffness, aging Author’s address Lauri Stenroth Department of Biology of Physical Activity University of Jyväskylä P.O. Box 35 40014 University of Jyväskylä Finland [email protected] Supervisors Professor Taija Finni, PhD Department of Biology of Physical Activity University of Jyväskylä, Finland Professor Sarianna Sipilä, PhD Department of Health Sciences University of Jyväskylä, Finland Docent Neil Cronin, PhD Department of Biology of Physical Activity University of Jyväskylä, Finland Reviewers Senior Researcher Kiros Karamanidis, PhD Institute of Movement and Sport Gerontology German Sport University Cologne, Germany Associate Professor Glen A Lichtwark, PhD The School of Human Movement and Nutrition Sciences University of Queensland, Australia Opponent Professor Bill Baltzopoulos, PhD Faculty of Science School of Sport and Exercise Sciences Liverpool John Moores University, UK ACKNOWLEDGEMENTS I began my studies in sports science majoring in biomechanics without really knowing what biomechanics is. However, it became clear to me at the very be- ginning of my studies that I had chosen the right discipline. Lectures given by Professor Taija Finni were the ones that got me really excited about biomechan- ics. She has continued to be a source of inspiration throughout my studies ever since. I am most grateful for my supervisors: Professors Taija Finni and Sarianna Sipilä and Docent Neil Cronin. One could not have hoped for better supervisors; Taija’s and Neil’s expertise in muscle-tendon biomechanics and Sarianna’s vast experience and expertise in exercise gerontology were an unbeatable combina- tion. With their guidance they ensured my growth from student to researcher. I started to work with tendons when I had a chance to work in Dr. Jussi Peltonen’s project for my bachelor’s thesis. That was the starting point of our collaboration and friendship. I have learned most of my skills in measurement techniques and analysis from Jussi. The numerous fruitful discussions led to great ideas and better understanding of the matters discussed. I would not be here today without your help. I want to thank all the students and staff both at the Department of Biolo- gy of Physical Activity and at the Gerontology Research Center at the Depart- ment of Health Sciences. It has been a privilege to work with and deepen my understanding of the human locomotor system with you. The atmosphere that such intelligent people create has been truly inspiring and you have made the journey pleasant and fulfilling. I particularly want to thank Arto Pesola who has walked the same path with me since the start of my studies. I thank the technical staff of the department, Markku Ruuskanen and Sir- pa Roivas, who keep the labs running and who have been miracle makers if some device happened to malfunction. I also want to take this opportunity to thank the department’s secretaries, Katja Pylkkänen and Minna Herpola, who keep the department running and help with various daily tasks. I also want to thank my high jump coach, Juha Isolehto. He has been an important person during my years in Jyväskylä. He inspired me to study sport science and biomechanics. My parents, Eija and Markku, planted the seed of my scientific career with their respect for education and scholarship. They gave me a safe and secure home to grow up in. I am also lucky to have an older brother, Ilari, to look up to. I am thankful to Teija and Ari, my mother and father in law, for their support and encouragement during the process. I am fortunate to have such a loving family. Financial support for the preparation of this theses and associated con- gress trips have been provided by The European Union, The Finnish Cultural Foundation, Emil Aaltonen Foundation and Jyväskylän yliopiston tieteentekijät RY. Also the Department of Biology of Physical Activity and the Department of Health Sciences have significantly contributed to this thesis by providing facili- ties to conduct the studies. None of the studies would have been possible with- out the subjects. I am thankful for your participation. I also want to thank all of my coauthors of the original publications for your help. Finally, I am most grateful to my wife Elisa. You have supported me daily throughout my studies and thesis writing. You have always managed to en- courage me and push me forward. You have shared the load when it has been too heavy to be carried alone. Most importantly, you have reminded me that there is still life outside science. I look forward to our future adventures. Jyväskylä 24.4.2016 Lauri Stenroth LIST OF ORIGINAL PUBLICATIONS This thesis is based on four original papers, which are referred to by the follow- ing roman numerals: I Stenroth L, Peltonen J, Cronin NJ, Sipilä S & Finni T. 2012. Age-related differences in Achilles tendon properties and triceps surae muscle archi- tecture in vivo. Journal of Applied Physiology 113(10), 1537-1544. II Stenroth L, Sillanpää E, McPhee JS, Narici MV, Gapaeyeva H, Pääsuke M, Barnouin Y, Hogrel J-Y, Butler-Browne G, Biljsma A, Meskers CGM, Maier AB, Finni T & Sipilä S. 2015. Plantarflexor muscle-tendon properties are associated with mobility in healthy older adults. The Journals of Gerontol- ogy. Series A, Biological Sciences and Medical Sciences 70(8), 996-1002. III Stenroth L, Cronin NJ, Peltonen J, Korhonen MT, Sipilä S & Finni T. 2015. Triceps surae muscle-tendon properties in older endurance- and sprint- trained athletes. Journal of Applied Physiology 120, 63-69. IV Stenroth L, Sipilä S, Finni T, Cronin NJ. Slower walking speed in older adults improves triceps surae force generation ability. Medicine & Science in Sports & Exercise, doi: 10.1249/MSS.0000000000001065. ABBREVIATIONS CSA Cross-sectional area EMG