A Biomechanical Characterisation of Eccentric and Concentric Loading of the Triceps Surae Complex A thesis submitted for the degree of Doctor of Philosophy by Saira Chaudhry School of Engineering and Material Science Centre for Sports and Exercise Medicine Queen Mary University of London December 2012 Abstract This thesis presents a biomechanical characterisation of eccentric (EL) and concentric loading (CL) of the triceps surae. EL is commonly adopted as an effective treatment for Achilles tendinopathy, with notably better treatment success compared with CL. However, there is a lack of consensus about the most appropriate protocols for completing triceps surae exercises. Exercise parameters such as speed and load are important and may affect the stimuli sensed by the muscle-tendon unit and thus influence repair. This thesis aims to biomechanically characterise and compare EL and CL as a basis for trying to understand treatment effects. A measuring system comprising motion tracking, 2D ultrasound, force plates and EMG was adopted and a semi-automatic tracking algorithm developed to track the muscle-tendon junction throughout the loading cycle (Chapter 3). Having validated the accuracy of measurements (Chapter 4), the effect of variables such as speed of exercise (chapter 5) and addition of load (Chapter 6) were assessed on Achilles tendon force, stiffness, stress, strain and force perturbations as well as muscle activation and contraction frequency (Chapter 7), in healthy subjects. It was found that EL and CL do not differ in terms of tendon force, stiffness or strain. However, EL is characterised by lower muscle activation and by 10 Hz perturbations present within the tendon. These perturbations were found to be significantly dependent on movement speed and load applied during EL movements only. However, no effect of speed was found on tendon force, stiffness and strain during either exercise movement. Finally, temporo-spatial analysis of the calf revealed region specific variations in muscle activation during both EL and CL, with 10 Hz perturbations coming predominantly from medial soleus and medial gastrocnemius muscle activity. These studies provide new information about the biomechanics of EL or CL, which should enhance understanding, and development, of conservative Achilles tendinopathy management. ii Acknowledgment Thanks to Almighty Allah and His prophet Muhammad (PBUH) and my Sarkar Mubarak to whom I would like to dedicate this thesis. I would like to give my sincere thanks to my supervisors, Dr. Hazel Screen and Dr. Dylan Morrissey for their guidance and much valued advice throughout the study. They have been a great source of inspiration. I am grateful for the freedom offered to explore my ideas and their continual encouragement to think beyond the limits. I could not have wished for better, more encouraging supervisors and I find myself indebted to them more than they know. Without their encouragement and effort, this thesis would not have been possible. I would like to express thanks to Professor Roger Woledge, for introducing me to the field of biomechanics and developing my knowledge of MatLab. His generous support and optimism throughout my PhD remained a great source of inspiration in developing confidence in my abilities. His great experience in the field of biomechanics helped me greatly to understand and explore analytical skills and mathematical models to analyse huge amount of data. I would also like to give a special thanks to Professor Dan Bader for his continual support, encouragement and analytical thoughts towards the project. These studies would not have been possible without the subjects who gave willingly of their time and Centre for Sports and Exercise medicine that helped with recruiting. My colleagues and friends were always there to discuss and help – Richard, Mark, Hassan, Ali and others were a great source of inspiration and encouragement. I would also like to thank three fellow students Dr Billy Leung for sketching the line drawings of the lower leg for this thesis, Dr Liz Sweeney and Jennifer Graham for helping in recruitment and data collection. And finally for their love, dedication and belief in me, I owe great thanks to my family, my spiritual mother Api Jan, my mother, my sister, my daughter Hafsa, son Muhammad Haseeb and my husband Amir. I certainly would not have gotten this far without them. iii Table of Contents Table of Contents ........................................................................................................................ iv List of Figures ............................................................................................................................ viii List of Tables ............................................................................................................................ xvii List of Abbreviations ............................................................................................................... xviii 1 Chapter 1: Introduction and Literature Review ...................................................................... 1 1.1 Introduction ............................................................................................................ 2 1.2 Anatomy ................................................................................................................. 4 1.2.1 Triceps surae complex ........................................................................................ 4 1.2.2 Achilles tendon ................................................................................................... 6 1.2.3 Tendon composition ........................................................................................... 9 1.2.4 Tendon microstructure ..................................................................................... 10 1.2.5 Ankle ................................................................................................................. 12 1.2.6 Joint coordinate system .................................................................................... 13 1.3 Tendon mechanics ................................................................................................ 15 1.3.1 Mechanical Properties ...................................................................................... 16 1.4 Tendon pathology ................................................................................................. 19 1.4.1 Tendon strain injury ......................................................................................... 19 1.4.2 Tendon rupture ................................................................................................. 19 1.4.3 Tendinopathy ................................................................................................... 20 1.5 Achilles Tendinopathy Diagnosis .......................................................................... 23 1.6 Tendinopathy Management ................................................................................. 25 1.7 Loading of the triceps surae complex ................................................................... 29 1.8 Eccentric Loading .................................................................................................. 29 1.9 Eccentric vs Concentric Loading ............................................................................ 32 1.10 Biomechanics of Eccentric training ....................................................................... 34 1.10.1 Tendon Loading ............................................................................................ 34 1.10.2 Muscle activation ......................................................................................... 35 1.10.3 Force Perturbations ...................................................................................... 37 1.11 Optimal application of Eccentric loading? ............................................................ 39 1.11.1 Speed ............................................................................................................ 45 1.11.2 Load.............................................................................................................. 48 1.11.3 Dose ............................................................................................................. 49 1.12 Conclusions ........................................................................................................... 52 2 Chapter 2: Aims and Objectives ........................................................................................... 53 2.1 Aims ...................................................................................................................... 54 2.2 Objectives ............................................................................................................. 54 2.3 Hypotheses ........................................................................................................... 55 3 Chapter 3: Materials and Methods ..................................................................................... 57 3.1 Introduction .......................................................................................................... 58 3.2 Experimental techniques and equipment ............................................................. 58 3.2.1 Electromyography ............................................................................................ 59 3.2.1.1 General background ...............................................................................