PLAYER PERCEPTIONS AND BIOMECHANICAL RESPONSES TO TENNIS COURT SURFACES: THE IMPLICATIONS TO TECHNIQUE AND INJURY RISK Submitted by Chelsea Starbuck, to the University of Exeter as a thesis for the degree of Doctor of Philosophy in Sport and Health Sciences September 2014 This thesis is available for Library use on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. I certify that all material in this thesis which is not my own work has been identified and that no material has previously been submitted and approved for the award of a degree by this or any other University. (Signature) ……………………………………………………………………………… 1 Abstract Elite tennis players are required to perform on a variety of tennis court surfaces which differ in mechanical characteristics, such as friction and hardness, influencing their performance and risk of injury. To understand the influence of surfaces on performance and injury risk, three studies were conducted to investigate tennis players’ perceptions and biomechanical responses during tennis-specific movements on different court surfaces. In study 1, tennis players perceptions of acrylic and clay courts were identified following a thematic inductive analysis of semi-structured interviews (n = 7) to develop of a series of visual analogue scales (VAS) to quantify perceptions during studies 2 and 3. Perceptions of predictability of the surface and players’ ability to slide and change direction emerged, in addition to anticipated perceptions of grip and hardness. Study 2 aimed to examine the influence of court surfaces and prior clay court experience on perceptions and biomechanical characteristics of tennis-specific skills. Perception, kinematic, insole pressure and mechanical data were collected on an acrylic and a clay court. In agreement with findings reported in study 1, lower mechanical friction and hardness on the clay court were perceived and accompanied by less predictability and greater difficulty to change direction whilst being easier to slide. As result of sliding, players’ adopted an altered technique on the clay court compared to the acrylic leading to reductions in loading provide evidence to explain lower injury risks previously reported on clay courts. Prior clay court experience did not influence players’ perceptions. However, biomechanical response to the clay surface differed, such that players with high clay court experiences contacted the ground with an everted foot, believed to contribute to controlling sliding. Differences in perception- response relationships were reported between experience groups suggesting players with greater clay court experience are better able to choose an appropriate response to improve their performance. Friction properties of the surface may change during play on clay courts due to player movements and sliding on the court. Therefore there may be areas of expected and unexpected changes to friction to which players must 2 respond to. Study 3 aimed to examine the influence of changes in friction and players awareness of these changes on perceptions and biomechanical response. Compared with study 1 and 2, players found it more difficult to identify differences in perceived grip during study 3, possibly due the smaller mechanical friction differences reported. Unexpected reductions in friction produced greater initial ankle inversion angles compared to the expected decreases in friction, increasing players’ risk of injury. Lower horizontal and vertical loading rates were reported on the lower friction conditions where further sliding was reported; suggesting a reduced injury risk by allowing longer time spent applying the forces. This thesis has identified key perception variables that enabled a holistic understanding of perceptions and their interaction with biomechanical response. Mechanical friction was an important factor influencing players’ ability to slide. Sliding on clay resulted in altered loading characteristics, pressure distributions and kinematics potentially reducing players’ injury risk. Tennis players’ experience of clay courts does not influence their perceptions of the surface but the response that players adopt, which lower their risk of injury and increase performance. It is important when playing on a clay court that friction properties are maintained across the court during a tennis match as much as possible to reduce injury risks, due to the influence of unexpected changes to friction on perceptions and response. 3 TABLE OF CONTENTS Abstract ................................................................................................. 2 List of Figures ...................................................................................... 11 List of Equations .................................................................................. 16 Symbols and Abbreviations ................................................................. 18 Declaration, Communications and Publications .................................. 20 Acknowledgements ............................................................................. 22 CHAPTER 1: Introduction................................................................................. 24 CHAPTER 2: Literature Review ....................................................................... 27 2.1 Surfaces Properties and Mechanical Tests ......................................... 27 2.1.1 The Influence of Cushioning Properties on Biomechanical Response ................................................................................................... 31 2.1.2 The Influence of Friction Properties on Biomechanical Response 33 2.2 Dynamic Stability Control .................................................................... 36 2.3 Tennis Injury Risks .............................................................................. 38 2.3.1 Biomechanical Risk Factors of Lower Limb Tennis Injuries .......... 38 2.3.2 Tennis Surfaces and Injury ........................................................... 41 2.4 Tennis Performance ............................................................................ 43 2.5 Perception ........................................................................................... 46 2.5.1 Why Examine Perceptions? .......................................................... 46 2.5.2 What are Perceptions? ................................................................. 46 2.5.3 Measuring Perceptions ................................................................. 47 2.5.4 Perceptions of Surfaces ................................................................ 49 2.6 Summary ............................................................................................. 52 2.7 Rationale ............................................................................................. 53 2.8 Thesis Aims ......................................................................................... 55 2.8.1 Specific Aims ................................................................................ 56 CHAPTER 3: Study 1: Identifying Tennis Players’ Perceptions........................ 57 3.1 Introduction ......................................................................................... 57 3.2 Methods .............................................................................................. 59 3.2.1 Participants ................................................................................... 59 3.2.2 General Overview ......................................................................... 60 3.2.3 Mechanical Data ........................................................................... 60 4 3.2.4 Tennis Shoes ................................................................................ 63 3.2.5 Tennis Drills .................................................................................. 64 3.2.6 Kinematic Data ............................................................................. 66 3.2.7 Interviews ..................................................................................... 72 3.2.8 Thematic Inductive Analysis ......................................................... 72 3.2.9 Statistical Analysis ........................................................................ 73 3.3 Results ................................................................................................ 73 3.3.1 Mechanical Data ........................................................................... 73 3.3.2 Kinematic Data ............................................................................. 74 3.3.2.1 Forehand Open Stance .......................................................... 74 3.3.2.2 Running Forehand ................................................................. 76 3.3.3 Perception Data ............................................................................ 79 3.3.3.1 Player-surface Interactions ..................................................... 79 3.3.3.2 Ball-surface Interactions ......................................................... 82 3.3.3.3 Performance ........................................................................... 83 3.3.3.4 Injury Risks ............................................................................. 85 3.3.3.5 Playing Environment .............................................................. 86 3.3.3.6 Structural Relationship Model ................................................ 87 3.4 Discussion ..........................................................................................