The effect of an abrupt change in functional surface properties on equine kinematics and neuromuscular activity Volume 1 of 1 by Danielle Holt A thesis submitted in partial fulfilment for the requirements for the degree of Doctor of Philosophy at the University of Central Lancashire September 2017 DECLARATION STUDENT DECLARATION FORM Concurrent registration for two or more academic awards I declare that while registered as a candidate for the research degree, I have not been a registered candidate or enrolled student for another award of the University or other academic or professional institution ____________________________________________________________________ Material submitted for another award I declare that no material contained in the thesis has been used in any other submission for an academic award and is solely my own work ____________________________________________________________________ Collaboration Where a candidate’s research programme is part of a collaborative project, the thesis must indicate in addition clearly the candidate’s individual contribution and the extent of the collaboration. Please state below: Signature of Candidate ______________________________________________________ Type of Award __PhD__________________________________________________ School __Sport and Wellbeing____________________________________ i ABSTRACT Arena surfaces used for training and competition are influenced by factors such as weather and maintenance, which can lead to spatial variations in functional surface properties. The ability of the horse to adapt to such changes may have implications for injury prevention. The aim of the PhD was to quantify kinematic and neuromuscular responses of horses to a camouflaged abrupt change in functional surface properties. Horses (n=7) were trotted in hand at a consistent speed across an arena surface that had been prepared in four ways: continuous firm; continuous soft and when the surface presented a camouflaged, abrupt change from firm to soft and soft to firm. Kinematic data (232Hz) synchronised with surface electromyography (sEMG) (1926Hz) from selected forelimb muscles were recorded. The first trial (no awareness of change) was categorised separately to the subsequent trials (2-8; aware of change). A General Linear Model was used to assess the effect of horse, stride location and awareness on kinematics and sEMG. There were limited stride to stride changes on the continuous surfaces. When travelling from firm to soft, fore F (2, 125) = 11.55, P <0.0001 and hind F (2, 116) = 12.47, P <0.0001 limb retraction significantly reduced as the horses stepped onto the soft surface. Awareness of the abrupt change also significantly reduced fore F (1, 125) = 7.28, P =0.008 and hind F (1, 116) = 10.16, P =0.002 limb retraction. When travelling from soft to firm, hindlimb stance duration F (1, 99) = 7.3, P =0.008 and duty factor F (1, 61) = 7.82, P =0.007 significantly increased and peak metacarpophalangeal extension significantly F (1, 93) = 7.85, P =0.006 reduced as the horses stepped onto the firm surface. Awareness of the abrupt change significantly increased stance duration F (1, 99) = 14.92, P <0.0001, duty factor F (1, 61) = 8.18, P =0.006 and peak metacarpophalangeal extension F (1, 93) = 3.98, P =0.049. There was some evidence of neuromuscular contributions that helped to stabilise the forelimb and control posture immediately before hoof impact and during stance. The gait modifications observed demonstrated horses can alter their balancing strategy to cope with a change in surface condition. Reduced limb retraction shifted the COM position relative to the hoof position at lift off more caudal and reduced a falling forward posture as the horses stepped down onto the soft surface and with awareness. When the horses travelled from soft to firm, vertical impulses increased in the hindlimb, which was thought to maintain pitch stability. Vertical impulses showed a more even distribution between the fore and hind limbs with awareness suggesting the fore limbs played a larger role raising the forehand. ii CONTENTS Section Title Page No. Preliminaries Declaration i Preliminaries Abstract ii Preliminaries Contents iii Preliminaries Acknowledgements xii 1.0 Introduction 1 2.0 Literature Review 3 2.1 Functional map of the equine trot 3 2.2 Hoof-surface interaction 12 2.3 Gait modifications 23 2.4 Measurement techniques 29 2.5 Summary 31 3.0 Aims and Objectives 33 4.0 Design and Development of Methods 35 4.0 Ethical Considerations and Health and Safety 35 4.1 Development of Measurement Techniques 35 4.1.1 Development of a kinematic model 35 4.1.2 Selecting muscles for surface 36 electromyographic analysis 4.2 General Methods: Experimental Set Up 39 4.3 General Methods: 3D kinematic marker application 44 4.4 General Methods: EMG sensor application 45 5.0 Materials and Methods: Main Study 47 5.0 Surface construction and preparation 47 5.1 Surface Development Work 48 5.2 Main Study 53 5.2.1 Study design: Surface preparation 53 5.2.2 Subjects 55 5.2.3 Experimental Protocol: Equine Response 56 5.2.4 Experimental Protocol: Surface Response 59 6.0 Optimisation of Methods for Data Processing 61 6.0 Optimisation of methods for processing kinematic data 61 6.0.1 Raw data files 61 6.0.2 Kinematic Data Processing 62 6.0.3 Kinematic Parameters 64 6.1 Optimisation of methods for processing EMG 68 6.1.1 Raw EMG Files 68 6.1.2 EMG Data Processing 68 6.1.3 EMG trace accept and reject criteria 76 6.1.4 EMG Signal Analysis 78 6.2 Statistical Analysis for kinematic and EMG data 81 6.3 Optimisation of methods for processing surface data 84 6.3.1 Surface data processing 84 6.3.2 Surface Parameters 85 6.3.3 Statistical analysis for the surface data 87 7.0 Kinematic Gait Event Detection Method: 89 Investigation on a Compliant Surface 7.0 Introduction 89 7.1 Methods 89 7.2 Results 93 7.3 Discussion 94 8.0 Accounting for inherent variation 96 8.0 Introduction 96 8.1 Methods 96 iii CONTENTS 8.2 Results and Discussion 97 9.0 Results 101 9.0 Results from the main study 101 9.1 Stride to stride temporal changes 101 9.1.1 The effect of an abrupt change in surface 101 condition 9.1.2 The effect of continuous surfaces 103 9.2 Stride to stride linear and angular changes 104 9.2.1 The effect of an abrupt change in surface 104 condition 9.2.2 The effect of continuous surfaces 110 9.3 Stride to stride changes in neuromuscular activity 112 during pre-activation and stance 9.3.1 The effect of an abrupt change in surface 116 condition 9.3.2 The effect of continuous surfaces 119 9.4 The effect of awareness of an abrupt change in 121 kinematics and neuromuscular activity 9.4.1 Kinematics 121 9.4.2 Neuromuscular activity 125 9.5 Stride to stride changes and the effect of awareness 128 on effective limb stiffness 9.6 Kinematic and EMG results summary 132 9.7 Post-hoc observational analysis 133 9.8 Surface response 138 10.0 Discussion 146 10.1 Strategies observed for stride to stride gait 147 modifications on firm soft and soft firm 10.2 Strategies observed when the horses were aware of 153 the abrupt change 10.3 Can horses alter limb stiffness as a function of surface 157 stiffness like humans can? 10.4 Observations on the continuous surface 160 10.4.1 Kinematic response 161 10.4.2 Neuromuscular response 163 10.5 Limitations of the project 165 10.6 General discussion 167 10.7 Conclusions 169 11.0 References 172 12.0 Appendices I Ethics form I II Risk assessment XIV III Gait event paper XXV IV MPhil to PhD transfer document XXXIV V Statistical grouping information for section 9.3 LVIII iv FIGURES Figure Page No. No. 2.1.1 A simple spring mass system consisting of a mass and a 7 single leg spring (joins the foot and COM of the animal). 2.1.2 Musculoskeletal structures within the forelimb 8 2.1.3 Musculoskeletal structures within the hindlimb 11 2.2.1 The stages of the hoof surface interaction 12 2.2.2 An illustration representing responsiveness 19 2.2.3 A contour plot revealing spatial variations of surface 19 cushioning within an indoor arena 2.3.1 COM displacement and surface displacement during a 24 transition from soft to hard surfaces. 4.2.1 An illustration of the experimental set up 41 4.2.2 Successful calibration results window 43 4.2.3 Mean (±SD) fetlock angle for each horse and calibration file. 43 4.2.4 Mean (±SD) stride length for each horse and calibration file 44 4.4.1 The illustration used to aid correct sensor placement in 46 alignment with muscle fibres. 5.1.1 A comparison between the cushioning on the different 51 preparations 5.1.2 A comparison between the impact firmness on the different 52 preparations 5.2.1 Structure of the dynamic trials performed throughout the 58 study with each horse 6.0.1 The AIM model applied to a static trial 61 6.0.2 The segments created in Visual 3D using actual markers and 62 virtual landmarks. 6.0.3 Residual Analysis used to identify the cut off frequency for 63 the low pass filter. 6.0.4 An illustration showing where the joint angles were derived 65 from 6.0.5 An illustration demonstrating where the inclination angles 66 were derived from for the limbs, neck and scapula 6.0.6 The distal and proximal springs of the forelimb 67 6.1.1 An example of movement artefact 69 6.1.2 An example of baseline noise 69 6.1.3 EMG signal-processing method used previously; A) The raw 71 EMG signal sampled with 1.2 kH; B ) The rectified EMG signal; C) The down-sampled EMG signal where the sampling rate has been reduced to 120 Hz; D) The EMG signal with a 7th order Butterworth low pass filter applied with a cut off frequency of 10 Hz.