title: Effect of fatigue loading on structure and functional behaviour of fascicles from energy-storing tendons.
abstract: Tendons can broadly be categorized according to their function: those that act purely to position the limb and those that have an additional function as energy stores. Energy-storing tendons undergo many cycles of large deformations during locomotion, and so must be able to extend and recoil efficiently, rapidly and repeatedly. Our previous work has shown rotation in response to applied strain in fascicles from energy-storing tendons, indicating the presence of helical substructures which may provide greater elasticity and recovery. In the current study, we assessed how preconditioning and fatigue loading affect the ability of fascicles from the energy-storing equine superficial digital flexor tendon to extend and recoil. We hypothesized that preconditioned samples would exhibit changes in microstructural strain response, but would retain their ability to recover. We further hypothesized that fatigue loading would result in sample damage, causing further alterations in extension mechanisms and a significant reduction in sample recovery. The results broadly support these hypotheses: preconditioned samples showed some alterations in microstructural strain response, but were able to recover following the removal of load. However, fatigue loaded samples showed visual evidence of damage and exhibited further alterations in extension mechanisms, characterized by decreased rotation in response to applied strain. This was accompanied by increased hysteresis and decreased recovery. These results suggest that fatigue loading results in a compromised helix substructure, reducing the ability of energy-storing tendons to recoil. A decreased ability to recoil may lead to an impaired response to further loading, potentially increasing the likelihood of injury.
authors.affiliation: Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, UK; Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, University of Liverpool, Leahurst Campus, Neston CH64 7TE, UK. Electronic address: c.thorpe@qmul.ac.uk.
authors.forename: Chavaunne T
authors.initials: CT
authors.lastname: Thorpe
authors.affiliation: School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.
authors.forename: Graham P
authors.initials: GP
authors.lastname: Riley
authors.affiliation: Institute of Orthopaedics and Musculoskeletal Science, University College London, Stanmore HA7 4LP, UK.
authors.forename: Helen L
authors.initials: HL
authors.lastname: Birch
authors.affiliation: Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, University of Liverpool, Leahurst Campus, Neston CH64 7TE, UK.
authors.forename: Peter D
authors.initials: PD
authors.lastname: Clegg
authors.affiliation: Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, UK.
authors.forename: Hazel R C
authors.initials: HR
authors.lastname: Screen
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D006736:Horses; D013314:Stress, Mechanical; D013710:Tendons / Q000033:anatomy & histology / Q000502:physiology*
keywords: Confocal microscopy; Fatigue damage; Hysteresis; Mechanical testing; Micromechanics