A Novel Framework to Model the Short and Medium Term Mechanical Response of the Medial Gastrocnemius

Musculoskeletal disorders (MSDs) are the second largest cause of disability worldwide and cost the UK National Health Service (NHS) over £4.7 billion yearly. One holistic approach to alleviate this burden is to create in silico models that provide insight into MSDs which will improve diagnostic and therapeutic procedures. This thesis presents a modelling framework that analyses the mechanical behaviour of anatomical skeletal muscles. The anatomical geometry and fibre paths of the medial gastrocnemius muscle were acquired from the Living Human Data Library (LHDL). The medial gastrocnemius model was further sophisticated by incorporating morphological representations of the aponeurosis and myotendon transition region. Having carried out a finite element analysis on the medial gastrocnemius, it was found that the morphology and size of the transition region significantly affected the mechanical response of the muscle. Three illustrative simulations were subsequently carried out on the model, to better understand the muscle’s mechanical response in differing mechanical environments: (1) the effects of high extensions on the muscle’s mechanical response, (2) lengthening of the aponeurosis - a phenomenon often observed following aponeurosis regression - and (3) the stress-strain regime of the muscle when the tendon experiences a laceration and heals over 21 days. These models show the regions that experienced the highest strains were the muscle-tendon transition regions. As MSDs tend to be of a degenerative nature and progress over time, the temporal changes of the mechanical response of skeletal muscle tissue is of great interest. In the penultimate chapter, the medial gastrocnemius was assessed across various remodelling regimes. It was found that the muscle returned to homeostasis only when both the muscle and tendon remodelled – albeit, at different remodelling rates. Whilst this observation seems intuitive, most other growth and remodelling models of skeletal muscles have only remodelled either the muscle or tendon constituent. The model developed in this thesis therefore has the potential to inform multi-scale musculo-skeletal muscle models thus providing a significant contribution to understanding MSDs.