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Title: The scapula in musculoskeletal modelling of extreme activities
Author: Prinold, Joe
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2013
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This thesis presents a musculoskeletal model that predicts the muscle and joint forces in the upper limb during an extreme activity. The scapula is an important link in the kinematic and dynamic chain of the upper limb; with its muscles acting as the primary stabilisers to the inherently unstable glenohumeral joint, thus allowing effective transmission of load through the kinematic chain of the shoulder. This bone is poorly represented in musculoskeletal models during these activities. Large soft-­‐tissue artefacts are a key reason for this. The shoulder is particularly prone to injury in overhead activities of the upper limb. Heavily loaded activities in these positions are of interest because they represent a limit, in that few people are capable of performing them. Pull-­‐ups are a common training activity that involve the movement of a large load with the arms overhead. Predicting the forces involved in such an activity allows a testing of current model limits and hypotheses on the function and biomechanics of the scapula. A novel methodology to track the dynamically moving scapula is validated using motion capture technology. This method is shown to improve measurement accuracy when compared to the literature. Kinematics of the scapula and upper limb are thus measured, presented and discussed for three types of pull-­‐up activity. The modelling aspects of the work build on a previous upper limb model, primarily adapting the kinematics representation. This better respects the measured kinematics through a relaxation of the closed-­‐chain mechanism as well as improving the ability to non-­‐homogeneously scale the model. The inverse dynamics description is modified to allow a variable hand load, muscle wrapping parameters and changed to prevent sudden unphysiological changes in moment arms and muscle bounds are increased to allow equilibrium to be reached with the inter-­‐segmental moments. Musculoskeletal loads are thus presented using a model that allows the dynamic analysis of extreme activities. Eccentric loading of the supraspinatus, deltoid and triceps was found to exist in potentially vulnerable positions, coinciding with a high incidence of impingement injury in pull-­‐up type activities. The glenohumeral joint reaction force is seen to be more centralised with a general increase in rotator cuff activation, although teres major and posterior deltoid seem to be key stabilisers. Pectoralis major was detrimental to stability, highlighting the importance of the scapula in positioning muscles during overhead activities. Comparison of model predictions with literature EMG results show good agreement.
Supervisor: Bull, Anthony Sponsor: Biotechnology and Biological Sciences Research Council ; Vicon Motion Systems Ltd
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available