A high degree of variability is commonly encountered in biomechanical investigations of the shoulder. Researchers have hypothesized that the variation between individuals explains why only certain workers are injured when performing the same tasks as other individuals. One source for the variability is inter-individual differences in shoulder musculoskeletal geometry. The purpose of this thesis was to use computational modeling to assess the functional roles of the scapulohumeral muscles, compare model-predicted data to the reviewed literature, and quantify the sensitivity of these functional roles to changes in muscle geometry. Muscle moment arms, lines of action, stability ratios, and forces were quantified throughout arm elevation in the scapular plane using a widely investigated upper extremity model. Monte Carlo simulations were performed to iteratively adjust muscle attachment locations in order to reflect potential inter-individual differences in muscle geometry. Model-predicted muscle moment arms agreed well qualitatively with the reviewed literature; however, several muscle lines of action were inconsistent between the model and previous data collected in cadavers available in the literature. Sensitivity of muscle functional roles to attachment changes was muscle-specific, and depended upon the elevation angle as well as outcome measure. Regressions were developed to identify which attachment locations at the clavicle, scapula, and humerus caused the greatest change in muscle functional roles. In general, muscle moment arms were most sensitive to changes of the muscle attachment closest to the joint centre (humeral attachment for rotator cuff muscles; scapular attachment for deltoids). Lines of action were most affected by perturbations in scapular attachment location. Overall, these findings indicate that inter-individual musculoskeletal geometry differences can substantially alter muscle functional roles, which are expected to require altered muscle activity and kinematic coordination patterns between people. These variations in musculoskeletal geometry may differentially affect risk of work-related shoulder musculoskeletal disorders among individuals. / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/23963 |
| Date | 11 1900 |
| Creators | Mulla, Daanish |
| Contributors | Keir, Peter, Kinesiology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
Page generated in 0.0018 seconds