Predicting muscle fibre type composition through joint mechanics

Tese de mestrado integrado em Engenharia Biomédica e Biofísica (Engenharia Clínica e Instrumentação) , apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2012Ageing, neurological diseases or certain conditions can result in changes in muscle properties, such as fibre type composition, which may influence muscle performance. Short-range stiffness (SRS) is a mechanical property of muscles which reflects mainly the stiffness of the attached cross-bridges. Different fibre types are believed to have different SRS and thus SRS might be important in characterizing muscle fibre type composition. Recently, a model-based estimation method was developed to estimate wrist muscles SRS in vivo. In this study, the same method was used to estimate leg muscles SRS using an ankle manipulator. Subjects (n=10) were measured with the leg extended and flexed at 90º at five torque levels, ranging from 0 to 20 Nm. It was expected that with the knee extended the recruitment of type II fibres would be greater at higher torques and thus, the estimated SRS would be lower. Two subjects were measured on different days for repeatability analysis. Furthermore, a geometrical model was developed to predict the contribution of tendon stiffness and muscle pennation angle to SRS. From the simulation results, the SRS model developed for the wrist seems adequate to estimate leg muscles SRS. However, some of the model parameters presented high standard error mean (SEM) values as well as high inter-trial standard deviations (ITSTD). Improvements in the equipment and in the attachment between the foot and the footplate might be necessary to confirm the goodness of the model fit. Regarding the estimated SRS at different knee angles, no significant differences were found. From the sensitivity analysis of the geometrical model, tendon stiffness seems to have a large influence on muscle stiffness and thus its inclusion in the SRS model should be considered