Exploring novel objective functions for simulating muscle coactivation in the neck.

Musculoskeletal modeling allows for analysis of individual muscles in various situations. However, current techniques to realistically simulate muscle response when significant amounts of intentional coactivation is required are inadequate. This would include stiffening the neck or spine through muscle coactivation in preparation for perturbations or impacts. Muscle coactivation has been modeled previously in the neck and spine using optimization techniques that seek to maximize the joint stiffness by maximizing total muscle activation or muscle force. These approaches have not sought to replicate human response, but rather to explore the possible effects of active muscle. Coactivation remains a challenging feature to include in musculoskeletal models, and may be improved by extracting optimization objective functions from experimental data. However, the components of such an objective function must be known before fitting to experimental data. This study explores the effect of components in several objective functions, in order to recommend components to be used for fitting to experimental data. Four novel approaches to modeling coactivation through optimization techniques are presented, two of which produce greater levels of stiffness than previous techniques. Simulations were performed using OpenSim and MATLAB cooperatively. Results show that maximizing the moment generated by a particular muscle appears analogous to maximizing joint stiffness. The approach of optimizing for maximum moment generated by individual muscles may be a good candidate for developing objective functions that accurately simulate muscle coactivation in complex joints. This new approach will be the focus of future studies with human subjects.

Preliminary characterization of a tentatively novel rumen bacterial species from the genus Treponema.

A new spirochetal strain was isolated from the rumen of a black-and-white Holstein cow and preliminarily characterized. The sugar fermentation tests and morphological observations indicated this organism to be a member of a novel, as yet undescribed spirochetal rumen species. The small subunit ribosomal RNA genes were amplified and the PCR products were cut with the restriction endonucleases TaqI, DdeI, HhaI and Sau3AI. The comparison of the observed RFLP with the hypothetical fragment lengths of the computer analyzed 16S rRNA sequences from the type strains of the ruminal spirochetes Treponema bryantii and T. saccharophilum confirmed the tentative novel identification. Transmission electron microscopy showed that the bacterium has the typical spirochetal structures, i.e. the outer sheath, the protoplasmic cylinder and the axial filament (it is not yet clear how many flagella compose the filament). An additional extracellular structure was observed which appeared as an exocytoplasmic polar flagellum, approximately 2 microns long and protruding from one tip of the cell. The average size of the cells was 0.5 x 10-15 microns and the wavelengths and the amplitudes of the primary coils were 2.9 and 1.3 microns, respectively.