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Musculoskeletal models of the cervical spine commonly represent neck muscles with straight paths. However, straight lines do not best represent the natural curvature of muscle paths in the neck, because the paths are constrained by bone and soft tissue. The purpose of this study was to estimate moment arms of curved and straight neck muscle paths using different moment arm calculation methods: tendon excursion, geometric, and effective torque. Curved and straight muscle paths were defined for two subject-specific cervical spine models derived from in vivo magnetic resonance images (MRI). Modeling neck muscle paths with curvature provides significantly different moment arm estimates than straight paths for 10 of 15 neck muscles (p < 0.05, repeated measures two-way ANOVA). Moment arm estimates were also found to be significantly different among moment arm calculation methods for 11 of 15 neck muscles (p < 0.05, repeated measures two-way ANOVA). In particular, using straight lines to model muscle paths can lead to overestimating neck extension moment. However, moment arm methods for curved paths should be investigated further, as different methods of calculating moment arm can provide different estimates.

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In this paper, we studied the effects of wrapping surfaces on muscle paths and moment arms of the neck muscle, semispinalis capitis. Sensitivities to wrapping surface size and the kinematic linkage to vertebral segments were evaluated. Kinematic linkage, but not radius, significantly affected the accuracy of model muscle paths compared to centroid paths from images. Both radius and linkage affected the moment arm significantly. Wrapping surfaces that provided the best match to centroid paths over a range of postures had consistent moment arms. For some wrapping surfaces with poor matches to the centroid path, a kinematic method (tendon excursion) predicted flexion moment arms in certain postures, whereas geometric method (distance to instant centre) predicted extension. This occurred because the muscle lengthened as it wrapped around the surface. This study highlights the sensitivity of moment arms to wrapping surface parameters and the importance of including multiple postures when evaluating muscle paths and moment arm.

Biomechanical analysis of the baseball pitch has been used for many years to improve pitching accuracy. Common biomechanical analysis has relied on motion analysis cameras in a laboratory setting. The primary aim of this descriptive case series study was to utilize a novel method using a portable wearable 3D motion analysis suit to measure leg length/stride length ratio, foot placement, and pitch accuracy. Four National Collegiate Athletic Association (NCAA) Division III varsity baseball pitchers participated in this study. The XSens™ MVN motion analysis suit was worn by each participant to measure body kinematics and a highspeed camera was utilized to record pitching accuracy. The average leg length to stride length ratio results was determined to be 77%. This ratio could be utilized rather than the traditional stride length to body height due to the variations in leg length. The results from this motion analysis procedure with a wearable portable suit and a high-speed camera may help improve pitching accuracy by identifying optimal mechanics for each individual pitcher.