Mechanical Effects of Canes on Postural Control: Beyond Perceptual Information

BackgroundNumerous studies showed that postural balance improves through light touch on a stable surface highlighting the importance of haptic information, seemingly downplaying the mechanical contributions of the support. The present study examined the mechanical effects of canes for assisting balance in healthy individuals challenged by standing on a beam. MethodsSixteen participants supported themselves with two canes, one in each hand, and applied minimal, preferred, or maximum force onto the canes. They positioned the canes in the frontal plane or in a tripod configuration. ResultsResults showed that canes significantly reduced the variability of the center of pressure and center of mass to the same level as when standing on the ground. In the preferred condition, participants exploited the altered mechanics by resting their arms on the canes and, in the tripod configuration, allowing for larger CoP motions in the task-irrelevant dimension. Increasing the exerted force beyond the preferred level yielded no further benefits, in fact had a destabilizing effect on the canes: the displacement of the hand on the cane handle increased with the force. ConclusionsDespite the challenge of a statically unstable system, these results show that, in addition to augmenting perceptual information, using canes can provide mechanical benefits and challenges. First, the controller minimizes effort channeling noise in the task-irrelevant dimensions and, second, resting the arms on the canes but avoiding large forces that would have destabilizing effects. However, if maximal force is applied to the canes, the instability of the support needs to be counteracted, possibly by arm and shoulder stiffness.

Efficient computational modelling of smooth muscle orientation and function in the aorta

Understanding the mechanical effects of smooth muscle cell (SMC) contraction on the initiation and the propagation of cardiovascular diseases such as aortic dissection is critical. Framed by elastic lamellar sheets in the lamellar unit, there are SMCs in the media with a distinct radial tilt, which indicates their contribution to the radial strength. However, the mechanical effects of this type of anisotropy have not been fully discussed. Therefore, in this study, we propose a constitutive framework that models the passive and active mechanics of the aorta, taking into account the dispersed nature of the aortic constituents by applying the discrete fibre dispersion method. We suggest an isoparametric approach by evaluating various numerical integration methods and introducing a non-uniform discretization of the unit hemisphere to increase its computational efficiency. Finally, the constitutive parameters are fitted to layer-specific experimental data and initial computational results are briefly presented. The radial tilt of SMCs is also analysed, which has a noticeable influence on the mechanical behaviour of the aorta. In the absence of sufficient experimental data, the results indicate that the active contribution of SMCs has a remarkable impact on the mechanics of the healthy aorta.