Optimal Muscular Arrangement Using Genetic Algorithm for Musculoskeletal Potential Method with Muscle Viscosity

Muscle contractions (or equivalent mechanical elements) are responsible for joint movement in systems with musculoskeletal structure. Because muscles can only transmit force in the tensile direction in such systems, the internal force exists between the muscles. By utilizing the potential field generated by the internal force, the musculoskeletal potential method makes it possible to control the position without complex real-time calculations or sensory feedback by entering step-inputs of the balanced internal force at the target posture. However, the conditions of convergence to the target posture strongly depend on muscular arrangement. Previous studies have elucidated the mathematical conditions of the muscular arrangement; however, they provide sufficient conditions that must be satisfied by the muscular arrangement to converge to the target posture, which do not necessarily lead to optimal muscular arrangement conditions. This study proposes a method to determine the optimal muscular arrangement of a two-joint six-muscle system, wherein muscle viscosity is considered, that uses a genetic algorithm and an evaluation function considering the motion response time. The effect of the obtained muscular arrangement is verified in a simulation.

Control of a Rehabilitation Robotic Device Driven by Antagonistic Soft Actuators

Stroke is becoming a widely concerned social problem, and robot-assisted devices have made considerable contributions in the training and treatment of rehabilitation. Due to the compliance and continuous deformation capacity, rehabilitation devices driven by soft actuators are attached to widespread attention. Considering the large output force of pneumatic artificial muscle (PAM) and the biological musculoskeletal structure, an antagonistic PAM-driven rehabilitation robotic device is developed. To fulfill the need for control of the proposed device, a knowledge-guided data-driven modeling approach is used and an adaptive feedforward–feedback control approach is presented to ensure the motion accuracy under large deformation motion with high frequency. Finally, several simulations and experiments are carried out to evaluate the performance of the developed system, and the results show that the developed system with the proposed controller can achieve expected control performance under various operations.

Investigation into thoracic asymmetry in ridden horses

Progressive training of horses focusses on the muscular development and flexibility to both the right and the left. However anecdotal evidence suggests that horses are not symmetrically structured through the thoracic region and this may have effects on saddle fitting and performance. The aim of this research was to determine if asymmetry exists in the thoracic musculoskeletal structure of ridden horses by analysing retrospective data of saddle fits (n=490) obtained from a saddle fitting company. A flexible wither tracer tool was used to obtain tracings of wither shape. Each tracing yielded four repeatable points (two on the left; two on the right) measured from the midline at the highest and lowest points of the withers. Descriptive assessments of shoulder, wither, and back shape, and demographic information on both horse and rider were recorded. A Wilcoxon signed-rank test compared the means of the wither shape measurements. A GLIMMIX procedure identified relationships between the wither measurements, descriptive assessments, and horse and rider demographics. The means of measurements from the wither tracer tool showed almost 60% of horses having larger measurements on the left side (P<0.0001). There was no effect of horse breed, age, sex, height or level of training on wither measurements (P>0.05). Rider age, gender, height, weight and level of training did not affect wither measurements (P>0.05). These results show that horses are asymmetric in their thoracic structure with a majority of horses larger on their left side than the right. This asymmetry may be due to genetics, environment or training and should be considered when fitting a saddle to the horse.

An aberrant bald eagle (Haliaeetus leucocephalus) with multiple anatomical abnormalities

Genetic abnormalities, especially polydactyly, are quite common among birds. Although there are numerous accounts of anatomically abnormal birds with polydactyly, few written anatomical descriptions have elucidated whether or not these physical aberrations extend to the musculoskeletal structure of the feet. Here, we present the findings of a dissection of a 14-week old female bald eagle that exhibited polydactyly and numerous other aberrations and discuss the functional impact these aberrations would cause. The specimen displayed a myriad of feather anomalies including missing feathers (i.e., had never grown in), ingrown feathers, stress bars, and most strikingly, bifurcated feathers wherein two feathers were seen to grow out of one rachis. Further, an extra, anomalous tendon was observed stemming from the tendinous origin of the m. extensor carpi radialis. The carpometacarpi were unable to reach full extension, stopping at less than 140º, and had phalanges bent downward at 45º. This mobility is limited in comparison to that of a normal bird. Most notably, the specimen exhibited polydactyly with one extra hallux on each foot. Several tendons of the left foot were seen to have aberrant connections as well.