Nobutoshi Yamazaki

Generation of human bipedal locomotion by a bio-mimetic neuro-musculo-skeletal model

Abstract. To emulate the actual neuro-control mechanism of human bipedal locomotion, an anatomically and physiologically based neuro-musculo-skeletal model is developed. The human musculo-skeletal system is constructed as seven rigid links in a sagittal plane, with a total of nine principal muscles. The nervous system consists of an alpha motoneuron and proprioceptors such as a muscle spindle and a Golgi tendon organ for each muscle. At the motoneurons, feedback signals from the proprioceptors are integrated with the signal induced by foot–ground contact and input from the rhythm pattern generator; a muscle activation signal is produced accordingly. Weights of connection in the neural network are optimized using a genetic algorithm, thus maximizing walking distance and minimizing energy consumption. The generated walking pattern is in remarkably good agreement with that of actual human walking, indicating that the locomotory pattern could be generated automatically, according to the musculo-skeletal structures and the connections of the peripheral nervous system, particularly due to the reciprocal innervation in the muscle spindles. Using the proposed model, the flow of sensory-motor information during locomotion is estimated and a possible neuro-control mechanism is discussed.

Biomechanical analysis of primate bipedal walking by computer simulation

Abstract A computer simulation technique was applied to make clear the mechanical characteristics of primate bipedal walking. A primate body and the walking mechanism were modeled mathematically with a set of dynamic equations. Using a digital computer, the following were calculated from these equations by substituting measured displacements and morphological data of each segment of the primate: the acceleration, joint angle, center of gravity, foot force, joint moment, muscular force, transmitted force at the joint, electric activity of the muscle, generated power by the leg and energy expenditure in walking. The model was evaluated by comparing some of the calculated results with the experimental results such as foot force and electromyographic data, and improved in order to obtain the agreement between them. The level bipedal walking of man, chimpanzee and Japanese monkey and several types of synthesized walking were analyzed from the viewpoint of biomechanics. It is concluded that the bipedal walking of chimpanzee is nearer to that of man than to that of the Japanese monkey because of its propulsive mechanism, but it requires large muscular force for supporting the body weight.

A biomechanical study of vertical climbing and bipedal walking in gibbons

Bipedal walking in gibbons is characterized biomechanically by its similarity to that in man. To clarify how gibbons acquired such characteristics, their vertical climbing and bipedal walking on the bough have been analyzed biomechanically. A computer simulation technique has been applied in which the inner body forces are calculated with a mathematical model. Necessary data, such as foot reaction force and movements of joints, were collected experimentally using a specially designed pole-type force detector and a 16 mm cine-camera. The subject was a white-handed gibbon ( Hylobates agilis ), an eight-year-old male, body weight 6·25 kg. It was found that vertical climbing needs a strong development of hip-joint extensors and of knee-joint extension, and that bipedal walking on the bough improves the knee-joint motion and develops the knee-joint extensors. The results may suggest that the daily locomotor activities are important for development of bipedality in gibbons, and that the pre-phase stage of hominid bipedalism might have been in the tree.

Computational evolution of human bipedal walking by a neuro-musculo-skeletal model

The acquisition process of bipedal walking in humans was simulated using a neuro-musculo-skeletal model and genetic algorithms, based on the assumption that the shape of the body has been adapted for locomotion. The model was constructed as 10 two-dimensional rigid links with 26 muscles and 18 neural oscillators. Bipedal walking was generated as a mutual entrainment between neural oscillations and the pendulous movement of body dynamics. Evolutionary strategies incorporated, for example, as fitness in the genetic algorithms were assumed to decrease energy consumption, muscular fatigue, and load on the skeletal system. An initial population of 50 individuals was created, and an evolutionary simulation of 5000 steps was conducted. As a result, the shape of the body changed from that of a chimpanzee to that of a modern human, and the body size nearly reached the size of a modern human. These simulation results show that improving locomotive efficiency and reducing the load on the musculo-skeletal system are important factors affecting the evolution of the human body shape and bipedal walking. Such computer simulations help us to understand the process of evolution and adaptation for locomotion in humans.

Analysis of sitting comfortability of driver's seat by contact shape

In order to evaluate sitting comfort qualitatively, a flexible and very thin sensor was developed to measure the contact shape between a seated man and the seat surface. Each tape has twenty strain gauges on it at regular intervals, and the fourteen tape sensors were arranged on the bottom and back surface of the experimental drivers seat. The contact shapes and postures in thirty two male drivers were measured with two types of seat cushion and sitting posture: free and recommended. Sensory evaluation was made for each experimental condition. The results of the interrelation between the characteristics of the surface deformation, the parameters of body build, sitting posture and feeling of comfort shows that the comfort of each morphological fitting does not correspond to one special and single parameter from those physical factors, but is represented by a function with many parameters related to the deformation, posture and body build. By using these relations, a sensory model for the prediction of the sitting comfort was constructed.

Gait analysis of patients with neurogenic intermittent claudication.

Study Design. The gait of patients with neurogenic intermittent claudication was analyzed before and after surgery using a ground reaction force plate. Objectives. To analyze the gait characteristics of patients with neurogenic intermittent claudication, to evaluate quantitatively their gait improvement after surgical treatment, and to examine the differences in gait characteristics and postoperative improvement among different types of neuropathy. Summary of Background Data. A number of reports have been published on the pathophysiology or treatment of neurogenic intermittent claudication. However, almost no detailed reports exist on the gait abnormalities associated with this condition. Methods. The subjects were 60 lumbar canal stenosis patients with intermittent claudication who underwent surgery at the authors’ hospital. A ground reaction force plate was used for the analysis, and factors related to time and distance (speed, stride, interval, and pitch) were analyzed, as well as factors related to the style of walking (symmetry, reappearance, smoothness, sway, rhythm, and impact). Results. Before surgery, there were abnormalities of various factors related to the style of walking soon after the patients began to walk. Gait analysis also showed that the pattern of gait abnormality and its improvement after surgery varied depending on the type of neuropathy. Conclusions. Gait analysis permits objective and quantitative evaluation of the gait characteristics of patients with lumbar canal stenosis and is useful for evaluating responses to surgical treatment in these patients.

THREE-DIMENSIONAL MAGNETIC RESONANCE IMAGING OF THE INTEROSSEOUS MEMBRANE OF FOREARM: A NEW METHOD USING FUZZY REASONING

We now report newly developed three-dimensional magnetic resonance imaging (3D-MRI) system which is based on semiautomatic tissue extraction from the axial MR images utilizing the fuzzy reasoning calculation method and 3D-image reconstruction with surface rendering. We also studied normal in vivo dynamic changes of the interosseous membrane (IOM) of forearm during rotation using this 3D-MRI. Serial axial MRI of right forearms of five healthy volunteers was obtained in five rotational positions, and extraction and 3D-reconstruction of the radius, ulna, and IOM was made using the system. Extraction results were well with the fuzzy reasoning method. 3D-MRI of the radius and ulna, IOM were reconstructed from these images respectively, and their 3D-shapes were almost identical to the anatomic shape. 3D-MRI showed there were wavy deformities on the IOM in pronation position in the all five subjects and dorsiflexion on the most dorsal portion of the IOM at maximum supination in three forearms. In neutral position, the IOM of all five volunteers was almost flat. From anatomic orientation, these dynamic changes of the IOM mainly occurred at the membranous portion, which is soft, thin, and elastic. Otherwise, the tendinous portion which is a thick and strong complex of 5 to 10 bundles run from proximal one third of the radius to distal one fourth of the ulna, demonstrated minimal dynamic changes on the 3D-MRI. Therefore, the tendinous portion is considered to be taut during rotation to provide stability between the radius and the ulna, while the membranous portion is easy to deform and allowing smooth rotation. Furthermore, because of wide-use, our 3D-MRI system is useful for in vivo analysis of soft tissue kinesiology in normal and abnormal musculoskeletal systems.

Normal kinematics of the interosseous membrane during forearm pronation-supination--a three-dimensional MRI study.

We studied in vivo dynamic shape changes of the interosseous membrane (IOM) during forearm rotation using three-dimensional magnetic resonance imaging (3D-MRI), and simultaneously analysed 3D-motion of the forearm rotation. Wavy deformities were seen in the IOM in the pronated position, and similar small changes were also seen at maximum supination (average 82 degrees ) and in the neutral position. These dynamic changes mainly occurred in the membranous part of the IOM, whereas the tendinous part demonstrated minimal dynamic changes during rotation in all subjects. On the dorsal aspect, deformity around the dorsal oblique cord was seen at maximum pronation. From this 3D-MRI observation, the tendinous part is considered to be taut during rotation to provide stability between the radius and ulna, because of its straightness and less dynamic changes. The more deformable membranous part is important to allow for smooth rotation, since it lies at a distance from the rotation axis. Inelasticity developing in the membranous part from trauma may pre-dispose to pronation-supination contracture. The radius rotated around the ulna from maximum supination to 45 degrees pronation. At maximum pronation (average 75 degrees ), the radius translated average 1.8 mm palmarly and rotated average 4.0 degrees ulnarward on the ulna. Incongruity of the distal radioulnar joint, contraction of the pronator quadratus and torsion between the radius and ulna at maximum pronation may produce this irregular motion of the radius and cause the dynamic changes of the IOM.

The three-dimensional measurement of unconstrained motion using a model-matching method

The measurement of motion is a basic technique for the quantitative mechanical analysis of human movement. However, previous methods of motion measurement using goniometry and surface markers have several associated problems: goniometers constrain human motion; and surface markers are missed, etc. To resolve these problems, a new technique of motion measurement using image processing is proposed. In this method, movements of the whole body are captured as image information, and a geometric model of a human body is fitted onto the contours of the image sequences. The joint angles are then estimated from the model. Usually, every segment has to be coloured separately so as to fit the geometric model automatically into the images; furthermore, this takes a very long time to process. Therefore, we reduced the processing time using the information in the overlap area between the models and images, instead of contour information. We estimated the joint angles of hidden segments with the grey scale image information. Thus there is no need to colour segments and attach surface markers; and unconstrained motion can be measured. Using the method developed, three-dimensional motion of the fingers including 21 segments was measured in 3-5 min per frame by a personal computer. The errors are 2 degrees maximally.

Topology-adaptive multi-view photometric stereo

In this paper, we present a novel technique that enables capturing of detailed 3D models from flash photographs integrating shading and silhouette cues. Our main contribution is an optimization framework which not only captures subtle surface details but also handles changes in topology. To incorporate normals estimated from shading, we employ a mesh-based deformable model using deformation gradient. This method is capable of manipulating precise geometry and, in fact, it outperforms previous methods in terms of both accuracy and efficiency. To adapt the topology of the mesh, we convert the mesh into an implicit surface representation and then back to a mesh representation. This simple procedure removes self-intersecting regions of the mesh and solves the topology problem effectively. In addition to the algorithm, we introduce a hand-held setup to achieve multi-view photometric stereo. The key idea is to acquire flash photographs from a wide range of positions in order to obtain a sufficient lighting variation even with a standard flash unit attached to the camera. Experimental results showed that our method can capture detailed shapes of various objects and cope with topology changes well.