In this study, we developed and evaluated a compact exercise device that can efficiently train the quadriceps to prevent disuse syndrome in the elderly. Lower-limb muscles play a crucial role in daily life; however, muscle strength declines with age, necessitating regular exercise. Large exercise machines are often limited by their required installation space and are not suitable for regions with poor transportation access. Thus, there is demand for compact exercise equipment that enables safe and efficient exercises. To address this need, we designed a compact stepping exercise device that can be used bedside and facilitates flexion and extension movements of the lower limbs. It features a mechanical structure in which the pedals move along a linear rail, with rubber tubing providing the stepping resistance. The objective of this study was to investigate the effects of using the compact exercise device on the muscles and joints of the lower limbs. For evaluation, we designed a pedal-type force sensor equipped with two triaxial force sensors. Three exercise conditions—stepping with high resistance (SHR), stepping with low resistance (SLR), and gait—were measured using the sensors and a motion-capture system. Inverse dynamics analysis was performed using AnyBody software to estimate lower-limb muscle activity and joint loading. Biomechanical analysis indicated that SHR resulted in higher muscle activity than SLR in some quadriceps muscles, suggesting that a quadriceps training environment can be easily configured to suit the user’s condition by changing the resistance tube. Furthermore, compared with gait, the stepping exercise exhibited higher average muscle activity in the knee and hip extensors and reduced maximum axial joint reaction forces at the hip, knee, and ankle. The simplicity and effectiveness of the proposed exercise device suggest its potential widespread adoption in rehabilitation programs for elderly individuals.

Reports have indicated that microvibration stimulation activates bone remodeling and promotes bone formation. However, the mechanism by which microvibration stimulation facilitates bone formation remains incompletely understood, and it is unclear how osteoblasts sense microvibration stimulation. In this study, we focused on the actin cytoskeleton, a key component of the mechanosensing mechanism. The actin cytoskeleton plays a role in mechanotransduction by physically transmitting mechanical stimuli from the cell surface to the interior of the cell. It is also known that actin stress fibers undergo structural remodeling in response to changes in the tension acting upon them. We investigated the structural remodeling of the actin cytoskeleton in osteoblasts subjected to microvibration stimulation using fixed cells and fluorescence staining of actin. Our results revealed that in osteoblasts subjected to microvibration, local actin depolymerization occurred around the cell nucleus for approximately 3 hours following the application of vibration. Furthermore, by 10 hours post-vibration, the actin cytoskeleton had repolymerized and returned to its pre-vibration state. These findings suggest that microvibration stimulation is transmitted from focal adhesions to the actin cytoskeleton surrounding the cell nucleus and then further into the cell.

The inertial properties (mass, center of gravity, and inertia tensor) of an object are fundamental and important input values. They have a significant effect on the accuracy of human motion simulation. Thus, an accurate identification method of inertial properties is crucial. All inertial properties of individual links modeled with multiple links cannot be identified from the link motion, interjoint torque, or external force data because they are redundant to the multibody dynamics model. Minimum dynamic parameters needed to represent the multibody dynamics model have been defined and identified. These dynamic parameters are obtained by combining the geometric parameters and inertial properties of the counterpart elements and are called the minimum set of inertial parameters (MSIP). A set of measured link motions and ground reaction forces are utilized in conventional identification methods. The MSIP for a sagittal plane can be identified from motions such as the walking motion of human bodies. However, it is difficult to perform three-dimensional identification, including planes beyond the sagittal plane. Therefore, a new method for identifying MSIP by expanding and applying free vibration measurements has been developed. With this method, highly accurate three-dimensional identification has been demonstrated using a mock-up model of the human body consisting of two links made of iron. However, the human body is complex and possesses flexibility due to muscles and organs, making it uncertain whether the developed method, which assumes a rigid body model, can be applied. In this study, appropriate identification procedures and conditions were examined to apply the developed method to the complex and multi-degree-of-freedom human body. The results demonstrated that valid identification of the MSIP can be obtained without exciting the body’s flexibility.

The commonly used screw propellers are known to suffer from issues such as sludge agitation and safety concerns for aquatic organisms. This has resulted in the exploration of biomimetic propulsion mechanisms. Previous research in bio-normative in-fluid propulsion systems has focused on mimicking the swimming patterns of organisms adapted to specific environments, including body and/or caudal fin (BCF) locomotion in fish for high Reynolds number (Re) regions and ciliary or wavelike motions in microorganisms for low Re regions. Thus, this study focused on the development of a flexible biomimetic propulsion mechanism inspired by the deformation movements of Euglena, aiming to create a propulsion system that achieves low environmental impact and universal adaptability. The objective was to enable advanced deformation and diverse motion patterns through the sliding motion of the pellicular strips on the cell surface, thereby replicating Euglena 's elastic and highly deformable movements to achieve multiple swimming modes. This technology can facilitate the realization of a versatile in-fluid propulsion mechanism that can emulate the swimming morphology of various organisms within a single system. To achieve this, we proposed a novel high-degree-of-freedom deformation mechanism using a composite sliding structure of porous polytetrafluoroethylene (PTFE) sheets driven by rectangular cross-section coil shape memory alloy (SMA) actuators (SMAAs). A prototype of the proposed mechanism was fabricated. Although the ultimate goal is to achieve three-dimensional motion, initial evaluations were conducted in two-dimensional motion for simplicity and foundational analysis. As a result, experiments were conducted to verify its effectiveness and evaluate its potential for reproducing EM and adapting to various swimming modes. The SMAA-loaded porous PTFE fibers exhibited S-shaped bending deformation owing to the sliding motion of multiple fibers, similar to the deformation principle of Euglena. Further experiments with different driving patterns indicated the possibility of locally controlling the deformation within the structure. Moreover, it was suggested that modifying the mechanism to increase the degree of freedom by ensuring a fixed distance between the porous PTFE fibers while facilitating sliding could enhance motion efficiency and adaptability, making it suitable for achieving various swimming modes, including those observed in both low- and high- Re regimes.