Accurate, objective estimation of subjective workload is critical issue in occupational health and safety, yet existing methods largely rely on observational assessments rather than quantitative metrics. To address this gap, this paper presents a novel approach for objectively estimating subjective workload by combining the substantial muscle activity ratio, which accounts for fatigue-induced reductions in muscle strength, with a logistic function approximating individual sensitivity curves. The method was applied to three shoulder muscles during a repetitive upper-limb task performed by healthy participants. The results indicated that, for each participant, the estimated subjective workload closely approximated the perceived workload in at least one of the three muscles. This finding demonstrates that the proposed method can simulate temporal changes in perceived workload despite inter-individual variability. Incorporating the logistic function allowed the model to account for nonlinear perception of workload. Further analysis suggested that the dominant muscle contributing to perceived workload differed across participants, depending on individual movement strategies during the task. Motion analysis confirmed that differences in shoulder joint kinematics were associated with the muscles most closely tracking perceived workload. These findings highlight the necessity of accounting for both biomechanical and kinematical factors when estimating subjective workload. Overall, the study demonstrates a physiologically grounded framework for predicting perceived workload and provides a foundation for developing generalized models applicable to real-world tasks, supporting more informed strategies for worker load management.

Vertical jump tests, including the squat jump and countermovement jump, are widely used to evaluate athletic performance or the muscular strength of the lower limbs. Biomechanical analysis using musculoskeletal models provides a valuable tool to clarify the mechanisms of body movement and muscular function in such physical tests because it is impractical to simultaneously measure the state of every muscle or joint in the body. Although the vertical jump is a multi-joint movement that requires coordinated activity of skeletal muscles throughout the body, few musculoskeletal models incorporating the muscles of the entire body have been proposed. The aim of this study was to conduct an exploratory investigation into the causal effects of individual muscle activities on the exertions in other muscles and resulting jump performances from the perspective of the coordinated motion or kinematic chain using a whole-body musculoskeletal model. A forward dynamics-based whole-body human musculoskeletal model with an appropriate range of articular motion was developed. The muscle dynamics are described using a biofidelic Hill-type muscle-tendon complex model, which includes concentric and eccentric contractions and the pennation angle with serial damping in the tendon. The moment arms of muscles in the model were validated against literature data. Using the developed musculoskeletal model, simulations of squat jumping were performed by inputting the activation level of each muscle. The results indicated that reducing the activity of the extensors in the shoulder, trunk, and neck indirectly decreased muscular forces in the lower extremities immediately before take-off, resulting in a lower jump height. These findings emphasize the importance of regarding the vertical jump as a coordinated motion driven by muscles throughout the body. Additionally, the developed musculoskeletal model is useful for investigating biologically plausible muscle control algorithms and enhancing human movement analysis.

The antenna of a male insect can capture pheromones generated by a female insect. In this study, the sensilla of an antenna are represented by a row of cylinders, and the mass of pheromones they capture along with the capture rate are calculated. The diameter of the real sensilla of a moth Bombyx mori is assumed in the calculation. Reynolds number and Péclet number, which are defined by the diameter of cylinders and the uniform flow, are 0.04 and 0.26, respectively. Calculation parameters are the gap between neighboring cylinders representing sensilla and their angle of attack. For a high angle of attack, the analytical exams show that the capture rate is maximized when the ratio of the gap between cylinders to their diameter is 10. In all the cases, the capture rate is maximum when the angle of attack is 90 degrees and the ratio of the gap between cylinders to their diameter is 10. This ratio is close to that observed in the sensilla of a moth Bombyx mori. When the ratio of the gap between cylinders to their diameter is smaller than 3, the capture rate is nearly independent of the ratio of the gap between cylinders to their diameter and the angle of attack.

Fibrosis is a condition resulting from tissue damage and inflammation that causes loss of function by hardening the tissue while accumulating collagen. Although there are drugs that inhibit the progression of fibrosis, there are few effective treatment options once fibrosis has developed. In response, we proposed a therapeutic technology that thermally denatures collagen in fibrotic tissues and restore flexibility to tissues stiffened by fibrosis. The purpose of this paper is to evaluate the above therapeutic technology using fractional laser as a heat source for collagen thermal denaturation. Using 450 nm semiconductor lasers with high absorption from surfaces, Fractional laser irradiation was applied to simulated fibrosis samples derived from bovine Achilles tendon. Laser irradiation was performed with irradiation patterns of 3, 6 and 12 dots/mm² and irradiation energy conditions of 65, 84, 99, 110 and 116 mJ/dot. Fibrosis that originates from tissue damage should have as low tissue damage as possible because of the possibility of re-fibrosis due to laser damage. Therefore, we performed CHP staining to verify thermal denaturation at the laser irradiation point, and based on the staining results, determined the laser energy settings that could induce thermal denaturation of collagen while minimizing tissue ablation. To evaluate the mechanical properties of the laser-irradiated samples under set conditions, tensile tests were carried out to verify the rate of change in Young's modulus, which showed a 22.1, 23.0 and 32.0% increase in flexibility for irradiation patterns of 3, 6 and 12 dots/mm², respectively. These results suggest that the thermal use of fractional laser can restore the flexibility of fibrotic tissue.

Conventional screw-type propellers are widely used but have pose environmental concerns, including sediment disturbance and potential harm to aquatic ecosystems. These concerns have prompted interest in biologically inspired propulsion mechanisms. Previous studies have explored biomimetic motion strategies, such as body-caudal fin (BCF) movements for high Reynolds number (Re) regimes and ciliary or undulatory locomotion for low Re environments. This study focuses on the latter and advancing a propulsion mechanism inspired by the pellicular strip gliding motion of Euglena, aiming for low environmental impact and cross-environmental adaptability. While our previous work demonstrated only two-dimensional deformation, the present study achieves three-dimensional motion by introducing a three-dimensional sliding deformation mechanism using circumferentially arranged porous polytetrafluoroethylene (PTFE) sheets actuated by tensioned wires. Unlike conventional sharp memory alloy (SMA) coil actuators, mechanical wire traction allows for rapid and spatially variable deformation. Time-series analyses of localized expansion and bending motion were conducted, and a geometric model was developed to describe surface profiles and fiber orientations along the longitudinal axis. Experimental results revealed asymmetric displacement distributions during both localized expansion and bending motions. The deformation patterns observed in localized expansion resembled the non-uniform peristaltic motion characteristic of Euglenoid movement. The surface function E(z₁) and fiber orientation function D(z₁), extracted via marker-based image tracking, effectively captured the deformation behavior. Although discrepancies in shrinkage ratios arose—likely due to structural limitations near constrained regions—the deformation cycle was completed within 1.2 seconds, corresponding to an actuation frequency of ~ 0.5 Hz. This frequency surpasses that of microorganisms like Euglena and is comparable to the lower end of swimming frequencies observed in fish. These findings demonstrate that the proposed mechanism can reproduce Euglena-like three-dimensional deformation and serve as a foundational platform for multimodal, bioinspired propulsion. With future improvements in constraint design and control coordination, this system shows strong potential for adaptive robotic applications across a wide range of Re conditions.

The 100-meter sprint is a central focus in sports biomechanics due to its relevance to performance enhancement. In this study, we reviewed electromyographic (EMG) data from ground sprinting and analyzed stride and joint kinematics from treadmill sprinting to examine and propose the coactive roles of femoral biarticular muscles alongside femoral monoarticular and lower leg muscles during sprint gait. The EMG data were interpreted using the static two-joint link model, which characterizes the functional coordination of human femoral muscles. According to the model, activity switches occur among three antagonistic pairs of femoral muscles at distinct phases of the sprint cycle. Concurrently, six muscle pairs generate sequential combined force outputs, applied to specific sectors of the ankle joint, contributing to coordinated movement at the hip, knee and ankle joints. During the stance phase, the coactivity of the gluteus maximus and/or biceps femoris long head facilitates hip extension and forward propulsion, while the gastrocnemius and soleus support plantar flexion and ground reaction force modulation. We conclude that femoral biarticular muscles play significant coactive roles with femoral monoarticular and lower leg muscles during sprinting. The EMG and treadmill kinematic analyses provide valuable insights into the biomechanics of sprint gait.

Interstitial flow (IF) across the aortic walls induces mechanical stress on smooth muscle cells, altering their function in response to the flow. Due to the heterogeneous structure of the aorta, IF velocity varies locally. We previously developed a method for measuring local IF velocity by directly visualizing the movement of a fluorescence dye driven by the fluid flow using fluorescence microscopy and quantifying the velocity based on a one-dimensional convection-diffusion equation (Fukui et al., Sci. Rep. 2022:12(1), 5381). However, the original method had low measurement reliability due to the widely scattered data points in kymograph-based analyses, leading to low correlation coefficients. This study aimed to refine the method for improved reliability. Several modifications were introduced, including replacing the forward difference scheme with a central difference scheme in the convection-diffusion equation, minimizing image drift, compressing the image size of kymograph, and optimizing the image analysis region. These modifications enhanced data fitting to a linear trend, leading to more accurate interstitial flow velocity measurements. When applied to the dataset from Fukui et al., the modified method significantly improved measurement reliability, yielding correlation coefficients above 0.90 and velocity values several times higher than those obtained before modification. The proposed approach provides a more reliable technique for quantifying IF velocity in the aortic wall for future biomechanical studies.