A fall can result in fractures, sequelae, or even death in the worst-case scenario. Falls often occur because people misjudge step height and do not lift their feet sufficiently. One strategy to combat this issue is the use of vertical stripes to make stairs appear taller than they really are, which can thus prevent underestimation of the real height. However, the appropriate size of the space between the stripes is different for everyone. This study demonstrates how the intensity of an illusion can influence the height of foot clearance when ascending stairs. We validate the feasibility of using a model for determining the striping that can be used to adapt the pattern to individual differences. We constructed the model based on a contrast-sensitivity function using a Gaussian model. In an experiment, we measured the location of the toe via motion capture as participants climbed stairs. As a result, the relationship between foot-clearance and the spatial frequency approximated the function described by the CSF, Contrast Sensitive Function. The coefficients of determination exceeded 0.9 for one participant, 0.8 for two participant and 0.6 for other two participants. We concluded that the model presented CSF would fit the foot clearance with striped stairs for any individual.

A numerical simulation model for the evaluation of the effectiveness of lifejackets against drowning in tsunamis considering both unsteady water currents and human movement was developed. The Constrained Interpolation Profile-Combined Unified Procedure scheme was combined with the link segment model to simulate interactions between the fluid and subjects in the developed model. The developed model was experimentally validated using a large flume. A manikin laid on blocks was swept down by a tsunami-like water current and caught by a vortex behind the blocks. The developed model accurately reproduced both water currents and the movement of the manikin and was thus considered adequate to analyze the movement of human bodies in tsunamis. The model was then used to analyze the movement of a human body in the same currents but with higher buoyancy, assumed to represent a lifejacket. Consequently, buoyancy greater than a human’s body weight was required to keep the subject afloat; a buoyancy corresponding to the body weight caused the total submergence of the entire subject. Through comparison of forces applied to the body with its movement, it is revealed that a human body receives strong downward force while and immediately after passing over the vortex. These forces are caused due to the attractive pressure at the center of the vortex and downward currents in the downstream side of the vortex. These forces are considered to be remarkable in the evaluation of lifejackets in actual tsunamis.

This study first examined the correlation between types of acute phase head injuries to cyclists and consciousness disturbance by using data from patients at the emergency room of Dokkyo Medical University Koshigaya Hospital in Japan. The injuries were compared for cases where the cyclists experienced consciousness disturbance and otherwise. The results showed that skull fractures and brain contusions were the most frequent consequences of head injuries to cyclists in general. However, the average number of head injuries by types for cyclists suffering consciousness disturbance was higher than that for cyclists who had not experienced it, for both head fractures (0.9 versus 0.7) and brain injuries (1.9 versus 0.5). This implies that head fractures and brain injuries may increase the probability of consciousness disturbance. Next, considering a cyclist who had sustained a head injury and suffered acute consciousness disturbance in an accident while not wearing a helmet, a case study was conducted to quantify the effectiveness of a bicycle helmet in reducing the intensity of traumatic head injuries by using a whole-body model, a finite element model of the human head, and a model of the bicycle helmet on a mathematical dynamic modeling software. A comparison of the peak values computed for cases of cyclists with and without a helmet showed that in the former, strain on the skull was reduced by 95.9% in cases of skull fractures, and the von Mises stress on the brain was reduced by 23.3% for cases of brain contusions. The results suggest that helmet use reduces the risk of skull fracture and brain contusions in cyclists because it considerably reduces the impact. Moreover, the use of helmets can reduce the probability of consciousness disturbance.

A theoretical model for the motion of tiny spherical particles in a nanopore device is developed. The nanopore has a low aspect ratio, and the particles have a radius slightly smaller than that of the nanopore. The translocation of the particle through the nanopore is driven by the difference in external electric potential between the entrance and the exit of the nanopore. The model includes the effects of electrophoresis, electroosmotic flow in the nanopore, and the repulsive potential of the nanopore wall. Using this model, the time-dependent velocity of the particles during translocation through the nanopore is calculated for various parameters, such as the particle radius, the nanopore height, and the surface charge density of the particle. The motion of the particles predicted by the present model qualitatively explains the important characteristics of temporal ionic current responses across the nanopore observed in previous experimental results.

We developed novel trunk musculoskeletal models with detailed muscle paths for predicting the thoracolumbar load, and validated the developed models under dynamic loading and various postures. Two types of musculoskeletal models with different paths of the trunk muscles were constructed: a Via-Point type (with linear muscles) and Wrapping type (with curved muscles along ellipsoids). We predicted the intradiscal pressure (IDP) with the models and compared the results with literature values. The IDP predicted using the wrapping-type model had an extremely strong correlation with IDP measurements from the thoracic spine. The results demonstrate the effectiveness of more accurate muscle paths in musculoskeletal models for predicting the thoracolumbar load.

This study focuses on observing and analyzing the occurrence of a fall for humans during normal gait, which perhaps results in severe injury. Previously, the insufficiency of a recovery step, which diminishes the forward rotation of the body after tripping, was suggested as a factor for the failure of fall avoidance motion. However, although it was identified that a slow and/or short recovery step resulted in the failure of fall prevention, the physical process of tripping and falling during the gait was not analyzed sufficiently. In this study, the subject’s reaction motion and fall process against tripping became clearer because the fall motion, which included the phase closer to the ground contact, could be recorded for a longer time than that in most previous studies. Although the subject attempted to mitigate the forward angular momentum and the descent of body induced by tripping by holding on his recovery foot, it was not effective, especially when the recovery step length was short. Among such trials, the larger forward inclination of the body, the excessive forward movement of the center of mass from the support point, and the smaller ground reaction force of the recovery foot in the normal direction was observed. Because the short recovery step resulted in the limitation of the moment arm, which affected the reaction torque of the recovery foot, it became difficult to decelerate the body rotation and prevent the fall. Furthermore, it was also suggested that the forward lean of the body and the decrease of the ground reaction force increased the impact speed and effective mass, which affected the impact force. The observation of such an advanced fall phase also contributes to a more realistic simulation of the human reaction motion for a more precise estimation of the fall injuries.