Knee joint contact force is related to knee joint pain and related diseases such as osteoarthritis. Joint loading during gait even on an intact knee may cumulatively lead to the joint diseases. Previous studies on forward dynamics simulation suggest that knee joint angle is a key factor to alter knee joint contact force during walking. However, current literature has not shown the relationship between the quantities in actual human gait motion. In the present study, an open gait database was used to investigate the relationship between the quantities. Knee joint contact force and muscle forces were estimated using a musculoskeletal model, and the quantities in the early stance phase were analyzed. The knee joint contact force showed decreased correlation with decreasing knee flexion angle. The force of the muscles on the thigh also systematically changed with the knee flexion angle. Nevertheless, the knee joint contact force was larger for subjects whose knee flexion angle was less than 10 degrees in the early stance phase. These results revealed a risk motion for larger joint contact forces. It is suggested that walking with a straighter leg can be a practical strategy to reduce knee joint contact force. A fully extended knee would change the gait mechanism and lead to a higher load on the knee.

Sitting down and standing up from a chair are essential daily activities. However, existing prosthetic knees often lack sufficient functionality to perform these motions, particularly when standing up. Consequently, unilateral transfemoral prosthetic users must rely more on their sound limb for these motions, which can potentially lead to injury or joint disease due to the increased load on the joints of the intact side. The present study aimed to develop a prosthetic knee mechanism that assists in sitting down and standing up from a chair. We proposed a new passive mechanism integrated into our previous prosthetic knee design. This mechanism stores mechanical energy in a spring during knee flexion when sitting down, providing flexion resistance. The stored energy is then released by the user's manipulation, assisting in knee extension. In the evaluation experiment, a subject equipped with a simulated thigh socket and the proposed prosthetic knee performed the motions of sitting down and standing up from a chair. The results demonstrated a higher symmetry index of the ground reaction force during these motions with the proposed mechanism compared to the literature, suggesting that the mechanism functioned appropriately. The proposed mechanism can be applied to other prosthetic knees, potentially allowing transfemoral amputees to gain the functionality for standing up without needing to replace their current prosthetic knee.

Existing prosthetic knees used by transfemoral amputees for running lack the functionality to prevent knee buckling, which poses a significant barrier to participating in sports and exercise owing to the risk of falls. In our previous study, a passive prosthetic knee that restricts flexion in response to the load on the prosthetic leg during the stance phase was developed. However, the mechanism depended on specific conditions of the load and was unable to fully prevent knee buckling. In the present study, we focused on the duration of the swing phase, which is generally constant regardless of running speed. The function of the proposed prosthetic knee allows flexion only during the first half of the swing phase and restricts flexion for the remaining duration. The mechanism involved the spur gear attached to the knee rotation axis, which restricts knee flexion by engaging with the rack. The rack was controlled by a spring and damper to separate from the spur gear for a certain period. To evaluate the mechanism, an able-bodied participant fitted with the simulated thigh socket and the prototype prosthetic knee ran at various speeds. The results demonstrated that the proposed mechanism restricted knee flexion before the stance phase at various speeds and prevented knee buckling. The proposed prosthetic knee is expected to promote sports participation among transfemoral amputees and lead to improvements in health.

The analysis of knee motion during walking is essential for understanding the mechanisms of knee joint contact force (KJCF), a factor associated with knee joint pain and related joint diseases. A comprehensive analysis of whole-body motion can provide valuable insights and practical strategies for mitigating KJCF. This study aimed to identify body segments whose motion is related to KJCF using a Convolutional Neural Network (CNN). We used a gait database to obtain three-dimensional motion data and calculated their KJCF using a musculoskeletal model. In addition, the peak values of KJCF during gait were classified into five classes to develop a learning model with CNN. Visualization using Gradient-weighted Class Activation Mapping revealed that the regions of interest identified by the trained CNN model were the bases of the middle and ring fingers of the right hand, the outside of the right thigh, the left side of the hip, and the thumb side of the left wrist. These findings suggest that the motions of the hand markers, which change with the arm swings, impact the variation of KJCF.

Measuring the muscle force during gait can provide crucial knowledge for clarifying the walking mechanism and preventing injuries. However, non-invasive muscle force measurement is a major challenge in biomechanics. Previous research has investigated the relationship between the amplitude of electromyography (EMG) and muscle force. By examining the EMG–force relationship of each muscle, the generated muscle force can be measured on the basis of the EMG amplitude during gait. This study aimed to investigate the angle–EMG–force relationship of lower limb muscles and estimate the muscle force during gait. The EMG and muscle force were measured in a static muscle force measurement task, and the angle–EMG–force relationship was analyzed based on these data. The results indicate that the muscle force can be estimated using the angle–EMG–force relationship during gait.Clinical Relevance—This study contributes to a more correct analysis of the muscle force during gait.

Transfemoral amputees who run are required to learn how to control their prosthetic leg motion to avoid falling with unintended prosthetic knee flexion because the function of the existing prosthetic knee for running is likened to a simple hinge joint during stance. However, the risk of falling and injury is a barrier to participation in sports and exercise. We have addressed this concern by developing a passive mechanism for a prosthetic knee; however, the mechanism that locks knee flexion with ground reaction forces (GRFs) could not completely avoid unintended prosthetic knee flexion. The present study aims to reconsider the function of the prosthetic knee for running and propose a new prosthetic knee mechanism. Time is an alternative way to control the lock/unlock of flexion without GRFs; therefore, the new prosthetic knee mechanism should limit flexion after a certain period from the moment that the prosthesis leaves the ground. We developed a rough prototype to confirm the function of the new prosthetic knee and conducted an evaluation experiment. The subject who was attached to the simulated thigh socket and prototype of the new prosthetic knee performed level walking. The results indicated that the new mechanism allowed flexion only during the first half of the swing phase, meaning the subject was able to walk without falling. According to the literature, swing time is approximately constant among different speeds. The new mechanism would appropriately function under actual running conditions. Clinical Relevance-This proposes a new passive prosthetic knee mechanism for above-knee amputees to run safely.

Frailty is associated with gait variability in several quantitative parameters, including high stride time variability. However, the associations between joint kinematics during walking and increased gait variability with frailty remain unclear. In the current study, principal component analysis was used to identify the key joint kinematics characteristics of gait related to frailty. We analyzed whole kinematic waveforms during the entire gait cycle obtained from the pelvis and lower limb joint angle in 30 older women (frail/prefrail: 15 participants; non-frail: 15 participants). Principal component analysis was conducted using a 60 × 1224 input matrix constructed from participants’ time-normalized pelvic and lower-limb-joint angles along three axes (each leg of 30 participants, 51 time points, four angles, three axes, and two variables). Statistical analyses revealed that only principal component vectors 6 and 9 were related to frailty. Recombining the joint kinematics corresponding to these principal component vectors revealed that frail older women tended to exhibit greater variability of knee- and ankle-joint angles in the sagittal plane while walking compared with non-frail older women. We concluded that greater variability of knee- and ankle-joint angles in the sagittal plane are joint kinematic characteristics of gait related to frailty.

Existing prosthetic knees used by transfemoral amputees have function almost akin to non-friction hinge joints during the running stance phase. Therefore, transfemoral amputees who wish to run need sufficient strength in their hip extension muscles and appropriate prosthetic leg swing motion to avoid falling due to unintended prosthetic knee flexion. This requires much training and practice. The present study aimed to develop a passive mechanism for a transfemoral prosthetic knee to prevent unintended prosthetic knee flexion during the running stance phase. The proposed mechanism restricts only flexion during the prosthetic stance phase with a load on the prosthetic knee regardless of the joint angle of the prosthetic knee. The load on the prosthetic knee required to maintain locked flexion was analyzed. We developed a rough prototype and conducted an evaluation experiment with an intact participant attached to a simulated prosthetic limb and the prototype. The results of level walking showed that the proposed mechanism limits knee flexion, as designed. The results of the preliminary trial suggest that the proposed mechanism functions appropriately during running, where the load on the prosthetic knee is larger than that during walking.

Walking is an essential physical activity in an increasingly aging society. However, sustained walking with an incorrect posture may cause excessive stress on the knee joint, causing knee abrasion. The elderly are particularly vulnerable to this issue. Walking motion features can be analyzed to reduce knee load and lead to sustainable living. This study proposes a method for analyzing the motion of walking that affects the load on the knees using a motion capture system, ground reaction force measurement, a convolutional neural network (CNN) model, and a visual explanation technique for CNN. We trained a CNN model to classify the joint contact forces at the knee using gait measurement data. The heat maps were calculated using gradient-weighted class activation mapping from the trained CNN model. The experiment analyzed the motion factors affecting the joint contact forces at the knee using heat maps.

We welcome the global community of professionals involved in the care of persons in need of prosthetic, orthotic, mobility and assistive devices to the ISPO 18th World Congress! [View Programme Overview in Oxford Abstracts](https://virtual.oxfordabstracts.com/#/e/ispo2021/program) I [View the Abstract Book](https://journals.lww.com/poijournal/toc/2021/12001) | [HowToTreat ISPO Edition](https://360-ot.de/howtotreat/)

Recovery sandals have been developed to enhance recovery from fatigue after sports. However, the previous studies suggested the sandals were alter lower extremity kinematics and increase muscle activity during gait. The recovery sandals may be increased muscle activity as well as the sandals. The aim of the present study was to investigate the effects of the recovery sandals on lower limb muscle activity during gait. Three men walked barefoot, with the recovery sandals and their own athletic shoes. The kinematic, kinetic and electromyography (EMG) data were input to a musculoskeletal model to estimate muscle force. As the results, the lower extremity joint kinematics altered with the recovery sandals, but the ground reaction forces showed no difference. In the stance phase, the peak muscle force reduced with the recovery sandals in all subjects. These results suggested the recovery sandals could reduce muscle forces during gait.

Stooped posture of the trunk during baseball pitching is able to cause shoulder injury. Although the rectus abdominis and erector spinae muscles significantly contribute to maintain the trunk posture, how activities of those muscles are related to the stooped posture is unknown. Therefore, the purpose of the present study was to determine whether the stooped posture was caused by the trunk muscles during the pitching motion. Three participates performed pitching in the stooped and upright postures. The electromyography (EMG) activity of the rectus abdominis and erector spinae muscles were measured. As a result, there was no difference in the rectus abdominis EMG activity between the stooped and upright conditions, and the erector spinae EMG activity was increased. These results suggest that the stooped posture during pitching was caused by other factors, such as abdominal pressure and the activity of the related muscles.

Transfemoral prosthetic users have motor functional impairments during running. A major impairment is unintended prosthetic knee flexion during weight bearing on the prosthetic side. Therefore, the present study aims to develop a passive mechanism for a transfemoral prosthetic knee to prevent flexion during the prosthetic stance phase. The proposed mechanism has a single axis for prosthetic knee flexion-extension. The shaft that functions as the prosthetic knee joint axis can move 3 mm along the long axis of the shank part to change functions between the stance and the swing phase. The prosthetic knee joint limits only flexion and allows extension possible during the stance phase. However, it rotates freely (flexion-extension) during the prosthetic swing phase. These functions of the proposed mechanism were verified using a rough prototype. The he participant with the attached prosthetic limb prototype performed level walking with habitual gait velocity on a 10 m straight walkway. The result shows that the kinematic data of the hip, knee, and ankle were similar to able-bodied gait. Moreover, the mechanism was able to mechanically limit only the flexion with compression force acting along the shank part. These proposed mechanisms and results of the preliminary trial suggest that transfemoral amputees can run safely.

Transfemoral prosthesis users are easy to fall during running because prosthetic knees for running do not have flexion lock function during stance phase. Therefore, the purpose of the present study was to propose a passive mechanism of transfemoral prosthetic knee to prevent unintended knee flexion during running. The proposed mechanism has a single axis for prosthetic knee flexion–extension. Knee flexion lock function was realized with the force on knee joint along the long axis of the shank part (ground reaction force), and we showed statics of the mechanism of the function. The mechanism limits only flexion and allows extension during the stance phase. During the prosthetic swing phase, it rotates flexion and extension. These functions of the proposed mechanism were verified using a rough prototype. The intact participant with a simulated thigh socket and the prototype performed level walking. As a result, when teeth of the spur gear and stopper in the mechanism were engaged, the knee joint produced extension moment without knee flexion as we designed. Smooth flexion and extension of the prosthetic knee were observed during the swing phase.

The purpose of this study was to develop a prosthetic knee joint unit suitable for pedaling by modeling pedaling using four-link mechanisms and examining the link length and joint torque that maximizes crank torque. As a result, the crank torque increased as the link length became shorter. The joint torque of the simulation switched the function of flexion and extension at the singular point of the mechanism. This was shown to be reproducible by a active prosthetic knee joint unit. And the joint torque of the simulation and the joint torque of the able-bodied person were different. Also, it was suggested that the relationship between knee joint angle and knee joint torque of able-bodied person can be reproduced using a passive mechanism.

The previous study showed that the knee joint contact force was increased with the knee flexion angle at the early stance of gait in numerical simulation. In the present study, we investigated the relationship between the knee flexion angle and contact force at the stance phase with the data of the real subjects. We used the data of 182 subjects in a gate database and calculated the knee joint contact force for each subject using a musculoskeletal modeling system. As the results, the knee flexion angle and contact force showed a middle correlation (r = 0.56) in the subjects whose knee flexion angle was more than 10°. In the early stance of gait, the knee joint contact force was reduced with less knee flexion angle, but the subjects whose knee flexion angle was less than 10° showed higher joint contact force. These results suggested an appropriate knee joint angle could reduce the knee joint contact force during gait.

We have currently been developing passive mechanism for multifunctional prosthetic knee joint unit that is an important part of transfemoral prosthesis. The passive mechanism for prosthetic knee that we previously developed allowed users to walk on the ground and ascend stairs. In the present study, a joint which rotation (knee flexion) was controlled by a damper was added to the previous mechanism to realize stair descent function. In the evaluation experiment with the proposed knee, level walk, stair ascent, and stair descent were succeeded.

The final goal of this study is to develop a wearable waist assist device. The developed device is driven with pneumatic actuators, which are constructed with cloths. Sensor-less force control method is proposed in this study based on the force characteristic of cloth actuator. In this paper, the structure of developed device is discussed and then the analysis model for sensor-less control is proposed. Further more simple human body model to control this device under constant assist rate is proposed. Finally, effectiveness of the developed device is verified based on iEMG.