Landing is a frequently executed motion in athletic activities, and injuries have been reported to occur often during landing, suggesting that legs are subjected to large loads during landing. Many studies, based on posture and floor reaction, have been conducted on this subject; however, few have been conducted from the muscular-activity perspective. Moreover, we found no studies investigating the functions of biarticular muscles (muscles that cross two joints). Therefore, we studied landing motion in which feet make ground contact after falling from a suspended position. Our objective was to clarify activity patterns of biarticular thigh muscles in two different trunk postures. Our results showed that the activity patterns of the antagonistic biarticular muscle pair at the thigh anterior and posterior were affected by trunk posture.

As the elderly population increases, independent living for the aged has become essential for extending a healthy life expectancy, and this requires the maintenance of mobility for daily activities, such as standing up and walking. Among these, standing up, a series of movements involved in getting out of a chair or bed, is the starting point of daily activities. Therefore, it is important to clarify the factors that contribute to accomplishing the transition from sitting to standing up. This study attempted to clarify the relationship between motor characteristics and the mechanism of muscle activity involved in the change from sitting to standing up. Specifically, we focused on the activity of the bi-articular muscles involved in the two joints simultaneously rather than joint torque that is the conventional standard for evaluating motion. We probed the mechanistic characteristics of bi-articular muscle activity as well as the main muscles that function during normal standing up motion, namely a natural standing up movement where the trunk is not vertically restricted, using electromyographic analysis, theoretical analysis using a link model based on the muscle arrangement of the lower limb, and experimental analysis using an actual model that reproduces the functions of these muscles to define the muscular activities of the thigh muscles.

It is very important to quantitatively calculate muscle strength and evaluate exercise in daily training and functional recovery training in the rehabilitation field. The value of joint torque at each joint of the limb is generally used for motion evaluation. However, bi-articular muscles in the limb might act antagonistically on one joint while acting cooperatively on the other joint. This bi-articular muscle action is known to cause lower power output than the power calculated from individual joint torque. Therefore, this study focused on the motion of the upper limb in the horizontal plane, and attempted to determine the relationship between the distribution of tip output and joint torque of each joint, and to simply estimate the muscle strength of bi-articular muscles from the commonly used joint torques.

We attempted to clarify the mechanical function of bi-articular muscles in the lower limb in the toe landing motion which enables the running motion. In the present study, the main working muscle was first clarified by electromyography analysis. An experimental analysis was subsequently performed using a real machine model, taking the protagonist muscle into consideration. The results of the electromyography analysis clearly demonstrated that stability of the body trunk involved switching the activity of the antagonistic pair of bi-articular muscles in the femur, suggesting a parallel link function. Based on this, an experimental analysis was performed using a real machine model with bi-articular muscles in the lower limb linked in parallel. The stability of the center of gravity of the model during dynamic motion due to switching of the muscle activity confirmed the parallel linkage, thus clarifying the involvement of the bi-articular muscles in the lower limb in body trunk stability at the time of toe landing.

本研究は踵を接地点とする体幹を安定させる着地において,ヒト下肢大腿部の筋配列を最も単純化したモデル,すなわ ち,股関節の拮抗一関節筋ペアと膝関節の拮抗一関節筋ペア,さらに,股関節と膝関節に同時に関与する拮抗二関節筋ペアを装備した二関節リンクモデルを提案し,それを基準に動作筋電図学的解析とロボット工学的理論解析をおこなった.その結果,動作筋電図学的解析において,踵着地時に大腿部の拮抗二関節筋ペアである前面の大腿直筋と後面のハムストリングスが同時放電することが明らかになった.この同時放電はロボット工学的な理論解析より,着地点である踵に発生する力と弾性を同時に調整することにより,着地時の姿勢安定性に大きく貢献していることが明らかになった.

We previously reported that the output force distribution at the wrist demonstrated in the hexagonal shape, and the characteristic of the hexagonal output force distribution was suggested by the theoretical analysis of the two joint link model with the muscle coordinate system. The muscle coordinate system is composed of the three pairs of antagonistic muscles consist of mono- and bi- articular antagonistic muscles. The difference between distribution calculated muscle coordinate system and distribution calculated joint coordinate system consists of two joint torques was clarified. The individual functional effective muscular strengths could be evaluated from the hexagonal output force distribution. And, we were proposed measuring method that used the portable measuring system of the functional effective muscular strengths. In this study, developed the application of the portable measuring system, and clarified the effectiveness of the application.

We previously reported that the output force distribution at the wrist demonstrated in the hexagonal shape, and the characteristic of the hexagonal output force distribution was suggested by the theoretical analysis of the two joint link model with the muscle coordinate system. The muscle coordinate system is composed of the three pairs of antagonistic muscles consist of mono- and bi- articular antagonistic muscles. The difference between distribution calculated muscle coordinate system and distribution calculated joint coordinate system consists of two joint torques was clarified. The individual functional effective muscular strengths could be evaluated from the hexagonal output force distribution. In this study, the relationship between output distribution and muscular strengths under approach by muscle coordinate system was more clarified. Proposal method may be of use when prescribing the portable measuring system of the functional effective muscular strengths.

The human action of standing up is regarded as a key aspect of rehabilitation for maintaining a basic standard of daily life. At clinical sites, a different phenomenon that departs from the standard theory for this action has been observed, suggesting that a distinctive biarticular muscle function is involved. We therefore performed electromyography (EMG) kinesiology to analyze the action of standing up and model the results in order to clarify the function of the biarticular muscle in the lower extremity. During standing up with a vertically upward movement of the trunk, EMGs demonstrated full activity of the monoarticular extensors of the knee joint and the biarticular muscle of rectus femoris. In experimental analysis with this model, parallel linkage function of rectus femoris allowed standing up with monoarticular extensors of the knee joint alone providing the driving force. The analysis further showed that in the dynamic action of standing up, parallel linkage retains the inertial force generated by contraction of the monoarticular extensors of the knee joint and thus retains the force of rearward trunk falling and effectively functions to direct floor reaction force toward the center of gravity.