Shinichirou Yamamoto

Mechanical and neural changes in plantar-flexor muscles after spinal cord injury in humans

Study design:Cross-sectional study.Objectives:To determine the effect of injury duration on plantar-flexor elastic properties in individuals with chronic spinal cord injury (SCI) and spasticity.Setting:National Rehabilitation Center for Persons with Disabilities, Japan.Methods:A total of 16 chronic SCI patients (age, 33±9.3 years; injury localization, C6-T12; injury duration, 11–371 months) participated. Spasticity of the ankle plantar-flexors was assessed using the Modified Ashworth Scale (MAS). The calf circumference and muscle thickness of the medial gastrocnemius (MG), lateral gastrocnemius and soleus were assessed using tape measure and ultrasonography. In addition, the ankle was rotated from 10° plantar-flexion to 20° dorsiflexion at 5 degu2009s−1 with a dynamometer, and the ankle angle and torque were recorded. After normalizing the data (the initial points of angle and torque were set to zero), we calculated the peak torque and energy. Furthermore, angle–torque data (before and after normalization) were fitted with a second- and fourth-order polynomial, and exponential (Sten–Knudsen) models, and stiffness indices (SISOP, SIFOP, SISK) and AngleSLACK (the angle at which plantar-flexor passive torque equals zero) were calculated. The stretch reflex gain and offset were determined from 0–10° dorsiflexion at 50, 90, 120 and 150 degu2009s−1. After logarithmic transformation, Pearson’s correlation coefficients were calculated.Results:MAS, calf circumference, MG thickness, peak torque and SIFOP significantly decreased with injury duration (r log-log=−0.63, −0.69, −0.63, −0.53 and −0.55, respectively, P<0.05). The peak torque and SIFOP maintained significant relationships even after excluding impacts from muscle morphology.Conclusion:Plantar-flexor elasticity in chronic SCI patients decreased with increased injury duration.

Effect of viscoelastic constraints to kinematic parameters during human gait

The aim of this study was to investigate the effect of viscoelastic factors on human gait forms, limb segment angles, and endpoint trajectories during walking in water relative to their effect during walking on land. Basic motion analysis methods were applied for each walking condition, and the joint angular displacements are shown in a three-dimensional (3D) plot. The drag force had little effect on the human gait form and the angle between the planar plane of the stance and swing phases in the 3D plot. These results suggest that the joint angular displacement controller, which consisted of three inputs and the feedback signals of the joint torque, was adopted in the central nervous system. In addition, the foot contact information might include the transition of the joint angular displacement controller from the stance / swing phase to the swing / stance phase.

Development of a tool system to support endoscope

Natural Orifice Translumenal Endoscopic Surgery (NOTES) is a type of minimally invasive surgery. This surgery needs working space for operating the endoscope, but there is no space for it in body cavity. Therefore, we have been developing a surgical tool system which can be inserted from the mouth and ensure space in body cavity. We use magnets and a tool to ensure space, like in abdominal wall lifting method, without use of wire. In this paper, we designed and realized a system which used a tool consisting of link mechanism and magnets. The link mechanism consists of four-bar linkage and a compression spring. It can be driven only by pulling wires, changing the diameter of the tool. We designed this surgical tool prototype, analyzed the stress and did basic experiments.

Changes of Muscle Fiber Length in Vivo during Walking as Revealed by Ultrasound Images

The objective of this study was to investigate our hypothesis involving treadmill walking as revealed by time series of ultrasound images. The hypothesis is that the changes in the length of muscle fiber (MFL) of the triceps surae muscle depend on the position of the center of mass (COM) relative to the ankle joint center of rotation. Seven healthy subjects participated in this experiment. The time series of ultrasound images in MG and the joint angular displacements in the hip, knee, and ankle were recorded while the subjects walked on a treadmill at speeds of 3.0 and 4.0 km/h. The MFL in MG was lengthened at the early stance phase and shortened at the late stance phase. Namely, the changes in the MFL of MG while treadmill walking followed our hypothesis, which was demonstrated while standing upright. These results suggest that the propulsive torque around the ankle joint is controlled by the shortening of the MFL in MG, whereas the MG muscle was in the eccentric contraction phase.

The development of endoscopic surgery for a training simulator

Recently there have been several cases of mistakes during endoscopic surgeries. In general, 89.2% of the endoscopic surgery medical errors in Japan are due to skill shortage of the doctor. Nowadays training machines for endoscopic surgery are being used. However, with the current training methods it is difficult to acquire the appropriate skills for a correct usage of the forceps. Because they cannot train how to use the forceps in the right way, the doctors have to depend on their senses. Therefore, a robot for training how to use the forceps is needed.

Different Contraction Pattern of Lower Leg Muscle Fiber between Swaying and Tiptoe Standing in Human Upright Posture

In recent studies, it is shown that gastrocnemius (GAS) muscle fiber movements in upright standing were paradoxical as compared to the movement of whole muscle length depended on the ankle joint movement. We hypothesized these muscle fiber movement depend on the position of the center of mass (COM) relative to the center of rotation of the ankle joint. The purpose of this study was to examine the change of muscle fiber length in GAS and tibialis anterior (TA) muscles while upright standing postures: swaying anterior-posterior and standing tiptoe-heel. Ultrasonography of the GAS and TA was recorded to detect the change of muscle fiber length in vivo. The center of pressure and the ankle joint angular displacements were recorded to use as visual feedback signals in two postural tasks.