Motomu Nakashima

• Doctor of Engineering
• Professor (Full) at Tokyo Institute of Technology

It is well-known among swimmers and coaches that the swimming speed of the underwater dolphin kick (UDK) is higher than that of the underwater flutter kick (UFK). This study aimed to clarify the differences in swimming performance between the two kicking styles in terms of kinematics, kinetics and muscle activity. Eight male swimmers performed UDK...

Accumulation of muscle fatigue and subjective fatigue are significant causes of decline in individual performance. Those fatigues can also lead to work errors and the associated musculoskeletal disorders. Thus, a quantitative evaluation of fatigue accumulation during work is required to manage the risk of industrial accidents. Most of the current a...

To improve a training paddle during the crawl stroke for swimmers with unilateral transradial amputation/deficiency, the paddle dimensions should be determined considering the balance of increases in shoulder joint torques between the intact and amputated/deficient limbs. The objectives of this study were (i) to propose a new index which was the ra...

This study aims to confirm the effects of a neck pillow on the postural stability of the head and neck and the variance of center of mass in a sitting position. Experiments were conducted on keeping a sitting posture at rest with and without the use of two types of neck pillows; the neck wrap pillow and the front neck pillow. During experiments, wh...

Transfemoral prosthesis users (TFPUs) typically have a high risk of balance loss and falling. Whole-body angular momentum ( ${\overrightarrow {H}}_{{\text {WB}}}{)}$ is a common measure for assessing dynamic balance during human walking. However, little is known about how unilateral TFPUs maintain this dynamic balance through segment-to-segment can...

This study aims to establish a monocular camera-based system that uses a generative adversarial network (GAN) to estimate a 3D pose of a human and his/her orientation relative to the camera from images by considering anatomical knowledge such as segment length and joint range of motion. The proposed network is trained by unsupervised learning using...

In sprint races for runners with upper limb amputation/deficiency, it is allowed to use arm prostheses. However, there are few studies about arm prostheses for sprint running and about runners with upper limb amputation/deficiency. The objective of this study was to investigate the dynamical and musculoskeletal effects of arm swing and prosthesis o...

One of the main limitations in the musculoskeletal modeling and analysis of swimmers is the acquisition of external forces, which precludes the estimation of internal forces, crucial for advancing knowledge on swimming biomechanics. Computational simulations allow an estimation of these forces, and Swumsuit (SWimming hUman Model with Synthetic User...

This study aims to integrate an open-source software capable of estimating hydrodynamic forces solely from kinematic data with a full-body biomechanical model of the human body to enable inverse dynamic analyses of swimmers. To demonstrate the methodology, intersegmental forces and joint torques of the lower limbs were computed for a six-beat front...

This work presents the development of a markerless optical motion capture system of the front-crawl swimming stroke. The system only uses one underwater camera to record swimming motion in the sagittal plane. The participant in this experiment was a swimmer who is active in the university’s swimming club. The recorded images were then segmented to...

A marker-based optical motion capture system is often used to obtain the kinematics parameters of a running analysis. However, the attached marker could affect the participant's movement, and the system is costly because of the exclusive cameras. Due to its drawbacks, the present research aimed to develop an affordable markerless optical motion cap...

Wheelchair sports have an important role as a tool of rehabilitation for people with physical disabilities in lower limbs, and have been a driving force for innovation in wheelchair technology and practice as well. In wheelchair tennis, it is important to evaluate the pushing motion by players as well as the performance of the wheelchair when pushi...

The purpose of this study was to determine the effects of the presence and characteristics of a neck pillow on head and neck posture in the resting sitting position with eyes closed. Sitting posture maintenance tests were conducted on four subjects using a middle-back office chair. The head and neck postures in the normal sitting posture and in the...

In skateboarding as a sports event, the riders compete in difficulty and completeness of acrobatic motions called “tricks”. As a basic trick, Ollie is performed popularly. However, the basic mechanical principle of the Ollie has not been discussed to date, especially for the Ollie jump (the jumping phase of Ollie). The objective of this study was t...

The aim of this study was to review the literature on front crawl swimming biomechanics, focusing on propulsive and resistive forces at different swimming velocities. Recent studies show that the resistive force increases in proportion to the cube of the velocity, which implies that a proficient technique to miminise the resistive (and maximise the...

The ability to sustain steady straight-ahead walking is one goal of gait rehabilitation for individuals with unilateral above-knee (UAK) amputation. Despite the morphological and musculoskeletal asymmetry resulting from unilateral limb loss, the mediolateral ground-reaction-impulse (GRI) should be counterbalanced between the affected and unaffected...

In the previous study, an experimental system to measure propulsive force during swimming using the humanoid robot SWUMANOID was constructed. However, the recovery motion of crawl stroke was not appropriate because of the earlier timing of the rolling motion, which was caused by an attaching device to SWUMANOID. Also in the previous study, the bett...

Comfort is required for soaking in bathwater. Although several studies investigated comfort during soaking from a biomechanical viewpoint, these previous studies employed two-dimensional models in the sagittal plane of a bather. The objectives of this study were to take three-dimensional postures of the bather into account and to evaluate the biome...

Every second year, the International Sports Engineering Association (ISEA) conducts a conference somewhere around the world. [...]

The swimming turn is one of the important factors in producing results in a race. Knowing the mechanical quantities in turns is useful to quantify the turning technique. However, experimental measurements often require considerable time and costs. The aim of this study was to construct a simulation model of a flip turn in the crawl stroke by extend...

Devices for swimmers with arm amputation/deficiency have not been developed a lot and therefore many improvements can be realized. Although swimmers often use paddles during training, paddles on the market are basically for swimmers without amputation/deficiency. The objective of this study was to analyze the swimming motion of a swimmer with unila...

To improve competitive skills, it is important to clarify the relationship between the propulsion motion (the propulsive force in the use of racing wheelchairs optimized for athletes) and aerodynamic drag, which can change during propulsive motion. Therefore, the purpose of this research was to construct a novel force sensor system that is attachab...

Background: Walking and mobility are essential for a satisfactory quality of life. However, individuals with transfemoral amputations have difficulties in preventing falls due to prosthetic knee buckling, defined as the sudden loss of postural support during weight-bearing activities. The risk of prosthetic knee buckling can be evaluated by determ...

Competitive swimming is a very complicated phenomenon from the viewpoint of physics. Most parts of a swimmer's body am underwater while some parts are above the water. A swimmer is performing three-dimensional motion with many degrees-of-freedom and the flow is high Reynolds number turbulent flow. Therefore, it is a very challenging task to be inve...

Since wheelchair tennis players sprint a short distance frequently, it is necessary to evaluate the pushing motion and the propulsion performance of the wheelchair in the pushing motion. In this study, the multibody dynamics simulation model of a human and a wheelchair was constructed for the evaluation without any experiments. The human and wheelc...

In this study, the paddle for a swimmer with unilateral transradial deficiency to wear on the deficient side during training was designed. An experiment to acquire the swimming motions of a swimmer with unilateral transradial deficiency was conducted and the swimming motions without a paddle were analyzed using the swimming human simulation model S...

Although athletics sprinters with transradial amputation/deficiency can wear arm prosthesis in competition, there have been few researches focusing on arm prosthesis for running and little is known about the effect of arm prosthesis on running motion. In order to investigate the muscle loads when running with forearm prosthesis, the basic musculosk...

The swimming humanoid robot called SWUMANOID was developed for underwater motion study. It had 24 servo motors that could achieve four swimming strokes, including crawl stroke, backstroke, butterfly stroke and breaststroke. However, the swimming direction of the robot was not stable and could not be controlled in the previous researches. In this st...

The present study focused on freestyle swimming by swimmers with unilateral transradial deficiency. It has not been clarified yet whether the deficient limb should move so as to match the tempo of the intact upper limb, or if it should move as fast as possible to produce thrust by itself. The objective of this study was to solve the theoretically i...

The objective of this study was to realize the backstroke with the swimming humanoid robot. By realizing the backstroke, the backstroke performance of the robot was assessed regarding the speed and the swimming behavior. The motion for the robot was generated based on the motion of an actual swimmer. However, since the robot did not have sufficient...

Soaking in bathwater has been a familiar custom for the Japanese for a long period of time. The authors discussed bathing comfort from the viewpoint of biomechanics in a previous study. However, it took a lot of effort to evaluate the joint torques during soaking in the water while conducting the experiments. Therefore, it was required to estimate...

The objective of this study was to simulate the swimming motion with bi-fins and investigate the effect of ankle joint motion by simulation. A model of a swimmer was constructed by utilizing the swimming human simulation model SWUM. The bi-fin was modeled as a series of five rigid plates. One rigid plate was connected to another by virtual springs...

The objective of this study was to develop a comprehensive method for musculoskeletal simulation in swimming. In the developed method, the motion capture data of a swimming motion were first transformed into input data for the swimming human simulation model Swimming Human Model (SWUM). Then, the output data from SWUM were transformed into input da...

Sprint canoe paddling is a dynamic and complicated motion performed with the entire body of the paddler. Not only the upper limb motion, but also the motions of the trunk and lower limbs contribute to the propulsion. The objectives of this study were to simulate sprint canoe paddling, and investigate the contributions of the upper and lower limbs,...

In order to reveal the effect of forearm prosthesis on running motion, we measured arm swing motion of the athletes with unilateral below-elbow amputation wearing forearm prosthesis by optical motion capture, and estimated net forces and torques exerted on the shoulder and elbow joints by inverse dynamics. The results showed that wearing forearm pr...

In the previous study, an experimental system to measure propulsive force during swimming using the humanoid robot SWUMANOID was constructed. However, the recovery motion of crawl stroke was not appropriate because of the earlier timing of the rolling motion, which was caused by attaching device to SWUMANOID. The objective of this study was to find...

This study focuses on the mechanics of skateboarding. Skateboard has become so popular that it has been officially certified at the 2020 Tokyo Olympics. There are many “tricks” in skateboarding. However, the tricks are acquired by the riders empirically. Its mechanical principle and conditions to succeed have not been clarified theoretically yet. I...

Since the impairment level and remaining ability change depending on the athlete in cross country sit-skiing, the optimal sitting posture and shape of the equipment also change. Generally, the shape of the equipment is determined by improving the prototype based on feedback from the athletes, so it costs and is time consuming. In this study, a mult...

The swimming humanoid robot called SWUMANOID was developed as an experimental platform for swimming research. The robot has 24 actuators to realize the swimming motion. To date, the front crawl, the breaststroke, and the butterfly stroke have been realized by this robot. In this study, the preliminary motion of backstroke was created and realized b...

Breaststroke swimming has been already realized by the swimming humanoid robot, SWUMANOID. This robot is half scale of human, has 24 servo motors, gyro sensors and wireless communication device. During the kicking motion, the knee joints are rotating shanks to generate propulsive force. In order to increase the swimming speed, it was found that the...

The purpose of this study was to compare active drag during front-crawl swimming performed by competitive swimmers with passive drag acting on the same group of swimmers with streamlined position at various velocities. Seven male competitive swimmers participated in this study, and the testing was conducted in a swimming flume. The active drag was...

The purpose of this study was to investigate the relationship between active drag and swimming velocity during front-crawl swimming using the MRT-method (a methodology using the measured values of residual thrust) and the MAD-system with the same group of swimmers. Six male swimmers swam front-crawl with (Whole stroke: WS) and without leg motion (a...

The purpose of this study was to examine the effect of leg kick on the resistance force in front-crawl swimming. The active drag in front-crawl swimming with and without leg motion was evaluated using measured values of residual thrust (MRT method) and compared with the passive drag of the streamlined position (SP) for the same swimmers. Seven male...

Several previous studies investigated comfort while soaking in hot bathwater from the perspective of thermal effects or physiology. However, few studies investigated bathing comfort from the perspective of biomechanics, although the biomechanical state in bathing, such as buoyancy on a human and the degree of muscle contraction is expected to be ch...

For the crawl stroke in swimming, it is important that the stroke made by the upper limbs and the flutter kick made by the lower limbs are well coordinated in order to enhance swimming performance. However, the training method to acquire the appropriate flutter kick timing has not been sufficiently established. In the present study, a biofeedback t...

The simulation model to assess the performance of diving fin was developed by extending the swimming human simulation model SWUM. A diving fin was modeled as a series of five rigid plates and connected to the human model by springs and dampers. These plates were connected to each other by virtual springs and dampers, and fin’s bending property was...

The purpose of this study was to compare the active drag values estimated by the MRT-method and the MAD-system. Six male competitive swimmers participated in this study and performed front crawl with arms only condition. The drag was compared at six-staged velocities ranged from 0.9 to 1.4 m/s between MRT-method and MAD-system. The drag estimated b...

Motion capture systems are used in various fields such as sports, medical, and robotics. Among the motion capture systems, optical systems are used most commonly, and these are also used in the experiments to obtain swimming motion in many studies. However, their own problems such as marker loss and marker misrecognition induce difficulties in expe...

For competitive swimmers with a physical disability, the ideal stroke for crawl swimming has not been clarified yet. It may be different from that of able-bodied swimmers because of differences in body structure. The objective of this study was to solve computationally the fastest arm stroke of crawl swimming for swimmers with unilateral forearm am...

In order to design a comfortable bathtub to soak, it is important to evaluate the biomechanical load in the soaking posture. In the previous researches, joint torques as the biomechanical load were calculated. However, in these researches, biomechanical models in the sagittal plane were used and therefore only two dimensional joint torques were cal...

The objective of this study was to construct an experimental system which can measure propulsive force during swimming motion by using a humanoid robot, SWUMANOID. First, a device to fix a robot to a circulating water tank was made. Using this device, the robot was fixed to a circulating water tank and the propulsive force was measured by a force s...

The objective of this study was to solve the theoretically ideal arm stroke for a swimmer with hemiplegia by using the optimizing simulation. The method of optimizing simulation for non-disabled swimmers was extended to a swimmer with hemiplegia. In order to evaluate the arm strokes in the optimizing calculation, the swimming human simulation model...

The swimming humanoid robot called SWUMANOID has been developed for research purpose. To date, the front crawl, the breaststroke, and the butterfly stroke have been realized by this robot. However, the backstroke has not been realized yet because of several problems. The first problem is the communication problem during an experiment. The second is...

In order to improve comfort in soaking in the bathwater, the relationship between the biomechanical load and the bathtub shape has to be clarified. For this purpose, many soaking experiments had to be conducted since it was necessary to measure the reaction forces acting on a human from the bathtub experimentally. The objective of this study was to...

The objective of this study was to realize the butterfly stroke by the swimming humanoid robot “SWUMANOID”, and to investigate the swimming performance of the robot. The robot was modified from its original condition in order to reduce the weight of the lower body. The swimming motion of the robot was generated based on that of an actual swimmer. B...

The objective of this study was to propose a CPG network which can generate the swimming motion of the crawl stroke. First, the CPG network for legs performing a flutter kick was constructed by connecting the neural oscillators for the leg joints. The flutter kick motion was successfully generated by the proposed CPG network. The propulsion by the...

We aimed to develop a new method for evaluating the drag in front-crawl swimming at various velocities and at full stroke. In this study, we introduce the basic principle and apparatus for the new method, which estimates the drag in swimming using measured values of residual thrust (MRT). Furthermore, we applied the MRT to evaluate the active drag...

The objective of this study was to improve the performance of crawl swimming for the swimming humanoid robot. The swimming humanoid robot had 24 servo motors for the whole body and could perform basic human swimming motion. This robot could swim freely by the crawl stroke. However, the robot sometimes failed the recovery motion in free swimming. Th...

In this study, pedaling motion was analyzed using a simulation model of a human-bicycle system. Pedaling motion was expressed by human body’s joint motion. In simulation, the joint motion was determined to satisfy geometric condition. And the pedaling motion was performed by PID control of the human body’s joints. First, with respect to the PID con...

There are many studies about swimming by kinematic and partial kinetic analysis. In order to obtain muscle activity during swimming, the experiments using the electromyogram were conducted as well. However, measurable muscles are limited in this experiment. And there are few musculoskeletal analysis of swimming, since it is difficult to compute the...

Since competitive fin swimming using bi-fin is a relatively new sport, there are no research about swimming motion considering the characteristic of the fin. Therefore players determine their swimming motion based on their own sense and experience. In this research, a simulation model to assess the swimming motion was constructed by extending the s...

For the competitive swimmers with physical disability, the optimized stroke of crawl swimming has not been clarified yet, and may be different from that of able-bodied swimmers. The objectives of this study was to solve computationally the arm stroke of the crawl swimming that maximized the swimming speed for swimmers with bilateral transfemoral am...

Our previous study proposed a biomechanical model in bathing postures. Methods to support upper body including trunk and head of bather were expected to affect physical relax and biomechanical state, such as joint torque or reaction force from bathtub, in bathing. This hypothesis was verified using the biomechanical model in bathing. Bathing postur...

Compression garments are widely used in various sports activities. Since the cloths in a compression garment are sufficiently attached to the human body, it is possible for a compression garment to have particular mechanical functions by appropriately arranging the tension distribution in the garment. However, the effects of such garment on muscle...

The cause and effect relationship between the paddling motion and the hull behavior of a kayak in a sprint race has not been sufficiently investigated. The objective of this study was to investigate the effect of the paddling motion on the hull behavior by numerical simulation. A dynamic simulation model of a paddler, paddle and hull in a single ka...

The main objective of this research was to develop a markerless optical motion capture system that can be used for daily use in swimming training. The butterfly stroke was targeted since it is considered bilaterally symmetric in motion. The system consisted of a segmentation process to obtain the participant’s silhouettes and a matching process to...

In order to clarify the mechanics of human swimming, a full-body swimming humanoid robot called “SWUMANOID” was developed as an experimental platform for research about human swimming. SWUMANOID had a detailed human body shape, created using three-dimensional scanning and printing equipment, and was developed as an experimental model substituting f...

In this paper, a compliant robotic manipulator is proposed as a mechanism to approximate the mechanical properties of the human trunk during wheelchair propulsion. This manipulator is a variant of the conventional Stewart Platform, modified by the addition of spring elements in series with the linear actuators. The spring elements add a compliance...

The swimming humanoid robot "SWUMANOID" was developed in the previous study for research of human swimming. The crawl stroke and breaststroke have been already realized by the robot. However, the butterfly stroke has not been realized to date. Therefore, the objective of this study was to realize the free swimming of the butterfly stroke with the r...

In order to improve the performance in wheelchair racing, it is important for players to use the optimum wheelchair and to propel it in the optimum manner. However, only trial and error is conducted in the present training situation to find them. In order to consider the whole dynamics of player and wheelchair, a simulation model was developed in t...

The objective of this study was to improve the stability of crawl swimming for the swimming humanoid robot. The swimming humanoid robot had 24 servo motors for the whole body and could perform basic human swimming motion. This robot could swim freely by the crawl stroke. However, this robot sometimes failed the recovery motion in free swimming. The...

For the competitive swimmers with physical disability, an ideal stroke to master has not been fully clarified yet. The objectives of this study were to solve computationally the arm stroke of the crawl swimming that maximized the swimming speed for swimmers with hemiplegia, and to investigate the features of the optimized stroke. For this objective...

Although several previous studies investigated bathing comfort from the viewpoint of thermal effect or physiology, few studies investigated that from the viewpoint of biomechanics. The objective of this study was to evaluate bathing postures from the biomechanical viewpoint. In the previous study, authors proposed a biomechanical model in bathing p...

Scuba diving is becoming popular as a leisure activity. Although manufacturers make various types of diving fin, these developments are based on qualitative methods because of the difficulty in estimating the fin efficiency quantitatively. In this research, a simulation model to assess the performance of diving fin was constructed by extending the...

During standing pedaling in a bicycle race, a human body and a bicycle are swinging in right and left. In order to investigate such movement, sagittal plane models and experiments using an ergometer in the previous studies were insufficient. In the present study, a three dimensional simulation model to analyze such problem was constructed using a m...

The bath room is the place where serious injury accidents might happen. In particular, stepping over bathtub apron is one of the most dangerous motions. There were few studies in which the load of stepping motion was discussed in detail. In order to improve safety of stepping motion for elder people whose muscle forces decline, the load of the moti...

The disabled sports get a great deal of attention. In fact, almost 40 million people watched the London Paralympic games on TV. Among them, the wheelchair racing has been popular after the first international wheelchair sporting competition for the disabled in 1952 and Japan got a lot of medals in the wheelchair racing. Due to advanced wheelchair q...

Bathing in a bathtub filled with water is a custom common in Japan. Since comfort is important in bathing, comfortable bathtub design is desired. In the previous study, the algorithm to estimate reaction forces from bathtub was constructed. However, in order to evaluate the comfort of the bathtub in simulation completely, it was necessary to know b...

The objective of this study was to improve the stability of crawl swimming for the swimming humanoid robot. The swimming humanoid robot had 24 servo motors for the whole body and could perform basic human swimming motion. This robot can swim freely by the crawl stroke. However, the robot sometimes changed the propulsive direction while free swimmin...

This paper reviews unsteady flow conditions in human swimming and identifies the limitations and future potential of the current methods of analysing unsteady flow. The capability of computational fluid dynamics (CFD) has been extended from approaches assuming steady-state conditions to consideration of unsteady/transient conditions associated with...

Although several previous studies investigated bathing comfort from the perspective of thermal effect or physiology, few studies investigated that from the perspective of biomechanics. The objective of this study was to ecaluate bathing postures from the biomechanical viewpoint. Bathing postures and reaction forces from the bathtub to a human was m...