Sports Research at the University of Tokyo
It is not just athletes who are seriously into sports at the University of Tokyo. In this section we introduce some of the "powerful Socrates" at the University, faculty members who are daily engaged in research and education relating to sports. Several sports researchers from among the many at the University of Tokyo describe the most interesting themes in sports research today.
Deciphering sports movements through the laws of mechanics
Fig. 2: Miyazaki Daisuke doing a jump shot. The arrows indicate the direction and amount of the ground reaction force.
― What kind of a research field is biomechanics?
Fig. 1: Daisuke Miyazaki, a professional handball player, prepares for an experiment. Coordination markers made of fluorescent materials are attached to various parts of his body.
“Bio-” covers life and living organisms, and “-mechanics” covers dynamics. As such, biomechanics is a research field that examines the structure and functions of living organisms from the perspective of mechanics. My research is focused on deciphering various sports movements using the methodology of biomechanics. I analyze the way the human body moves using the optical motion capture system method and high speed video-recording (Fig. 1), and extrapolate how joint torque and muscle force are exerted during movement. Additionally, I create virtual skeletons and muscle models using computer software, and simulate movements for better performance by issuing orders to the muscles. Using this two-pronged approach, I try to understand human movements in sports as a phenomenon caused by the interaction between internal forces that exert their effect within the human body (muscles and joints), and external forces, such as gravitation, ground reaction, and air resistance (Fig. 2).
― What is the biomechanics interpretation of sprint running, for instance?
The graph in Figure 3 estimates the torque (force of rotation) of three joints (ankle, knee, and hip) in the lower limbs during a sprint. The ankle joint generates torque only when the leg lands on the ground, and the knee joint generates bending torque a little before landing. The hip joint, on the other hand, is active the entire time, and generates substantial torque when the whole leg moves forwards from behind and backwards from the front. Due to the torque of the hip joints, both legs swing forwards and backwards like a pendulum.
Fig. 3: Changes in the joint torque on the lower limbs during running.
This research has clarified the specific joints that should be activated in order to run fast and the precise timing for their activation, as shown in Figure 4. In the past, athletes were told to raise their thighs high in order to run fast, but, in fact, making conscious efforts to raise the thighs delayed exerting force and had the opposite effect on athletes’ speed.
― So athletes do not have to raise their thighs when running? I did not know that.
Flexion of joints is controlled by two types of muscles that always work in pairs: one agonist muscle of the joint, and the other on the opposite side to put a brake on movements as an antagonist muscle. When sprinting, it is necessary to repeatedly switching on and off this pair of muscles at very high speed, alternating between the right and left leg. When coaches advise athletes to relax, what they mean is turn off the muscle activity that puts a brake on joint flexion. If athletes relax completely, they will not be able to run at all. At school athletic meets, for example, there are children who overexert themselves when cheered and are unable to run fast. This happens because not only the agonist muscles that activate the joints, but also the antagonist muscles that put a brake on joint flexion, are switched on. As a result, such children are unable to run fast despite their great effort and the feeling of great exertion.
Fig. 4: Biomechanics of sprint running. The athlete swiftly moves forward the swinging leg using hip joint flexion, while the support leg kicks back as a single segment, without bending at the knee. The key is to swing both legs forwards and backwards like a pendulum from the hip joint.
―Are there any misunderstandings or misperceptions in the process of mastering movements?
Scientific analysis of movements frequently discovers that practices that were considered common sense in sports training, such as the raising of the thigh when running, are in fact wrong. Sometimes it even proves that certain methodologies that sports instructors believed to be common sense produce exactly the contrary effect.
Movements are determined by the senses, and every coach or athlete has their own perceptions about the way they move. But the scientific true essence of motion, as seen from the perspective of mechanics and anatomy, is only one. Biomechanics thoroughly investigates the relation between cause and effects based on the principle that if a certain cause exists, it will invariably produce specific effects. This is the scientific method. Additionally, sports have some artistic aspects related to the way athletes deal with their individual characteristics determined by physical type and muscle build.
In sprinting, for instance, it has been proven scientifically that in order to run faster it is necessary to develop the hamstrings and iliopsoas muscles and swing the legs from the hip joints. This is science and as such it is common for all athletes. On the other hand, it is also necessary to make slight adjustments to the swinging of the arms and the body trunk torsion in a manner that will produce the optimal results for each athlete taking into consideration their physical characteristics. Coaches and runners work together to make these adjustments, and, in my opinion, their work is nothing short of art. The ideal approach combines scientific reasoning applicable to all with artistic practice methods customized to the athlete’s individual characteristics.
Incidentally, the name of our school in the University of Tokyo is College of Arts and Sciences. In other words, it is a faculty where science coexists with art. Both are composed of various levels, and, by skillfully linking them, it is possible to produce significant results. This trend is particularly pronounced in sports science, so I think that the Komaba Campus, where the College of Arts and Sciences is situated, is the perfect location for the sports science laboratories.
― Tell us about your recent research.
Fig. 5: Batting motion in baseball and bat trajectory
Presently, I am mainly working on motion analysis of the body trunk, which functions as the core of dynamic physical exercise. Our bodies are an anatomically-linked system in which muscles located near them set the limbs in motion. For instance, the muscles that set the hand in motion are located in the forearm, and the muscles that move the forearm are located in the upper arm. In other words, the muscles that move the arms and legs overall are located in the body trunk, which means that the trunk performs some very important functions. Despite this fact, we do not have sufficient accumulation of scientific knowledge about the body trunk.
In our laboratory, we separate the trunk into two or three segments and analyze torsion in baseball batting and tennis strokes. In doing so, we observe mechanical energy flows from the swinging motion of the hips (through the legs) and lower waist to the swinging motion of the upper trunk. If we could trace, through simulation experiments in various types of movements, the factors in the swinging motion that determine the amount of these energy flows, it will be possible to establish objectively the mechanics of body trunk torsion (Fig. 5).
Fig. 6: The Wave Revive shoes developed by Professor Fukashiro in a joint project with MIZUNO using the structure of traditional Japanese waraji sandals, which were worn with the toes protruding slightly over the front edge. These modern day waraji sandals help reduce the burden on the knees and make walking easier.
Sports biomechanics is an applied science, so I hope that our analysis data will help people improve the way they move in their everyday life and contribute to the competitive sports of Japanese athletes. Regarding our contribution to people’s daily life, I have developed walking shoes in cooperation with MIZUNO (Fig. 6). As for our contribution to the performance of top athletes, through our research we have supported Japanese sprinters for a quarter of a century now. One specific example of our work in this field is the analysis of running motions and baton passing technique. Our efforts bore fruit in the bronze medal that Japan won in the men’s 4x100m relay in the 2008 Summer Olympics held in Beijing. I take pride in the fact that Japan’s sports biomechanics, which helped an agricultural nation learn to run fast, is the most advanced in the world. The theoretical principles of running fast can be applied to children as well, so we have proposed various drills. I hope children will use them to train secretly and aim to win their school athletic meets.
― What other examples for practical application of biomechanics research can you give us?
When Nadeshiko Japan (the Japan women’s national football team) won the 2011 FIFA Women’s World Cup, the public praised the team composed of relatively short players for overcoming their much taller foreign opponents. However, smaller athletes have the advantage of being able to move faster. Weight is proportional to the cube of height, while muscular tension, the force that initiates movement, is proportional to the physiological cross-sectional area of muscle, or, in other words, the square of height. This means that the taller athletes are, the more difficult it becomes for their muscle force to catch up with the increased weight. Consequently, their movements become slower. This is known as “the scale effect.”
In this way, we intend to dispel any common misunderstandings or misperceptions and decipher sports through reasoning based on solid data. If athletes sharpen their sensitivity and work on their movements backed by scientific reasoning, we can harbor high expectations for their performance in sports traditionally dominated by nations of hunters, in which Japan has not done so well in the past. (Of course, I hope the sports activities of the Athletic Foundation of the University of Tokyo, too, will improve.)
*(Sources: Encouragement on Intelligent Sports by Senshi Fukashiro, University of Tokyo Press, for Figures 1, 2, and 5; Science of Sports Motions from a viewpoint of Biomechanics by Senshi Fukashiro et al., University of Tokyo Press, for Figures 3 and 4.)