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biomechanics

Details of movement

System assesses athletes and people with motor deficiency

EDUARDO CESARSoftware analyzes the Movements of the Guarani players EDUARDO CESAR

To Analyze human movement using video images and use these images as a tool for professionals working with physical activities, sport, or motor rehabilitation. This is the objective of the Dvideow – the Digital Vídeo for Biomechanics system, created by physical education teacher Ricardo Machado Leite de Barros, the coordinator of the Instrumentation for Biomechanics Laboratory (LIB) of the Campinas State University (Unicamp). Dvideow was designed to be used in different applications. Four have already been developed: the analysis of or walking, the analysis of respiratory movements, automatic tracking down of soccer players, and reconstruction of surfaces of the human body. “We are trying to develop an open and structured system with a great potential for dissemination”, Barros explains.

It is made up of software developed at Unicamp, six digital video cameras and six computers of the PC kind. In the context of motor rehabilitation, biomechanical analysis makes it possible to quantify any alterations in the normal patterns of movement, such as, for example, the ability to bend the knees or move the arms while walking. Accordingly, it is possible to assess progress in recovery processes with people who have suffered an accident, are victims of paralysis, or need prostheses. When applied to sport, biomechanical analysis has the objective of assessing the sportsman’s performance, helping to prevent lesions from overdoing, comparing teaching methods for a given sporting technique, and appraising sports gear. The methodology may also be used to assess degrees of ability or adroitness, in ergonomic studies.

Although it is not totally a novel system , Dvideow shows several novelties compared with what there is on the market. The first of them is precisely its flexibility, as several kinds of applications can be developed using the same software. Another point that differentiates it and also represents an advantage is the fact that it is totally based on video.

Walk analysis
Unlike other systems, Dvideow does not work with infrared cameras to which active light emitting diodes (LED) markers attached to the person’s body emit infrared light recorded by the camera. “This prevents, for example, the development of an application to accompany soccer players”, the researcher explains. In each one of the applications, specific and innovative tools were developed. In the application for analyzing walking, for example, a model was put together, to monitor the human body in its entirety, and not just the lower limbs.

Walk analysis will probably be the main application of the system. This methodology sets out to do describe and to quantify the movements of the lower limbs and other parts of the body of a person while he or she walks. To do so, dozens of reflective markers are fixed at previously defined points, making it possible to identify the various segments of bones (arms, forearms, thighs, knees, etc.). The six cameras are adjusted and the person with the markers on the body moves in front of them. The images are transferred to the computers, and the position of each marker is measured automatically.

Using the position of the markers, calculations are made of the angles between the segments of the body, the rotations, the distances covered and speeds of movement. The walk analysis methodology is now used by several motor recovery laboratories in the country, such as the Association for Assistance for Handicapped Children (AACD in the Portuguese acronym) in São Paulo. It helps the professionals to decide which kind of intervention should be applied to the patient. “The difference between Dvideow and the one used by the AACD is that our system uses the recording of images, and theirs is based on infrared light”, says the researcher. “The system in use at the AACD facilitates the automatic measurement of movement, but it does not provide the visual information”.

The disadvantage of not having the image is that the team carrying out the assessment is left without a qualitative (visual) parameter of movement, along with the quantitative one. “The visual record often provides the doctor with important information. Some characteristics not taken in by the graph may be a result of the movement of an arm, for example. And this will only be noticed in a system that monitors upper limbs and works with images, as is the case of ours”, Barros explains. Another of Dvideow’s advantages is its low cost. “The AACD’s system must cost around US$ 300,000, while the cost of ours has not gone beyond R$ 50,000”, explains the researcher.

Soccer players
Dvideow can also be used to accompany and analyze the movement of players during a soccer match. To make the development of this methodology feasible, the researcher made an agreement, two years ago, with the Guarani football team, from Campinas. Four cameras were placed in the club’s stadium on match days, to capture the images, which were exhaustively studied afterwards. “We recorded several games, and now, with the system concluded, we intend to provide Guarani’s coach and the physical training team with information, or other teams that may be interested”.

The idea of this application is to be able to identify automatically the position of all the players during the game, drawing up a map of the ground that each one covers during the 90 minutes of the match. To make this possible, each player is identified by the operator of the system in an initial image and, from then on, he is accompanied automatically in the 40,000 or so images recorded by each camera. When situations occur in which the system may be confused in identifying the players – for example, a cluster of players in front of the goal -, an operator checks whether there have not been any mistakes in identification. After being captured, the images are processed and transferred into graphs, making a sort of inventory of the player’s behavior during the match.

The first benefit of the methodology is the possibility of assessing variables related to the physical conditioning of the players during the match. “We will be able to know the distance the player has covered, what was the average speed of his moves, and for what percentage of time he stood still, ran, or reached peak speed”, Barros says. This information is useful for the professionals responsible for the preparation and planning of the team’s physical activities, as well as helping with the team’s tactical scheme. “The system takes a sort of snapshot of the game, at a speed of seven and a half images a second. This gives us the evolution of the team’s tactical design”, says the researcher.

Respiratory movements
The third application of the system is the analysis of respiratory movements. To do so, reflective markers are placed on the person’s trunk, and the images are captured by four cameras. The most common method for assessing respiratory capacity is spirometry, which works with the volume of gases exchanged between the individual and the machine, in this case a spirometer. The Dvideow methodology represents an advance on this technique, because it not only assesses the respiratory capacity, but is also capable of identifying which compartments of the thorax and the abdomen are most used in respiratory movement. This makes it possible to see functional alterations induced by physical exercises, pathologies or accidents.

“We want to identify how physical activity changes breathing patterns or ways”, says Barros. According to the researcher, a study carried out with the system showed people who had practiced yoga for a long time and came to have a certain kind of respiration, different from how sedentary people breathe. “The system showed a pattern change. The first alteration to be perceived was a lowering of the respiratory frequency, tending towards a deeper and broader respiration. This is an aspect that could be detected by other methodologies, but the interesting thing was to see that in people who practice yoga there is a more pronounced work in the abdominal region, compared with the thoracic region”.

Reconstruction of surfaces
The last of Dvideow’s applications is aimed at the three-dimensional reconstruction and analysis of surfaces of the human body. This is important, for example, in making anatomical orthopedic seats or shoe designs. The technique used is the projection of light over the body. “The advantage of this technique is that we do not use markers fixed on the individuals, because they are limited to a few dozens. We use a slide projector that emits a light with a pattern of hundreds of dots, which cover the person”, Barros explains. “Using the image captured by the cameras, we reconstruct each one of these dots, at a density of one or two dots per square centimeter, forming a sort of three-dimensional topographical map of the region being studied”.

The footwear industry is already using a similar technique, with laser scanning equipment, for creating shoe models. “The disadvantage of this technique is that the person’s leg is kept immobile while an optical reader reconstructs the surface of the foot”, the researcher explains. With Dvideow it is also possible to analyze movements. “In the case of shoes, we intend to observe how the foot is deformed when walking and undergoes deformations that are often not respected by the shoes”.

German doctorate
The Dvideow system was born during the researcher’s studies for a doctorate at the Biomechanics Institute of the German Sport University Cologne, in 1997. “Going back to Brazil, I brought a prototype of the system, which was still working with analog cameras and 486 PCs. Afterwards, we went into a partnership with Unicamp’s Computing Institute, in particular with Professors Neucimar Leite and Ricardo Anido, and part of the system was developed during the doctorate of their student, Pascual Figueroa.

The next step was to pass the system to the Windows interface, more friendly, and to introduce some more advanced mathematical theories and techniques, applied to the processing of images”, says Barros. “But it was with financial support from FAPESP that we managed to migrate to a more efficient technology, namely a digital one, both for the cameras and for the analysis of the recordings”. The project also had the participation of two professors from Unicamp’s Biomechanics Laboratory, René Brenzikofer and the late Euclydes Custódio Lima Filho, who died this May.

According to Ricardo Barros, in spite of the enormous commercial potential, the system was planned and develop to do research. “At first, our intention was to meet the demand from the Instrumentation for Biomechanics Laboratory, which needed a system like ours for analysis”. At a second moment, the professor made Dvideow available, without charge, to other research institutions, like Unesp’s Physical Education Department in Rio Claro. “We do not yet have any commercial prospects, since our main purpose really is to do research. But we are open to any interest there may be on the part of any company that wants to market it”.

The project
Development of a System for Biomechanical Analysis of Human Movements (nº 00/01293-1); Modality Regular Research Benefit Line; Coordinator
Ricardo Machado Leite de Barros – Faculty of Physical Education – Unicamp; Investment R$ 70,647.50

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