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MEDICAL PHYSICS IN THE BALTIC STATES 7 (2009) Proceedings of International Conference “Medical Physics 2009” 8 - 10 October 2009, Kaunas, Lithuania CHANGES OF SWIMMER‘S BODY TEMPERATURE OBTAINED BY THERMOVISION METHOD Virgilijus Minialga*, Birutė Statkevičienė** *Kaunas University of Technology; **Lithuanian Academy of Physical Education Abstract: The temperature of swimmer’s body changes when he swims certain distance. It can correlate with sportsman’s state. It is essential in cold water and can influence the results of competition. Fast non-contact method for temperature measurement was used for the research. The temperature was measured by thermovision device. It enables to obtain surface temperature in several seconds. The method is based on warm body thermal radiation. The temperature was measured after swimmer covered several distances. Changes of temperature in different parts were different. Keywords: thermal radiation, temperature measurement, thermovision, body temperature 1. Background of measurements The temperature of human body can be measured by non-contact method according to the changes of infrared radiation of heated bodies [1]. The total power emitted per unit area R from the body surface depends on temperature T and for black body it can be calculated by equation defined as Stefan – Boltzmann Law [2]: R= σ T 4 , (1) where σ is called the Stefan – Boltzmann constant is given by σ =5,67 10 -8 W m -2 K -4 . According to this law the observed spectral distribution function R(λ) of emitted power increases with the increase of temperature. The total emissive power from a gray (not black) body is smaller than from black body and can be calculated by empirical law [2] R= e σ T 4 , (2) where e < 1 is called the emissivity of gray body. It is particular for every different body and should be measured or evaluated for every different surface. The power radiated from the body under the investigation in a thermovision device is evaluated according the above mentioned laws. It calculates the temperature of remote body and shows it on the device monitor. The newest devices show the temperature distribution in different colors according to the temperature-color scale. 79 2. Measurements of human temperature The device Flir i5 was used for investigation the temperature of swimmer’s body. Infrared radiation images are shown on the device’s monitor. These photos can be transformed to the computer for the further usage. They are colored in artificial colors for better comprehension. The colors in different photos mean the different temperature values, e.g. red color in the first photo can mean 23 o C and the same red color can mean 30 o C in the second photo. Therefore colortemperature accordance in the bottom of monitor should be observed. The temperature of central part of image is written in the upper left corner. The error of device is 0.1 o C. However one must know that human body is not a black body. The emissivity e in equation (2) should be taken into account. The situation during measurements is shown in Fig. 1. FLIR i5 Fig. 1. Scheme of taking humans body infrared images 3. Conditions for infrared images Water is not transparent for infrared radiation, the same is for window glasses. Therefore there is no possibility
V. Minialga et al. / Medical Physics in the Baltic States 7 (2009) 79 - 82 to take infrared photo of person during swimming. Some additional errors are in case of wet bodies. Several series of thermal images were taken for investigation of temperature changes on the swimmer’s body. All photos were taken of persons in bathing suits. Skins in images were dry in some photos and wet in the others. 4. Temperature measurement results The experiment of some load influence was carried out. The first set of infrared photos was taken of dry swimmer before the start. One can see that the highest temperatures according to the temperature lines in each image are in front of the upper part ( 36 o C ). The lowest temperature is in legs region ( 34 o C ).. Fig. 2 represents swimmer ready to the start, the glasses seem to be cool. This is because they are not transparent for infrared radiation. Fig. 2. Swimmer is ready for the start; glasses are not transparent for infrared radiation and seem as being cool (dark in the image). Infrared photos of swimmers body before the start in front of the person and in back of the person are shown in Fig. 3. Measurements of the temperature were carried out using the above mentioned photos. Photos taken after 50 m of swimming distance show that skin temperature is reduced (Fig.4). Measured temperatures of swimmers body are lower than in the first case by 1 o C – 2 o C. Photos taken after 200 m of swimming distance show that measured temperatures of swimmers body are lower than in the first case by 1 o C – 2 o C. The research of infrared pictures allow to conclude that the temperature distribution on the surface of body after 200 of swimming distance is of higher contrast (Fig.5). This means that only narrow regions of human body have comparatively high temperature. Temperature of those places does not change considerably, it reduces only by several degrees. The 80 highest temperature after swimming remains on the head, on the shoulders, on the spine, on the knee, on the shin’s surfaces. Graphs in Fig.6 show that the main decrease of the temperature with distance is on the upper part of the swimmers body. The temperature on the biceps surface a) b) Fig. 3. Infrared photos the upper part of the swimmer’s body before the start; a) the front of the person; b) the back of the person.
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2009 PROCEEDINGS OF THE 7 th INTERN
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