It is no secret to anyone: if you are cold, move actively – jog or jump. Muscular work makes it possible to warm up, as the warmth is produced as a by-product of movement. But which muscles produce the most warmth while working? Is it possible to see it?
Warmth by nature is an infrared radiation – though we cannot see it, as our eyes do not see this spectrum of the electromagnetic waves, we only feel it as warmth. Furthermore, everyone feels warmth differently – an object of the same temperature for one person may seem colder, while the object may seem warmer to another person. Therefore, sometimes there is a need for precise measurements and they can be made with different measuring instruments. The most widespread, of course, are different thermometers, but to perform the measurement all of them need to come into contact with the body, or at least to be placed in its proximity to determine the temperature. Placement of the thermometer on the body is not always convenient and handy, especially, if the person is actively moving.
Special cameras were invented in the previous century, which were capable of capturing the warmth radiated by an object (or more precisely – the infrared radiation) and transform it into an image. Owing to this invention, we can “see” warmth. Historically, the first cameras were quite large and complex in operation, however, along with the new era of digital technology, infrared cameras have become much more convenient to use and the quality of image has significantly improved (Fig. 1). The method was named as the digital infrared thermography or thermovision. It allows measuring the surface temperature from a distance very accurately avoiding contact with the object. Application of thermography is not a new thing – it is widely used in various industries for technical purposes (for example, determining the location of an overheated component in a device), in construction (for example, detecting the defects in building insulation), for military purposes (for example, in search of hiding people), for epidemiological security (for example, during the epidemics, while measuring human body temperature from a distance, it is possible to identify the sick at the airports), in the environmental sciences (for example, to measure river water temperature near the sewage emission), in veterinary medicine (for example, to detect inflammatory foci in animals, as animals, unlike humans, cannot tell about the painful areas in their bodies), as well as in medicine.
Digital thermography image of the human spine (the red areas reflect higher temperature; the asymmetry in colour intensity means uneven blood flow and load)
Also, in medicine, the use of this method is quite widespread – special high-definition digital infrared cameras most commonly are used to determine the superficial inflammatory foci, tumours or blood supply disorders. This method is sometimes used, for instance, during tissue transplantation to ensure the recovery of blood circulation in a transplanted organ. Lately, the use of digital infrared thermography has been commenced in sports medicine, for example, to identify the muscles overloaded during exercise. While doing some work or going in for sports, different muscles are loaded (or overloaded), thus thermography also allows spotting tissue overload caused by working conditions.
Whatever may seem, the temperature of the surface of human skin is not the same everywhere; under normal circumstances, the temperature is higher in areas, where large blood vessels come close to the skin surface, and in skin folds. By contrast, in areas, where there is a thicker fat layer under the skin, and further from the centre of the body, the temperature is usually lower than, for example, in the armpits. While working, muscles consume much energy and develop warmth themselves. To receive energy resources for their work timely from the blood in sufficient quantities, the muscles must have a well-developed vascular network. When muscles initiate active work, these blood vessels are able to expand and thereby increase the amount of blood carried. Both due to the influx of warm blood and the fact that the muscles themselves are actively producing warmth, the temperature rises in the active area of the body, which can be seen with the help of thermography (Fig. 2). The more actively we move, the more energy muscles consume and the more warmth is produced. That is why in workplaces, where people carry out physically hard work, it is necessary to maintain a lower temperature, so that people feel comfortable and do not overheat.
Welder's arms at the end of the working day (the red area near the right elbow reflects the overload and inflammation of the area of attachment of the palm and finger straightening muscles, as the welder has been working all day with his right hand operating a heavy tool for several years)
In contrast, during sedentary work and work involving little movement, the muscles produce much less warmth. In this case, most of the work is done by the muscles that keep the working posture. The longer time is spent sitting, the more our body cools, especially in the parts of the body located further from the heart (Fig. 3). Therefore, higher temperature must be maintained in a workplace, where people perform sedentary work. It is also highly recommended to move actively from time to time.
The effect of sedentary work with computer on the arm temperature (the image on the left – at the beginning of the working day the temperature of the arm skin is higher; the image on the right – after 3 hours of continuous work with a mouse, the finger temperature is approaching the ambient temperature)
If the work is performed in uncomfortable working positions or similar movements are repeated, such as working with heavy tools, as well as, if the procedures are not ergonomically correct, and the work is too hard, some muscles work with excessive load. With time, such muscle, tendon and ligament overload can cause very painful inflammation and tissue damage, which can lead to a significant reduction of capacity for work and even disability. Therefore, it is crucial to timely spot the initial muscular overload in order to improve or change the working conditions. However, even the modern medicine is not always able to „notice” such initial tissue overload (as long as there is no major damage) and it is very difficult and sometimes even impossible to identify it – that is where digital infrared thermography methods can be used successfully, as they are based on the on-going physiological processes in the body and allow to spot even a small muscular overload during the operation (Fig. 2). Moreover, thermography does not expose the body to ionizing radiation, as only the infrared radiation coming from the body (warmth) is being registered. During the examination, it is not necessary to touch the skin or cause tissue damage (for example, making an injection or incision). Thermography allows monitoring the changes of the work posture taken in the workplace or work techniques (or ergonomics), as the drawing visible in in thermography and generated by the warmth of the body will change along with the muscular load.
This article was prepared in cooperation with the specialists of the Occupational Safety and Environmental Health Institute of Rīga Stradiņš University within the framework of the project “The development of modern diagnostic and research methods for the risks created by nanoparticles and ergonomic factors in workplace” (Agreement No: 2013/0050/1DP/188.8.131.52.0/13/APIA/VIAA/025).