## 1 Introduction  
At an international level, there are many studies on health impacts due to occupational and environmental exposure to noise. In general, these studies were developed using voluminous samples involving patient reports, distributing questionnaires, adopting cross-sectional studies based on databases, and comparing environmental noise levels measured using criteria curves. However, there are still few studies focusing exclusively on health impacts and discomfort due to low-frequency noise. One of the main reasons is the low sensitivity of the human auditory system to low frequencies. On the other hand, this type of noise has very particular characteristics and causes much more discomfort and long-term non-auditory effects [1; 2; 3; 4]. Until the 1930s, it was believed that the effects of noise on health were restricted only to hearing loss. In a study published in the Journal of the Acoustical Society of America, [PERSON] et al. [5] concluded that the effects of noise on human health went beyond hearing loss. The 1970s were marked by the emergence of a series of studies addressing the annoyance caused by environmental noise [3; 6; 7; 8; 9; 10; 11]. The most cited effects on human health refer to emotional changes, such as agitation and distraction [12; 13; 14; 15; 16; 17], in addition to the association of low-frequency noise with cognitive alterations [18], the development of cardiovascular diseases [19; 20; 21], sleep disorders [22; 23], and high blood pressure [24]. Thus, the effects of noise pollution comprise \"auditory effects\", which directly affect the human auditory system and \"non-auditory effects\", i.e., the impact of noise on physiological functions. Regarding \"non-hearing effects\", discomfort has been reported as the most frequent effect caused by exposure to low-frequency noise in humans [5; 25; 26]. In addition, discomfort may vary from individual to individual and depends not only on the noise pressure levels but also on the exposure time, as well as the low frequency components present in the noise. Thus, noise levels that contain low frequency components tend to be more annoying than noise without such components [5; 27]. Since 2000, the World Health Organization has recognized low-frequency noise as an environmental problem. In addition, the health impacts of low-frequency components on noise are estimated to be more severe [5]. As urbanization has increased, noise pollution has become more acute and is currently the second most harmful environmental stressor in Europe. In Europe, this type of pollution has been considered a public health problem, whereby Portugal ranks fourth as the most affected country concerning noise pollution (23.0% of the population is affected by this type of pollution--[28]). In Portugal, the northern region is the territory that suffers the most demographic pressure and where the electrical substation with the highest voltage at national level is located, the Substation of Riba d'Ave (south-west of the municipality of Guimaraes). The village of Serzedelo is one of the 69 villages (until 2013) in the municipality of Guimaraes and has the largest installed electrical substation in the country. Moreover, 80% of the region is under the influence of power poles and power lines, including 90 power poles and 12 power lines of high and very high voltage. In a survey carried out in 2010 by [PERSON] [29], out of the 1022 dwellings located in the village of Serzedelo, only 98 are at 250 m or more from the power poles and power lines of high and very high voltage, that is, 9.6% are very close to these elements (up to 250 m) [29]. This generates a conflict regarding the use of space. [PERSON] et al. (2015), in an evaluation of the impact of low-frequency noise pollution on the population of the village of Serzedelo, concluded that the measured low-frequency sound levels exceeded the criterion curve of the Department for Environment, Food and Rural Affairs methodology [30], which makes that type of noise audible and annoying to the population.