# Progress in the Knowledge, Application and Influence of Extremely Low Frequency Signals
## 3 Results and Discussion
### Community Analysis  
Next, the main nodes of each community were analyzed, considering their sizes and their most-significant contributions. The community ELF in health consists of research studies tackling the influence of ELF electric and magnetic fields on human health. The isolated distribution of this community is represented in Figure 7a where the most important publications are observed according to the size of the nodes. The references, according to Scopus, of the three most-important nodes of this community were determined according to their size:  
Figure 5: Representation of the 20 most-repeated global keywords. Figure 6: Representation of all global keywords. 1. \"Environmental Health Criteria 238: Extremely Low Frequency Fields\" with a total of 15 references [56]. 2. \"Interaction of Static and Extremely Low Frequency Electric and Magnetic Fields With Living Systems: Health Effects And Research Needs\" with 294 references [57]. 3. \"Biological Responses to Electromagnetic Fields\" with 307 references [58]. The 10 most-repeated keywords in this community are represented in Figure 7, where \"electromagnetic fields\" ranks first with 417 repeats, followed by the search word \"extremely low frequency\" with 363 repetitions. The following words according to number of repetitions are very generic words of all communities, \"magnetic fields\" with 297 repeats, \"extremely low frequency-electromagnetic field\" with 243 repeats and \"electric field\" with 73 repetitions. Also, some words of the theme of this community such as \"cancer\" and \"exposure assessment\" appear 56 and 53 times respectively. The population is exposed to an increasing exposure to different electromagnetic fields (EMF) ELF, so the need to establish the effects of these exposures is a widely researched topic, which explains why this community is the largest. The most important work of this community is [56]. It dates from 2007 and is closely related to publications from its own community and from other neighboring communities, such as the electrophysiological effects community. [56] is a monograph that presents different environmental health criteria (EHC) before exposure to ELF-EMF, evaluates the risks that such exposure entails, and intends to establish recommendations to national authorities on health protection programs. Its importance also lies in establishing the first division of the evidence found in health. It can be considered as \"limited\" evidence, since it is limited to a single study or there are unresolved questions about the design, performance, or interpretation of several studies. It can also be considered \"inadequate\" evidence for studies in which the presence or absence of an effect cannot be interpreted due to the presence of significant qualitative or quantitative limitations, or when no data is available. The following important publications in this community date from end of the decade of the 1990s [57] where various issues are considered mainly issues related to the determination of the existence of human health hazards arising from exposure to ELF fields, although several important biological responses are forgotten. Some of these answers are raised in [58], where a review and analysis of the studies based on the main cellular responses to the ELF-EMF is carried out, as well as their replication attempts. The quantitative aspects of exposure and the presence of cancers that have been correlated with these fields are discussed, since several epidemiological studies have concluded that such fields may be related to an increased risk of cancer [31]. A publication that should be noted for having numerous relationships with the electrophysiological effects community is [59], a book in which the biological effects of ELF emissions are considered from an energy point-of-view.