sound is part of people 's lives and is present in many forms . in modern society , there are many unpleasant and undesirable sounds and these are called noise .
the effect of noise on individuals depends on its characteristics ( amplitude , frequency , and duration ) as well as individual attitudes and relations to that noise .  
the ability to recognize sounds allows humans to effectively detect relevant events , even in the absence of visual information1 . however , hearing loss is one of the most common occupational diseases in industrialized countries . in brazil ,
noise - induced hearing loss is one of the main health problems facing workers , and researchers have stated that it is as one of the occupational diseases with the highest incidences2 . for intensity , sound levels of 8590  db ( a ) may cause irreversible cell damage .
the consequences for hearing are also directly proportional to exposure time ; thus , the longer this exposure is , the more severe the changes to hearing are . in cases where there is noise in the workplace that is harmful to workers ' hearing , hearing protection measures should be undertaken3 
 4 .
nevertheless , there may be no association between frequency ranges with intense noise levels and the frequencies affected by hearing loss .
there are , for example , cases in which noise intensity can be a major risk factor for hearing loss , regardless of the frequency band5 .
the labor ministry ( 1994 ) limits that are based on the standard of the american conference of governmental industrial hygienists : 16  h for exposure to 80  db ( a ) ; 8  h for 85  db ( a ) ; 4  h for 90  db ( a ) ; 2  h for 95  db ( a ) ; 1  h for 100  db ( a ) ; 30  min for 105  db ( a ) ; and 7  min for up to 115  db ( a ) .
thus , maximum daily exposure is halved with every additional 5  db ( a ) increase in the sound pressure level ( spl)6 . in a study conducted in florida , usa , researchers found that noise is a comprehensive and influential source of stress either due to the acute effects of noise or due to the influence of chronic exposure to high spls . in that study , the effects of noise during various tasks was tested and performance was measured ; the type , intensity , and duration of the noise were all observed .
studies on the exposure to high spls have generally been conducted on workers who are exposed to noises that are considered unpleasant ( in the fields of civil construction , metallurgy , mechanical and the military , among others)5 
 8 
 9 
 10 .
however , noises that are considered pleasant , as in the case of music , can also cause significant damage to the inner ear11 .
studies conducted in brazil and abroad have investigated the different effects of high intensity music on the auditory system11 
 12 
 13 . for professionals such as gymnasts and dance teachers
generally , such professionals are not submitted to audiometric tests when they are hired or dismissed , and do not undergo periodic evaluations of their hearing .
moreover , these professionals often ignore the effects of noise on the body , subjecting themselves to high sound intensities for long periods , without using individual protection equipment ; this can cause significant damage to their hearing14 .
krishnamurti and grandjean ( 2003 ) investigated the association between exercise in a class environment and sound levels of moderate to severe intensity .
they found that teachers used high spls in indoor cycling programs because students required them and felt more motivated if the music was louder15 .
this finding was also reported by deus et al.16 .   however , few studies have looked at exposure to high spls among dance professionals .
when there was approval for its realization , the people in charge of the schools signed an institutional consent form .
after that , we contacted the teachers to explain the objectives of the research and to invite them to participate .
individuals who agreed to participate also signed an individual consent form . the study sample comprised male and female dance teachers .
there was no prior selection as to the dance style because many of the teachers had practiced various styles of dance when they were students ; further , the classes covered more than 1 style .
the inclusion criteria were as follows : being an active dance teacher , being willing to participate in the study , and allowing a researcher to measure sound intensity in their dance classes .
after signing the individual consent form , participants completed a sociodemographic questionnaire specifically developed for this study this comprised questions about the individual 's dance history ( professional education , time as a performing dancer , time as a dance teacher , and styles performed ) .
in addition , we asked directed questions that allowed for assessment of teachers ' opinions on music intensity during classes .
furthermore , we were able to ask for details on how much information the dance teachers had received on the effects of high levels of sound pressure on the body .
a researcher then measured the normal sound intensity levels used by the study participants in their classes .
the researcher attended the classes of all participants and recorded the sound intensity level used by the teacher in the classroom 3 times : 5  min after the start of the class , 30  min into the class , and 5  min before the end of the class .
when class durations were shorter or longer , the second measurement was made at a time point equivalent to half of the class duration .
the measurement time was approximately 1  min , as in previous studies17 . for the above measurements
, we used a sound pressure meter ( dl-4020 icel manaus , manaus , brazil ) .
the teacher 's usual location in the classroom during classes was selected for taking measurements ; this was mostly at the front of the class or in the middle of the room .
the meter was adjusted to the weighting curve  a  and the slow time constant ( i.e. , slow rms sound pressure in 1 s ) . with these settings ,
this scale shows correlation with the subjective tests . and , this is the compensation circuit used for measuringement of continuous noise18 .
when the measurements were completed , teachers were informed about the values and advised about the effects of exposure to high spls .
this project was approved by the research and ethics committee and research institute of psychology at the federal university of rio grande do sul ( no 2011009 ) .
we calculated the absolute and relative frequencies and average spls that the teachers were exposed to .
the sample comprised 35 individuals including 11 ( 31.42% ) men and 24 ( 68.57% ) women .
the average time spent working as a dance teacher was 12.81 years ( range , 137 years ) , and the average daily teaching load was 4.48  h ( range , 110 h ) .
details on teacher training are presented in table 1 . for self - reported intensity of the music used in classes ,
questionnaire results revealed that 1 teacher ( 2.85% ) classified this intensity as soft , 19 teachers ( 54.28 ) described this as average , and 15 ( 42.85% ) said it was strong . when asked about the reasons for using loud music , 14 teachers ( 40% ) reported that they believed it improved student performance .
in addition , 24 teachers ( 68.57% ) said they never received information about the effects of high pressure sound levels on the body
. measurements of sound intensity levels were taken in 15 classical ballet classes ( 42.85% ) , 4 tap dance classes ( 11.42% ) , 5 jazz dance classes ( 14.28% ) , 2 arab dance classes ( 5.71% ) , 6 street dance classes ( 17.14% ) , and 3 ballroom dance classes ( 8.57% ) . the minimum value observed during the initial phase of the classes was 65  db ( a ) and the maximum value was 95  db ( a ) . the average for this first time point was 80.91  db ( a ) .
for the measurements taken half - way through the class , the minimum and maximum values were 70  db ( a ) and 95  db ( a ) , respectively , with the average being 83.22  db ( a ) . in the final period of the classes , the minimum value was 72  db ( a ) and the maximum value was 98  db ( a ) ; the average at this final time point was 85.19  db ( a ) .
measurements of spls at different time points during the classes are presented in table 2 . after measuring the average intensity level of music found in different types of dance classes at different time points
, we found that the street dance classes had the highest levels of sound intensity .
dance teachers are continually exposed to high spls and may suffer hearing damage due to this exposure .
furthermore , dance teachers do not generally undergo periodic hearing checkups or control the sound intensity during their classes .
it is estimated that 25% of the population is exposed to occupational noise and has some degree of hearing impairment3 .
dance teachers may be part of this group although studies on this population are few .
our study sample included mainly female participants ; this reflects the reality of most dance schools and dance - related fields where female dance teachers and students prevail .
the gender issue is noteworthy and men are rarely found , especially in styles such as classical ballet , belly dancing , and modern dance .
one relevant factor is that dance performers are not afforded the same prestige as performers of other artistic activities such as theater and cinema19 .
thus , many men take dance classes as an ancillary complement to their acting in other areas , but do not dedicate themselves to it professionally .
the average age of the study subjects was 31.5 years , and 9 professionals were aged over 40 years .
although this is a small number , the presence of middle - aged dancers working on a daily basis as teachers seems to shatter the myth that people need to abandon the practice of dancing as they get older .
thus , we disagree with the findings of previous studies , which indicate that , even today , it is rare to find cases of older dancers working professionally19 .   in terms of the training undertaken by teachers ( table 1 )
, we found that many of our study subjects ( 51.42% ) had trained in classical ballet at dance schools although few had completed college degrees in the same field .
this can be attributed to the lack of higher education courses in dance in brazil .
specifically , in rio grande do sul , the first such course was only offered in 2002 at a state university . in addition , the state capital only offered its first graduate degree course in 2009 and the first batch of students have not graduated thus far20 
 21 .
thus , it is believed that the training profile of teachers will change in the long run , with graduate students being absorbed into the workplace . in the present study , the average daily teaching load was 4.48  h , but many teachers are exposed to high spls for longer periods of time ; this is because they reported using high intensity music outside of the classroom in the questionnaire .
continuous exposure to high spls can lead to other adverse health effects besides hearing loss , such as changes related to sleep , breathing , anxiety , cardiovascular function , the immune system , and fatigue22 .
therefore , it is important that teachers are aware of the auditory and extra - auditory effects due to noise .  
thus , we developed an extension project comprising printed information that aimed to prevent hearing loss induced by high spls . 

tables 2 and 3 show that the spls measured in some of the classrooms were above the limits of acoustic comfort for indoor environments ; further , they were above the limit of 85  db ( a ) .
analysis by dance style revealed that street , tap , and ballroom dance classes had sound intensities above 85  db ( a ) .
it should be noted that in tap dance , along with the effects of music , the effects of metal hitting against floor was also registered ; this must have caused an increase in sound intensity in the class rooms studied .
taking into account that high spls were also used to improve class performance , we recommended that teachers look at possible new ways to motivate students .
our data are consistent with the findings of research from health clubs registered in the city of florianopolis ( sc ) , in which most of the spls measured were above the recommended limits .
that study found that 86% of academies had average noise values above the legal limit16 . in a similar study conducted in the city of curitiba ( pr ) , researchers found that spls ranged from 73.9  db ( a ) to 94.2  db ( a ) and that the most common complaints among teachers were tinnitus , muffled hearing , and difficulties in concentration23 .
high spls during the lessons can , therefore , become a serious occupational health problem for workers .
thus , we wish to highlight once again that dance teachers do not undergo periodic hearing tests and do not use individual protection equipment as workers in other fields ( e.g. , metallurgy , mechanics , and wood sawing ) .
furthermore , dance teachers ' workplaces are not submitted to audio checkups , in which spls are measured .
thus , it is believed that dance teachers should be targeted for speech therapy . as is the case for all other workers who are exposed to noise ,
the role of speech therapists in the area of worker 's health must not be restricted to conducting audiometric evaluations .
hearing loss resulting from high intensity music may be evolving into a significant public health problem because increasing numbers of adolescents and young adults have symptoms such as neurosensory hearing loss , tinnitus , and hyperacusis25 
 26 .
previous studies on spls measured in dance classes were limited in scope ; future studies should look at sound intensity as well as hearing loss .
dance teachers are usually exposed to music early in life , because training in many styles including , for example , classical ballet , begins in early childhood .
individuals frequently go on to practice several styles , and the teachers in our study sample reported that they used music at high intensity to motivate students to improve their performance .
thus , exposure to noise may begin very early , and hearing loss and other symptoms might affect individuals in childhood or adolescence . in summary , professionals exposed to high intensity music at the work place should be informed about the importance of using music at appropriate spls .
in addition , dance shools should have classrooms with better acoustic properties including the use of noise - absorbing wall , floor , and ceiling materials .
well - designed speakers should be used and placed in the best position17 
 27 .
the data obtained in this study shows that the average spls used by dance teachers in their classes were below or equal to the recommended limits .
however , analysis of intensities by the dance style revealed that noise levels in several tap and street dance classes were above 85  db ( a ) .
 summary 
 introduction :  dance teachers are exposed to high sound intensities . 
 aim : to verify the sound intensity of music used by dance teachers during classes . 
 
 method :  this was a transversal and prospective study . 
 dance teachers were evaluated with a sociodemographic questionnaire , and sound intensity level measurements were taken at the beginning , middle , and end of dance classes . 
 
 results :  the sample comprised 35 teachers ( average age , 31.8 years ) . 
 the duration of their career as dance teachers was 137 years ; they worked daily for approximately 110 h. among the classes followed , there were 15 ( 42.85% ) classical ballet classes , 4 ( 11.42% ) tap dancing lessons , 5 ( 14.28% ) jazz dance classes , 2 ( 5.71 ) arab dance lessons , 6 ( 17.14% ) street dance classes , and 3 ( 8.57% ) ballroom dancing lessons . 
 the average values observed at the beginning , middle , and end of the classes were 80.91  db ( a ) , 83.22  db ( a ) , and 85.19  db ( a ) , respectively . 
 the music played in the street dance classes exposed teachers to the highest sound intensity . 
 
 conclusion :  the average level of sound intensity of the dance classes in this study was either below or equal to the limit considered harmful for hearing health . 
 analysis of different class types showed that the sound densities of street , ballroom , and tap dance classes were above the recommended limits . 
Introduction
Method
Results
Discussion
Conclusion