firefighters and aid workers are considered to be victims of heat stress in physiological activities . moving and lifting heavy objects or saving people under stressful conditions are such activates done by firefighters while wearing protective clothes and a compressed air breathing apparatus . numerous studies indicated that individuals appropriate physical performance depends on vo2-max , which is defined as the maximum amount of oxygen that can be absorbed by the respiratory system and be sent to operating muscles . previous studies showed that vo2-max ranged from 33.5 to 45 ml / kg body weight per minute among firefighters . 's study conducted in belgium , the rate of vo2-max was estimated to be 46.5 ml / kg body weight per minute among firefighters . moreover , pulmonary function test or spirometry is identified as another method to assess cardiorespiratory system 's health . spirometry is the most common pulmonary function test , giving the rate , volume , speed , or flow of an individual 's inhalation and exhalation . the test consists of three main parameters , namely , forced expiratory volume in 1 s ( fev1 ) , forced vital capacity ( fvc ) , and fev1/fvc . fvc refers to the amount of air an individual exhales from one 's lung after a deep inhalation . fev1 is also defined as the amount of air an individual forcefully exhales from one 's lung in the first second of exhalation . finally , fev1/fvc is the ratio of the second to the first parameter and indicates the percentage of fvc exhaled from lung in the first second of exhalation . in comparison with the society , firefighters have better pulmonary function , particularly in fvc and fev1 parameters . however , due to the increase in utilization of chemical materials in buildings in the recent decades , concerns have risen about this group 's health . regarding the results of some studies , exposure to smoke and fumes including acrolein , carbon monoxide , hydrogen chloride , hydrogen cyanide , nitrogen oxides , sulfur dioxide , particles , aldehydes , and carcinogens led to chronic pulmonary damages followed by reduction of pulmonary function . numerous studies revealed the acute effects of exposure to smoke on firefighters health , particularly pulmonary function . for instance , according to a study conducted on 28 firefighters , a considerable obstructive pulmonary disease within few hours after exposure to smoke was found . in addition , the findings of musk et al . revealed that occurs a significant reduction in fev1 among smoker peoples . considering what was mentioned above and firefighters heavy physical requirements , it is essential to assess their cardiorespiratory function accurately . hence , this study aimed to investigate respiratory complications and assess of vo2-max , lung volumes , and their associated factors among firefighters in one of the central cities of fars province , iran . this is a cross - sectional study on firefighters who were participating in fire suppression and rescue operations in one of the central cities of fars province , iran . using a systematic random sampling approach and based on a priori sample size calculation , 110 firefighters were selected from various stations among which 104 participants agreed to participate in all the stages of the research . all participants with at least 1 year of working experience were interviewed and those with any history of cardiovascular or respiratory disorders and smoking were excluded from the study . an self - administered questionnaire was used to collect information on the participant 's demographic and respiratorystatus . this questionnaire used in several studies and pulmonary function tests were measured based on ats guidelines using a spirometer ( vitalograph compact ii , england ) . three acceptable spirometry maneuvers , therefore , were obtained from each participant and the best one was recorded . vo2-max was evaluated using the protocol developed by tuxworth - shahnavaz on an iranian society in 1977 . in this protocol , individuals go up and down step ( height : 40 cm ) with a cadence of 25 times in a minute for 5 min . then , they sit on a chair , their heart rate is measured in three 30 s stages ( m1 : 3060 s , m2 : 90120 s , and m3 : 150180 s [ figure 1 ] ) , and vo2-max is computed using the following equations . diagram of tuxworth - shahnavaz protocol index b  y = 0.378x + 4.67 at the end of the interview , anthropometric indexes ( weight and height ) were measured . participants with minimal clothing and no wearing shoes were weighed with a calibrated digital platform balance scale ( imperial bs 412 , us ) and the numbers were rounded to the nearest 100 g. height was measured while the participants were in standing position with the shoulders in a normal resting and also 3 regions of their body ( buttocks , heel , and head ) touching the wall , without wearing shoes . in addition , temperature and relative humidity were measured using thermometer , spinning thermometer ( casella , england ) , and psychrometric chart . environmental measurements indicated that the mean humidity was 52 and the mean temperature was 17c . moreover , the noise of environment was measured using sound level meter ( model tes-1351 ) manufactured by taiwan . the sample size was calculated to detect at least 2.3 kg change in weight with alpha value of 0.05 and a power of 80% . data were analyzed using statistical package for social sciences 19 ( spss inc , chicago , il , usa ) . the main study variables included both quantitative ( age , height , weight , waist circumference , body mass index [ bmi ] , and job tenure in firefighting ) and qualitative measures ( marital status , level of education , second job , and job satisfaction ) . pearson 's correlation coefficient was used to assess the association between demographic and anthropometric variables with respiratory volume and maximal oxygen consumption . pulmonary function tests were measured based on ats guidelines using a spirometer ( vitalograph compact ii , england ) . given device was calibrated each day and after per 10 tests . three acceptable spirometry maneuvers , therefore , were obtained from each participant and the best one was recorded . vo2-max was evaluated using the protocol developed by tuxworth - shahnavaz on an iranian society in 1977 . in this protocol , individuals go up and down step ( height : 40 cm ) with a cadence of 25 times in a minute for 5 min . then , they sit on a chair , their heart rate is measured in three 30 s stages ( m1 : 3060 s , m2 : 90120 s , and m3 : 150180 s [ figure 1 ] ) , and vo2-max is computed using the following equations . diagram of tuxworth - shahnavaz protocol index b  y = 0.378x + 4.67 at the end of the interview , anthropometric indexes ( weight and height ) were measured . participants with minimal clothing and no wearing shoes were weighed with a calibrated digital platform balance scale ( imperial bs 412 , us ) and the numbers were rounded to the nearest 100 g. height was measured while the participants were in standing position with the shoulders in a normal resting and also 3 regions of their body ( buttocks , heel , and head ) touching the wall , without wearing shoes . in addition , temperature and relative humidity were measured using thermometer , spinning thermometer ( casella , england ) , and psychrometric chart . environmental measurements indicated that the mean humidity was 52 and the mean temperature was 17c . moreover , the noise of environment was measured using sound level meter ( model tes-1351 ) manufactured by taiwan . the sample size was calculated to detect at least 2.3 kg change in weight with alpha value of 0.05 and a power of 80% . data were analyzed using statistical package for social sciences 19 ( spss inc , chicago , il , usa ) . the main study variables included both quantitative ( age , height , weight , waist circumference , body mass index [ bmi ] , and job tenure in firefighting ) and qualitative measures ( marital status , level of education , second job , and job satisfaction ) . pearson 's correlation coefficient was used to assess the association between demographic and anthropometric variables with respiratory volume and maximal oxygen consumption . environmental measurements indicated that the mean humidity was 52 and the mean temperature was 17c . based on table 2 , more than 80% of the participants had no respiratory disorders . accordingly , the means of fvc , fev1 , and fev1/fvc were 92% 9.4% , 87% 9.2% , and 80% 6.1% , respectively . the mean of vo2-max was 2.79% 0.29 l / min or 37.34  4.27 ml / kg body weight per minute . some demographic characteristics of the studied fire - fighting personnel ( n=110 ) distribution of respiratory complications among studied fire - fighting personnel ( n=110 ) mean , standard deviation , minimum and maximum lung volumes , and maximal oxygen consumption of studied fire - fighting personnel ( n=110 ) the results of table 4 show a significant association between age and peak expiratory flow ( pef ) ( r = 0.19 , p = 0.045 ) . in addition , height was directly associated with vital capacity ( vc ) ( r = 0.23 , p = 0.016 ) , fvc ( r = 0.26 , p = 0.007 ) , and vo2-max ( r = 0.39 , p = 0.001 ) . however , there was an inverse and significant association between height and fev1/fvc ( r = 0.23 , p = 0.017 ) . moreover , a significant and direct association between weight and fvc ( r = 0.20 , p = 0.034 ) , pef ( r = 0.24 , p = 0.012 ) , and vo2-max ( r = 0.53 , p = 0.001 ) . in addition , the finding revealed a significant direct association between bmi and vo2-max ( r = 0.39 , p = 0.001 ) . finally , waist circumference showed a significant direct association with vo2-max ( r = 0.33 , p = 0.001 ) . this is a cross - sectional study that examined the relationship between some factors linked to individuals capabilities with the cardiorespiratory factors . moreover , considering the importance of pulmonary function tests in diagnosis and treatment of respiratory disorders , determination of normal lung volumes is essential in different societies . in addition to lung volumes , determination of vo2-max seems to play an important role in occupational ergonomics . however , few studies have been conducted in this area among firefighters . as a result the aim of this study was to investigate cardiorespiratory health among firefighters in one of the central cities of fars province , iran . accordingly , the mean of fvc , fev1 , and fev1/fvc was normal which is in accordance with the report published by michael et al . based on the sharifian 's findings , based on the results from a study conducted by alizadeh , height is one of the effective factors in lung volumes . accordingly , the lower lung volumes in the present study which is not in accordance with the michael 's finding might be attributed to height differences between both societies . in the current study , the firefighters main complaints included shortness of breath followed by phlegm and cough , which is consistent with the findings of the study by rothman et al . in addition , rahimi moghaddam ( 2014 ) suggested that the most frequent complaints were phlegm , wheezing , and cough among welders . aminian also showed that cough is the most common complaint among the individuals working in textile industries . the results of the present study showed a significant and direct association between age and pef , whereas other studies could not find such direct associations . accordingly , significant reduction of these parameters with age is most probably due to their unprotected exposure to smoke . in the present study , weight , on the other hand , showed direct association with vc , fvc , and pef which are in accordance with the result of a study conducted by alizade et al . mehrabi and kargarfard on the other hand found an inverse association between weight and lung volumes . it could be attributed to overweight resulting from fat tissues and lack of physical activity among the participants . according to the results of the present study , participants had high bmi due to increase in their muscle mass resulting from regular physical activities . 2011 ) , excess fat tissues hinder appropriate pulmonary function that can , in turn , affect cardiovascular function . suggested that vo2-max ranges should be from 33.5 to 42 ml / kg body weight per minute among firefighters . however , the previous studies raised some controversial issues over the vo2-max values and suggested that certain circumstance including physical , mental , environmental , and physiological factors of different individuals might be significantly different . role of the protocol utilized in the current study should be taken into account as well . in this study , the researchers made use of tuxworth - shahnavaz protocol that has been proposed for iranian communities . furthermore , the difference between the results of our study and the one performed by kianmehr and nazem might be attributed to the participants mean age because vo2-max decreases with increase in age and the highest amount of vo2-max has been observed in the age range of 1825 years . results of the present study indicate a significant and direct association between height , weight , bmi , and waist circumference with vo2-max . these results are not fully in accordance with a report published by daneshmandi et al . detected a direct but not significant association between height and vo2-max . , the authors suggested that reduction in vo2-max decrease height due to change in muscles structure and faded the relationship between height and vo2-max . although the present study findings demonstrated a descending trend in vo2-max with increase in age , the association was not significant . the nonsignificant association observed in the current study might be attributed to the participants small age range , which might have faded the effect of age . furthermore , vo2-max was significantly lower in the individuals with normal bmi compared to those with high bmi . however , the results of the study conducted by daneshmandi et al . ( 2013 ) revealed an inverse linear relationship between vo2-max and bmi ( r = 0.158 ) . what 's more , vo2-max was higher in the individuals with normal bmi in comparison to overweight and obese ones . the ability of people to do their job is influenced by the person 's capabilities , the job demand , and the condition under which the person is carrying out the job . the findings of this study showed that the amount of maximum oxygen consumption is close with the proposed range of this parameter among firefighters in other studies . furthermore , the results of the study revealed that participants had normal amounts of lung volume index . the present study was financially supported by shiraz university of medical sciences , shiraz , iran . the present study was financially supported by shiraz university of medical sciences , shiraz , iran .