physical inactivity is one of the main risk factors for chronic diseases , which are responsible for 5.3 million deaths annually worldwide ( 1 ) . in 2009 ,
the global prevalence of inactivity was 17% ( 2 ) , with more than 30% of the world population not meeting the minimum recommendations for physical activity ( 3 ) . in iran , 40% of adults ( 31.6% men and 48.6% women )
are reported to be in the low physical activity category , while about 15% ( 4.7 million people ) do not have any physical activity ( 4 ) . to reduce the burden of diseases like cardiovascular disease , cancer , diabetes mellitus , obesity , and depression , it is strongly recommended that individuals engage in regular physical activity of at least moderate intensity ( 5 ) .
given this scenario , information on changes in health - risk behaviors like physical activity over time is vital to planning effective programs and policies .
hence , evaluating changes in physical activity levels of populations over time has become a public health priority ( 3 , 6 ) .
since no data are available on time changes of physical activity in iran , this study was designed to evaluate changes in physical activity levels over a median follow up of 6.5 yr among tehranian adults .
the tehran lipid and glucose study ( tlgs ) is a prospective population based study performed on a representative sample of tehran s population , with the aim of determining the prevalence of noncommunicable disease ( ncd ) risk factors and developing a healthy lifestyle to improve them ( 7 ) .
the baseline survey was performed from 1999 to 2001 and 4751 families , which included over 15000 residents of district 13 of tehran , aged  3 yr were selected by cluster random sampling method .
after this cross - sectional prevalence study of ncd risk factors , subjects were enrolled into a cohort and a prospective interventional study and were followed every three years .
data on the physical activity status of subjects were collected using the modifiable activity questionnaire ( maq ) from phase ii of tlgs .
considering the high numbers of missing physical activity data in phase iii , in the current paper , subjects were examined just for phases ii ( from 2002 to 2005 ) and iv ( from 2008 to 2011 ) i.e. a 6.5 yr - follow up .
the study was approved by the ethics committee of the research institute for endocrine sciences of shahid beheshti university of medical sciences .
all participants provided written informed consent . from 7268 subjects who completed the follow up period , participants who took part in lifestyle intervention through community education ( n=3753 ) were excluded ; the data of 3515 subjects aged  20 yr ( 2100 females and 1415 males ) were analyzed to determine the changes of physical activity levels over a median follow up of 6.5 yr .
high reliability ( 98% ) and moderate validity ( 47% ) were found for the maq translated into persian ( 9 ) .
intra - class correlation coefficients between the two pretest and post - test maqs for all activity domains in the past year , including leisure time , occupational , and total ( leisure and occupational combined ) physical activity were 0.94 , 0.98 , and 0.97 , respectively .
participants were asked to report the activities that they had participated in ( at least 10 sessions ) during the past 12 mo in their leisure time and then identified the frequency and duration for each ltpa .
total numbers of minper year , calculated for every physical activity were summed up and then divided by 52 to estimate the minper wk of total leisure time physical activity .
the calculation of met - min / wk is summarized as met - min / wk = ( met  mo per year  sessions per mo  minper session ) / 52 .
met - min / wk of leisure time activity was calculated by multiplying the number of minper wk of each leisure time activity to its metabolic equivalent ( met ) .
one met is set at 3.5 ml of oxygen consumed per kg of body weight per min and represents the resting metabolic rate .
the numbers of mets corresponding to each activity were calculated using the average metabolic cost for each activity ( 10 ) .
employed persons were asked to indicate how many h a wk they usually worked . according to the questionnaire , individuals had to identify the number of mo and h they participated in physical activity at work ( standing , housework , work activities more intense than standing ) over the past year .
the assessment of occupational activity was based on summing up the number of h per wk of light , moderate and hard intensity activities , multiplying the sum by 60 in order to express minper wk of occupational activity over the past year .
final occupational ( met - min / wk ) activity was calculated by multiplying the number of minper wk of each of the three categories of occupational activity by met values ( 10 ) .
total physical activity was expressed in met - min / wk by adding leisure time to occupational activity ; scores < 600 mets - min / wk were considered as low physical activity ( 11 ) .
analyses were carried out using spss software version 20.0 ( spss , chicago , il , usa ) .
from 7268 subjects who completed the follow up period , participants who took part in lifestyle intervention through community education ( n=3753 ) were excluded ; the data of 3515 subjects aged  20 yr ( 2100 females and 1415 males ) were analyzed to determine the changes of physical activity levels over a median follow up of 6.5 yr .
high reliability ( 98% ) and moderate validity ( 47% ) were found for the maq translated into persian ( 9 ) .
intra - class correlation coefficients between the two pretest and post - test maqs for all activity domains in the past year , including leisure time , occupational , and total ( leisure and occupational combined ) physical activity were 0.94 , 0.98 , and 0.97 , respectively . data were collected by participants , assisted by trained interviewers when needed .
participants were asked to report the activities that they had participated in ( at least 10 sessions ) during the past 12 mo in their leisure time and then identified the frequency and duration for each ltpa .
total numbers of minper year , calculated for every physical activity were summed up and then divided by 52 to estimate the minper wk of total leisure time physical activity .
the calculation of met - min / wk is summarized as met - min / wk = ( met  mo per year  sessions per mo  minper session ) / 52 .
met - min / wk of leisure time activity was calculated by multiplying the number of minper wk of each leisure time activity to its metabolic equivalent ( met ) .
one met is set at 3.5 ml of oxygen consumed per kg of body weight per min and represents the resting metabolic rate .
the numbers of mets corresponding to each activity were calculated using the average metabolic cost for each activity ( 10 ) .
employed persons were asked to indicate how many h a wk they usually worked . according to the questionnaire , individuals had to identify the number of mo and h they participated in physical activity at work ( standing , housework , work activities more intense than standing ) over the past year .
the assessment of occupational activity was based on summing up the number of h per wk of light , moderate and hard intensity activities , multiplying the sum by 60 in order to express minper wk of occupational activity over the past year .
final occupational ( met - min / wk ) activity was calculated by multiplying the number of minper wk of each of the three categories of occupational activity by met values ( 10 ) .
total physical activity was expressed in met - min / wk by adding leisure time to occupational activity ; scores < 600 mets - min / wk were considered as low physical activity ( 11 ) .
analyses were carried out using spss software version 20.0 ( spss , chicago , il , usa ) .
in both phases , 59.8% of adults were women and the mean  sd of age was 44.3  14.6 years in phase ii and 50.9  14.6 yr in phase iv .
after 6.5 years , a significant decrease in ltpa was observed among women , but not among men ( fig .
1 ) . levels of physical activity domains ( mets - min / wk ) in tehranian men and women in phases ii and iv of tehran lipid and glucose study ltpa , leisure time physical activity level ; ocpa , occupational physical activity level 
 p<0.05 between phases the prevalence of low physical activity in the total population decreased significantly between phases ii and iv , being 45.9% and 42.6% respectively ( p<0.05 ) . as shown in table 1 , the decrease was significant in men , but not in women .
regarding age groups , this table also indicated that the prevalence of low physical activity has decreased significantly among older men ( 60 yr ) .
prevalence of low physical activity ( < 600 mets - min / wk ) stratified by sex and age groups in phases ii and iv of tlgs tlgs , tehran lipid and glucose study p<0.05 by mcnemar test regarding the activities in ltpa , there was a significant increase in proportion of individuals participating in swimming , aerobics / dancing , martial arts , and football / handball ; however , there was a significant decrease in jogging / walking ( table 2 ) .
comparison of ltpas in phases ii and iv of tlgs tlgs , tehran lipid and glucose study ; ltpa , leisure time physical activity .
the results of present study indicated a 3.3% decrease in the prevalence of low physical activity during a 6.5 yr follow up from 45.9% to 42.6% , among a tehranian adult population .
although this is encouraging , it is difficult to estimate the clinical impact of such superficial changes , although , on a population level they may lead to decrease in morbidity ; i.e. , recently , from the nhanes data it has been indicated that each additional min daily of high intensity activity lod the odds of obesity by 2% for men and by 5% for women
similar to our findings , a brazilian and a peri - urban nepalese population showed a high prevalence of low physical activity , i.e. 43.3% and > 50% , respectively ( 13 , 14 ) . although most studies indicated a decreasing trend in physical activity levels of populations ( 1517 ) ; recently , in an urban swiss population , a significant increasing trend was reported in physical activity levels from 1999 to 2009 ( 18 ) , indicating a shift from low intensity physical activity towards moderate / high or vigorous physical activity among this population .
surprisingly , this increasing change occurred outside the occupational setting , demonstrating an increase in ltpa .
with respect to ocpa , our results indicated a decrease over time , which is a result of the greater automation in the workplace , a problem that most populations are facing ( 1923 ) .
similar to our findings , in the madrid region , a decrease in ltpa , which mainly resulted in increased physical inactivity , was accompanied by a decreased ocpa ( 17 ) , demonstrating a shift from occupations that need moderate to high intensity physical activity to occupations that mostly include sedentary and sitting behavior .
the same results were reported in the peri - urban nepalese population ( 13 ) i.e. , the reduction in ocpa was not compensated by an increase in ltpa .
hence , concerns for public health are increasing since ocpa is a major portion of total physical activity and as long as the decrease in ocpa is not counteracted by increase in ltpa , the approach mentioned above that led to increase physical activity levels in the swiss population ( 18 ) , overall physical activity will most likely declined .
another main finding of the current study was that ltpa decreased significantly among women during a median follow up of 6.5 years .
the association between employment and ltpa reports earlier in this population ( 24 ) indicated higher prevalence of inactivity among those employed compared to the unemployed .
these findings can be easily explained by less leisure time among employed individuals , which is often reported as a barrier to participate in physical activity and exercise programs .
again , in another study of this population ( 25 ) , the prevalences of obesity and abdominal obesity in women were found to be higher than in men , indicting the urgent need to target women for prevention and implementation of public educational programs to promote physical activity levels and ltpa in particular , to curtail the rising trend in obesity and abdominal obesity .
physical inactivity is responsible for 610% of the major non - communicable diseases includes coronary heart disease and type 2 diabetes ( 1 ) . taking into account
that , regarding coronary heart disease risk , about one - quarter of tehranian adults are reported to be eligible for therapeutic interventions ( therapeutic lifestyle changes and/or additional drug therapy ) ( 26 ) and also there is a marked increase in the prevalence of obesity and abdominal obesity ( 25 ) , significant importance given to our results .
furthermore , since the increasing trend in abdominal and general obesity is also observed in tehranian adolescents ( 27 ) and taking into account that sports activities in iran is publicized mostly through physical education classes , schools can play an important role in promoting physical activity in younger groups of this society .
the increasing proportion of individuals participating in physical activities such as swimming and aerobics / dancing reflects a preference shift in the type of physical activity performed by adults in leisure time . such preferences in types of activities may be a result of the growing number of gyms , increased knowledge and awareness about the beneficial effects of physical activity for health , and achieving a desirable body shape .
similar to our findings , in the madrid region ( 17 ) , activities which mostly contribute to the decrease in ltpa were those of low and moderate intensity , like walking and jogging , implying that a significant decrease in the proportion of subjects participating in these activities can be responsible for decrease in overall ltpa in this population .
the major strength of current study is its large and diverse population , which is representative of tehranian adults .
moreover , the reliability and convergent validity of the persian version of questionnaire used for physical activity assessment ( maq ) had been confirmed before .
however , some limitations may have affected accuracy ; first , the questionnaire we used ( maq ) differs to those of other studies , and any comparison of physical activity domains between studies using different methods is problematic
; second , it can not be overlooked that health promotion publicity induces a tendency for socially desirable answers ; lastly , in such studies , the clinical significance of the changes in physical activity is difficult to determine .
our analysis of physical activity level changes over a 6.5 yr follow up in tehranian adults indicates a decreasing trend in the proportion of subjects with low physical activity .
however despite these encouraging findings , approximately fifty percent of tehranian adults still have physical activity levels below the minimum level recommended , emphasizing the necessity to implement programs encouraging increase in physical activity levels of tehranian adults .
moreover , significant decrease in ltpa among women indicates the urgent need to target women for prevention and implementation of public educational programs to promote physical activity levels and ltpa in particular , to compensate the reduction in ocpa .
ethical issues ( including plagiarism , informed consent , misconduct , data fabrication and/or falsification , double publication and/or submission , redundancy , etc . ) have been completely observed by the authors .
 background : considering the lack of data available on changes of physical activity over time in iran , this study was designed to evaluate changes in physical activity levels among iranian adults over a median 6.5 yr period.methods:in this population - based cohort study , 3515 participants , aged  20 yr ( 2100 females and 1415 males ) were followed from phase ii ( 20022005 ) to phase iv ( 20082011 ) of the tehran lipid and glucose study . 
 information on physical activity , both leisure time ( ltpa ) and occupational ( ocpa ) , was collected using the modifiable activity questionnaire . 
 scores 600 mets - min / wk were considered as having low physical activity . 
 wilcoxon test was performed for comparing met values between the two phases . 
 mcnemar test was used to evaluate differences between paired qualitative data.results:in both phases , 59.8% of adults were women , with meansd age 44.314.6 and 50.914.6 yr , in phases ii and iv respectively . 
 the prevalence of low physical activity decreased significantly in the follow up period ( from 45.9% in phase ii to 42.6% in phase iv , p=0.004 ) . in both genders , a non - significant decrease in ocpa 
 was observed , however , there was a significant decrease in ltpa among women ( p=0.031 ) , but not in men.conclusion:despite the high levels of physical activity in tehranian adults , a decreasing trend was observed . 
 significant decrease in ltpa among women indicates the urgent need to target women for prevention and implementation of public educational programs to promote physical activity levels and ltpa in particular , to compensate the reduction in ocpa . 