participants were employees of the tokyo gas company that supplies natural gas to the tokyo area .
all employees received annual health checkups and completed a health questionnaire in accordance with the industrial safety and health law .
the participants for this study were 5,984 male employees who had participated in an annual health checkup and annual submaximal exercise tests in 1985 . among these men ,
335 were excluded because they were found at the health checkup to have at least one of the following : diabetes ( n = 102 ) , cardiovascular disease including hypertension ( n = 228 ) , tuberculosis ( n = 3 ) , or gastrointestinal disease ( n = 9 ) . for the present study
, we also required participants to have at least four submaximal exercise tests in the previous 7 years ( 19791985 ) .
this excluded 1,462 men , leaving 4,187 men , who were followed until june 1999 for the development of type 2 diabetes .
the initial exercise loads were 600 , 525 , and 450 kilopond meter / min for participants aged 2029 , 3039 , and 4049 years , respectively .
heart rate was calculated from the r - r interval on an electrocardiogram , and 85% of the age - predicted maximal heart rate ( 220  age [ years ] ) was set as the target heart rate .
the exercise load was increased by 225 kilopond meter / min for each stage among all age - groups , until heart rates during the course of the exercise reached the target heart rate or until the completion of the third stage .
maximal oxygen uptake ( vo2max ) was estimated using the strand - ryhming nomogram ( 11 ) and the strand age correction factors ( 12 ) .
first , we used a simple linear regression of vo2max against time to assess the individual regression coefficient ( slope ) of fitness over 7 years .
next , all participants were divided into quartiles based on the slope from their individual model .
the annual health checkup included measurement of height , body weight , and blood pressure and a urinary glucose test .
, participants were followed for the development of type 2 diabetes , which was based on any one of the following three diagnostic parameters : 1 ) plasma glucose levels exceeded 11.1 mmol / l ( 200 mg / dl ) 2 h after an oral glucose tolerance test , conducted in men with urinary glucose detected at a follow - up annual health checkup , 2 ) participants themselves reported current therapy with hypoglycemic medication ( insulin or oral hypoglycemic agent ) when they were interviewed at their health checkup , or 3 ) fasting plasma glucose levels were > 7.0
we first compared baseline characteristics of participants according to quartiles of the fitness trend using one - way anova for continuous variables and a  test for categorical variables as appropriate .
we used cox proportional hazards models to estimate the hazard ratios ( hrs ) of the incidence of type 2 diabetes .
we adjusted for age , initial fitness level ( continuous vo2max ) , bmi ( continuous variable ) , systolic blood pressure ( continuous variable ) , cigarette smoking ( nonsmokers , 120 cigarettes / day , and 21 cigarettes / day ) , alcohol intake ( none , 145 g / day , and 46 g / day ) , and a family history of diabetes ( present or not ) in a multivariate model .
a family history of diabetes was defined as the known presence of family members with diabetes in any of three generations , as determined by self - report on the health questionnaire .
the proportionality assumption of the model was tested using a log - minus - log plot ; no evidence of violation was found .
all analyses were performed using spss 15.0j for windows ( spss , chicago , il ) .
the initial exercise loads were 600 , 525 , and 450 kilopond meter / min for participants aged 2029 , 3039 , and 4049 years , respectively .
heart rate was calculated from the r - r interval on an electrocardiogram , and 85% of the age - predicted maximal heart rate ( 220  age [ years ] ) was set as the target heart rate .
the exercise load was increased by 225 kilopond meter / min for each stage among all age - groups , until heart rates during the course of the exercise reached the target heart rate or until the completion of the third stage .
maximal oxygen uptake ( vo2max ) was estimated using the strand - ryhming nomogram ( 11 ) and the strand age correction factors ( 12 ) .
first , we used a simple linear regression of vo2max against time to assess the individual regression coefficient ( slope ) of fitness over 7 years .
next , all participants were divided into quartiles based on the slope from their individual model .
the annual health checkup included measurement of height , body weight , and blood pressure and a urinary glucose test .
, participants were followed for the development of type 2 diabetes , which was based on any one of the following three diagnostic parameters : 1 ) plasma glucose levels exceeded 11.1 mmol / l ( 200 mg / dl ) 2 h after an oral glucose tolerance test , conducted in men with urinary glucose detected at a follow - up annual health checkup , 2 ) participants themselves reported current therapy with hypoglycemic medication ( insulin or oral hypoglycemic agent ) when they were interviewed at their health checkup , or 3 ) fasting plasma glucose levels were > 7.0
we first compared baseline characteristics of participants according to quartiles of the fitness trend using one - way anova for continuous variables and a  test for categorical variables as appropriate .
we used cox proportional hazards models to estimate the hazard ratios ( hrs ) of the incidence of type 2 diabetes .
we adjusted for age , initial fitness level ( continuous vo2max ) , bmi ( continuous variable ) , systolic blood pressure ( continuous variable ) , cigarette smoking ( nonsmokers , 120 cigarettes / day , and 21 cigarettes / day ) , alcohol intake ( none , 145 g / day , and 46 g / day ) , and a family history of diabetes ( present or not ) in a multivariate model .
a family history of diabetes was defined as the known presence of family members with diabetes in any of three generations , as determined by self - report on the health questionnaire .
the proportionality assumption of the model was tested using a log - minus - log plot ; no evidence of violation was found .
all analyses were performed using spss 15.0j for windows ( spss , chicago , il ) .
the mean age of the participants was 32.0 years ( range 2240 years ) at baseline .
the mean  sd number of fitness tests during 7 years was 6.0  0.96 .
the time between the first and last fitness test in each single individual was 6.5  0.73 years .
the median follow - up time was 14 years , with a total of 56,749 man - years of observation . during follow - up
there were 42 deaths , and 143 participants were lost to follow - up due to retirement .
men in the lowest fitness trend quartile ( quartile 1 ) decreased their average vo2max from 45.3 to 36.6 ml / kg / min ( median slope 1.25 ml / kg / min ) between 1979 and 1985 , whereas men in the highest fitness trend quartile ( quartile 4 ) increased their average vo2max from 36.3 to 45.6 ml / kg / min ( median slope 1.33 ml / kg / min ) over the same time .
the men in the lowest fitness trend quartile had the highest level of fitness in 1979 , whereas those in the highest fitness trend quartile had the lowest level of fitness .
the men in the highest quartile were more likely to have lower systolic and diastolic blood pressure and a lower rate of smoking compared with those in the lowest quartile .
baseline characteristics by cardiorespiratory fitness trend data represent median ( range ) , mean sd , or % .
men with higher initial fitness had lower hrs for type 2 diabetes than men in the lower initial fitness group .
in addition , older age , high bmi , high systolic blood pressure , alcohol intake , and a family history of diabetes all significantly increased the risk of type 2 diabetes . adjusted hr for incidence of type 2 diabetes by potential risk factors at baseline ( 1985 ) data are n ( % ) unless otherwise noted . *
table 3 shows the hrs for type 2 diabetes by fitness trend quartiles , with the lowest quartile used as the referent .
there were progressively lower age - adjusted hrs of type 2 diabetes across fitness trend quartiles .
after further adjustment for initial fitness level , bmi , systolic blood pressure , cigarette smoking , alcohol intake , and a family history of diabetes , there remained a strong inverse association between type 2 diabetes risk and fitness trend quartiles ( ptrend < 0.001 ) .
men in the highest quartile of fitness trend had an 70% lower risk of developing type 2 diabetes compared with men in the lowest quartile .
hrs of incidence of type 2 diabetes , according to quartiles of cardiorespiratory fitness trend data are means ( range ) unless otherwise indicated . * adjusted for age , initial cardiorespiratory fitness level , bmi , systolic blood pressure , cigarette smoking , alcohol intake , and a family history of diabetes .
we next investigated the hrs of type 2 diabetes associated with quartiles of fitness trend , among men classified according to their initial fitness levels in 1979 .
the inverse gradient for diabetes across long - term trends in fitness categories was generally observed for all levels of fitness in 1979 , except for men in the highest category of initial fitness ( 45.0 ml / kg / min ) .
we also investigated the hrs of type 2 diabetes among men with different levels of bmi at baseline ( 1985 ) .
again , there generally was an inverse gradient for diabetes risk across long - term trends in fitness categories for all bmi categories except the lowest .
hrs for incidence of type 2 diabetes associated with quartiles of cardiorespiratory fitness trend , among men categorized by initial ( 1979 ) cardiorespiratory fitness level ( top ) or baseline ( 1985 ) bmi ( bottom ) .
hrs were adjusted for age , systolic blood pressure , cigarette smoking , alcohol intake , a family history of diabetes , and bmi ( top ) or initial cardiorespiratory fitness level ( bottom ) .
in this study , we prospectively investigated the relationship between long - term trends in fitness and the incidence of type 2 diabetes in nondiabetic japanese men .
there was a strong inverse relationship between long - term trends in fitness and the incidence of type 2 diabetes , with men increasing their fitness over a 7-year period having lower risks than men with decreasing fitness over the same span .
the observed association is biologically plausible , because physical activity or fitness is a strong independent predictor of lower type 2 diabetes incidence rates ( 2,3 ) .
physical activity or fitness may prevent and delay type 2 diabetes by improving glucose levels , reducing adiposity , increasing muscle mass and the glut4 in muscle tissues , and reducing insulin resistance ( 13,14 ) .
the major strength of this study is the objective measurement of fitness , repeated over time .
fitness , an objective marker of daily physical activity , is a stronger predictor of morbidity or mortality than self - reported physical activity ( 15 ) .
terslinna et al . investigated the relationship , among 31 subjects , between measured vo2max and estimated vo2max using the strand - ryhming nomogram and correction factors used in the present study , obtaining a correlation coefficient of 0.92 ( 16 ) .
furthermore , we used values obtained in oral glucose tolerance tests or fasting blood glucose levels as objective measures of the study outcome , type 2 diabetes .
individuals at high risk of type 2 diabetes , such as those with impaired glucose tolerance or obesity , have been studied in randomized controlled trials of lifestyle , including physical activity and type 2 diabetes ( 810 ) .
however , there are no data in low - risk populations . in addition , most of the data have been in caucasian subjects .
type 2 diabetes is a global problem ; thus , data are needed not only in high - risk populations but also in low - risk populations and in other racial / ethnic groups .
one limitation of the present study is that subjects may not be representative of the entire japanese population and women were not included .
another limitation is that possible changes in fitness levels were taken into account between 1979 and 1985 but not during the follow - up period , 19851999 .
however , not accounting for changes during the latter period would probably dilute the true association between fitness and the risk of developing diabetes . in conclusion , this cohort study showed a strong inverse relationship between long - term trends in fitness and the development of type 2 diabetes in japanese men .
this relationship was independent of age , initial fitness level , bmi , systolic blood pressure , cigarette smoking , alcohol intake , and a family history of diabetes .
thus , regular physical activity , which is associated with an increase or preservation of fitness , should be promoted by health professionals , because it decreases the risk of type 2 diabetes , in addition to decreasing the risks of many chronic diseases ( 17 ) .
 objectivewhereas single assessments of cardiorespiratory fitness have been shown to predict lower incidence of type 2 diabetes , there are no data on long - term trends in fitness and risk . 
 we investigated the relationship between long - term trends in fitness and the incidence of type 2 diabetes.research design and methodsa cohort of 4,187 japanese men free of diabetes completed annual health checkups and fitness tests for estimated maximal oxygen uptake at least four times over 7 years ( 19791985 ) . 
 we modeled the trend in fitness over 7 years for each man using simple linear regression . 
 men were then divided into quartiles based on the regression coefficient ( slope ) from the model . during the follow - up period ( 19851999 ) , 274 men developed diabetes . 
 hazard ratios ( hrs ) and 95% cis for the incidence of diabetes were obtained using the cox proportional hazards model.resultsmen in the lowest quartile of the distribution decreased in fitness over the 7 years ( median slope 1.25 ml / kg / min ) , whereas men in the highest quartile increased in fitness ( median slope 1.33 ml / kg / min ) . with adjustment for age , initial fitness level , bmi , systolic blood pressure , cigarette smoking , alcohol intake , and a family history of diabetes and use of the lowest quartile , the hrs ( 95% ci ) for the second through fourth quartiles were 0.64 ( 0.460.89 ) , 0.40 ( 0.270.58 ) , and 0.33 ( 0.210.50 ) , respectively ( ptrend < 0.001).conclusionsthese results 
 indicate that the long - term trend in fitness is a strong predictor of the incidence of type 2 diabetes in japanese men . 
RESEARCH DESIGN AND METHODS
Cardiorespiratory fitness test
Diagnosis of type 2 diabetes
Statistical analysis
RESULTS
CONCLUSIONS