measuring the maximal oxygen consumption ( vo2max ) during an incremental test provides relevant information on risk or prognosis of various diseases [ 13 ] . in addition , precisely assessing the subject 's functional capacity allows tailoring of rehabilitation programmes . proper interpretation of the measured vo2max requires its comparison with well - selected reference values . the use of some equations has been recommended in international guidelines [ 6 , 7 ] . however , most of these equations have been elaborated from small series , and include subjects under the age of 71   or 74  years [ 911 ] . as a result , these validated reference equations provide predicted values for the elderly that are largely extrapolated from the models established by these authors . other authors provide specific reference values for healthy ageing men and women [ 1214 ] , but only one study   has been referenced in guidelines . in addition , earlier reference values published in the 1970s and 1980s [ 810 ] may no longer be adapted to the current ageing population , which , with respect to previous ones , has a different history and lifestyle , and increased longevity . consequently , it may be justified to use reference values derived from studies that include contemporary population samples . in view of this , these well - designed studies are population - based and provide predicted vo2max values over a wide range of ages . taking into account the disparities between the studies discussed above , we hypothesised that predicted vo2max values for older people may vary significantly according to the selected reference equation . therefore , to evaluate the impact of selection of reference values on the categorisation of vo2max as  normal  or  abnormal  , we compared the measured maximal oxygen consumption ( vo2peak ) on a cycle ergometer in 99 healthy caucasian subjects aged 70  years with the predicted vo2max provided by five different studies . we calculated the differences between the measured vo2peak and the predicted vo2max , and also examined relationships between the measured vo2peak and the lower limit of normal ( lln ) . this study was approved by the ethics committees of the medical , dentistry and pharmacy faculties ( university of strasbourg , strasbourg , france ) and of the strasbourg hospital , strasbourg , france ( administration number : 2013/26 ) . table 1 provides the reference equations / predicted values and llns we used in this study . to compare predicted vo2max values to measured vo2peak , 99 healthy subjects referred by their general practitioner before participating in an exercising programme offered by their medical insurance or before joining sports clubs or associations between january 2009 and december 2012 were included . all subjects lived in the department of bas - rhin , in alsace , france . subjects were free of chronic diseases , but mild and controlled hypertension or dyslipidaemia , tobacco consumption or overweight were not exclusion criteria [ 8 , 1013 ] . an activity questionnaire ( adapted from ) a maximal symptom - limited incremental exercise test was performed using an electrically braked cycle ergometer ( ergoselect 200p ; ergoline , bitz , germany ) following recommendations . oxygen uptake ( vo2 ) was measured using a breath - by - breath method ( ultima cardio2 ; medgraphics , milan , italy ) . we measured vo2peak since , as expected , a vo2 plateau was not achieved by all subjects [ 12 , 13 ] . the exercise test was considered maximal if it was symptom - limited with overall fatigue ( borg scale rating 910 , on a 010 scale ) and inability to maintain the pedalling rate > 60  rpm . table  1equations used for calculation of predicted maximal oxygen consumption ( vo2max)first author [ ref . ] , yearcharacteristics of the population samplesprediction equations for vo2maxwasserman , 1999the published equations were modified from :  hansen 
 et al . 77 males , 3474  years  asbestos exposed workers with normalcardiorespiratory function , california , usa  bruce 
 et al . 138 males , 157 females , 2973  years  general population , washington , usamen  ( 50.72(0.372age))weight ( units of mlmin )  example : predicted value : 1.92  lmin ; no lln can be calculatedwomen  ( 22.78(0.17age))(weight+43 ) ( units of mlmin )  example : predicted value : 1.16  lmin ; no lln can be calculatedjones , 198550 males , 50 females , 1571  years subjects recruited by advertising from the local university and general population , ontario , canada(0.046height)(0.021age)(0.62sex)4.31 ( units of lmin)sex : male=0 ; female=1men  example : predicted : 2.09  lmin ; lln : 1.14 ( 55% pred)women  example : predicted : 0.92  lmin ; lln : 0.15 ( 16% pred)blackie , 198981 males , 47 females , 5580  years subjects recruited locally by advertising from hospital and community centres , british columbia , canadamen  ( 0.0142height)(0.0494age)+(0.00257weight)+3.015  ( units of lmin )  example : predicted : 2.11  lmin ; lln : 1.25 ( 60% pred)women  ( 0.0142height)(0.0115age)+(0.00974weight)0.651 ( units of lmin)example : predicted : 1.45  lmin ; lln : 0.90 ( 62% pred)koch , 2009disease - free subjects , 253 males , 281 females , 2580  years representative sample selected from the population registration offices in pomerania , germany47.7565(0.988age)(0.2356age)(8.8697sex)+(2.3597bmi )  (2.0308agebmi)(3.7405sexbmi)+(0.2512agesex )  + ( 1.3797agesexbmi ) ( units of lkgmin)with : age > 65  years=5 ; sex male=1 , female=2 ; bmi 25  kgm=0 , bmi > 25  kgm=1men  example : predicted : 1.97  lmin ; lln : 1.43 ( 73% pred ) women  example : predicted : 1.35  lmin ; lln : 1.13 ( 84% pred)hakola , 2011nondiseased subjects , 117 males , 112 females , 5778  years subjects randomly selected from the town of kuopio , finlandmen  4.846(0.039age ) ( units of lmin )  example : predicted : 1.91  lmin ; lln : 1.12 ( 59% pred)women  3.475(0.031age ) ( units of lmin )  example : predicted : 1.32  lmin ; lln : 0.70 ( 53% pred)exercise tests were performed using cycle ergometers . lln : lower limit of normal ; bmi : body mass index . : for all equations , age is in years , height in cm and weight in kg ; : predicted vo2max and lln ( lmin ) have been calculated for an illustrative individual ( 72  years - old ; male : 80  kg and 172  cm ; female : 67  kg and 160  cm ) . equations used for calculation of predicted maximal oxygen consumption ( vo2max ) exercise tests were performed using cycle ergometers . : for all equations , age is in years , height in cm and weight in kg ; : predicted vo2max and lln ( lmin ) have been calculated for an illustrative individual ( 72  years - old ; male : 80  kg and 172  cm ; female : 67  kg and 160  cm ) . results are expressed as meansd or proportions . predicted vo2max was calculated using five different sets of reference equations , by wasserman 
 et al . , jones 
 et al . , blackie 
 et al . , hakola 
 et al .   and to compare measured vo2peak with predicted vo2max , we calculated the mean difference ( vo2peak minus predicted vo2max ) , and the 90% confidence interval of the differences for each predicted equation . only one author provided equations to calculate the fifth percentile , used as lln . for the other studies , we determined lln as mean2sd . since no standard deviation was available in the publication by wasserman 
 et al . the percentage of subjects with values below the lln of vo2max was calculated for each equation . vo2peak was compared according to the grade of physical activity using a two - way anova . this study was approved by the ethics committees of the medical , dentistry and pharmacy faculties ( university of strasbourg , strasbourg , france ) and of the strasbourg hospital , strasbourg , france ( administration number : 2013/26 ) . table 1 provides the reference equations / predicted values and llns we used in this study . to compare predicted vo2max values to measured vo2peak , 99 healthy subjects referred by their general practitioner before participating in an exercising programme offered by their medical insurance or before joining sports clubs or associations between january 2009 and december 2012 were included . all subjects lived in the department of bas - rhin , in alsace , france . subjects were free of chronic diseases , but mild and controlled hypertension or dyslipidaemia , tobacco consumption or overweight were not exclusion criteria [ 8 , 1013 ] . an activity questionnaire ( adapted from ) a maximal symptom - limited incremental exercise test was performed using an electrically braked cycle ergometer ( ergoselect 200p ; ergoline , bitz , germany ) following recommendations . oxygen uptake ( vo2 ) was measured using a breath - by - breath method ( ultima cardio2 ; medgraphics , milan , italy ) . we measured vo2peak since , as expected , a vo2 plateau was not achieved by all subjects [ 12 , 13 ] . the exercise test was considered maximal if it was symptom - limited with overall fatigue ( borg scale rating 910 , on a 010 scale ) and inability to maintain the pedalling rate > 60  rpm . table  1equations used for calculation of predicted maximal oxygen consumption ( vo2max)first author [ ref . ] , yearcharacteristics of the population samplesprediction equations for vo2maxwasserman , 1999the published equations were modified from :  hansen 
 et al . 77 males , 3474  years  asbestos exposed workers with normalcardiorespiratory function , california , usa  bruce 
 et al . 138 males , 157 females , 2973  years  general population , washington , usamen  ( 50.72(0.372age))weight ( units of mlmin )  example : predicted value : 1.92  lmin ; no lln can be calculatedwomen  ( 22.78(0.17age))(weight+43 ) ( units of mlmin )  example : predicted value : 1.16  lmin ; no lln can be calculatedjones , 198550 males , 50 females , 1571  years subjects recruited by advertising from the local university and general population , ontario , canada(0.046height)(0.021age)(0.62sex)4.31 ( units of lmin)sex : male=0 ; female=1men  example : predicted : 2.09  lmin ; lln : 1.14 ( 55% pred)women  example : predicted : 0.92  lmin ; lln : 0.15 ( 16% pred)blackie , 198981 males , 47 females , 5580  years subjects recruited locally by advertising from hospital and community centres , british columbia , canadamen  ( 0.0142height)(0.0494age)+(0.00257weight)+3.015  ( units of lmin )  example : predicted : 2.11  lmin ; lln : 1.25 ( 60% pred)women  ( 0.0142height)(0.0115age)+(0.00974weight)0.651 ( units of lmin)example : predicted : 1.45  lmin ; lln : 0.90 ( 62% pred)koch , 2009disease - free subjects , 253 males , 281 females , 2580  years representative sample selected from the population registration offices in pomerania , germany47.7565(0.988age)(0.2356age)(8.8697sex)+(2.3597bmi )  (2.0308agebmi)(3.7405sexbmi)+(0.2512agesex )  + ( 1.3797agesexbmi ) ( units of lkgmin)with : age > 65  years=5 ; sex male=1 , female=2 ; bmi 25  kgm=0 , bmi > 25  kgm=1men  example : predicted : 1.97  lmin ; lln : 1.43 ( 73% pred ) women  example : predicted : 1.35  lmin ; lln : 1.13 ( 84% pred)hakola , 2011nondiseased subjects , 117 males , 112 females , 5778  years subjects randomly selected from the town of kuopio , finlandmen  4.846(0.039age ) ( units of lmin )  example : predicted : 1.91  lmin ; lln : 1.12 ( 59% pred)women  3.475(0.031age ) ( units of lmin )  example : predicted : 1.32  lmin ; lln : 0.70 ( 53% pred)exercise tests were performed using cycle ergometers . lln : lower limit of normal ; bmi : body mass index . : for all equations , age is in years , height in cm and weight in kg ; : predicted vo2max and lln ( lmin ) have been calculated for an illustrative individual ( 72  years - old ; male : 80  kg and 172  cm ; female : 67  kg and 160  cm ) . equations used for calculation of predicted maximal oxygen consumption ( vo2max ) exercise tests were performed using cycle ergometers . : for all equations , age is in years , height in cm and weight in kg ; : predicted vo2max and lln ( lmin ) have been calculated for an illustrative individual ( 72  years - old ; male : 80  kg and 172  cm ; female : 67  kg and 160  cm ) . predicted vo2max was calculated using five different sets of reference equations , by wasserman 
 et al . , jones 
 et al . to compare measured vo2peak with predicted vo2max , we calculated the mean difference ( vo2peak minus predicted vo2max ) , and the 90% confidence interval of the differences for each predicted equation . only one author provided equations to calculate the fifth percentile , used as lln . for the other studies , we determined lln as mean2sd . since no standard deviation was available in the publication by wasserman 
 et al . the percentage of subjects with values below the lln of vo2max was calculated for each equation . vo2peak was compared according to the grade of physical activity using a two - way anova . table 1 provides the reference equations we used [ 8 , 1113 , 17 ] , as well as the characteristics of the population samples selected by the authors to elaborate these equations . predicted vo2max and lln ( lmin ) have been calculated for an illustrative individual ( 72  years - old ; man : 80  kg and 172  cm ; woman : 67  kg and 160  cm ) using each equation . 83% of men and 63% of women had a body mass index > 25  kgm . most subjects ( 53% of men and 66% of women ) reported moderate physical activity , while 19 males and females reported intense physical activity . these physical activities included heavy gardening and yard work , yoga and gymnastic / fitness , walking / hiking , cycling , swimming , and cross - country skiing . the 19 ( 19% ) subjects who reported intense physical activity practiced at least two sports . vo2peak was 23.055.47  mlminkg in men and 18.944  mlminkg in women , and maximal workload was 12737  w ( 1.57  wkg ) in men and 8418  w ( 1.27  wkg ) in women . maximal heart rate , ventilation , respiratory exchange ratio and respiratory equivalents were not different in men and women . n5841age years73.64.073.22.7weight kg81.313.367.711.5height cm172.20.1159.50.1body mass index kgm28.03.626.23.6current smokers5 ( 8.6)0 ( 0)former smokers32 ( 55.0)9 ( 21.9)intense physical activity13 ( 22.4)6 ( 14.6)moderate physical activity31 ( 53.4)27 ( 65.8)sedentary14 ( 24.2)8 ( 19.6)fvc l3.70.72.80.6fvc % predicted101.720.1122.825.4fev1 
 l2.70.62.20.4fev1 
 % pred99.622.8117.121.6fev1/fvc % 74.18.978.76.3oxygen uptake at rest lmin0.300.070.230.06heart rate at rest beatsmin76127713ventilation at rest l11.522.618.421.64maximal oxygen uptake lmin1.880.411.260.24  mlminkg23.055.4718.944.00maximal workload w127.3336.6684.2018.29maximal heart rate beatsmin1422113718  % pred87.213.085.810.6maximal ventilation l72.7718.3149.5013.22  % pred77.617.468.016.7maximal ve / vco234.194.6334.835.66maximal ve / vo238.387.3739.406.91maximal respiratory exchange ratio1.140.101.150.07data are presented as meansd or n ( % ) , unless otherwise stated . the exercise test was performed on an electrically - braked cycle ergometer . fvc : forced vital capacity ; fev1 : forced expiratory volume in 1  s ; ve : minute ventilation ; vco2 : carbon dioxide output ; vo2 : oxygen uptake . : predicted maximal ventilation was calculated as the subject 's fev135 ; predicted maximal heart rate was calculated as 2100.65(age ) . subjects ' characteristics , spirometry and exercise test results data are presented as meansd or n ( % ) , unless otherwise stated . fvc : forced vital capacity ; fev1 : forced expiratory volume in 1  s ; ve : minute ventilation ; vco2 : carbon dioxide output ; vo2 : oxygen uptake . : predicted maximal ventilation was calculated as the subject 's fev135 ; predicted maximal heart rate was calculated as 2100.65(age ) . table 3 provides means and 90% confidence intervals of the differences between measured and predicted vo2 values . figure 1 illustrates the measured vo2peak in our subjects and the normal values calculated with the five equations for an 80  kg and 172  cm man , and a 67  kg and 160  cm woman . table 3 shows that mean vo2peak ranged from 89% and 108% of predicted , and mean ( measuredpredicted ) differences ranged from 250  ml to + 150  ml in men , according to the reference values used . in women , mean vo2peak ranged from 88% and 164% of predicted , and mean ( measuredpredicted ) differences ranged from 190  ml to + 350  ml . the proportion of men below the lln ranged from 5% to 14% , and the proportion of women ranged from 0% to 22% . the dispersion of the ( measuredpredicted ) differences ( reflected by the bounds of the 90% ci ; table 2 ) was wider using the equation of jones 
 et al .   for women , because of the huge dispersion of the predicted values using this equation ( 0.141.54  lmin ) . . 
 figure  1measured maximal oxygen consumption ( vo2peak ) in a ) 58 men and b ) 41 women , aged > 70  years and free of chronic diseases . predicted maximal oxygen consumption ( vo2max ) reference values and their changes with age were calculated using reference equations by wasserman 
 et al . for an illustrative individual ( male : 80  kg and 172  cm ; female : 67  kg and 160  cm ; mean heights and weights in our study ) . table  3comparison of measured maximal oxygen consumption ( vo2peak ) versus predicted maximal oxygen consumption ( vo2max ) according to prediction equations from five studiessampleprediction equationvo2peak 
 % predictedvo2peak 
 minusvo2max 
 lminsubjects 
 with 
 vo2peak 
 < lln58 disease - free men ,  > 70  years oldwasserman 
 et al . 108230.15 ( 0.500.79)jones 
 et al . 103240.04 ( 0.650.74)3 ( 5)41 disease - free women ,  > 70  years oldwasserman 
 et al . 98180.03 ( 0.410.35)0 ( 0)data are presented as meansd , mean difference ( 90% ci ) or n ( % ) . did not provide lln . measured maximal oxygen consumption ( vo2peak ) in a ) 58 men and b ) 41 women , aged > 70  years and free of chronic diseases . predicted maximal oxygen consumption ( vo2max ) reference values and their changes with age were calculated using reference equations by wasserman 
 et al . , jones 
 et al . , blackie 
 et al . , hakola 
 et al .   and for an illustrative individual ( male : 80  kg and 172  cm ; female : 67  kg and 160  cm ; mean heights and weights in our study ) . comparison of measured maximal oxygen consumption ( vo2peak ) versus predicted maximal oxygen consumption ( vo2max ) according to prediction equations from five studies data are presented as meansd , mean difference ( 90% ci ) or n ( % ) . in this study , we expressed the measured vo2peak of 99 disease - free , 70  year - old subjects as the percentage of the reference values calculated using five different reference equations . mean vo2peak ranged from 89% to 108% of predicted in men , and from 88% to 164% in women , depending on the reference equation used . in addition , we found that the proportion of subjects showing vo2peak below the lln ranged from 5% to 14% in men and 0% to 22% in women , depending on the reference equation . numerous reference equations or normal values have been published for vo2max , which do or do not include older people . we did not perform a comprehensive review of these equations , but aimed to show that vo2peak expressed as per cent predicted as well as proportions of subjects with  low vo2peak differ markedly according to the equation used . among the five studies we selected , the studies by jones 
 et al . , wasserman 
 et al .   and blackie 
 et al .   were regarded by the 1997 european respiratory society task force   to fulfil the minimum requirements to be used in the clinical setting . the 2003 american thoracic society / american college of chest physicians committee   concluded that , even if not optimal , the reference values of jones 
 et al .   and wasserman 
 et al . we tested these equations on subjects aged 70  years , whose demand for exercise testing and rehabilitation is growing . however , the validity of the predicted vo2max values may be questioned for this age group . indeed , the oldest subjects in the studies by jones 
 et al .   and wasserman 
 et al .   were only 71 and 74  years old , respectively . as a result , predicted values for people aged > 70  years people are mainly extrapolated from their linear models . since the vo2max / age relationship has been found to be nonlinear in some studies [ 16 , 17 , 19 ] using these equations may lead to improper reference values . the studies by hakola 
 et al .   and blackie 
 et al . included 15 and 36  subjects aged > 70  years , which is not that high . when using this equation , the predicted vo2max for a given subject with stable weight and height does n't vary beyond age 65  years , since age is not a continuous variable . .   took into account the effect of obesity or overweight on vo2max , whereas height and weight were not included in the equation used by hakola 
 et al . . first , a lack of disease or risk factors beyond the age of 70  years is uncommon . however , we included , as did other authors , subjects who strictly speaking could not to be considered as smokers or ex - smokers [ 12 , 13 , 15 , 17 ] or overweight subjects [ 11 , 13 , 15 , 17 ] were not excluded from most studies . koch 
 et al .   showed that arterial hypertension and/or beta blocker treatment did not have a significant influence on vo2max , and these were not regarded as exclusion criteria . we recorded normal end - exercise cardiorespiratory values for this age group , in both men and women . compared with younger subjects , it has been demonstrated that maximal vo2 , carbon dioxide output ( vco2 ) , heart rate , ventilation and end - tidal carbon dioxide tension significantly decline with age , whereas minute ventilation ( ve)/vco2 and ve / vo2 slightly increase , and respiratory exchange ratio and end - tidal oxygen tension do not change significantly . secondly , our selection of subjects was inherently biased as no formal random selection from a large population was used . our subjects were referred before joining sports clubs or exercise programmes , lived in alsace , and were part of our routine clinical practice . thirdly , comparison of our maximal vo2 , ventilation and heart rate values to recently published values [ 15 , 16 ] may suggest that the efforts of some of our subjects may have been submaximal . these observations are of course of relevance . however , our purpose was not to provide normal values for french older people , but to use vo2peak results obtained routinely , in  healthy this study led to some findings that could guide the selection of reference equations for ageing people . in men , predicted vo2max were not very different from one another and fitted with our subjects ' measured vo2peak , whatever the reference equation . in women , predicted values were more widely distributed than in men . the studies by jones 
 et al .   and wasserman 
 et al . provided the lowest predicted vo2max values . in our opinion , the equation of jones 
 et al . provides unsuitable predicted vo2max for ageing women , as our mean vo2peak value corresponded to 164% of predicted . interestingly , predicted vo2max values provided by two recent studies are very high compared with those we selected [ 15 , 16 ] . for instance , the predicted vo2max is 2.81  lmin for men aged > 70  years and 1.85  lmin for women aged > 70  years in the study by loe 
 et al . . the subjects were tested on a treadmill and not on a cycle , and the use of a treadmill usually results in 1015% higher vo2max . however , after application of the corrective factor , these predicted vo2max remain higher than the previous ones , raising the question of a secular trend . the main finding of this study is that lln differed a lot from one study to another . as a result , depending on the selected reference equation , 514% of men and 022% of women were categorised as  abnormal  . for women were very low and seem unsuitable for clinical practice , whatever the studied female population . the data of wasserman 
 et al .   did not allow calculation of the lln . in such a case , a < 80% of predicted cut - off is frequently used in practice to define as shown in table 1 , we found that after excluding the extremes , lln ranged between 53% and 73% of the predicted value in both men and women . this demonstrates that the choice of an 80% cut - off leads to overestimate the proportion of  abnormal  older subjects and should not be used . again , we found that the lln was more widely distributed in women ( 1684% of predicted ) than in men ( 5573% of predicted ) ( table 1 ) . altogether , these results provide evidence that lln needs to be well characterised in published studies and applied in clinical practice . in addition , the wide range of lln recorded in the literature should prompt additional studies in women . the heterogeneity of the reference values we examined can be partly explained by technical reasons ( e.g. exercise protocol and type of gas exchange analyser ) and partly by methodological issues ( e.g. sample size , criteria for subject selection and maximal effort , and treatment of data ) . however , the main factor is probably the characteristics of the reference population from which the sample is drawn . obviously , reference equations can not be used irrespective of the population from which a subject comes . guidelines recommend testing a sample of healthy volunteers and selecting the reference values that better characterise this sample , emphasising the importance of matching reference values to the population base . to conclude , this study stresses the importance of the selection of vo2max reference equations , especially for older subjects , and offers clinicians some information to guide their choice . however , an alternative approach to the difficult issue of subjects ' categorisation as normal  or not would be to evaluate mortality risk or prognosis associated with vo2max results , which would be particularly relevant in ageing subjects . indeed , the question of how healthy older people should be to be regarded as
we evaluated the impact of selection of reference values on the categorisation of measured maximal oxygen consumption ( vo2peak ) as  normal  or 
 abnormal  in an ageing population.we compared measured vo2peak with predicted values and the lower limit of normal ( lln ) calculated with five equations . 
 99 ( 58 males and 41 females ) disease - free subjects aged 70  years completed an incremental maximal exercise test on a cycle ergometer.mean vo2peak was 1.88  lmin1 in men and 1.26  lmin1 in women . 
 vo2peak ranged from 89% to 108% of predicted in men , and from 88% to 164% of predicted in women , depending on the reference equation used . 
 the proportion of subjects below the lln ranged from 5% to 14% in men and 022% in women , depending on the reference equation . 
 the lln was lacking in one study , and was unsuitable for women in another . 
 most llns ranged between 53% and 73% of predicted . 
 therefore , choosing an 80% cut - off leads to overestimation of the proportion of  abnormal  subjects.to conclude , the proportion of subjects aged 70  years with a  low 
 vo2peak differs markedly according to the chosen reference equations . in clinical practice 
 , it is still relevant to test a sample of healthy volunteers and select the reference equations that better characterise this sample .