  determinar valores de referncia para a distncia caminhada ( dc ) e para respostas fisiolgicas durante o teste de caminhada com carga progressiva ( tccp ) e desenvolver equaes preditivas para essas variveis em adultos saudveis .
  foram avaliados 103 participantes saudveis com idade  40 anos ( 54 mulheres e 49 homens ) . os participantes usaram um sistema de anlise de gases durante o tccp .
consumo de oxignio ( vo2 ) , liberao de gs carbnico , ventilao minuto , frequncia cardaca ( fc ) , dc e velocidade mxima da caminhada ( vmc ) foram obtidos como desfechos primrios .
avaliamos tambm a fora de preenso manual ( fpm ) e a massa magra corporal ( mmc ) .
  os modelos de regresso utilizando variveis fisiolgicas , dc e vmc ajustados por idade , massa corporal , estatura e sexo apresentaram valores de r entre 0,40 e 0,65 ( para fc e pico de vo2 , respectivamente ) .
os modelos incluindo mmc e fpm no aumentaram consideravelmente os valores de r na previso do pico de vo2 , embora esses modelos tenham aumentado discretamente os valores do r para dc e vmc ( 8% e 12% , respectivamente ) . as variveis dc , vmc e dc  massa corporal , respectivamente , explicaram 76,7% , 73,3% e 81,2% da variabilidade
  nossos resultados originaram valores de referncia para a dc e respostas fisiolgicas ao tccp , que podem ser estimados adequadamente por caractersticas demogrficas e antropomtricas simples em adultos saudveis com idade  40 anos . o tccp poderia ser utilizado na avaliao da capacidade fsica na populao geral de adultos e no desenvolvimento de programas de caminhada individualizados . 

the incremental shuttle walk test ( iswt ) was developed in order to assess the functional exercise capacity of patients with copd . 


 
the test subject walks back and forth along a 10-m flat course , with progressive increases in pace imposed by audio signals , until no longer able to maintain the pace .
the incremental character of the iswt yields physiological responses closer to those observed in cardiopulmonary exercise testing ( cpet ) . 


 
some authors argue that , as an externally paced walk test , the iswt is more reproducible and yields greater physiological responses in comparison with self - paced walk tests . 


 
the incremental shuttle walk distance ( iswd ) is generally used as an index of cardiorespiratory fitness and has been suggested as a prognostic indicator in patients with chronic disease . 


  because of its simplicity and low cost , walking is the most popular exercise for middle - aged and older adults . in healthy subjects ,
the heart rate variability threshold was reported to be a valid tool for estimating the ventilatory threshold during the iswt . 


 
the iswt has also proven useful for quantifying the benefits of a walking program designed for healthy individuals . 


 
studies evaluating the iswt in healthy subjects have shown that the iswt is valid and responsive . despite the widespread use of the iswt in clinical settings ,
recently , the iswd has been investigated in healthy subjects , and regression equations have been developed , allowing a better interpretation of walking performance . 




 
two such studies enrolled participants with comorbidities , 




  whereas another included only healthy individuals . 


 
however , to our knowledge , there have been no studies evaluating physiological responses to the iswt in healthy subjects in other than a superficial manner .
although the operational simplicity of walk tests is recognized as their most important quality , the iswt has been evaluated with the aid of sophisticated telemetric gas analysis systems in order to evaluate physiological responses , especially in patients with cardiorespiratory diseases . 




  in such patients , the peak oxygen consumption ( vo2 ) achieved on the iswt exhibits a strong correlation with that achieved in cpet performed on a treadmill or on a cycle ergometer . 




 
therefore , the iswt appears to induce a maximum exercise response that is appropriate for assessing functional capacity . 


 
elucidation of such physiological responses might be useful for assessing exercise capacity and for designing walking programs for middle - aged and older adults .
in addition , reference values , especially for vo2 and iswd , might provide an easy way to assess the functional exercise capacity in patients with chronic diseases .   in this study ,
our primary objective was to determine reference values for iswd and peak physiological responses during the iswt , developing a series of simple predictive equations for those variables in healthy middle - aged adults and in healthy older adults .
we also assessed the influence that body composition and muscle strength have on the main physiological variables obtained during the iswt .
we conducted a cross - sectional study to evaluate the physiological responses to the iswt in 103 healthy adults aged 40 years and older .
the research ethics committee of the federal university of so paulo , located in the city of so paulo , brazil , approved the study , and all participants provided written informed consent .
we recruited a convenience sample from among employees of the institution and residents of the surrounding community .
the following individuals were ineligible for inclusion in the study : those with a body mass index > 35 kg / m ; those who used a walking aid ; those who exhibited abnormal post - bronchodilator spirometric results 


 ; those who reported having cardiorespiratory , metabolic , neuromuscular , or musculoskeletal disease ; and those who were current smokers .  
eligible participants underwent a series of evaluations over the course of two mornings , with a 7-day interval between the two . on day 1 , the participants completed a physical activity readiness questionnaire , a face - to - face interview based on the main cardiovascular risk factors , and a physical activity questionnaire in accordance with the american college of sports medicine recommendations 


  so that we could exclude those involved in high - intensity exercise and sports .
they also underwent spirometry , hand grip strength ( hgs ) assessment , and anthropometric and body composition measurements .
those who met the eligibility criteria returned on day 2 and underwent three iswts , 20 min apart .
body mass ( in kg ) and height ( in m ) were measured , and the body mass index ( in kg / m was calculated .
body composition was assessed using a portable scale with a tetrapolar bioelectrical impedance system ( tbf-310gs ; tanita , arlington heights , il , usa ) . 


 
total body fat ( tbf ) , total body water , and lean body mass ( lbm ) were assessed using regression equations . 


 
spirometry was performed using a hand - held spirometer ( spiropalm ; cosmed , pavona di albano , italy ) in accordance with the criteria established by the brazilian thoracic association . 


 
the hgs of the dominant side was assessed using a hydraulic dynamometer ( hs5001 ; carci , so paulo , brazil ) . 


 
we conducted the iswts in a 10-m corridor , increasing the pace by 0.17 m / s every minute . 


 
dyspnea and leg fatigue were quantified before and after each test with the borg scale .
the iswd ( in m ) and maximum walking velocity ( mwv , in m / s ) obtained on the third test were selected for further analysis . because the iswt was developed to assess the functional exercise capacity of patients with lung disease , the original protocol consisted of 12 levels ( total distance , 1,020 m ) . 


 
however , because we applied the test to healthy subjects , we extended it to 15 levels ( 1,500 m ) in order to minimize the ceiling effect . during the third iswt ,
expired gases were collected and assessed by a portable telemetric gas analysis system ( k4b2 ; cosmed ; pavona di albano , italy ) .
the physiological responses were analyzed breath - by - breath , and the data were filtered every 15 s. the following variables were focused at the peak of the iswt : vo2 , carbon dioxide production , hr , and minute ventilation .
sex - related differences in the main physiological variables and the rate of perceived exertion were evaluated using student 's t - test or the mann - whitney test .
pearson 's or spearman 's coefficients were used in order to assess bivariate correlations . to ensure that the iswd obtained in the third test , carried out using the gas analysis system , was not inferior to that obtained in the second test , conducted without the equipment
, we evaluated the intraclass correlation coefficient ( icc ) with its 95% ci between those measures and compared their mean values using paired student 's t - test .
we calculated the sample size considering a minimum acceptable coefficient of correlation of 0.70 or a coefficient of determination ( r of 0.49 .
assuming an alpha error of 0.05 and a beta error of 0.20 , a minimum of 12 observations for each variable included in the model would be sufficient .
therefore , 80 participants were necessary , and we were able to include up to 8 variables in each model .
a series of multiple linear regression equations was developed using the main physiological responses as dependent variables .
the models were first adjusted for age , body mass , height , and sex .
this procedure was applied because these variables are easily obtained . for vo2 , mwv , and iswd ( the most important variables related to aerobic exercise capacity ) , the models were also adjusted for body composition variables and hgs . regarding body composition , we chose lbm and tbf , which presented the strongest correlations in the previous bivariate analysis .
in addition , we used linear regressions in alternative prediction models to determine whether peak vo2 correlated with iswd , with iswd  body mass , and with mwv .
we performed the statistical analysis with the statistical package for the social sciences , version 15.0 ( spss inc . , chicago , il , usa ) and sigmastat , version 3.1 ( systat software inc . , san jose , ca , usa ) .
the sample comprised 103 participants ( 54 women and 49 men ) , and the mean age was 60  10 years ( table 1 ) .
the participants were distributed within the following age brackets : 40 - 49 years ( 13 women and 12 men ) ; 50 - 59 years ( 12 women and 11 men ) ; 60 - 69 years ( 14 women and 14 men ) ; and  70 years ( 15 women and 12 men ) . there were no significant differences among the four age groups studied in terms of the proportions of women and men . between the second and third iswt , the iswd reliability was excellent ( icc = 0.973 ; 95% ci : 0.960 - 0.982 ) and there was no significant difference between the mean values ( 510  148 m vs. 519  161 m ) . 

= 54)(n = 49)meansdmeansd 
 age , year5911599 
 bm , kg * 
 68148012 
 height , m * 
 1.570.071.710.07 
 bmi , kg / m 
 275273 
 tbf , kg * 
 3110207 
 tbf , % of total bm * 
 356255 
 lbm , kg * 
 395587 
 lbm , % of total bm * 
 646745 
 lbm , % of predicted 10271035 
 lbmi , kg / m 
 * 
 171201 
 hgs , kgf * 
 265438bm : body massbmi : body mass indextbf : total body fatlbm : lean body masslbmi : lean body mass indexhgs : handgrip strength*p < 0.05 ( females vs. males ) 
  : lean body mass index p < 0.05 ( females vs. males ) the regression analysis models , using physiological variables , iswd , and mwv as dependent variables and adjusted for age , body mass , height , and sex , showed r values ranging from 0.40 to 0.65 ( for hr and peak vo2 , respectively ; table 2 ) . applying the model including lbm and that including hgs did not result in a significant increase in the r values for predicting peak vo2 ( table 2 ) , although the use of those models did result in slight increases in the r values for iswd and mwv ( of 8% and 12% , respectively ) .
we selected iswd , mwv , and iswd  body mass as the sole determinants of peak vo2 . in three different models , those variables determined 76.7% , 73.3% , and 81.2% of the peak vo2 , respectively ( figure 1 ) . 

table 2linear prediction equations , adjusted for age , body mass , height , sex , body composition , and muscle function , for peak physiological responses , total distance walked , and maximum walking velocity related to the incremental shuttle - walk test.variablemodel 

 constantage , yearsbody mass , kgheight , msex 

 hgs , kgflbm , kgtbf , % r 
 sy.xmeanlln 


 ve , l / mina43.767.20.5 * 
 0.169.2 * 
 13.0 * 
 ---0.5414.3 
 hr , bpma146.2117.91.1 * 
 0.4 * 
 55.5 * 
 2.1 - --0.4017.2 
 vco2 , ml / mina137.6493.222.5 * 
 5.4 * 
 1,317.9 * 
 554.5 * 
 ---0.63383.5 
 peak vo2 , ml / mina268.6337.921.1 * 
 9.2 * 
 1,101.1 * 
 535.6 * 
 ---0.65368.1 
 b134.1750.616.2 * 
 8.8938.7 * 
 297.514.8 * 
 --0.65374.9 
 c1,206.31,731.712.6 * 
 21.0883.3207.8 - 56.0 * 
 27.80.65319.2 
 iswd , ma347.7186.87.2 * 
 3.0 * 
 472.3 * 
 137.2 * 
 ---0.6597.8 
 b223.786.15.8 * 
 3.2 * 
 421.367.14.8 * 
 --0.7383.6 
 c54.6198.45.8 * 
 4.3666.0 * 
 75.3 - 2.10.640.6887.4 
 mwv , m / sa1.591.320.01 * 
 0.004 * 
 0.70 * 
 0.22 * 
 ---0.600.17 
 b0.890.660.008 * 
 0.005 * 
 0.92 * 
 0.060.008 * 
 --0.720.14 
 c0.550.320.009 * 
 0.0071.23 * 
 0.11 - 0.0030.0020.670.14lln : lower limit of normal ( calculated as 1.646  sy.x)hgs : handgrip strengthlbm : lean body masstbf : total body fatsy.x : standard error about linear regressionve : minute ventilationvco2 : carbon dioxide productionvo2 : oxygen uptakeiswd : incremental shuttle walk distancemwv : maximum walking velocityamodel a included age , body mass , height and sex ; model b included age , body mass , height , sex , and hgs ; and model c included age , body mass , height , sex , lbm , and tbf.buse " mean " column for prediction of the expected values and " lln " column for lower limit of normal .
csex : males = 1 ; females = 0*significant predictors ( p < 0.05 ) . 
  : lower limit of normal ( calculated as 1.646  sy.x ) : standard error about linear regression : carbon dioxide production : incremental shuttle walk distance : maximum walking velocity model a included age , body mass , height and sex ; model b included age , body mass , height , sex , and hgs ; and model c included age , body mass , height , sex , lbm , and tbf .
use " mean " column for prediction of the expected values and " lln " column for lower limit of normal .  
sex : males = 1 ; females = 0 significant predictors ( p < 0.05 ) . 

figure 1significant correlations between peak vo2 and incremental shuttle walk distance ( iswd ) , as well as between peak vo2 and maximal walking velocity ( mwv ) , during the incremental shuttle walk test . 

we derived a series of equations that can predict iswd , as well as cardiovascular , ventilatory , and metabolic responses during the iswt .
age and sex had significant influences on those variables . however , after adjusting for sex and age , we found that mwv and iswd were the main determinants of peak vo2 , regardless of body composition and peripheral muscle strength .
the main finding of this study was the considerable influence that mwv and iswd had on the peak vo2 obtained on the iswt .
the correlations between peak vo2 and iswd , between peak vo2 and mwv , and between peak vo2 and iswd  body mass ranged from 0.75 to 0.90 .
these values are similar to those described in the literature for the correlation between iswd and peak vo2 obtained under laboratory conditions in patients with cardiopulmonary disease .
consistent correlations between peak vo2 and iswd or between peak vo2 and iswd  body mass obtained in cpet have been described in copd patients ( range , 0.73 - 0.88 ) . 








 
correlations of this magnitude have also been described during cpet in patients with idiopathic pulmonary fibrosis 


  and in patients with heart disease . 




 
these results support the assertion that the iswt is a suitable tool to assess the functional capacity of such patients .
our results indicate that the peak vo2 obtained during the iswt might be adequately estimated by using iswd , mwv , or body mass .
in fact , lger & lambert 


  reported similar results in the study in which they developed the precursor to the iswt ( the incremental shuttle run test ) . in that study ,
the peak vo2 of young adults was adequately predicted by the running speed , with a correlation of r = 0.84 . in a study conducted by cooper , who used the 12-min run test , 


 
the 12-min run distance was also the most important determinant of cardiorespiratory fitness in healthy young adults , a finding similar to those of the present study .
even in cpet , the work rate , or power , has been identified as the main determinant of peak vo2 . 


  because the iswt is performed on a flat surface
sex and age influenced the main variables obtained on the iswt ( peak vo2 , iswd , and mwv ) .
several studies have reported that peak vo2 suffers a decline with advancing age and is lower in women , 




  even when allometric correction is used . 


  in the present study , r values for iswd , adjusted for age , body mass , height , and sex , ranged from 15% to 22% , which are higher than those reported in the study conducted by jrgensen et al . , 


  in which those attributes explained 50% of the iswd variability .
this difference might be attributable to the characteristics of the sample evaluated in that study , which included individuals with mild hypertension and smokers , whereas only healthy participants were included in the present study .
we found that body composition and hgs , although presenting consistent correlations with peak vo2 , did not sufficiently increase the predictive power of the equations adjusted only for demographic and anthropometric attributes .
reported similar results in a study involving cpet on a cycle ergometer . in that study
, the residuals of the equations involving muscle strength and body composition were narrowed , although the r was not sufficiently increased . 


 
our results suggest that equations including age , sex , body mass , and height are useful because those variables are very simple to obtain and provide r values similar to those of models with variables that are more difficult to obtain , such as body composition and muscle function ( table 2 ) . 
 
various cardiovascular and ventilatory variables were determined in the present study by a combination of age , sex , height , and body mass ( r ranging from 0.54 to 0.65 ) .
our results are similar to those described by neder et al . , 


  who reported that several cardiovascular and ventilatory variables might be determined by the combination of age , sex , height , and body mass , with an r ranging from 0.102 to 0.691 .
the use of a gas analysis system did not result in worse performance during the third iswt in the present study , given that the results of the second and third iswts were not significantly different and exhibited excellent reliability .
our results differ from those described by singh et al . , 


  who reported a shorter iswd with the use of a telemetric gas analysis system .
this discrepancy might be explained primarily by the total weight of the equipment we used , which was lower than the 4.1 kg of that used by singh et al . 


 
in addition , those authors 


  evaluated copd patients , whereas our study involved only healthy participants .
our results show that , despite some minor discomfort related to the use of a face mask , the use of the equipment had no impact on the iswd .
however , comparing our results with those expected for cpet on a cycle ergometer derived from a randomized study , 


  the measured peak vo2 during the iswt was significantly higher than the expected values for cpet on a cycle ergometer ( 1,760  608 ml / min vs. 1,568  438 ml / min , p = 0.017 ) .
regarding cpet on a treadmill , when we compare our results with those found in another study conducted in brazil , 


  albeit qualitatively , the peak vo2 achieved during the iswt corresponded to 80.6 - 108.2% of the peak vo2 expected in that study .
another limitation was the convenience sampling technique that we used , which might have resulted in overestimation of the normal physiological responses .
however , we took care to include only healthy individuals who were not involved in sports or vigorous physical activity .
our results provide reference values for iswd and physiological responses to the iswt , which can be properly estimated by determining simple demographic and anthropometric characteristics in healthy adults  40 years of age .
the inclusion of body composition and muscle function data improved the power of those estimations only slightly .
therefore , the iswt could be used in assessing physical fitness in the general adult population and in designing individualized walking programs . because the pace set in the initial levels of the iswt
is too slow for healthy individuals , future studies should investigate ways in which the original protocol can be adapted for use in this population .
the authors would like to thank the faculty of the american thoracic society and the methods in epidemiologic , clinical and operations research ( mecor ) program , especially dr .
william m. vollmer , for their support in the statistical analysis during the first mecor global course , held in nairobi , kenya , in 2011 .
 objective : to determine reference values for incremental shuttle walk distance ( iswd ) and peak physiological responses during the incremental shuttle walk test ( iswt ) , as well as to develop a series of predictive equations for those variables in healthy adults . 
 methods : we evaluated 103 healthy participants  40 years of age ( 54 women and 49 men ) . 
 we fitted each participant with a gas analysis system for use during the iswt . 
 oxygen consumption ( vo2 ) , carbon dioxide production , minute ventilation , heart rate ( hr ) , iswd , and maximal walking velocity ( mwv ) were obtained as primary outcomes . 
 we also assessed hand grip strength ( hgs ) and lean body mass ( lbm ) . 
 results : the regression analysis models , including physiological variables , iswd , and mwv ( adjusted for age , body mass , height , and sex ) , produced r2 values ranging from 0.40 to 0.65 ( for hr and peak vo2 , respectively ) . using the models including lbm or hgs 
 , we obtained no significant increase in the r2 values for predicting peak vo2 , although the use of those models did result in slight increases in the r2 values for iswd and mwv ( of 8% and 12% , respectively ) . the variables 
 iswd , mwv , and iswd  body mass , respectively , explained 76.7% , 73.3% , and 81.2% of peak vo2 variability . 
 conclusions : our results provide reference values for iswd and physiological responses to the iswt , which can be properly estimated by determining simple demographic and anthropometric characteristics in healthy adults  40 years of age . the iswt could be used in assessing physical fitness in the general adult population and in designing individualized walking programs . 
 
OBJETIVO:
MTODOS:
RESULTADOS:
CONCLUSES:
Introduction
Methods
Results
Discussion
Acknowledgments