thanks 
 to dynamic stability , a subject displaces and controls the center of gravity ( cog ) within 
 the base of support in dynamic functional conditions , performing complex combined movements 
 such as striding forward ( forward - lunge , fl ) , going up and down a step ( step - up - over , suo ) , 
 and standing up from a seated position ( sit - to - stand , sts)1 .
many researchers have studied the ability of the computerized dynamic posturography to 
 characterize several features of balance in different populations2 , 3 .
this test provides 
 accurate values regarding parameters such as impact , rising , distance , time , impulse and cog 
 sway , during the aforementioned movements in dynamic functional conditions3 . using computerized dynamic posturography
, 
 these tests show the balance impairments of patients who could benefit from rehabilitation 
 treatment during activities of living involving dynamic conditions4 .
however , only one study has reported the reliability of the 
 fl and suo dynamic functional tests and none have reported the reliability of the sts 
 test5 , which makes the clinical 
 applicability of these dynamic balance tests controversial . in this study ,
the intrasession 
 and intersession reliability of measurements obtained in the fl , suo and sts tests were 
 assessed .
this study also calculated the standard error of measurement ( sem ) , which shows 
 the ability of the tests to exclude the noise from measurements6 , 7 .
the absolute and 
 relative minimal detectable changes ( mdc ) were also calculated to estimate the real change 
 between two measurements of the same subject across time , as this parameter is clinically 
 more relevant8 .
the sample size was 
 determined considering a two - tailed hypothesis , a 0.05 type i error , a 0.93 intraclass 
 correlation coefficient ( icc ) estimated for the impulse variable in the fl test and a 0.075 
 accuracy level9 .
forty - five healthy subjects were randomly selected from the general university population 
 ( 24 males and 21 females ; 23.89  5.49  years ; 1.69  0.08  cm ; 68.43  10.97  kg ; 32 
 right - handed , 12 left - handed , 2 ambidextrous ) .
subjects with balance affectation10 , musculoskeletal diseases or related 
 surgery , or previous balance training were excluded . before beginning the tests , each 
 participant signed an informed consent form .
the ethics committee of seville university 
 approved this study ( code : m2012/024/20130226 ) , which was carried out at the physiotherapy 
 unit of a sports medicine center .
measurements were carried out using the platform balance master system 8.2 
 ( usa ) under controlled laboratory conditions by an experienced examiner , and following a 
 standardized protocol so all the participants were given directions in the same way .
data 
 were collected in two assessment sessions , 68 days apart . during the first session ,
initially , the participants practiced 
 each dynamic test to acquaint themselves with the movement exertion when receiving a visual 
 prompt from a screen10 .
, the three tests were performed only once , with 
 three trials performed for each .
forward - lunge ( fl ) test : the participants stayed as upright and as still 
 as possible on the platform .
on seeing the prompt go on the screen , they moved their foot 
 forward as far and fast as they could , bending the knee .
the trunk was kept in a vertical position while the cog 
 transferred from one foot to the other quickly .
the subjects were instructed not to use 
 their arms for help during the movement .
the outcome variables 
 were the distance reached ( distance ) defined as the stride length , measured from the cog 
 location during the standing position to the furthest point reached by the cog while 
 stepping forward , expressed as a percentage of the subject s height ( % ) .
the impact index 
 was defined as the maximal reaction force generated by the swinging forward leg when it 
 contacted the ground , expressed as a percentage of the body weight ( % ) .
the contact time 
 ( contact time ) was defined as the lapse of time ( s ) between the moment when the swinging 
 forward leg left the ground to when it made contact with the ground again ; and the impulse 
 force was defined as the total amount of work done by the swinging forward leg during the 
 stance phase , and the push back force of the movement , expressed as a percentage of the body 
 weight multiplied by the time that the force was exerted ( %  s ) .
the mean of three trials 
 per test was used following the manufacturer s protocol and previous recommendations 
 regarding the highest relative and absolute reliabilities of biomechanical variables in the 
 forward - lunge test11 .
step - up - over ( suo ) test : the participants stayed as upright and as still 
 as possible on the platform .
on seeing the prompt go on the screen , they put one foot on a 
 21-cm high step and then lifted the other foot , passed it over the step without touching it 
 and placed it back on the ground .
the outcome variables were : the lift - up index , defined as the 
 maximal strength exerted by the lower limb on the step during the lift - up phase , expressed 
 as a percentage of the body weight ( % ) ; the movement time , defined as the lapse of time when 
 it contacted the ground again ; and the impact index , defined as the maximal reaction force 
 generated by the swinging forward leg when it contacted the ground again , expressed as a 
 percentage of the body weight ( % ) .
although the platform manufacturer states that this test 
 should be carried out  quickly  , in our prior experience we observed that this instruction 
 resulted in performance of the movement while  running  .
this caused the other variables  the 
 lift - up index and impact index  to exhibit characteristics not related to the subjects 
 behaviors in activities of daily living .
as a consequence , the participants were instructed 
 to mount the step in a  spontaneous  way , as they would in normal daily life .
sit - to - stand ( sts ) test : the participants sat quickly on a 41-cm high box 
 placed on the platform . on seeing the prompt go on the screen , they stood up as quickly as 
 possible without using their arms and stood still .
the outcome variables were the rising 
 index , defined as the maximal strength exerted by the lower limbs during the rising phase , 
 expressed as a percentage of the body weight ( % ) , and the cog sway velocity ( cog sway 
 velocity ) , defined as the velocity of the cog during the rising phase and the next five 
 seconds ( /s ) .
each test was carried out three times and the mean was 
 used the statistical analysis .
the mean as well as 
 the differences between each pair of measurements were calculated ( the first was compared to 
 the second one for intrasession reliability , and the first to the third , for intersession 
 reliability ) giving the sixteen variables , and the skewness coefficient and the kurtosis 
 were also calculated also .
the relative reliability was analyzed considering the icc , which was calculated following 
 two procedures : a two factor mixed - effect model ( icc a ) with absolute agreement ; and a one 
 factor random - effect model ( icc b ) .
the absence of a systematic error in the measurements 
 was verified due to the equality of icc a and the icc b12 .
the sem was calculated following the stratford and goldsmith procedure7 . the absolute reliability or 
the repeatability , also known as minimal 
 detectable change ( mdc95 ) because it refers to  the minimal change that falls 
 outside the measurement error of an instrument used to measure a symptom14 , was calculated using the equations : sem  
 1.96  2 , 95% confidence level . according to one - way analysis of variance ( one - way anova ) , 

the square root of the quadratic mean of the residual from the intrasubject effect test is 
 the intrasubject standard deviation , which allows calculation of the systematic error12 , 13 .
the sem and the mdc95 were also calculated as percentages 
 of the measurement mean6 , 8 . in this way ,
therefore , mdc95 indicates a real change with 95% confidence for 
 individual participants and demonstrates the repeatability of the test .
the statistical tests were performed using a 95% confidence interval ( ci ) ( p<0.05 ) .
fifty subjects were enrolled , but five of them dropped out from the second session due to 
 issues not related to the research .
for that reason , 
 the estimated icc value for a 0.075 accuracy level was 0.902 .
table 1table 1.mean values , standard deviations and ranges of unilateral and bilateral variables 
 in the forward - lunge , step - up - over and sit - to - stand testssession 1 : trial 1session 1 : trial 1session 2forward - lungemean ( sd)rangemean ( sd)rangemean ( sd)rangedistance ( % ) right56.5 ( 6.3)(4069)56.6 ( 6.2)(3969)56.8 ( 6.2)(4369)left56.3 ( 5.8)(4167)55.8 ( 6.0)(4269)56.3 ( 6.0)(4470)impact index ( % ) right27.4 ( 7.6)(1250)26.3 ( 7.1)(1546)27.3 ( 6.8)(1549)left26.7 ( 6.7)(1241)25.8 ( 6.3)(1541)27.9 ( 6.8)(1745)contact time ( s)right1.0 ( 0.2)(0.51.3)1.0 ( 0.2)(0.61.4)1.0 ( 0.2)(0.61.4)left1.0 ( 0.2)(0.61.4)1.0 ( 0.2)(0.61.3)1.0 ( 0.2)(0.61.4)impulse force ( % xs)right106.8 ( 16.3)(69139)106.6 ( 17.2)(64144)107.4 ( 16.1)(73148)left104.3 ( 16.4)(71142)103.8 ( 15.3)(72134)104.6 ( 15.4)(75145)step - up - overlift - up index ( % ) right43.0 ( 9.3)(1860)48.9 ( 11.2)(2377)48.3 ( 11.8)(2280)left40.2 ( 9.7)(1861)43.8 ( 10.0)(1968)45.4 ( 12.0)(1979)movement time ( s)right1.3 ( 0.2)(1.01.7)1.2 ( 0.2)(0.91.5)1.2 ( 0.2)(1.01.6)left1.3 ( 0.2)(1.01.7)1.2 ( 0.1)(0.91.5)1.2 ( 0.2)(0.91.6)impact index ( % ) right42.1 ( 13.1)(1174)44.4 ( 13.7)(1579)43.5 ( 13.6)(1176)left44.1 ( 12.7)(2070)48.0 ( 13.6)(1580)47.6 ( 14.4)(1785)sit - to - standrising index ( % ) 29.6 ( 8.5)(1250)31.9 ( 8.4)(1749)32.3 ( 8.9)(1854)cog swayvelocity ( /s)3.1 ( 1.1)(1.05.4)3.4 ( 1.0)(1.25.3)3.4 ( 1.0)(1.25.4)cog : center of gravity ; sd : standard deviation ; distance ( % subject s height : cm ) , 
 impact index ( % body weight :  kg ) , contact time ( s ) , force impulse ( % body weight :  kg  
 time : s ) lift - up index ( % body weight :  kg ) , movement time ( s ) , rising index ( % body 
 weight :  kg ) , cog sway velocity ( /s ) gives a descriptive analysis of the collected data .
the normality of all the 
 variables registering a skewness coefficient and kurtosis 1.5 was calculated . in all cases , 

icc a was not different from icc b , implying that there were no systematic errors . 

accordingly , only icc a is shown in tables 
 2table 2.forward-lunge testintrasessionintersessionicc ( 95% ci)sem ( % ) mdc95 ( % ) icc ( 95% ci ) sem ( % ) mdc95 ( % ) distance ( % ) right0.9 ( 0.90.9)1.8 ( 3.1%)4.9 ( 8.6%)0.9 ( 0.80.9)2.2 ( 3.8%)6.0 ( 10.6%)left0.9 ( 0.91.0)1.7 ( 3.0%)4.7 ( 8.3%)0.9 ( 0.70.9)2.3 ( 4.2%)6.5 ( 11.5%)impact index ( % ) right0.8 ( 0.60.9)3.4 ( 12.6%)9.4 ( 34.8%)0.6 ( 0.40.7)4.3 ( 15.9%)11.9 ( 44.1%)left0.8 ( 0.60.9)3.1 ( 11.4%)8.5 ( 31.7%)0.7 ( 0.50.8)3.8 ( 14.4%)10.7 ( 39.8%)contact time ( s)right0.9 ( 0.80.9)0.1 ( 6.1%)0.2 ( 16.2%)0.7 ( 0.50.8)0.1 ( 10.1%)0.3 ( 27.3%)left0.9 ( 0.80.9)0.1 ( 5.2%)0.1 ( 13.5%)0.8 ( 0.60.9)0.1 ( 8.3%)0.2 ( 22.9%)impulse forceright0.9 ( 0.80.9)5.8 ( 5.4%)16.1 ( 15.1%)0.7 ( 0.50.8)9.4 ( 8.8%)26.0 ( 24.3%)(%xs)left0.9 ( 0.80.9)5.1 ( 4.9%)14.2 ( 13.6%)0.8 ( 0.70.9)7.2 ( 6.9%)20.0 ( 19.2%)ci : confidence interval ; icc : intraclass correlation coefficient ; mdc : minimal 
 detectable change ; sem : standard error mean ; distance ( % subject s height : cm ) , impact 
 index ( % body weight :  kg ) , contact time ( s ) , impulse force ( % body weight :  kg  time : 
 s ) p<0.001 , 3table 3.step-up-over testintrasessionintersessionicc ( 95% ci ) sem ( % ) mdc95 ( % ) icc ( 95% ci ) sem ( % ) mdc95 ( % ) lift - up index ( % ) right0.6 ( 0.20.8)5.1 ( 11.0%)14.2 ( 30.5%)0.7 ( 0.30.9)5.0 ( 10.7%)13.8 ( 29.5%)left0.7 ( 0.40.8)5.3 ( 12.4%)14.7 ( 34.2%)0.6 ( 0.30.8)6.0 ( 14.0%)16.7 ( 38.8%)movement time ( s)right0.7 ( 0.30.9)0.1 ( 5.7%)0.2 ( 15.3%)0.6 ( 0.40.8)0.1 ( 8.1%)0.3 ( 21.8%)left0.5 ( 0.10.8)0.1 ( 7.1%)0.3 ( 19.8%)0.5 ( 0.10.8)0.1 ( 7.9%)0.3 ( 21.4%)impact index ( % ) right0.8 ( 0.70.9)5.0 ( 11.5%)13.8 ( 31.8%)0.9 ( 0.80.9)5.0 ( 11.4%)13.7 ( 31.7%)left0.7 ( 0.50.8)6.7 ( 14.3%)18.5 ( 39.7%)0.7 ( 0.50.8)7.0 ( 15.0%)19.3 ( 46.6%)ci : confidence interval ; icc : intraclass correlation coefficient ; mdc : minimal 
 detectable change ; sem : standard error of mean ; lift - up index ( % body weight :  kg ) , 
 movement time ( s ) , impact index ( % body weight :  kg ) p<0.001 and 4table 4.sit-to-stand testintrasessionintersessionicc ( 95% ci)sem ( % ) mdc95 ( % ) icc ( 95% ci)sem ( % ) mdc95 ( % ) rising index ( % ) 0.8 ( 0.60.9)3.4 ( 10.8%)9.4 ( 30.0%)0.7 ( 0.50.8)4.5 ( 14.5%)12.5 ( 40.0%)cog swayvelocity ( /s)0.7 ( 0.50.8)0.6 ( 17.7%)1.6 ( 48.8%)0.6 ( 0.30.7)0.7 ( 21.7%)2.0 ( 59.8%)ci : confidence interval ; cog : center of gravity ; icc : intraclass correlation 
 coefficient ; mdc : minimal detectable change ; sem : standard error of mean ; rising index 
 ( % body weight :  kg ) , cog sway velocity ( /s ) p<0.001 . the weir classification for icc was used15 : scores from 0.50 to 0.69 , good ; from 0.70 to 0.89 , very good ; and 
 from 0.90 , excellent ; sem% lower than 35% , good ; mdc95% lower than 
 30% , reasonable ; and mdc95% lower than 10% , excellent16 .
cog : center of gravity ; sd : standard deviation ; distance ( % subject s height : cm ) , 
 impact index ( % body weight :  kg ) , contact time ( s ) , force impulse ( % body weight :  kg  
 time : s ) lift - up index ( % body weight :  kg ) , movement time ( s ) , rising index ( % body 
 weight :  kg ) , cog sway velocity ( /s ) ci : confidence interval ; icc : intraclass correlation coefficient ; mdc : minimal 
 detectable change ; sem : standard error mean ; distance ( % subject s height : cm ) , impact 
 index ( % body weight :  kg ) , contact time ( s ) , impulse force ( % body weight :  kg  time : 
 s ) p<0.001 ci : confidence interval ; icc : intraclass correlation coefficient ; mdc : minimal 
 detectable change ; sem : standard error of mean ; lift - up index ( % body weight :  kg ) , 
 movement time ( s ) , impact index ( % body weight :  kg ) p<0.001 ci : confidence interval ; cog : center of gravity ; icc : intraclass correlation 
 coefficient ; mdc : minimal detectable change ; sem : standard error of mean ; rising index 
 ( % body weight :  kg ) , cog sway velocity ( /s ) p<0.001 table 2 shows icc and 95% confidence intervals 
 of the fl test .
they were excellent to very good for the intrasession reliabilities ( range 
 0.90.8 ) , and very good to good for the intersession reliabilities ( range 0.90.7 ) .
the sem% 
 scores for all the parameters were much lower than 35% and the mdc95% of most of 
 the parameters were lower than 30% ( except for the impact index ) , with excellent scores 
 ( around 10% ) for the distance variable , which was the most reliable , followed by the impulse 
 and the contact time .
they were very good to good for the 
 intra- and inter - session reliabilities ( range 0.90.5 ) .
the sem% scores of all the 
 parameters were much lower than 35% and the mdc95% scores of most of all the 
 parameters were around 30% , though the lift - up and impact index of the suo showed poorer 
 ability to detect real change than the fl variables .
table 4 shows the iccs ( 95% ci ) of the sts test , which were very good for the 
 intrasession reliability ( range 0.80.7 ) and very good to good for the intersession 
 reliability ( range 0.70.6 ) .
the sem% scores of both parameters were much lower than 35% and 
 the most reliable variable was the rising index , which had an intersession mdc95% 
 of 30% , whereas the cog sway exceeded this limit in intra- and inter - session 
 reliabilities .
the main finding of this study was the good absolute reliability of most fl variables , 
 which means that this test is a potential diagnosis tool for musculoskeletal diseases . 

however , comparisons with other research are difficult due to the icc 
 context - dependence17 , 18 the icc being affected by factors such as the number of 
 subjects , the number of repetitions , the lapse of time between assessment sessions , the 
 protocol followed , the number of examiners and systematic errors7 . however , the 0.9 icc hypothesis for the impulse variable of 
 the fl test was not been proven , as the intersession icc for the impulse values of the fl in 
 the present study were 0.7 and 0.8 for the right and left legs , respectively . the relative variability of the fl measurements made with a 1-week lapse of time 
 ( intersession ) is bigger than that observed between the measurements made during the same 
 session ( intrasession ) .
this shows that time is a factor influencing on the fl parameters 
 intersubject variability .
furthermore , fl contact time may differ with dynamic movement 
 exertion due to anterior cruciate ligament ( acl ) pathology11 .
fl contact time data collected in this present study were longer 
 than those of a study following the same protocol and methods5 , even though subjects were specifically asked in both studies to 
 perform fl as quickly as possible .
the age range and nature of the sedentary subjects 
 enrolled in the present study ( 1840  years compared to 1826 ) might explain the longer 
 contact time duration .
thus , these slight differences may show the impact of age or physical 
 condition on this variable .
the fl contact time was longer in another previous study , possibly because a greater number 
 of test repetitions and the absence of a specific instruction to perform fl as quickly as 
 possible11 .
also , a previous study 
 reported a 270  ms difference in the fl contact time between control and experimental 
 subjects who had not fully recovered from acl surgery19 . in our study
, the absolute reliability of the fl contact time was calculated using the sem 
 values of 50 to 100  ms .
the mdc95 was lower ( 130270  ms ) indicating the ability 
 of the fl test ability to discriminate between subjects with or without acl pathologies .
the 
 fl test was also able to highlight the variation in the fl contact time between two 
 measurements made on the same subject suffering from this kind of pathology .
furthermore , our results for the fl and suo impact when down a step ( similar to a short 
 stride ) are higher than the impact values of a long stride .
since a longer stride elicits 
 less stress than a shorter one , previous studies have reported that the distances achieved 
 ( the stride length ) in the fl test affects the impact force and the stress borne by the 
 patellofemoral joint20 .
therefore , the 
 shorter the step , the bigger the force that the lower limb absorbs . also , the fl test mainly 
 involves the hip extensors ; therefore , it would be worthwhile to investigate whether this 
 test is sensitive and specific to pathologies involving these muscles21 .
similarly , our results for the movement times of the suo test were longer than those of 
 similar studies5 . in the present study
, 
 the subjects were not asked to perform this test quickly as the manufacturer recommends ; 
 rather , they were asked to perform it at that in their daily life .
the difference in 
 instructions may explain the longer times observed in the present study as well as the 
 differences seen in the impact and rising indices , which were lower in the present 
 study .
parameters based on the vertical reaction forces during descending stairs tests are able to 
 monitor the rehabilitation progress after acl surgery22 .
patients suffering from patellofemoral pain minimize the reaction 
 forces both in ascent and descent phase of stairs to maintain normal levels of stress in the 
 joint23 .
accordingly , the suo lift - up 
 and impact index ( derived from the reaction forces ) may show these adaptations .
it is our 
 opinion that this test should be accompanied by other functional tests to help to determine 
 their limitations .
although the relative variabilities of these parameters in our present 
 research were high , their absolute reliabilities persuaded us that this test is a useful 
 tool .
the sts cog velocity exhibited relative and absolute reliability values lower than the sts 
 rising index . in agreement with our present findings ,
goldie et al.25 determined that 
 measurements based on ground reaction forces in a unipedal stance were more reliable than 
 those based on centers of pressure ( cop)25 . the sts and suo rising and lift - up indices theoretically represent 
 similar aspects of the ground reaction forces in two movements of daily living ( going 
 upstairs and standing up ) .
thus , they may complement each other and enhance the possibility 
 of discriminating between subjects with and without a musculoskeletal disease .
a limitation of this study was that the intrasession and intratest reliabilities were 
 calculated from measurements made within 1 hour , which features the internal consistency of 
 the measurements ( i.e. , the ability of the tool to reproduce measurements and the accuracy 
 of the measurements in stable subjects ) . moreover , although the test - retest and 
 intraexaminer reliabilities were calculated , the interexaminer reliability was not .
however , 
 this factor affects the variability of measurements made in tests that depend on the 
 explanation that an examiner gives to subjects ; i.e. results that are based on subjects 
 understanding17 .
consequently , these 
 aspects should be considered when discussing the reliability of the results . in conclusion , the contact time , distance and force impulse variables of the fl test showed 
 excellent absolute and relative reliabilities .
the variables based on cop changes in the sts 
 tests did not show enough reliability in a healthy population .
the collected data establishes a range of normal values for the variables of the tests , as 
 well as relative and absolute reliabilities and mdc95% ( minimal detectable 
 change ) of dynamic postural stability measurements of a healthy population .
 [ purpose ] to examine the intrasession and intersession reliability and the absolute 
 reliability of three functional dynamic tests  forward - lunge , step - up - over and sit - to - stand 
 tests  using computerized dynamic posturography . 
 [ subjects and methods ] an intra - test and 
 test - retest , repeated measure study was designed . 
 forty - five healthy subjects twice 
 carried out the forward - lunge test , step - up - over test , and sit - to - stand test on two days , 
 one week apart . 
 the intrasession and intersession reliabilities as judged by the 
 intraclass correlation coefficient ( icc ) and the minimal detectable change of the three 
 functional tests were calculated . 
 [ results ] excellent to very good intrasession 
 reliability of the forward - lunge test ( icc range of 0.90.8 ) was found . very good to good 
 intrasession reliability of the step - up - over test ( icc range of 0.90.5 ) was found and 
 very good intrasession reliability of the sit - to - stand test ( icc range of 0.80.7 ) was 
 found . 
 the minimal detectable change at the 95% confidence level of most of the measures 
 was lower than 30% . 
 [ conclusion ] the forward - lunge , step - up - over and sit - to - stand tests 
 are reliable measurement tools . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION