measurements of spatio - temporal parameters of gait are used to identify walking 
 difficulties for diagnostics1 , and to 
 determine prognosis2 . the most common 
 parameters selected for gait analysis are spatio - temporal parameters , which include walking 
 speed , cadence , step length , stance time , swing time , and double support time3 . these parameters are commonly measured by 
 video - based visual observation4 , 5 , using a stopwatch6 , or using paper walkways7 , 
 8>. however , these methods require considerable time , are labor - intensive , and 
 are prone to inter - examiner and test - retest errors . consequently , gait analysis system using 
 computers are being increasingly used to obtain objective and accurate measurements of 
 spatio - temporal gait parameters in clinical settings9 , 
 10 . the gaitrite system is a portable walkway system that calculates spatio - temporal parameters 
 using a pressure sensor mat . it is already in use in clinical settings as its results 
 correspond well with those of other tests11,12,13 
 and it produces reliable results for subjects with various diseases14,15,16,17 . the 
 optojump system ( microgate , bolzano , italy ) is being used to measure 
 functional parameters relevant to sporting activities such as vertical jumping . since its 
 validity and reliability are known , this system is widely used in clinical settings for 
 assessment and research purposes18,19,20 . when the optojump system was upgraded to optogait , it received attention as a 
 possible means of analyzing gait and functional movement , as well as for measuring and 
 recording spatio - temporal parameters . the optogait system ( optogait , microgate s.r.i , italy , 
 2010 ) is composed of photoelectric cells sited along transmitting - receiving bars of 1  m in 
 length that can be extended to 100  m with a maximum distance of 6  m between them . the 
 transmitting - receiving bars contain infrared led diodes , which enable communication between 
 the two bars . when a subject passes between the transmitting bar and receiving bar , the 
 system automatically calculates spatio - temporal parameters by sensing interruptions in 
 communication . the assessment results of a gait analysis system should be both valid and reliable . concurrent validity can be established when concurrent measurements obtained from a device 
 are verified to meet certain standards21 . 
 furthermore , the reliability of a gait analysis system is essential to determine whether a 
 measure is actually due to a change in actual gait pattern rather than a systematic 
 measurement error , in addition to determining differences in gaits between test 
 sessions14 . in a recent study , it was 
 reported that the gaitrite and optogait systems lack test - retest reliability of the elderly 
 as well as total knee arthroplasty patients22 . to use the optogait system to assess spatio - temporal gait 
 parameters of different subjects , thus , the aims of this study were to provide useful information 
 on the optogait photoelectric cell system by measuring the spatio - temporal gait parameters 
 of healthy adults walking at a comfortable speed , by examining the concurrent validity of 
 the optogait versus the gaitrite system , and by assessing its test - retest reliability . twenty young and healthy subjects ( age = 27.35  7.4  years ) , recruited from among the staff 
 and students of a university , voluntarily participated in the experiment ( 9 females , 11 
 males ; height 170.9  8.8  cm ; weight 62.3  12.4  kg ; bmi 21.13  2.7  kg / m ) . subjects were free from any cardiovascular , neurological , or musculoskeletal diseases , and 
 had no walking difficulties . the study was conducted after obtaining approval from the 
 ethics committee of sahmyook university , and all participants provided their written 
 informed consent . general 
 information , including height and weight , was recorded . to measure gait parameters , walk 
 slowly at a comfortable speed  from 3  m in front of the walkway until 2  m beyond the end , 
 after which they were instructed to turn around and walk back to the starting point . a 
 3-minute interval was given between individual assessments to transmit and save the data as 
 well as to prepare for the next assessment . participants took part in the experiment wearing 
 socks but not shoes . only steps in the sensor areas spatio - temporal gait parameters were measured by placing the optogait unit on the gaitrite 
 unit and operating both simultaneously . for the optogait system ( optogait , microgate s.r.i , 
 italy , 2010 ) , the transmitting - receiving bars were 4  m long with a distance of 0.6  m between 
 them . ninety - six led diodes are positioned on each bar 1  cm apart at 3  mm above the ground . when subjects pass between two bars positioned in parallel with the ground , transmission and 
 reception are blocked by their feet . timing , size , and distance are sensed , and 
 spatio - temporal parameters are automatically calculated . data were extracted at 1,000  hz and 
 saved on a pc using optogait version 1.6.4.0 software ( microgate s.r.i , italy ) . the gaitrite electronic walkway system ( gaitrite , cir system , inc . , ny , usa , 2011 ) used in 
 this study was of standard size ( length 460  width 89  height 0.625  cm ) and contained 
 13,824 pressure sensors spaced at intervals of 1.27  cm , arranged in a grid formation . these 
 pressure sensors are located on a mat , 3.6  m in length and 0.61  m in width . when subjects 
 walk on the mat , sensors react to the contact . using these reactions as an input , size , 
 distance , and time data 
 were extracted at 80  hz , and the system was connected to a pc via a serial interface cable . data saved on the computer were analyzed using gaitrite gold version 4.45 gait analysis 
 software ( cir systems ny , usa ) . data were analyzed using spss version 19.0 . the spatio - temporal gait parameters measured 
 were speed , cadence , step length , step time , stride length , single limb support time , double 
 limb support time , and swing and stance times . the results are presented as means and standard deviations of 3 measurements taken at a 
 comfortable walking speed . the paired t - test was used to determine systematic differences 
 between the gait parameters obtained using the two systems . concurrent validities between 
 optogait and gaitrite were calculated using iccs ( 2 , 1)21 , 23 . coefficients of 
 variation of method errors ( cvme)24 and 95% limits of agreement ( loa)25 were calculated for the absolute comparison of parameters obtained 
 using the two systems . as shown in the formula below , cvme values were converted 
 into percentages by calculating coefficients of variation of method errors obtained using 
 the standard deviations of differences between the results obtained using the two 
 systems24 , and 95% loa values were 
 calculated as described by bland and altman25.me = sd / 
 2cvme = 2me / ( x1+x2 )  100% the test - retest reliabilities of gait parameters measured using the optogait system were 
 expressed as iccs ( 3 , 1 ) by comparing gait parameters obtained in the first and third 
 sessions , as described by shrout and flessiss23 . the paired t - test was used to identify systematic differences 
 between the two sessions . for absolute comparison of the results obtained during the two 
 sessions , cvme24 and 95% 
 loa25 in addition , standard errors of measurement 
 ( sem ) were calculated to measure the range of error of each gait parameter . sem were 
 calculated according to the formula sd  ( 1  icc2 , 1 ) using the higher of the 
 two sd measurements . for convenience of interpretation , sem were expressed as the 
 percentages of mean values ( sem%)25 . in 
 addition , to determine the smallest amount of change that is real and beyond the bound of 
 measurement error , minimum detectable changes ( mdc95 ) at a confidence level of 
 95% were calculated . this was performed by conversion to the percentage of the mean 
 ( mdc95% ) after calculating it using the formula 2  1.96  sem23 , 26 . the mean and standard deviations of the spatio - temporal gait parameters are presented in 
 table 1table 1 . mean ( sd ) of spatiotemporal gait parameters of subjects and concurrent validity 
 measured with gaitrite and optogaitgait parametersgaitriteoptogaiticc ( 2,1 ) 95%ci95% loacv(%)speed ( m / s)1.16 ( 0.18 ) 1.18 ( 0.17 ) * * * 0.993 ( 0.9880.996)0.0620.0221.37cadence ( steps / min)103.84 ( 10.17 ) 105.08 ( 10.10 ) * * * 0.988 ( 0.9800.993)4.431.861.00step length lt . ( cm)67.56 ( 5.11 ) 67.77 ( 5.18 ) * 0.991 ( 0.9840.994)1.5871.1680.56step length rt . ( cm)66.65 ( 6.01 ) 67.07 ( 6.16 ) * * * 0.996 ( 0.9930.997)1.7121.1350.61step time lt . ( cm)134.05 ( 10.55 ) 134.40 ( 10.65 ) * * * 0.998 ( 0.9970.999)1.6650.9790.32stride length rt . ( cm)134.59 ( 11.19 ) 134.94 ( 11.30 ) * * * 0.998 ( 0.9970.999)1.6720.9810.32sls lt . ( s)0.43 ( 0.04 ) 0.41 ( 0.04 ) * * * 0.973 ( 0.9560.984)0.0050.0413.98sls rt . ( s)0.43 ( 0.04 )   0.41 ( 0.04 ) * * * 0.969 ( 0.9480.981)0.0060.0424.07dls ( s)0.27 ( 0.05 ) 0.31 ( 0.06 ) * * * 0.963 ( 0.9390.978)0.0740.01911.30stance phase lt . ( s)0.72 ( 0.08 ) 0.75 ( 0.08 ) * * * 0.929 ( 0.8830.957)0.0910.0273.60stance phase rt . ( s)0.72 ( 0.08 ) 0.75 ( 0.09 ) * * * 0.953 ( 0.9220.971)0.0840.0183.36swing phase lt . ( s)0.43 ( 0.04 ) 0.41 ( 0.04 ) * * * 0.969 ( 0.9480.981)0.0060.0424.07swing phase rt . ( s)0.43 ( 0.04 ) 0.41 ( 0.04 ) * * * 0.973 ( 0.9560.984)0.0050.0413.98icc , intra - class correlation coefficient ; loa , limits of agreement ; cvme , 
 coefficients of variation of method error ; sls , single limb support ; dls , double limb 
 support . significant difference between the two measuring instruments ( * , p < 0.05 ; 
 * * * , p  0.001 ) . the paired t - test was used to determine systematic differences between the 
 gait parameter values obtained by the two systems , and it was found that all spatio - temporal 
 parameters were significantly different , except step time . speed , cadence , step length , 
 stride length , dls time , and stance phase were greater in the optogait system , whereas sls 
 time and swing phase were longer in the gaitrite system . icc , intra - class correlation coefficient ; loa , limits of agreement ; cvme , 
 coefficients of variation of method error ; sls , single limb support ; dls , double limb 
 support . significant difference between the two measuring instruments ( * , p < 0.05 ; 
 * * * , p  0.001 ) with regard to the spatio - temporal gait parameters , the concurrent validity between the two 
 systems was excellent with icc ( 2 , 1 ) within the range of 0.9290.998 . cvme were 
 relatively small for speed , cadence , step length , step time , and stride length ( 0.321.37% ) , 
 whereas they were relatively large for sls , dls ( 3.9811.30% ) , stance phase ( 3.373.60% ) , 
 and swing phase ( 3.984.07% ) . at 95% loa , sls ( lt . 0.0050.041 ; rt . 0.0060.042 ) , dls 
 ( 0.074  0.019 ) , and swing phase ( lt . 0.0060.042 ; rt . 0.0050.041 ) did not contain zero 
 and were skewed to one side ( table 1 ) . mean ( sd ) of the gait parameters and test - retest reliability of optogaitgait parameterssession 1session 3icc ( 3 , 1 ) 95%ci95% loacv ( % ) semsem%mdc95mdc95%speed ( m / s)1.18 ( 0.19 ) 1.18 ( 0.18)0.952 ( 0.8830.981 ) 0.0180.1162.740.043.530.129.78cadence ( steps / min)104.46 ( 10.10 ) 105.78 ( 9.35)0.949 ( 0.8760.979 ) 4.7807.4201.682.282.176.326.01step length lt . ( s ) 0.59 ( 0.07 ) 0.58 ( 0.06)0.828 ( 0.6160.928 ) 0.0790.0732.720.034.960.0813.76step time rt . ( s)0.42 ( 0.04 ) 0.41 ( 0.03)0.789 ( 0.5410.911 ) 0.0560.0362.590.024.430.0512.27dls ( s)0.32 ( 0.06 ) 0.32 ( 0.05)0.899 ( 0.7640.959 ) 0.0470.0524.060.025.960.0516.52stance phase lt . ( s)0.41 ( 0.04 ) 0.40 ( 0.04)0.789 ( 0.5410.911 ) 0.0560.0393.280.024.540.0512.58icc , intra - class correlation coefficient ; loa , limits of agreement ; cvme , 
 coefficients of variation of method error ; sem , standard error of measurement ; mdc , 
 minimum detectable change ; sls , single limb support ; dls , double limb support shows the means and standard deviations of gait parameters of the first and 
 third sessions obtained by the optogait system . the results of the paired t - test indicate 
 that there was no significant difference between the two sessions . icc , intra - class correlation coefficient ; loa , limits of agreement ; cvme , 
 coefficients of variation of method error ; sem , standard error of measurement ; mdc , 
 minimum detectable change ; sls , single limb support ; dls , double limb support test - retest reliability of the gait parameters between these two sessions showed a high 
 level of correlation with icc ( 3 , 1 ) within the range of 0.7850.952 . the cvme 
 values of all parameters were relatively low , ranging from 1.66% to 4.06% . for the two sessions , 
 all parameters showed a low level of sem between 2.175.96% , indicating strong and absolute 
 reliability . mdc95% values ranged from 6.0116.52% , indicating a low level of 
 variation between the two sessions ( table 
 2 ) . this study was conducted to investigate the concurrent validity between the optogait and 
 gaitrite systems with respect to the measurement of spatio - temporal gait parameters as well 
 as to examine the test - retest reliability of optogait of healthy young adults . systematic differences were found between the spatio - temporal parameter measurements made 
 by the two systems . single limb support time and swing phase time were both 4.65% higher as 
 determined by the gaitrite system . however , by the optogait system , double limb support time 
 and stance phase time were 14.81% and 4.17% higher , respectively . as described by lienhard 
 et al.22 , the led diodes of the optogait 
 system are positioned 3  mm higher than the pressure mat of gaitrite , and sensing of heel 
 contact occurs sooner , and sensing of toe lift - off occurs later in the gait cycle . systematic differences were also found for speed , cadence , step length , and stride length . in contrast to the study by lienhard et al.22 , measurements by optogait were slightly greater than those by 
 gaitrite . a previous study compared one 
 side of the lower leg of elderly people , who had a wide base due to obesity ( average weight : 
 79.6  kg , height : 171  cm , and bmi : 26.97 ) , with the affected limb of total knee arthroplasty 
 patients . most participants could not walk in a straight line and gait asymmetry was 
 observed . in consequence , the gaitrite system , considering the line of progression , had a 
 larger value than that of the optogait system , which quantifies step length parallel to the 
 bars regardless of the line of progression . however , considering that this study was 
 conducted with normal healthy adults who tend to walk in a straight line , the slightly 
 higher measurement obtained using the optogait system is probably attributable to 
 differences in the equipment , including sensor type and spacing . despite systematic differences between the two systems , a high level of correlation was 
 found between the two systems with icc within the range of 0.9290.998 , which is similar to 
 the icc of > 0.933 reported by lienhard et al.22 menz et al.14 
 suggested that although icc is a more appropriate indicator of reliability than simple 
 correlation coefficients ( pearson s r , spearman s rho ) , a higher icc does not necessarily 
 mean high reliability . if the values of a sample are distributed over a wide range , a 
 relatively high icc can be achieved , even though score differences between the two 
 measurements are widely distributed . thus , it has been asserted that both coefficients of 
 variation and limits of agreement25 must 
 be used simultaneously in order to reduce the effects of such intrinsic limitations , and to 
 ensure absolute reliability . cvme expresses the differences between values 
 obtained using the two systems as a percentage . by doing so , cvme can be used as 
 a clinically useful indicator of consistency , since it is unaffected by sample 
 heterogeneity14 . 95% loa represents the 
 expected range of the difference between two measurements , and it is used to identify the 
 presence of significant bias between two measurements when they are measured repeatedly . the cvme for all spatio - temporal gait parameters obtained using the two systems 
 were low , and 95% loa values were distributed over a narrow range . however , the 
 cvme for sls ( 3.98% , 4.07% ) , dls ( 11.30% ) , stance phase ( 3.60% , 3.36% ) , and 
 swing phase ( 4.07% , 3.98% ) were relatively higher than those for speed ( 1.37% ) , cadence 
 ( 1.00% ) , step length ( 0.56% , 0.61% ) , step time ( 0.49% , 0.52% ) , and stride length ( 0.32% , 
 0.32% ) , indicating large differences between each measured parameter . similarly , the 95% loa 
 values of sls , dls , and swing phase did not include zero or were skewed to one side compared 
 to other values , indicating the presence of systematic bias . these results can be attributed 
 to the different characteristics of the measurement methods used by the two systems , as 
 mentioned earlier . this study demonstrated high test - retest reliability and consistency with respect to the 
 derivation of spatio - temporal gait parameters of healthy young adults using the optogait 
 system . for all parameters , icc was > 0.789 , indicating excellent test - retest 
 reliability . moreover , cvme values for all parameters were between 1.664.06% , 
 and 95% loa values including zero were within a narrow range with a symmetric distribution . these findings indicate slight changes between repeated measures using optogait , and 
 systematic bias was rarely observed . sem is a quantitative 
 expression of the range of error that can occur whenever the same participant repeats 
 certain tests21 . in this study , sem 
 calculated for test - retest were converted to percentages of mean values ( sem % ) and showed a 
 low level of measurement error , between 2.175.96% , indicating strong absolute 
 reliability . mdc is defined as the minimum change that can occur during measurement , not due to 
 accidental change . since it represents the degree of sensitivity to change , mdc is needed to 
 assess whether or not actual change occurs during the performance of two sessions27 . this value can be a straightforward 
 criterion for assessing changes in a performed process . mdc values calculated in this study 
 were relatively low ( 6.0116.52% ) when expressed as a percentage of means . this means that 
 the measurements were sufficiently sensitive to change and indicate that all spatio - temporal 
 parameters measured using the optogait system can be usefully used to sense changes that 
 occur in the gait process . in this study , we demonstrated that the optogait photoelectric cells system is a valid 
 instrument for the assessment of spatiotemporal gait parameters of healthy young adults , and 
 this is the first study of its kind to examine the test - retest reliability optogait . the 
 optogait system has the benefit of being quick to setup , simple to use , and it is 
 inexpensive , making it attractive to clinicians who need accurate gait data . however , when 
 measuring gait parameters using the optogait system , the gait characteristics of subjects 
 should be considered . for example , it is difficult to use measurement equipment for a 
 subject who drags his / her foot while walking , walks with step length shorter than his / her 
 foot length , or uses an assistive device like a cane . in addition , studies are 
 needed to determine the suitability and validity of equipment , including electromyography 
 ( emg ) and treadmills . clinicians could implement the assessment of spatio - temporal gait 
 parameters using optogait in a clinical setting or by monitoring patient progress during an 
 intervention .
[ purpose ] the purpose of this study was to investigate the concurrent validity and 
 test - retest reliability of the recently introduced optogait photoelectric cell system for 
 the assessment of spatio - temporal parameters of gait . 
 [ subjects ] twenty healthy young 
 adults ( mean age = 27.35 , sd = 7.4 ) were asked to walk 3 times on walkway at a comfortable 
 speed . [ methods ] concurrent validity was assessed by comparing data obtained using the 
 optogait and gaitrite systems , and reliability was assessed by comparing data from the 
 first and third optogait sessions . [ results ] concurrent validity , as identified by 
 intra - class correlation coefficients ( icc ( 2 , 1 ) = 0.9290.998 ) , coefficients of variation 
 ( cvme = 0.3211.30% ) , and 95% limits of agreement , showed high levels of 
 correlation . 
 in addition , the test - retest reliability of the optogait photoelectric cell 
 system was demonstrated as showing a high level of correlation with all spatio - temporal 
 parameters by intra - class correlation coefficients ( icc ( 3 , 1 ) = 0.7850.952 ) , 
 coefficients of variation ( cvme = 1.664.06% ) , 95% limits of agreement , 
 standard error of measurement ( sem = 2.175.96% ) , and minimum detectable change 
 ( mdc95% = 6.0116.52% ) . 
 [ conclusion ] the optogait photoelectric cell system 
 has strong concurrent validity along with relative and absolute test - retest reliabilities . 
 this portable system with easy - to - use features can be used for clinical assessments or 
 research purposes as an objective means of assessing gait .