balance is the ability to control and maintain the center of gravity of a body toward the 
 base of support in a given environment1 . 

even healthy individuals experience limited function once they lose their ability to 
 balance , and evaluating balance ability makes it possible to predict the risk of falls . 

the equipment used to measure balance ability includes 
 stabilometer3 , good balance system4 , bpm5 , f - scan6 , and 
 biodex balance system7 .
in contrast , smartphones are readily available and do not 
 have substantial temporal or spatial limitations . moreover ,
as smartphones incorporate 
 various sensor technologies , they may be used as measuring equipment for balance ability . 

measurement of the shoulder range of motion using a smartphone was reported by lim et 
 al.9 , and the measurement of heart rates 
 using a smartphone was investigated by matsumura and yamakoshi10 .
however , the reliability of measuring dynamic balance 
 ability using a smartphone was considered in only a few studies .
therefore , the 
 identification of the reliability of smartphones as measuring equipment for dynamic balance 
 ability was the goal of this study .
the subjects in this study were 30 healthy young students in their 20s , attending youngdong 
 university in chungbuk , south korea .
absence of musculoskeletal or neurological disorders 
 affecting the upper or lower extremities and lesions , and zero history of surgery of the 
 spine or upper extremities were the criteria used for selecting the subjects .
the subjects 
 of the study were selected randomly from among those who met the aforementioned criteria . 

the mean age , height , and weight of the subjects were 22.0  0.0  years , 169.2  8.6  cm , and 
 61.9  11.0  kg , respectively .
ethical approval for the study was granted by the 
 institutional review board of youngdong university .
all subjects were fully informed of the 
 objectives and methods of the study beforehand , and informed consent to participate in the 
 experiments was obtained from them .
the footboard of this system can be adjusted from level 1 to 12 
 according to the level of difficulty .
the smartphone used in this study was a galaxy note 4 lte ( sm - n910  k , samsung , 
 korea , 2014 ) with an android 5.1.1v operating system and the application sensor kinetics pro 
 ( ver.2.1.2 , innoventions inc .
the first and second rounds of measurements were taken at a 1-day interval to confirm 
 test - retest reliability . in each round , the dynamic balance ability was measured thrice when 
 the subjects kept their eyes open and thrice when they closed their eyes . during the 
 measurement of balance ability
, a smartphone was attached to the skin between the third and 
 fourth lumbar vertebrae using velcro made of spandex and a plastic bag .
the subjects were 
 instructed to stand on the footboard of biodex balance system with their bare feet together 
 and each of their hands holding their opposite shoulder . the verbal order 
start  was given 
 3  s after the application began running , and the verbal order 
stop  was given around 40  s 
 after the application stopped running ( fig .
1.the smartphone was attached to the skin between the third and fourth lumbar vertebrae 
 using velcro made of spandex and a plastic bag ) .
the smartphone was attached to the skin between the third and fourth lumbar vertebrae 
 using velcro made of spandex and a plastic bag the interclass correlation coefficient ( icc ) was identified using spss 12.0 for statistical 
 analysis in this study .
the values measured for 30  s , excluding the first and last 5  s , were 
 extracted for use .
all gyroscope values were multiplied by 1,000 because the extracted 
 values were too small . for the acceleration and gyroscope values ,
the value for each of the 
 three axes was raised to the second power , and the square root of the sum of the three 
 resultant values was used .
when the eyes of the subjects were open , the acceleration rates were 2.7  2.2 at the first 
 measurement and 3.3  1.5 at the second measurement , and the icc ( 1,1 ) was 0.8 .
when the 
 eyes of the subjects were closed , the acceleration rates were 4.1  2.4 at the first 
 measurement and 4.5  1.8 at the second measurement , and the icc ( 1,1 ) was 0.9 .
when the 
 eyes of the subjects were open , the gyroscope rates were 1.7  1.2 at the first measurement 
 and 2.3  1.5 at the second measurement , and the icc ( 1,1 ) was 0.7 .
when the eyes of the 
 subjects were closed , the gyroscope rates were 6.7  2.4 at the first measurement and 6.6  
 2.3 at the second measurement , and the icc ( 1,1 ) was 0.6 ( table 1table 1.reliability study of dynamic balance abilities measure using a smartphonemean  sdiccfirst second accelerationopen eye2.7  2.23.3
 1.50.8closed eye4.1  2.44.5  1.80.9gyroscopeopen eye1.7  1.22.3  1.50.7closed eye6.7  2.46.6  2.30.6 acceleration : .
anterior and 
 posterior stability were measured using the biodex balance system and a smartphone by 
 patterson et al . ;
no statistically significant difference was reported between the two sets 
 of values11 . in agreement with this 
 previous study
, statistically significant conformity was confirmed in this study too when 
 dynamic balance ability was measured using a smartphone .
timed up - and - go tests conducted 
 using a smartphone were found to be sufficiently reliable and accurate by galn - mercant et 
 al.12 ; in contrast to the present 
 study , an iphone and a different set of tasks were used in the study of galn - mercant et al . 

however , given that in both studies , 
 an inertial sensor in a smartphone was used to identify the potential of a smartphone as the 
 measuring equipment for determining balance ability , similar results have been obtained for 
 both . good balance system s inter - examiner reliability for postural sway measurement in 
 post - stroke patients
biodex balance system s intra - examiner reliability for 
 dynamic balance ability when the subjects stood on one foot was reported to be 0.8 arifin 
 and abu14 .
the peak pressure over the 
 metatarsal heads proved to have the best indices of reliability at approximately 0.8 , and 
 the equivalents for the heel , whole foot , and hallux ranged from 0.5 to 0.8 according to the 
 study by ahroni et al15 . in relation to 
 this , in the present study , an index of at least 0.7 was obtained for all items , except the 
 icc of the gyroscope values , when the subjects closed their eyes . in particular , the icc of 
 all acceleration values was at least 0.8 , showing a high level of conformity .
this suggests 
 that smartphones have sufficient potential as measuring equipment for dynamic balance 
 ability . while the existing expensive devices designed to measure balance ability can 
 provide more varied and specific data regarding balance ability , including sway length , sway 
 area , and sway speed , this study indicates that using a smartphone can present highly 
 limited data regarding balance ability . while the problem of limited data will be overcome 
 to a certain extent with the future development of specialized applications , they are 
 unlikely to replace the existing expensive devices entirely .
however , smartphones may be 
 highly useful in environments in which an expensive device has not been introduced or when 
 dynamic balance ability should be measured in a few hours or immediately .
therefore , based 
 on the findings of this study , specialized applications should be developed to measure 
 dynamic balance ability using smartphones .
in addition , future studies should address 
 various dynamic tasks in terms of the level of difficulty , ages , diseases , and types of 
 smartphones .
 [ purpose ] evaluation of the reliability of smartphones as measuring equipment for dynamic 
 balance ability was the goal of this study . 
 [ subjects and methods ] subjects were 30 
 healthy young students in their 20s . the first and second rounds of measurements were 
 taken at a one - day interval to confirm test - retest reliability . 
 the subjects stood on the 
 footboard of the biodex balance system . 
 balance was measured using a smart phone . 
 
 [ results ] acceleration rates corresponding to subjects with open eyes were 2.7  2.2 
 ( first measurement ) and 3.3  1.5 ( second measurement ) , and the interclass correlation 
 coefficient icc ( 1,1 ) was 0.8 . 
 acceleration rates corresponding to subjects with closed 
 eyes were 4.1  2.4 ( first measurement ) and 4.5  1.8 ( second measurement ) , and the icc 
 ( 1,1 ) was 0.9 . 
 gyroscope rates corresponding to subjects with open eyes were 1.7  1.2 
 ( first measurement ) and 2.3  1.5 ( second measurement ) , and the icc ( 1,1 ) was 0.7 . 
 
 gyroscope rates corresponding to subjects with closed eyes were 6.7  2.4 ( first 
 measurement ) and 6.6  2.3 ( second measurement ) , and the icc ( 1,1 ) was 0.6 . [ conclusion ] 
 the results of this study suggest that smartphones have sufficient potential as measuring 
 equipment for dynamic balance ability . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION