this means 
 that smartphones are used as personal computers as often as they are used to make phone 
 calls . due to conveniences in terms of portability , various smartphone functions
may be 
 utilized while walking or working . in particular , listening to music , sending messages , web 
 surfing , and playing games are frequent activities performed while walking . performing two tasks at the same time
is called dual - tasking , while 
 performing more than two tasks simultaneously is referred to as multitasking1 . walking or working while using
however , such dual - tasking 
 may lead to a fall or injury resulting from decreased cognitive ability in an accidental , 
 unexpected situation .
the ability to maintain balance in a static or dynamic situation is 
 the basis for functional activities while performing various ordinary activities2 .
the dynamic balance necessary for 
 functional activities is the result of interaction among the ankle joints , knee joints , hip 
 joints and their surrounding muscles , and shoulder joints and their surrounding muscles . 

dual- tasking 
 using a smartphone while walking , such as listening to music , sending a message , web 
 surfing , or playing a game , is considered to affect the dynamic balance necessary for 
 functional activities by reducing cognitive ability .
most previous studies concerned electromyography3 , 
 4 on muscles around the neck according 
 to the forward movement of the head bone from the perspective of musculoskeletal system 
 postural misalignment or dispersion of cognitive ability5 according to the performance of dual task
. therefore , the aim of the 
 this study was examine the effects of dual tasks while different functions of a smartphone 
 while walking or working on dynamic balance , based on prior studies of cognitive ability 
 dispersion while dual - tasking .
the subjects of this study were 36 healthy college students ( 18 male , 18 female ) .
their 
 average age , weight , and height were 20.4  years , 63.4  kg , and 168.8  cm .
the subjects had no 
 musculoskeletal or neurological problems , listened to the overall procedure and purpose of 
 this study , and voluntarily consented to participate in the study .
their informed consent 
 and approval from korea nazarene university s life ethics review committee ( korea nazarene 
 university irb 14 - 0417 - 02 ) were obtained .
the samsung galaxy noteii ( samsung , seoul , south korea ) was used for the experiment .
the 
 star excursion balance test ( sebt ) was performed during single - tasking without a smartphone 
 and during dual - tasking with a smartphone , that is , when listening to music using a 
 smartphone , when sending a message using a smartphone , when web surfing using a smartphone , 
 and when playing games using a smartphone . in the experiment conducted while performing a 
 dual task using smartphone functions ,
subjects were assigned experiments via a casting of lots , to prevent 
 them from learning about experimental tasks .
after each experiment , the subjects rested for 
 five minutes before going on to the next experiment .
it was also used to measure the 
 distances a leg could reach when the subjects stretched his / her nondominant leg to maximum 
 extension in eight directions ( anterior , anterior lateral , lateral , posterolateral , lateral , 
 posteromedial , medial , anter medial ) with a 45-degree interval while maintain his / her 
 balance with the dominant leg .
the sebt is a method used to measure dynamic balance , with a 
 level of reliability ( icc 0.880.96)6 .
hyong and kim6 presented three directions  anterior , posterolateral , and 
 posteromedial  as the base directions for a simple sebt ; this study conducted the experiment 
 based on these directions .
measurements were taken for each direction and averaged values 
 were used for analysis . due to differences in each subject
s leg length , a each subject s 
 actual leg length was measured ; the percentages of their leg length were used as the 
 measured values7 .
the actual leg length 
 were measured from the anterior superior iliac spine of the femur to the medial 
 malleolus8 .
the measured values were 
 analyzed with repeated measures analysis of variance using spss version 17.0 .
according to the sebt , the subjects who performed dual tasks using a smartphone saw 
 significant changes in their dynamic balance in the three tested directions relative to 
 those who carried out single tasks without a smartphone ( p<0.05 ) ( table 1table 1 .
sebt results according to the type of double task 
 ( n=36)nusmusicmessageweb surfinggameanterior ( % ) 99.96.796.37.2 * 91.77.7 * 927.3 * 89.97.2*posterolateral ( % ) 82.410.775.610.3 * 69.110.2 * 709.8 * 66.710.2*posteromedial ( % ) 73.8411.0365.111.2 * 57.611.6 * 6012.1 * 53.89.8*nus : did not use a smartphone .
a : nus , music , b : nus , message , c : nus , web surfing , 
 d : nus , game . * : p<0.05 ) .
dynamic balance decreased in all three for playing games , sending messages , 
 web surfing , and listening to music ( table 
 1 ) .
nus : did not use a smartphone . a : nus , music , b : nus , message , c : nus , web surfing , 
 d : nus , game . * : p<0.05
such dual - tasking 
 reduces cognitive ability , affecting postural control . for postural control , sensation , 
 cognition , and
this study aimed to look at the effects of dual - tasking using a 
 smart phone on dynamic balance . according to the results of measuring dynamic balance using 
 the sebt , dynamic balance decreased in all three directions during dual - tasking using 
 smartphone functions relative to single - tasking without using a smartphone .
in addition , dynamic balance decreased in all three directions for playing games , sending 
 messages , web surfing , and listening to music using a smartphone .
playing games most 
 significantly decreased cognitive ability , resulting in the greatest decrease in dynamic 
 balance .
this was followed by sending a message , web surfing , and listening to music in 
 their effect on decrease in dynamic balance . in this experiment , double tasking while 
 listening to music . in this experiment ,
dual - tasking was significantly significant relative 
 to single - tasking , and caution is needed even when listening to music with a smartphone 
 while performing other work ( p<0.05 ) . using the sebt , won1
also measured , in 
 eight directions , dynamic balance during single - tasking without using a smartphone and 
 during dual - tasking when listening to music , making a phone call , and sending a message . 
 according to the dynamic balance results , sending messages most greatly decreased dynamic 
 balance and making a phone call also led to reduced dynamic balance in the lateral 
 direction .
in the present study , 
 dynamic balance decreased in all three directions while sending a message , with a greater 
 decrease in dynamic balance in the posteroateral and posteromedial directions than in the 
 anterior direction .
won1 asserted that 
 dynamic balance decreased while sending a message , and that caution was needed while 
 performing the task . on the other hand
, the present study showed that playing games reduced 
 dynamic balance more than sending messages . in wons1 study , the dual task of listening to music did not influence dynamic 
 balance , but it did in the present study .
this differences is attributed to difference in 
 the kind of and speed of music ; in the present study , the subjects listened to the fast - beat 
 k - pop ( korean pop ) enjoyed by young people .
nonetheless , in the present study the dual task 
 of making a phone call , which had been included in the experiment by won1 , was excluded due to the characteristics of 
 the smart phone used .
lacour et al.10 noted that , although 
 there was no problem with postural control while performing a single task , during a dual 
 task , postural control ability decreased ; the more difficult a cognitive task , the more 
 reduced the postural control ability became .
such an assertion is a consistent with the results of the present study . in particular , 
 although playing game is an ordinary adolescent hobby , playing games while walking reduces 
 cognitive ability , which decreases dynamic balance and may lead to injury .
dual - tasking 
 using a smartphone , while walking or working , which may look trivial , can be a cause of fall 
 or injury .
accordingly , performing a single task rather than employing the diverse functions 
 of a smart phone while walking or working is considered to be a good way to present falls or 
 injuries .
a limitation of this study was that it did not take into account balance when just 
 holding a smartphone .
 [ purpose ] this study aimed to compare dynamic balance with respect to completing a single 
 task while not using smartrphone function and completing two task while using different 
 smartphone functions , therby preventing falls or injuries resulting from completion of 
 dual tasks . 
 [ subjects and methods ] the subjects of this study were 36 healthy males and 
 females . 
 the experiment was conducted for five situations : a star excursion balance test 
 ( sebt ) was performed ( 1 ) during single - tasking without a smartphone and during 
 dual - tasking with a smartphone , ( 2 ) when listening to music using a smartphone , ( 3 ) when 
 sending message using a smartphone , ( 4 ) when surfing the web using a smartphone , and ( 5 ) 
 when playing a game using a smartphone . 
 the condition were the same for all five 
 experimentes . 
 random selection was done to prevent learing . 
 all experiments were conducted 
 three times , and the averaged values were used for analysis . 
 the sebt was performed in 
 three directions : anterior , posterolateral , and posterormedial . in consideration the 
 differences in leg length of the subjects , 
 their actual leg length were measured to be 
 used as percentages . 
 their leg length was measured from the anterior superior iliac spine 
 of the femur to the medial malleolus . 
 [ results ] compared with single task not done using a 
 smartphone , dynamic balance statistically significantly changed for dual tasks done using 
 a smartphone in all three directions . 
 dynamic balance decreased in all three directions 
 when playing games , sending messages , web surfing , and listening to music . 
 [ conclusion ] 
 completing two tasks using a smartphone reduced cognitive ability , decreasing dynamic 
 balance . 
 therefore , performing a single task rather than using the diverse functions of a 
 smartphone while walking or working is considered a factor that can prevent falls and 
 injuries . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION