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Journal of The Korean Society of Physical Medicine, 2013; 8(4): 601-608 http://dx.doi.org/10.13066/kspm.2013.8.4.601 Online ISSN: 2287-7215 Print ISSN: 1975-311X Research Article Open Access 컴퓨터작업시책상과체간사이거리가전방머리자세와목과어깨근육들의근활성도에미치는영향 이원휘 전주비전대학교물리치료학과 Effect of Distance Between Trunk and Desk on Forward Head Posture and Muscle Activity of Neck and Shoulder Muscles During Computer Work Won-Hwee Lee, PT, PhD Department of Physical Therapy, Vision University, College of Jeonju Received: September 26, 2013 / Revised: October 28, 2013 / Accepted: October 31, 2013 c 2013 Journal of the Korean Society of Physical Medicine Abstract PURPOSE: The purpose of this study was to investigate the effect of distance between trunk and desk on forward head posture and muscle activity of neck and shoulder muscles during computer work. METHODS: Twenty subjects who have healthy conditions were asked to perform computer work in two conditions (distance between trunk and desk was 0 and 15 cm). Forward head angle was analyzed with a SIMI motion analysis system. Surface electromyography recorded the upper trapezius and splenius capitis muscles. The significance of differences in distance between trunk and desk (0cm and 15cm) was tested by paired t-test. The alpha level was set at.05. RESULTS: The results showed that the change of forward head angle was significantly higher during the computer work when the distance between trunk and desk was 15cm than 0cm. The muscle activity of upper trapezius and splenius capitis was also significantly higher during the computer work when the distance between trunk and desk was 15cm than 0cm. Corresponding Author : wampus@naver.com CONCLUSION: Our study suggest that the distance between trunk and desk was should minimized for prevention of forward head posture during computer work. Key Words: Computer work, Electromyography, Forward head posture, Motion analysis Ⅰ. 서론목통증은일생동안 70% 의사람들이경험하는일반적인증상으로유병률이매우높다 (Falla와 Farina, 2007; Javanshir 등, 2011). 또한목통증은작업관련성근골격계질환의한부분을차지하며특히컴퓨터를장시간동안사용하는직업에서주로나타난다 (Babski-Reeves등, 2005). 컴퓨터를사용하는작업은모니터를주시하기위해목과몸통은정적인자세를유지함과동시에상지는동적인키보드작업을요구하므로작업자는이러한부자연스런자세에장시간노출된다 (Yi 등, 2006). 컴퓨터작업이근골격계통증을일으키게되는원인들중전방머리자세 (forward head posture) 가있다. 전방

602 대한물리의학회지제 8 권제 4 호 머리자세는장시간모니터를응시하는자세로인해아래목뼈는과도하게전방커브가되고균형유지를위해위등뼈는과도하게후방커브가되는자세이다 (Szeto 등, 2002). 우리몸에서머리의무게는체중의약 1/7로목주변구조물들은항상머리의부하를유지하고있다. 하지만, 전방머리자세를취하는경우중립자세일때보다약 3.6배의더큰부하를목주변에전달한다고한다 (Yi 등, 2006). 그러므로지속적인전방머리자세는목주변근육들의근활성도를증가시킨다고알려져있다 (Schuldt 등, 1986). 전방머리자세는영상표시단말기 (visual display terminal) 와스마트폰의대중화와함께더욱빈번히나타나고있다 (Kang 등. 2012). Moore (2004) 는이러한자세를장시간유지하면상지교차증후군 (upper crossed syndrome) 과같은근골격계질환및균형장애도유발할수있다고하였다 (Kang 등, 2012; Szeto 등 2005; Yoo와 Kim, 2010). 또한만성목질환뿐만아니라등뼈및어깨뼈의근골격계질환도유발한다 (Burgess- Limerick 등, 1998; Griefel-Morris 등, 1992). Szeto 등 (2005) 도머리, 목, 어깨의근골격계증상이있는사무실근로자와그렇지않은근로자들을비교하였을때근골격계질환이나타나는근로자들에게는머리의기울임각도와목의굽힘자세가증가되어있다는것을보고하였다. Chiu 등 (2002) 도목과어깨의통증을호소하는환자들의 60% 가전방머리자세를취하고있다고보고하였다. 그러므로많은연구들이컴퓨터작업을하는동안전방머리자세를방지하기위한적절한작업환경적인요인의통제가필요하다고제시하였다 (Chiou 등 2012; Moffet 등, 2002). 컴퓨터작업을하는동안전방머리자세에영향을미치는환경적요인들로는모니터의높이와위치, 의자의높이와의자의팔걸이의유무등이있다 (Psihogios 등, 2001; Straker 등, 2008). 하지만, 최근에는이러한환경적인요인외에도컴퓨터작업시앉는자세와같은개인적인요인들이전방머리자세에영향을미친다는연구들도진행되었다 (Caneiro 등, 2010; Kim과 Yoo, 2011). Caneiro 등 (2010) 은앉는자세에따라전방머리자세와목과등뼈의근육들의근활성도 가영향을받는다고보고하였는데, 구부정하게앉는자세는허리골반을수직으로세워앉는자세와등뼈를수직으로세워앉는자세에비해전방머리자세와목뼈폄근의근활성도가유의하게증가한다고하였다. 즉, 환경적인요인들을적절히통제하여도구부정하게앉은자세에의해서전방머리자세가나타나므로컴퓨터작업동안전방머리자세와같은자세를교정하고방지하기위해서는환경적인요인도중요하지만이와함께작업자세와같은개인적인요인들도중요한요소로고려되어야한다. Kim과 Yoo (2011) 의연구에서도컴퓨터작업시올바른자세를유지하기위해엉덩관절의모음을유지하도록시각되먹임을주었더니배바깥빗근, 배속빗근과다섯번째허리뼈주위근육들의근활성도가유의하게증가하여전방머리자세와체간의굽힘각도가유의하게감소하였다고보고하였다. 이러한컴퓨터작업동안전방머리자세를유발하는작업자세와같은개인적인요인들에대한연구들은환경적인요인에대한연구들에비해부족한실정이다. 그러므로본연구에서는컴퓨터작업자세중책상과체간사이의거리가증가할수록전방머리자세를유발할수있다는가설을세우고책상과체간사이거리가전방머리자세와목과어깨근육의근활성도에어떻게영향을미치는지알아보기위한목적으로본연구를진행하였다. Ⅱ. 연구방법 1. 연구대상본연구대상자는실험전에본연구의목적과방법에대해충분히설명을듣고, 연구참여에동의를한자들로선정하였다. 연구대상자의선정기준은최근 1년동안 1일평균 2시간이상씩지속적으로컴퓨터를사용하고목과어깨및상지의근골격계질환 (musculoskeletal disorder), 신경학적징후나최근 6개월이내목과어깨및상지의통증으로병원에서치료를받은경험이없는건강한자로하였다. 연구대상자중예비실험을통해컴퓨터작업동안안경이나콘택트렌

컴퓨터작업시책상과체간사이거리가전방머리자세와목과어깨근육들의근활성도에미치는영향 603 즈를착용하였음에도화면의글씨가명확하게보이지않아자세에영향을줄수있는경우연구대상자에서제외하였다. 그러므로본연구는총 20명의남녀성인을대상으로연구를실시하였다. 2. 실험방법 1) 동작분석시스템컴퓨터작업시전방머리각도를측정하기위해작은반사마커 ( 지름 14mm) 를오른쪽귀구슬 (tragus) 과일곱번째목뼈의가시돌기에부착하였다. 대상자의전방머리각도를측정하기위해한대의비디오카메라를대상자로부터 1m 거리에위치하였고, 카메라화면에대상자의시상면과마커및영점조절을위한 30cm 길이의바가나올수있도록촬영하였다. 전방머리각도측정을위해 2차원동작분석캡처프로그램인 SIMI Motion Analysis System (SIMI motion 5.0 Reality motion systems, Unterschleissheim, Germany) 을사용하였으며전방머리각도는일곱번째가시돌기를지나는수평직선에서귀구슬에부착된마커사이의각도를측정하였다 (Park과 Yoo, 2012). 컴퓨터작업동안촬영된비디오파일은 Twinner Pro video motion analysis system 소프트웨어 (SIMI motion 5.0 Reality motion systems, Unterschleissheim, Germany) 를통해서분석되었으며, 시작자세를기준각도로하여컴퓨터작업동안변화된전방머리각도를측정하였다. 2) 표면근전도시스템컴퓨터작업시전방머리자세에작용하는목과어깨의근육인위등세모근 (upper trapezius) 과머리널판근 (splenius capitis) 의근전도자료수집을위해무선표면근전도시스템인 BTS Pocket EMG system (BTS bioengineering, Millan. Italy) 을사용하였다. 표면근전도의표본추출률 (sampling rate) 은 1,000 Hz로설정하였다. 근육의근전도신호는제곱평균제곱근법 (Root Mean Square: RMS) 처리하여분석하였다. 표면전극부착부위는피부저항의감소를위해털을제거하고, 가는사포로 3 4회문지른다음, 알코올솜 으로피부각질층을제거하고전극을부착하였다. 위등세모근의전극부착위치는일곱번째목뼈와봉우리돌기사이중간지점이고 (Cram 등, 1998), 머리널판근은두번째와세번째목뼈높이에서목빗근과등세모근의사이지점으로 (Falla 등, 2008) 표면전극을양쪽위등세모근과머리널판근에부착하였다. 전극부착후, 위등세모근과머리널판근의근전도값을정량화 (normalization) 하기위해자발적기준수축 (Reference Voluntary Contraction: RVC) 을사용하였다. 자발적기준수축의측정자세는서있는자세에서양팔을바깥회전하고팔꿈치관절은완전히펴지도록하였고, 어깨뼈의연장성과팔꿉관절이곧게유지되도록한후, 손등이위를향하게하여양손에 1kg 아령을들고 15초동안유지하는동안위등세모근과머리널판근에서근전도신호를각각 3회반복측정하였다 (Hansson 등, 2000). 3회반복하여구한값에서각각중간 5초동안의평균값으로자발적기준수축을구하였다. 3) 실험절차대상자들은컴퓨터작업을하는동안무릎관절과엉덩관절은모두 90도가되고발은바닥에닿아있도록의자의높이를조절하였고, 전완은책상에수평으로위치하며고용노동부의기준에따라바닥에서책상의높이가 65 70cm 사이에서대상자의체형에맞도록책상의높이를조절하였다 (Ministry of employment and labor, 2012; Segher등, 2010; Yoo와 Kim, 2010). 모니터의크기는 20인치이고모니터의위치는몸의정중앙에위치하고모니터와눈사이의거리는 50cm로고용노동부의기준에따라 40cm 이상으로하였고, 모니터의시야범위는눈높이에서 12도아래에위치하였다 (Ministry of employment and labor, 2012). 많은연구에서컴퓨터작업시전완의지지유무에따라위등세모근의근활성도의차이가있다고하여이를통제하기위해전완은책상에완전히지지하도록하였다 (Straker등, 2008). 키보드의위치는몸의정중앙에위치하고고용노동부의기준에따라책상끝면에서키보드사이의거리는 15cm 이상을확보하도록제시되어대상자의전완의길이를측정하여책상끝면에서전완의길이만

604 대한물리의학회지제 8 권제 4 호 큼거리를두어키보드를위치하였으며, 대상자의전완의길이는모두 15cm 이상이었다. 컴퓨터작업은한컴타자연습을실시하였으며, 두가지조건에서각각 5분간실시하였다. 첫번째조건은대상자는체간을책상에붙인자세로컴퓨터작업을하였으며, 두번째조건은대상자는체간과책상사이거리를 15cm 떨어진자세를유지하도록의자를배치하고컴퓨터작업을실시하였다. 이때허리뼈와하부등뼈는의자의등받이에붙이고떨어지지않도록하였다. 각각조건의순서는무작위한순서로하였으며, 각각의조건이다음조건에영향을미칠수있으므로각각의조건사이 10분의휴식을취하도록하였다. 각각의조건에서 5분동안측정한근전도자료와동작분석자료중실험환경에서나타날수있는긴장으로인한근활성도의영향및의식적인자세수정의영향을없애기위해앞의 1분을제외한나머지 4분동안의근활성도및전방머리각도의변화량을비교하였다. 3. 자료분석두가지조건에서근활성도의변화와전방머리각도의변화량을비교하기위해짝비교 t-검정 (paired t-test) 을사용하였다. 통계적유의성을검정하기위한유의수준 (a) 은.05로하였고, SPSS 12.0 for window 프로그램을이용하였다. Ⅲ. 결과 1. 연구대상자의일반적특성전체연구대상자의일반적인특징은 Table 1과같다. 성별은남자 10명 (50%), 여자 10명 (50%) 이었고, 전체대상자의평균연령은 23.75± 4.83세, 평균신장은 168.35±10.18 cm, 평균체중은 66.5±15.39 kg 이었다. Table 1. General characteristics of subjects. Male(n=10) Female(n=10) Total(N=20) Age(year) 25.81±5.41 21.59±2.95 23.75±4.83 Height(cm) 175.61±6.55 161.19±7.69 168.35±10.18 Weight(kg) 79.91±8.61 53.19±5.22 66.51±15.39 (Mean±SD) 2. 책상과체간사이거리에따른전방머리각도비교책상과체간사이거리를없앤첫번째조건에서전방머리각도의변화는평균 6.15±4.65도이었으며, 책상과체간사이거리를 15cm로설정한두번째조건에서전방머리각도의변화는평균 13.10±6.05도로두가지조건에서유의한차이가있었다 (p=.007)(table 2). 3. 책상과체간사이거리에따른위등세모근과머리널판근의근활성도비교책상과체간사이거리를없앤첫번째조건에서위등세모근의근활성도는오른쪽위등세모근은 22.18±13.04%, 왼쪽위등세모근은 18.35±13.6% 였으며, 책상과체간사이거리를 15cm로설정한두번째조건에서는오른쪽위등세모근은 31.92±18.91%, 왼쪽위등세모근은 29.1±25.24% 로위등세모근의근활성도는두가지조건에서유의한차이가있었다 (p=.010,.036) (Table 3). 또한머리널판근의근활성도는첫번째조건에서, 오른쪽머리널판근은 51.92±33.15%, 왼쪽머리널판근은 39.54±23.35% 이었으며, 두번째조건에서는각각 67.94±46.53%, 53.92±32.08% 로머리널판근의근활성도도두가지조건에서유의한차이가있었다 (p=.029,.032). Table 2. Change of forward head angle according to distance between desk and trunk Unit : distance between change of forward desk and trunk (cm) head angle a t p 0 6.15±4.65-6.178.007 * 15 13.1±6.05 * p<.05 a mean ± standard deviation

컴퓨터작업시책상과체간사이거리가전방머리자세와목과어깨근육들의근활성도에미치는영향 605 Table 3. The comparison of muscle activity in upper trapezius and splenius capitis muscle according to distance between desk and trunk Unit : %RVC Muscle Right upper trapezius Left upper trapezius Right splenius capitis Left splenius capitis distance between desk and trunk (cm) * p<.05 a mean ± standard deviation Muscle activity a t p 0 22.18±13.04-2.842.010 * 15 31.92±18.91 0 18.35±13.60-2.259.036 * 15 29.10±25.24 0 50.92±33.15-2.366.029 * 15 67.94±46.53 0 39.54±23.35-2.318.032 * 15 53.92±32.08 Ⅳ. 고찰 본연구는컴퓨터작업시책상과체간사이거리가전방머리자세와목과어깨근육의근활성도에어떻게영향을미치는지알아보았다. 연구결과책상과체간사이거리가증가하였을때전방머리각도의변화가유의하게증가하였다 (p<.05). 이는책상과체간사이거리가증가함에따라작업시더욱전방머리자세를취한다는것을의미한다. 또한목과어깨근육인위등세모근및머리널판근의근활성도도책상과체간사이거리가증가하였을때유의한증가가있었다 (p<.05). 많은연구들에서도본연구결과와동일하게전방머리자세가될수록위등세모근및머리널판근의근활성도가증가한다고제시하였다 (Kim 등, 2008; Park, 2005; Tepper 등, 2003). 즉책상과체간사이거리가증가함에따라더욱전방머리자세를취하고전방머리자세가됨으로써위등세모근및머리널판근의근활성도도유의하게증가했을것이라고사료된다. 책상과체간사이거리가증가하였을때전방머리각도와목과어깨근육들의근활성도가유의하게증가 된첫번째원인으로는책상과체간사이거리가증가함에따라모니터와눈사이의거리와눈과모니터상단의높이차이등이변하게된다. 우리나라에서영상표시단말기취급근로자작업관리지침에따르면영상표시단말기취급근로자의시선은화면상단과눈높이가일치할정도로하고화면상의시야범위는수평선상으로부터 10 15도밑에오게하도록한다 (Ministry of employment and labor, 2012). Seghers 등 (2003) 은모니터의높이가높아질수록시야는고정되므로머리가폄되는경사각도가증가하고, 위등세모근의근활성도도증가한다고하였다. 체간과책상사이에거리가멀어질수록눈과모니터상단의높이차이가적어지며이는모니터의높이가높아지는것으로머리의폄되는각도가증가할것이고, 이에따라위등세모근의근활성도도증가할것이다. 책상과체간사이거리가증가하였을때전방머리각도와목과어깨근육들의근활성도가유의하게증가된두번째원인으로는책상과체간사이의거리가증가할수록체간은전방으로움직일공간이생겨구부정하게앉은자세를쉽게취할수있을것이다. Caneiro 등 (2010) 의연구에서도구부정하게앉은자세에서목뼈폄근의근활성도가다른자세들보다유의하게증가하였으며더욱전방머리자세를취한다고보고하였다. 그러므로본연구결과를통해책상과체간사이거리라는변수가구부정하게앉은자세를일으키는원인이될수있을것이라고사료된다. 마지막원인으로비록본연구에서는대상자의시력이라는변수를정확하게통제하지는못했지만작업자의시력이안좋을수록모니터를보기위해머리는더욱전방으로움직일것이다. 그러므로책상과체간의거리가멀어질수록모니터와눈과의거리가멀어지므로시력에문제가있는작업자인경우그렇지않은작업자보다더욱전방머리자세를취하게될것이라고사료된다. 일반적으로대다수의컴퓨터작업자들은이동성을고려하여책상과체간사이거리를띄우고작업을하려는경향이있다. 이러한자세는체간이전방으로움직일공간이생기므로구부정한자세를쉽게취할수있고본연구결과와같이전방머리자세를유발할수있다.

606 대한물리의학회지제 8 권제 4 호 그러므로본연구방법처럼책상과체간을붙여사이거리를최소화시켜컴퓨터작업을실시한다면체간이전방으로움직이는거리가감소되어구부정한자세가감소될것이고이로인해전방머리자세를줄일수있는하나의방안으로써제시할수있을것이다. 지금까지많은연구들은컴퓨터작업시전방머리자세를일으키는요인들로모니터의높이, 키보드혹은마우스모양과위치, 책상과의자의높이, 의자의팔걸이유무, 시트의종류와같은환경적인요인등을제시하였고, 이러한환경적인요인들을적절히통제하는것이전방머리자세로인한목및어깨의근골격계질환을예방하는방법이라제시하였다. 하지만본연구를통해서이러한환경적인요인을잘통제하여도작업하는동안개인적인요인에속하는작업자세에서책상과체간과의거리와같은요인이구부정한작업자세를유발하여근골격계질환을유발시킬수있다는것을알수있었다. 그러므로컴퓨터작업시환경적인요인과개인적인요인이모두잘통제되면더욱효과적으로근골격계질환을예방하고관리할수있다는것을제시할수있다. 그러므로컴퓨터작업시환경적인요인을잘통제해주고, 이러한환경속에서지속적으로근무할수있는적절한작업자세에대한지속적인연구와교육도필요하다고사료된다. 본연구의제한점은대상자의수가적고, 대부분의연구대상자가 20대성인이므로연구결과를일반화시키기힘들다. 또한컴퓨터작업시간을 5분으로설정하여실제컴퓨터작업을하는작업시간보다는적은시간동안의변화를보았으며, 체간과책상의거리에따라일어나는체간의움직임에대한측정을하지못하였다. 추후연구로는머리각도뿐만아니라체간의굽힘각도등도측정하여체간과책상간의거리가전방머리각도로인한목및어깨의근골격계질환뿐만아니라등및다른부위의근골격계질환에도영향을미치는지알아보는연구가필요하며연구대상자들도실제로컴퓨터작업에종사하는사람들을대상으로하고, 이러한책상과체간과의거리에따라서목과어깨근육들의근피로도도알아보는연구들도필요하다고사료된다. Ⅴ. 결론본연구는컴퓨터작업시책상과체간사이거리에따라전방머리각도의변화및목과어깨근육의근활성도를비교하였다. 본연구를통해컴퓨터작업시책상과체간사이의거리의증가는전방머리자세를유발하고목과어깨근육의근활성도를유의하게증가시킨다는것을알수있었고작업자세와같은개인적인요인에의해서도근골격계질환은유발될수있다는것을알수있었다. 그러므로책상과체간사이의거리를최소화하여환경적인요인과개인적인요인을모두통제하면더욱효과적으로근골격계질환을예방할수있을것이다. 그러므로컴퓨터작업시적절한작업자세와같은개인적인요인들에대한지속적인연구와교육도필요하다고사료된다. References Babski-Reeves K, Stanfield J, Hughes L. Assessment of video display workstation set up on risk factors associated with the development of low back and neck discomfort. Int J Ind Ergon. 2005;35:593-604. Burgess-Limerick R, Plooy A, Ankrum DR. The effect of imposed and self-selected computer monitor height on posture and gaze angle. Clin Biomech. 1998;13(8): 584-92. Caneiro JP, O Sullivan P, Burnett A, et al. The influence of different sitting postures on head/neck posture and muscle activity. Man Ther. 2010;15(1):54-60. Chiou WK, Chou WY, Chen BH. Notebook computer use with different monitor tilt angle: effects on posture, muscle activity and discomfort of neck pain users. Work. 2012;41(Suppl):2591-5. Chiu TT, Ku WY, Lee MH, et al. A study on the prevalence and risk factors for neck pain among university academic staff in Hong Kong. J Occup Rehabil. 2002;12(2):77-91.

컴퓨터작업시책상과체간사이거리가전방머리자세와목과어깨근육들의근활성도에미치는영향 607 Cram J, Kasman G, Holtz J. Introduction of surface electromyography. Gaithersburg, MD: Aspen Publishers; 1998. Falla D, Farina D. Neural and muscular factors associated with motor impairment in neck pain. Curr Rheumatol Rep. 2007;9(6):497-502. Falla D, Farina D, Kanstrup Dahl M, Graven-Nielsen T. Pain-induced changes in cervical muscle activation do not affect muscle fatigability during sustained isometric contraction. J Electromyogr Kinesiol. 2008;18(6):938-46. Griegel-Morris P, Laeson K, Mueller-Klaus K, et al. Incidence of common postural abnormalities in the cervical, shoulder and thoracic regions and their association with pain in two age groups of healthy subjects. Phys Ther. 1992;72(6):425-31. Hansson GA, Nordander C, Asterland P, et al. Sensitivity of trapezius electromyography to differences between work tasks-influence of gap definition and normalisation methods. J Electromyogr Kinesiol. 2000;10(2):103-15. Javanshir K, Mohseni-Bandpei MA, Rezasoltani A, et al. Ultrasonography of longus colli muscle: A reliability study on healthy subjects and patients with chronic neck pain. J Bodyw Mov Ther. 2011;15(1):50-6. Kang JH, Park RY, Lee SJ, et al. The effect of the forward head posture on postural balance in long time computer based worker. Ann Rehabil Med. 2012;36(1):98-104. Kim MH, Yi CH, Kwon OY et al. Changes in neck muscle electromyography and forward head posture of children when carrying schoolbags. Ergonomics. 2008;51(6):890-901. Kim MH, Yoo WG. Effects of a visual feedback device for hip adduction on trunk muscles and sitting posture in visual display terminal workers. Asia Pac J Public Health. 2011; 23(3):378-85. Ministry of employment and labor, Video display terminal (VDT) Guidelines (Notification : 2012-72);2012. Moffet H, Hagberg M, Hasson-Risberg E, et al. Influence of laptop computer design and working position on physical exposure variables. Clin Biomech (Bristol, Avon). 2002;17(5):368-75. Moore MK. Upper crossed syndrome and its relationship to cervicogenic headache. J Manupulative Physiol Ther. 2004;27(8):414-20. Park SD, Electromyographic activities of neck and shoulder muscle during the computer typing in forward head posture. Master s thesis. Yonsei university. 2005 Park SY, Yoo WG. Effect of EMG-based feedback on posture correction during computer operation. J Occup Health. 2012;54(4):271-7 Psihogios JP, Sommerich CM, Mirka GA, et al. A field evaluation of monitor placement effects in VDT users. Appl Ergon. 2001;32(4):313-25. Seghers J, Jochem A, Spaepen A. Posture, muscle activity and muscle fatigue in prolonged VDT work at different screen height settings. Ergonomics. 2003;46(7): 714-30. Schuldt K, Ekholm J, Harms-Ringdahl K, et al. Effects of changes in sitting work posture on static neck and shoulder muscle activity. Ergonomics. 1986;29(12): 1525-37. Straker L, Pollock C, Burgess-Limerick R, et al. The impact of computer display height and desk design on muscle activity during information technology work by young adults. J Electromyogr Kinesiol. 2008;18(4):606-17. Szeto GP, Straker L, O sullivan PB. A comparison of symptomatic and asymptomatic office workers performing monotonous keyboard work-2: Neck and shoulder kinematics. Man Ther. 2005;10(4):281-91. Szeto GP, Straker L, Raine S. A field comparison of neck and shoulder postures in symptomatic and asymptomatic office workers. Appl Ergon. 2002;33(1):75-84. Tepper M, Vollenbroek-Hutten MMR, Hermens JH, et al. The effect of an ergonomic computer device n muscle activity of the upper trapezius muscle during typing. Appl Ergon. 2003;34(2):125-30.

608 대한물리의학회지제 8 권제 4 호 Yi CH, Yoo WG, Kim MH. The effect of forward head posture correctional device during computer work. Phys Ther Kor. 2006;13(1):9-15. Yoo WG, Kim MH. Effect of different seat support characteristics on the neck and trunk muscles and forward head posture of visual display terminal workers. Work. 2010;36(1):3-8.