Journal of the Ergonomics Society of Korea Vol. 30, No. 3 pp.381-387, June 2011 DOI:10.5143/JESK.2011.30.3.381 Investigation of the Effects of Resting Time and Trial on the Maximal Grip Strength Doo-Hwan Kwak 1, Kyung-Sun Lee 1, Jong-Seon Kwag 1, Myung-Chul Jung 1, Yong-Ku Kong 2 1 Department of Industrial and Information Systems Engineering, Ajou University, Suwon, 440-749 2 Department of Industrial Engineering, Sungkyunkwan University, Suwon, 440-746 ABSTRACT Objective: The aim of this study was to investigate the maximal grip strength for the combinations of resting time and trial and to provide guideline of resting time for the maximum gripping task associated with the number of trials. Background: Despite many previous researches for the maximal grip strength, few studies have considered the effect of both trials and rest time on the maximum grip strength. Methods: A total of thirty subjects participated in the study. The average of maximum grip strength was measured using JAMAR hydraulic hand dynamometer. The testing position was same as the position recommended by the American Society of Hand Therapists. The between-subject experimental design has been conducted in this study. Trials(1~20 trials) and rest time(2, 3, and 4min) were considered as independent variables, and the maximum grip strength was considered as dependent variable, respectively, in this study. Results: According to the result of the number of trials, the maximal grip strength decreased gradually as the number of trials increased. The ANOVA result showed that the main effect was significant for both resting time(p<.0001) and trial(p<.0001), and the interaction was significant(p<0.0086). Conclusions: The maximal grip strength decreased gradually as the number of trials increased. Thus, basic guideline of resting time was suggested for the number of trials of maximal grip strength tests in this study. Keywords: Grip strength, Resting time, Trial 1. Introduction 작업관련성근골격계질환 (Work-related Musculosk eletal Disorders: WMSDs) 의비율은해가거듭될수록매년높게증가하는추세이다 (Kim and Bae, 2006). 우리나라의노동부 (2009) 에서제공한산업재해통계에따르면, 2004 년에는전체산업재해자 88,874명중에서근골격계질환자수 4,112 명으로전체산업재해자의 4.6% 을차지하였으며, 2009년도에는전체산업재해자 97,821명중에서 6,234명으로전체산업재해자의 6.4% 을나타냈다. 이처럼근골격계질환자의비율은최근 6년동안 1.8% 증가하였다. 신체부위별발생하는근골격계질환의비율을살펴보면요통질환 보다는상지에서발생하는근골격계질환 (Musculoskeletal Disorders of Upper extremities) 이많이발생한다 (Baker, 1995; Kim et al., 2010). 또한, 스웨덴산업재해통계자료에서도손가락, 손그리고손목이포함된직업적상해가 32% 를차지한다고한다 (Mital and Kilbom, 1992). 상지에서발생하는근골격계질환의위험요인으로는반복동작, 과도한힘, 부자연스런자세, 낮은온도와진동등으로보고되고있는데 (Hertzberg, 1955; Putz-Anderson, 1988; Armstrong et al., 1989), 이와같은위험요인들의지속적인노출은통증, 부움, 저림과함께악력의감소등을유발한다 (Kattel et al., 1996). 이러한다양한위험요인중에서특히, 과도한힘과지속적인단순반복동작은근골격계질환유발을높이는주요원인이되고있다 (Moore et al., Corresponding Author: Yong-Ku Kong. Department of Industrial Engineering, Sungkyunkwan University, Suwon, 440-746. E-mail: ykong@skku.edu Copyright@2011 by Ergonomics Society of Korea(pISSN:1229-1684 eissn:2093-8462). All right reserved.
382 Doo Hwan Kwak Kyung Sun Lee Jong Seon Kwag Myung Chul Jung Yong Ku Kong JESK 1991; Hägg et al., 1997). 이는산업의발달에따른작업환경의자동화및제조공정의자동화로인한반복적인동작이상지에서흔히발생하기때문이다. 상지에서발생하는근골격계질환중손과관련된근골격계질환을평가하기위한대표적인방법으로악력측정기법이사용되며이러한악력측정은일상생활을생활하는데있어서작업의수행능력과그에따른인체손상의평가 (Richard, 1997), 상지기능평가 (Richard, 1997; Watson and Ring, 2008), 인간공학적수공구개발및평가하는데사용되고있다 (Kong et al., 2005; Lu et al., 2008). 또한, 의학분야와재활분야에서는일반인과환자와의기능차이를평가하며그에따른치료를위한지표로사용되고있다 (Boissey et al., 2001; Lau and Ip, 2006). 악력측정방법을통하여반복성이신체에끼치는영향을분석하기위한연구는활발히진행되어왔다. Montazer and Thomas(1991) 은로그함수를활용하여반복횟수에따른최대악력의변화에대해예측하였으며이때휴식시간은최대악력측정후 15초를부여하였다. 그결과, 30번의반복측정시 1회와비교하였을때최대악력은약 30% 감소한다고예측하였다. 또한, 이들은이결과를검증하기위하여 200번의반복악력측정을통해최대악력변화를분석하였는데, 그결과 100번과 200번의반복악력을측정하였을때각각최대악력의약 40% 와 50% 가감소한다는결과를제시하였다 (Montazer and Thomas, 1992). Mathiowetz (1990) 은총 3번의반복측정동안각각 15초의휴식시간을부여하였을때최대악력은통계적으로차이를나타내지않았으나, 반복횟수가증가할수록악력은감소한다는결과를제시하였다. Shechtman(2003) 또한 24회의반복측정동안에반복횟수가증가할수록최대악력은감소한다는결과를제시하였다. 이처럼악력은반복횟수가증가할수록감소하는현상을나타낸다. 이와같은결과의원인은, 반복악력측정에의하여피로효과 (fatigue effect) 가발생하기때문이며, 이러한피로효과를최소화하기위하여적절한휴식시간을부여하는것이중요하다 (Mathiowetz, 1990). 악력측정과휴식시간과의관계를파악한선행연구를살펴보면, Trossman and Li (1989) 는 5회악력측정동안 60초, 30초그리고 15초의휴식시간차이가악력에미치는영향을분석하였다. 그결과, 60초의휴식시간은 30초와 15초에비해반복측정횟수에의한악력감소가가장적기때문에정적수축의측정에는 60초의휴식시간을부여하는것이좋다고권고하였다. 이에반해, Caldwell(1974) 는악력측정시최소휴식시간을 2분부여하는것이좋다고권고하였으며그밖의많은연구에서는최대정적악력측정에서피로효과를최소화하기위하여 3분의휴식시간을사용하였다 (Garg et al., 2005; Chow and Dickerson, 2009). 국내에서진행된악력과관련된연구들을살펴보면, 대부분의연구들이관절의각도및자세의변화에따른최대악력에대해서만연구가진행되어왔다 (Kim et al., 2006; Kong et al., 2009). 또한반복측정과휴식시간에관한국내연구는찾아보기힘들며, 대부분의연구들이기존선행연구에따라 2~3분의휴식시간을부여하여악력실험을진행하고있다. 선행연구결과에서도알수있듯이, 최대악력은반복횟수와휴식시간에따라영향을받는다. 하지만반복횟수와휴식시간과의조합에따른최대악력변화를명확하게규명하기위한연구가부족하며, 몇몇진행된연구들또한국외의연구이기때문에국내실정에맞는연구가필요하다. 따라서본연구의목적은 1~20 회의반복측정횟수와 2분, 3분, 그리고 4분의휴식시간이최대악력에미치는영향을분석하는것이다. 이를통하여, 측정횟수에따른적정휴식시간에대한가이드라인을제시하는것이본연구의궁극적인목적이다. 2.1 Subjects 2. Method 본실험은 20대남성 30명을대상으로실시하였다. 이들은모두오른손잡이로손과손목관련질병이나질환이없었다. 전체피실험자의평균연령은 23.9±1.2 세이고, 신장및몸무게의평균은각각 175.2±4.0cm와 74.6±10.9kg이었다. 피실험자는무작위방법으로 10명씩 3그룹으로나누었다. 실험에참가한피실험자들의기본인체측정치는 Table 1과같다. Table 1. Anthropometric information of subjects Variable Mean(SD) Variable Mean(SD) Age (years) Weight (kg) Hand width 2.2 Equipment 23.9 (±1.2) 74.6 (±10.9) 8.2 (±0.3) Height Sitting height Hand length 175.2 (±4.0) 91.8 (±3.1) 18.7 (±0.8) 최대악력은악력계 (Model No, PC 5030J1, JAMAR Hydraulic Hand Dynamometer, USA) 를사용하여측정
Vol. 30, No. 3. 2011. 6. 30 Investigation of the Effects of Resting Time and Trial on the Maximal Grip Strength 383 하였다. 악력계의쥐기간격은악력측정시가장흔히사용되는 3.8cm 로설정하였다 (Mathiowetz et al., 1984). 또한, 피실험자의기본적인인체치수 ( 키, 앉은키, 손너비와손길이 ) 를측정하기위해마틴식인체측정기 (Yamakoshi Seisakusho, JAPAN) 를사용하였다. 2.3 Experimental design 본실험의독립변수로는측정횟수 (20수준 : 1~20회 ) 와휴식시간 (3수준 : 2분, 3분그리고 4분 ) 이다. 종속변수로는각피실험자의 1회측정악력에대한변화비율이다. 이는개인차를감안하는방안으로첫번째측정시의최대악력을 100% 로하여그외실험조건에서의값을상대적으로나타냈다. 본연구에서는독립변수의조건에대해 20 3 Between-subjects Design을사용하여실험을실시하였으며, 각각의실험변수들이최대악력에미치는영향을통계적으로검증하기위하여유의수준 0.05로한분산분석 (2- way ANOVA) 를실시하였다. 또한통계적으로유의한차이를나타낸변수들에있어서변수수준별차이를알아보기위하여 Tukey HSD Test 를실시하였다. 자료의통계분석에는 SAS Ver 9.1(SAS, institute Inc.) 을사용하였다. 2.4 Procedure 실험전모든피실험자들에게실험방법및진행절차에대한정보를제공한후피실험자의참가동의를얻었다. 그리고마틴식인체측정기를이용하여키, 앉은키, 손너비와손길이를측정하였다. 피실험자는 ASHT(American Society of Hand Therapists, Fess and Moran, 1981) 의권고대로, 의자에곧게 Figure 1. Experimental posture 앉아있는자세에서어깨각도 0, 팔꿈치각도 90 그리고손목각도 0 의자세에서최대악력을 5초간측정하였다 (Figure 1). 3그룹으로구분된그룹은각각 1그룹은 2분휴식, 2그룹은 3분휴식, 3그룹은 4분휴식을부여하였으며, 피실험자당총 20회반복적인최대악력을측정하였다. 실험은피실험자당당일에걸쳐진행되었으며, 실험시간은 1그룹 ( 약 42분 ), 2그룹 ( 약 62분 ), 3그룹 ( 약 82분 ) 소요되었다. 독립변수조합에대한실험순서는무작위로선정하여실험을실시하였다. 3. Results 분산분석을실시한결과, 주효과로서측정횟수 (p<0.001) 와휴식시간 (p<0.001) 은통계적으로유의한결과를나타냈다. 측정횟수와휴식간격의교호작용 (p=0.0086) 또한통계적으로유의한차이를나타냈다 (Table 2). Table 2. Results of ANOVA Source DF SS MS F p-value Trial 19 1.287 0.068 50.44 <.0001 Rest time 2 0.031 0.016 11.65 <.0001 T R 38 0.085 0.002 1.67 0.0086 통계적으로유의한결과를나타낸측정횟수에대한 Tukey Test 결과, 1~5, 5~8, 8~11, 11~13, 13~17, 17~19, 19~20 trial으로 7그룹으로구분되었다 (Table 3). 최대악력은 1회측정시와비교하였을때 6회가넘어서부터 5% 로감소하는것으로나타났으며, 13회가넘어서부터 10% 감소를나타냈다. 또한통계적으로유의한차이를나타낸휴식시간에대한 Tukey test 결과는 Figure 2와같다. 휴식시간을 2분 (91.68%) 부여하였을때평균최대악력의변화가가장크게나타났으며, 3분 (93.12%) 과 4분 (93.26%) 에서의평균악력의차이는통계적으로유의하지않았다. 이처럼 2분의휴식시간은 3분과 4분의휴식시간과는차이를나타내지만 3분과 4분간에는차이를나타내지않았다. 측정횟수와휴식시간과의교호작용은통계적으로유의한결과를나타냈으며, 측정횟수와휴식시간에따른최대악력을살펴보면 Table 4와같은결과를나타냈다. 1회측정시의악력과비교하였을때, 5% 이하의차이를나타내는반복횟수는 2분의휴식상태에서는 6회, 3분 7회,
384 Doo Hwan Kwak Kyung Sun Lee Jong Seon Kwag Myung Chul Jung Yong Ku Kong JESK Table 3. Maximal grip strengths (%) according to trials Trial Mean(SD) Trial Mean(SD) 1 100.00 A 11 92.45(±5.99) EF 2 99.89(±2.01) A 12 90.78(±5.74) FG 3 98.87(±2.63) AB 13 90.58(±5.81) FGH 4 98.40(±3.64) AB 14 89.05(±5.58) GHI 5 97.94(±3.74) ABC 15 88.54(±4.87) GHI 6 96.42(±3.99) BCD 16 88.43(±5.44) GHI 7 94.76(±4.49) CDE 17 87.68(±6.00) GHI 8 94.72(±4.68) CDE 18 87.29(±6.88) HIJ 9 94.20(±6.54) DE 19 86.47(±6.87) IJ 10 93.27(±5.61) DEF 20 84.79(±7.44) J [Note: Superscript letters represent groupings by statistical significance. light grey area- less than 5% reduction area of maximum grip strength; dark grey area- 5~10% reduction area of maximum grip strength] Table 4. A reduction (%) of maximal grip strength according to trial and resting time (Continued) Resting time Trial 2 min. 3 min. 4 min. 9 93.48% 93.80% 95.35% 10 93.32% 93.11% 93.38% 11 91.92% 93.27% 92.16% 12 89.14% 90.79% 92.40% 13 88.35% 91.23% 92.15% 14 87.69% 90.17% 89.30% 15 87.00% 89.62% 89.30% 16 86.48% 89.74% 89.08% 17 85.36% 87.39% 89.29% 18 83.33% 88.66% 89.88% 19 83.07% 87.06% 89.28% 20 81.69% 84.83% 87.86% [Note: light grey area- less than 5% reduction area of maximum grip strength; dark grey area- 5~10% reduction area of maximum grip strength] 그리고 4분은 6회를나타냈다. 이처럼 1회측정시와비교하였을때 5% 이하의감소폭은 2분, 3분, 그리고 4분에서크게차이를나타내지않았다. 하지만, 1회측정시와 10% 이상의차이를나타내는반복횟수에서는휴식시간에따라큰차이를나타냈다. 2분휴식을부여하였을경우, 반복횟수가 12회이상에서부터 10% 이상의감소율을나타냈으며, 3분과 4분의휴식시간을부여하였을때에는각각 14회그리고 15회로두그룹간에는차이를나타내지않았다. Figure 2. Maximal grip strengths according to resting time [Note: Superscript letters represent groupings by statistical significance] 4. Discussion Table 4. A reduction (%) of maximal grip strength according to trial and resting time Resting time Trial 2min. 3min. 4min. 1 100% 100% 100.00% 2 99.67% 100.44% 99.52% 3 99.84% 98.87% 97.46% 4 99.10% 99.05% 96.90% 5 99.34% 98.15% 97.33% 6 96.29% 96.88% 96.06% 7 94.09% 96.88% 94.63% 8 95.79% 93.76% 94.62% 본실험의결과, 측정횟수와휴식시간은최대악력변화에미치는영향이통계적으로유의한것으로분석되었으며마찬가지로측정횟수와휴식시간의교호작용은유의한결과를나타냈다. 측정횟수에따른최대악력변화추이를살펴보면, 측정횟수가증가함에따라최대악력또한점차감소하는현상을나타냈다. 본연구의결과 1회측정시와비교하였을때, 10 회반복측정시최대악력은약 6.7% 의감소를나타냈으며, 20회측정시에는약 15.2% 의감소를나타냈다. 본연구의결과는선행연구의결과와유사하게실험횟수의증가에따라최대악력은점차감소하는현상을나타냈다. Montazer and Thomas(1991) 의연구결과에서는 1회
Vol. 30, No. 3. 2011. 6. 30 Investigation of the Effects of Resting Time and Trial on the Maximal Grip Strength 385 측정과비교하였을때 10회측정시최대악력은약 15.0% 감소를나타냈다. 또한 Knudson and Noffal(2005) 의연구에서는 10회측정시최대악력은 1회측정시와비교하였을때약 9.3% 로감소함을나타냈다. 이처럼측정횟수는최대악력과강한상관관계를나타낸다. 선행연구들의결과와본연구의결과를비교하였을때, 반복횟수에따른최대악력의감소폭이다소차이를보이고있지만, 이는각각의연구마다휴식시간부여, 성별, 측정자세의차이때문으로예상된다. 휴식시간차이에따른최대악력의변화결과를살펴보면, 3분과 4분사이의휴식시간에서는최대악력에차이를나타내지않았으나, 2분과는통계적으로유의한최대악력의차이를나타냈다. 즉, 반복횟수 20회일때의휴식시간에따른최대악력을비교해보면 2분의휴식시간을부여하였을때의최대악력은 4분의휴식시간을부여하였을때보다 6.2% 정도감소하는경향을나타냈다. 휴식시간에대한선행연구의결과를본연구의결과와비교하여보면 Trossman and Li(1989) 는 5번측정시 1 분의휴식시간을권고하고있다. 이와유사하게 Patternson and Baxter(1998) 의연구에서도 3번측정시휴식시간을 1분부여하였을때에는최대악력이변함없이유지된다고하였다. 위의권고와는다르게 Caldwell et al.(1974) 은정적상태의힘 (static strength) 을 3번반복측정하고자할때, 최소한 2분의휴식시간을부여하는것을권고하고있다. 본연구의결과에서도 1회측정시의최대악력과 5회측정시의최대악력을휴식시간에따라비교해보면, 2분, 3분, 4 분을부여하였을때약 2% 의감소를나타내며차이를보이지않았다. 이처럼측정횟수가 5회이하에서는기존연구의결과와유사한결과를나타냈다. 하지만본연구와같이측정횟수가많은경우에는 2분의휴식시간을부여하였을때의최대악력은 3분과 4분의휴식시간을부여하였을때와차이를나타냄을알수있다. Pitcher and Miles(1997) 의연구에따르며, 쥐는힘 (hand-grip force) 측정동안최대악력값이정상적으로회복되는데걸리는최소한의시간은 3.5분이라고한다. 본연구의결과에서 3분과 4분의휴식시간에따른최대악력의차이가통계적으로유의하지않은이유도이와같이회복시간때문으로예상된다. 본연구의결과에서는측정횟수와휴식시간과의교호작용은통계적으로유의한결과를나타냈다. 본실험의결과, 6회이하의반복측정실험의경우에는 2분의실험시간을부여하여도 5% 이하의감소율을나타내기때문에실험결과에큰영향을주지않는다. 따라서, 6회이하의반복측정실험에서는휴식시간을 2분부여하는것을권고한다. 피실험자의최대악력측정치간의차이를 10% 이내의 ( 즉, 피실험자의최대악력 90% 이상유지 ) 허용오차범위로한다 면, 총실험측정횟수가 1~10 회이하인경우에는 2분, 총실험측정횟수가 1~14회이하인경우에는 3분의휴식시간을권장하며비록 10% 보다는다소크지만 1~19 회이하인경우에는 4분의휴식시간을권장한다 (Table 4의짙은회색부분 ). 본연구는최대악력측정시 ASHT 에서제안하는자세에있어서측정횟수와휴식시간과의관계를분석하였다. 본연구의장점은기존연구에서몇몇한정된측정횟수에대하여휴식시간과의관계를파악한문제점을해결하기위하여다양한측정횟수와휴식시간을고려한점이다. 본연구는악력과관련된손목의자세, 어깨의자세그리고쥐기간격등다양한변수를고려하지않았다는한계점이있다. 따라서추후악력과관련된다양한변수에따른측정횟수와휴식시간과의관계를파악하는연구를수행해야할것이다. 본연구결과의활용방안은악력실험시반복측정횟수에따른적절한휴식시간선정에가이드라인으로활용될것이다. References Armstrong, T. J., Ulin, S. and Ways, C., "Hand tools and control of cumulative trauma disorders of the upper limb", International Occupational Ergonomics Symposium, 3(pp.43-50), Philadelphia, PA, 1989. Barker, K. L., Repetitive strain injury - A review of the legal issues, Physiotherapy, 81, 103-106, 1995. Boissey, P., Bourbonnais, D., Carliotti, M. M., Gravel, D. and Arsenault, B. A., Maximal grip force in chronic stroke subjects and its relationship to global upper extremity function, Clinical Rehabilitation, 13(4), 354-362, 1999. Caldwell, L. S., Chaffin, D, B., Dukes-Dobos, F. N., Kroemer, K. H., Laubach, L, L., Snook, S, H. and Wasserman, D. E., A proposed standard procedure for static muscle strength testing, American Industrial Hygiene Association Journal, 35(4), 201-206, 1974. Chow, A. and Dickerson, C. R., Shoulder strength of females while sitting and standing as a function of hand location and force direction, Applied Ergonomics, 40(2), 303-308, 2009. Fess, E. E. and Moran, C., Clinical assessment recommendations. Indianapolis, American Society of Hand Therapist, Monograph, 1981. Garg, A., Hegmann, K. T. and Kapellusch, J., Maximum one-handed shoulder strength for overhead work as a function of shoulder posture in females, Occupational Ergonomics, 5(3), 131-140, 2005. Hägg, G. M., Öster, J. and Byström, S., Forearm muscular load and wrist angle among automobile assembly line workers in relation to symptoms, Applied Ergonomics, 28(1), 41-47, 1997. Hertzberg, T., Some contributions of applied physical anthropometry to human engineering. Annals of the New York Academy of Science, 63,
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Candidate, Department of Industrial and Information Systems Engineering, Ajou University Areas of interest: Ergonomics, Hand Biomechanics, Work Design Jong-Seon Kwag: jskwag@enterpriz.net Highest degree: MS, Department of Industrial Engineering, Han Yang University Position title: PhD. Candidate, Department of Industrial and Information Systems Engineering, Ajou University Areas of interest: Biological Signal Processing, Work Design, Ergonomics Myung-Chul Jung: mcjung@ajou.ac.kr Highest degree: PhD, Department of Industrial and Manufacturing Engineering, Pennsylvania State University Position title: Associate Professor, Department of Industrial and Information Systems Engineering, Ajou University Areas of interest: Work Design, Ergonomics, Product Development
Vol. 30, No. 3. 2011. 6. 30 Investigation of the Effects of Resting Time and Trial on the Maximal Grip Strength 387 Yong-Ku Kong: ykong@skku.edu Highest degree: PhD, Department of Industrial and Manufacturing Engineering, Pennsylvania State University Position title: Professor, Department of Industrial Engineering, Sungkyunkwan University Areas of interest: Physical Ergonomics, WMSDs, Finger/Hand Modeling Date Received : 2010-12-29 Date Revised : 2011-04-19 Date Accepted : 2011-04-20