The Asian Journal of Kinesiology Original Research The Differences of Wearing Shoes and Barefoot on Lower Limb Muscle Functions in Martial Arts Athletes of University Tae-whan Kim 1, Tae-hyun Lee 2, Tae-beom Seo 3, JI-hoon Cho 4, Ki-hyuk Lee 5, Jong-baek Lee 1* 1 Korea Institute of Sport Science, Seoul, Korea 2 Yong In University, Yongin, Korea 3 Jeju National University, Jeju, Korea 4 Shingyeong University, Hwaseong, Korea 5 Korea National Sport University, Seoul, Korea ABSTRACT Received: May 3, 2018 Accepted: July 31, 2018 Published online: July 31, 2018 Keywords: 1RM Balance Barefoot Squat EMG Muscle power OBJECTIVES The purpose of this study was to examine the differences of wearing shoes and barefoot on lower limb muscle functions in martial arts athletes of university. METHODS Fourteen martial arts athletes participated in this study. Lower limb muscle functions (maximum strength, power, and electromyography) and balance were measured when wearing shoes (WS) and barefoot (BF). Measured data were analyzed using IBM SPSS Statistics ver. 23.0 (IBM Co., Armonk, NY, USA). Paired t-test was used for comparison between WS and BF. RESULTS Maximum muscle strength (absolute and relative squat 1RM) and static balance (Standing on one leg with eyes close) were significantly higher in BF compared to WS. Although maximum muscle power and dynamic balance were higher in BF compared to WS, were non-significant. Muscle activities of rectus femoris and vastus lateralis were higher during WS than BF. CONCLUSIONS The results of this study suggest that Application of barefoot training seems to be effective on expression of lower limb maximum muscle strength and static balance in martial arts athletes of university. The Asian Society of Kinesiology and the Korean Academy of Kinesiology 서론 근력은스포츠선수들의운동수행능력향상에많은영 향을미치는요인으로근력을발달시키기위해서근력훈 련초기에는최대근력의측정을실시한다. 이는개인의근 력수준을평가하고수준에맞는근력훈련을실시하여부 *Correspondence: Jong-baek Lee, Department of Sports Science, Korea Institute of Sport Science, 727 Hwarang-ro, Nowon-gu, Seoul, Korea. E-mail: supertomcat100@hanmail.net 상의위험을낮추고적합한운동강도와운동량의처방을통해훈련의성과를효율적으로달성하기위해서이다. 이처럼최대근력은선수들의근력상태에대한평가와운동처방뿐만이아니라최대근력수준의훈련을통하여더높은수준의파워를생성해낼수있는밑바탕이된다는많은연구들이보고되고있다 [1-5]. 또한최대근력수준의높은강도의훈련은골밀도의증가에효과적이며 [6, 7] 심혈관능력의실질적인향상에도높은기여를하는것으로보고되고있다 [8]. 한편씨름을비롯한유도와레슬링과같은무도종목에 This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Asian Journal of Kinesiology 57
서는최대근력과파워가특히중요한체력요인으로알려져있다 [9]. 최대근력은더높은수준의파워를생성해낼수있는가장밑바탕이되는체력요인으로파워와직접적인상관관계가높다 [1-5]. 최대근력을향상시키는방법으로는개인이들어올릴수있는최대무게 (maximum) 의저항을이용하는방법과최대하무게 (submaximum) 를실패할때까지반복하는방법, 그리고최대하무게를최대스피드로반복하는방법등이존재한다 [10-12]. 최대근력을효과적으로향상시키기위해서는높은수준의운동단위들을활성화시켜야하고이를위해서는최대근력수준의부하가필요하다. 이러한이유에서최대무게수준에서의훈련방법은운동선수들의최대근력향상을위한가장효과적인훈련방법이라고할수있다. 한편스쿼트 (squat) 는여러스포츠종목에서하지부위최대근력향상과컨디셔닝및재활운동을위해보편적으로수행하고있는동작이다 [13, 14]. 그러나스쿼트동작은대표적인다관절운동 (multi-joint exercise) 방법이기때문에자세를제어하기어렵고, 동작시자세가불안정하면그로인해허리와무릎등의부상발생위험률이높은것으로알려져있다 [15-17]. 이러한동작의위험성으로인하여여러선행연구에서는스쿼트동작시기본적인자세와지침에대하여권고하고있으며자세의안정성을확보하기위한방법을제안하고있다 [18-20]. 선행연구들은스쿼트동작에서몸통과발목및발바닥부위가스쿼트동작의자세안정성에중요한역할을하는것으로보고하고있다 [21]. 이에따라발목과발바닥부위의안정성을높이기위한방법으로맨발인조건에서의스쿼트동작에관한연구가보고되었으며맨발인조건은발바닥에서부터의구심성감각 (afferent neuron) 을향상시키고신체의고유수용성감각 (proprioception) 을향상시켜신체의자세안정성을개선하는것으로알려지고있다 [22-24]. 이에따라맨발과신발의착용유무조건하에서많은연구가보고되고있으나대부분의연구는달리기나보행및밸런스와관련된연구가주를이루고있으며 [25-27] 근력과관련된연구는부족한실정이다. Sato et al. [28] 는스쿼트동작시발목과발바닥부위의자세안정성을확인하기위하여맨발인조건과신발을신은조건에서스쿼트동작시각관절각도의차이를살펴보았으나 1RM의 60~80% 의운동강도에서실시하였으며 [28] 선수들의최대근력발현시위험성을이유로최대근력과관련된연구 와이해는부족한실정이다. 이에본연구는맨발 (barefoot) 과신발을신은조건 (shoes foot) 하에서의차이가스쿼트최대근력및파워의발현과평형성등운동기능에미치는영향과근전도 (electromyography) 를분석하여최대근력과파워가중요한무도선수들의훈련프로그램구성에활용하는것을목적으로하였다. 연구방법연구대상본연구는국내 Y대학에재학중인남자무도학과선수를대상으로하였다. 실험실시전본연구에취지에관하여설명을한후동의서를작성하도록하였으며동의에응한 14명의선수들이본연구에참가하였다. 연구대상자들의신체적특성은 (Table 1) 과같다. 측정변인및방법체력측정을목적으로태릉선수촌을방문한 Y대학무도학과선수를대상으로신발을신었을때와맨발일때의하지근기능을비교하기위해하지최대근력 (Squat 1RM), 최대파워 (Squat jump), 평형성 ( 눈감고외발서기, 동적평형성 ), 표면근전도 (Electromyogram) 를측정하였다. 신발은같은무게와충격흡수기능을가진일반적인러닝화로통일하여모든측정자들의신발발바닥의높이와신발의충격흡수능력의차이는없었다. 신발의조건외각각의측정변인에대한측정방법은다음과같다. 최대근력 (Squat 1RM) 최대근력의차이를객관적이고정밀하게평가하기위하여유압식형태의단축성 (Concentric contraction) 최대근력을측정하는전자식최대근력측정기 (ACE-2000, Ariel Dynamic INC, USA) 를활용하여 1RM(1Repetition Maximum) 을측정하였다 [29]. 피험자 Table 1. Research participants (exploratory analysis) Variables Mean ± SD Age(years) 22.29 ± 1.07 Height(cm) 178.36 ± 6.88 Body weight(kg) 94.99 ± 13.40 BMI 29.96 ± 4.66 Experience(years) 8.57 ± 2.44 58 The Asian Journal of Kinesiology
들은동일한조건에서각각신발을신었을때와맨발일때로나누어 3회씩측정을실시하였다. 측정동작은바닥과허벅지가평행이되는위치까지내린후시작구호로실시하였다. 1회 1RM 측정이끝난후 5분의휴식을가지고반복측정을실시하였으며, 다른조건으로넘어가는시점에서 10분가량의휴식시간을가졌다. 이러한휴식시간을고려한근거는 Baker et al. [30] 의지속적인근수축을하는운동이후 5분내에힘과무기인산이회복되었다는연구결과를근거로하였다 [30]. 한편모든변인은사전준비운동이후신발을신은상태에서먼저측정을실시한후다음측정에영향이없도록충분한휴식시간을가진다음맨발로조건을변경하여측정을계속진행하였으며가장좋은측정값을비교하였다. 최대파워 (Squat jump) 최대파워를측정하기위해스쿼트점프를 3회씩실시하였다 [29]. 점프는신발을신은상태에서양손은허리를붙잡고무릎각도는 90 까지내려간후바로최대점프를실시하였다. 측정값의오차를최소화하기위하여일정한목표물을제시하여목표물에닿을만큼최대한점프를유도하였다. 차렷자세에서최고높이까지의높이차를분석하여비교하였다. 정적평형성정적평형성의차이를비교분석하기위하여눈감고외발서기를실시하였다 [29]. 자신의주된발을사용하여측정하였으며신발을신은상황에서먼저측정한다음 5분간의휴식을취한후에다시신발과양말을모두벗고맨발인상황에서동일하게실시하였다. 동적평형성동적평형성의차이를비교분석하기위하여동적평형성측정장비 (Balance system SD Biodex, USA) 를활용하여전후, 좌우, 전체의안정성을측정하였다 [31]. 신발을신은상태에서동적평형성을측정한다음맨발인상황에서동일하게실시하였으며조건을변경하는측정간에는 5분간의휴식을취한후측정을실시하였다. 동적평형성의결과는세부위의측정값을표준점수를구하여비교하였으며표준점수가낮을수록안정성이높은결과를의미한다. 표면근전도 (Electromyography: EMG) 근육의활동정도를알아보기위해우측하지의넙다리곧은근 ( 대퇴직 근, Rectus Femoris), 가쪽넓은근 ( 외측광근, Vastus Lateralis), 넙다리두갈래근 ( 대퇴이두근, Biceps Femoris), 앞정강근 ( 전경골근, Tibialis Anterior), 큰볼기근 ( 대둔근, Glutaus Maximus), 중간볼기근 ( 중둔근, Gluteus Medius), 장딴지근 ( 비복근, Gastrocnemius), 가자미근 ( 넙치근, Soleus) 등 8부위에표면전극 (Trigno wireless system, Delsys Inc., USA) 을각각부착하였다 [32]. 근전도자료의표준화를위하여스쿼트의앉는자세는어깨넓이의범위에서무릎의각도는 90 에서시작하도록하여측정하였으며, 무릎의각도가 0 ( 측정장비의압력이 0) 이되는시점까지기준으로적용하였다. 개인의각근육의활동을측정하기위해무선근전도시스템 (DTS Probe Transmitter, Noraxon USA, Inc, sample rates 1500 fixed, input impedance > 100MΩ, CMRR > 100dB, Input Range +/- 3.5V, center to center distance=15mm ) 을사용하였다. 이때동작의이벤트및국면을정하기위해디지털캠코더를사용하여수행하는모습을촬영하였으며근전도자료와동기화하였다. 측정된원자료는연구대상자의움직임과실험환경적인요인으로인한노이즈 (noise) 를제거하기위하여 FIR high pass filter 방법에의한차단주파수 (cut-off frequency) 10Hz 처리를하였다. 이후 full wave Rectification을적용한후 RMS 100 ms으로정량화하였다. 근전도의자료분석은근육활동의표준화를위해 RVC(Reference Voluntary Contractions) 형태로맨발인조건에서의근활성도를표준으로신발을신은조건에서의값을나누어백분율로나타내어활용하였다 [33]. 자료처리측정된자료는 SPSS WIN ver. 23.0을이용하여분석하였으며각각의측정변인들은평균과표준편차를산출하여제시하였다. 변인들은신발착용시와맨발일때를비교하기위해종속 t-검증 (paired t-test) 을실시하여평가하였으며통계적유의수준은 α=0.05로설정하였다. 결과최대근력측정결과스쿼트동작시최대근력 (1RM) 을측정한결과, 맨발의경우가신발착용시보다절대근력값과 (p=.044) 체중으로나눈상대근력값 (p=.05) 모두유의하게높은것으로나타났다. 자세한결과는 (Table 2) 와같다. The Asian Journal of Kinesiology 59
Table 2. Comparison of squat 1RM between WS and BF (Mean±SD) Variables Application N Mean ± SD t p Absolute WS 14 194.86 ± 20.91 1RM (kg) BF 14 202.14 ± 23.69-2.229.044* Relative WS 14 207.57 ± 28.57 1RM (%BW) BF 14 215.06 ± 28.96-2.163.050* * p<.05, WS: wearing shoes, BF: bare foot Table 3. Comparison of squat jump between WS and BF (Mean±SD) Variables Application N Mean ± SD t p Absolute WS 14 43.79 ± 7.19 squat jump -1.408.183 (cm) BF 14 45.21 ± 7.86 WS: wearing shoes, BF: bare foot 한결과, 맨발의경우가신발착용시보다최대파워값이모두높았으나통계적으로유의한차이는없었다. 자세한결과는 (Table 3) 과같다. 평형성측정결과정적평형성 ( 눈감고외발서기 ) 과동적평형성을측정한결과, 정적평형성은맨발의경우가신발착용시보다유의하게높은것으로나타났다 (p=.026). 그러나동적평형성의경우전후, 좌우전체모두에서맨발의경우가신발착용시보다안정성이높았으나통계적으로유의한차이는없었다. 자세한결과는 (Table 4), (Table 5) 와같다. EMG 측정결과신발을신었을때와맨발인조건하에서하지8부위에대한근활성도를비교한결과, 신발을신었을때가맨발인조건대비넙다리곧은근과가쪽넓은근이각각 18%, 11% 더활성화되었다. 자세한결과는 (Table 6) 과같다. Table 4. Comparison of SOE between WS and BF (Mean±SD) Variables Application N Mean ± SD t p SOE (sec) 최대파워측정결과 WS 14 22.55 ± 14.84 BF 14 36.33 ± 27.09-2.505.026* * p<.05, SOE: Standing on one leg with eyes close, WS: wearing shoes, BF: bare foot Table 5. Comparison of dynamic balance between WS and BF (Mean±SD) Variables Application N Mean ± SD t p Anterior/ Posterior (index) Medial/ Lateral (index) Overal stability (index) WS: wearing shoes, BF: bare foot WS 14 7.52 ± 5.21 BF 14 5.84 ± 2.72 WS 14 3.85 ± 2.05 BF 14 3.62 ± 1.91 WS 14 9.17 ± 5.30 BF 14 7.45 ± 3.57.949.361.380.710.934.369 하지의최대파워를비교하기위해스쿼트점프를측정 논의본연구는신발착용의유무가하지의최대근력을포함한운동수행능력 ( 최대근력, 최대파워, 동적 / 정적평형성, 근육의활성부위 ) 에어떠한영향을미치는지비교분석하는데목적이있었다. 스쿼트동작시최대근력을측정한결과신발을신고있는조건보다맨발인조건에서최대근력이유의하게향상된것으로나타났다. 맨발스쿼트는충격흡수기능이없는바닥과쐐기모양의뒤꿈치, 미끄럼을방지할수있는소재를이용하여 Weight lifting의힘의증가를목적으로하는역도화의이점에착안하여사용되기시작한방법이다. 몸통과발목및발바닥의안정성은최대근력수행력을높이는데중요한역할을하는것으로보고되었으며 [21] 맨발일때의운동감각은신체적인자세안정성을개선한다는연구결과들이보고되고있다 [22-24]. 이에따라맨발인상황은신발착용시보다안정성을향상시켜최대근력의발현을증가시키는데영향을미치는것으로사료된다. 최대파워평가를위해실시된제자리스쿼트점프는맨발인조건이신발착용한조건과비교하여평균적인높이는높았지만통계적으로는유의한차이를나타내지못하였다. 이는맨발인조건과신발을착용한조건하에서 60 The Asian Journal of Kinesiology
Table 6. Difference in lower limb muscle activity between WS and BF (unit: %RVC) Subjects RF VL TA GM GM' BF' G S S1 91% 101% 69% 99% 88% 114% 80% 107% S2 118% 103% 69% 90% 93% 108% 92% 104% S3 158% 112% 140% 118% 120% 88% 125% 113% S4 120% 124% 89% 85% 84% 67% 118% 127% S5 123% 113% 99% 107% 107% 104% 101% 98% S6 125% 121% 139% 129% 110% 123% 106% 87% S7 105% 105% 96% 91% 99% 111% 68% 86% S8 160% 116% 106% 98% 94% 91% 101% 81% S9 94% 94% 67% 72% 76% 71% 69% 87% S10 137% 123% 94% 88% 107% 80% 76% 64% S11 104% 107% 91% 86% 87% 87% 86% 83% S12 97% 115% 107% 88% 95% 109% 86% 106% S13 107% 112% 104% 117% 121% 113% 129% 122% S14 113% 103% 60% 83% 87% 68% 85% 90% Mean 118% 111% 95% 97% 98% 95% 94% 97% SD 21% 9% 24% 16% 14% 19% 20% 17% WS: wearing shoes, BF: bare foot, RF: rectus femoris, VL: vastus lateralis, TA: tibialis anterior, GM: glutaus maximus, GM : gluteus medius, BF : biceps femoris G: gastrocnemius, S: soleus. 맨발인조건이능동적인점프능력의차이에는별다른영향을미치지못하고착지동작시충격흡수에만신발의착용유무가영향을미친다는연구결과들과일치하는결과이다 [34-37]. 또한스쿼트점프는최대파워보다는각하지근육들의조화가점프높이에더큰영향을미치는것으로보고되고있으며 [38] 이러한연구결과와본연구에서의결과를토대로판단하였을때점프에동원되는각근육들간의조화가맨발인조건에서자세의안정성이향상된요인보다제자리점프능력에높은영향을미친것으로판단되며, 이러한이유에서점프높이의차이에있어서유의한영향을미치지못한것으로사료된다 [39]. 한편정적평형성 ( 눈감고외발서기 ) 에서신발착용시보다맨발인조건에서정적평형능력이향상된이유로는첫째, 발목과발바닥의움직임에대한감각이맨발인조건에서보다명확하게구별되며 [24] 이러한발바닥에서부터의구심성감각의향상은신체의고유수용성감각을촉진시키고, 이러한향상된신체감각은신체의직립상태 유지를위한되먹임 (Feedback) 의증가로이어져신체적동요를빠르게지각시켜자세안정성을개선한다는연구결과와일치한다고할수있다 [22-24]. 둘째, 맨발인상황은신발을착용했을때보다발가락을모두사용하여지면을내리누를수있기때문에발바닥부위의기저면을넓게만들어서안정성을향상시킨다 [36]. 본연구에서맨발의상황이정적평형성을향상시킨요인으로이러한신체감각향상과기계적인안정성의향상으로인한것으로사료된다. 하지만본연구에서는동적평형성에서는맨발인조건이신발착용한조건과비교하여평균적으로높은안정성을나타냈지만통계적으로는유의한차이는나타내지못하였다. 이는동적평형능력은움직이는지면발판을통하여선수의균형능력을평가하였기에정적평형능력측정시맨발인상황에서의발가락을사용하여기저면을향상시켜안정성을높일수있었던특성 [37] 이동적평형성에서는상쇄되며통계적인유의수준까지는영향을미치지못한것으로보인다. The Asian Journal of Kinesiology 61
마지막으로신발을착용한것과맨발인조건의스쿼트동작에서표면근전도를측정한결과넙다리곧은군과가쪽넓은근의평균근활성도는신발을착용한상태에서맨발인조건보다높았다. 그외에넙다리두갈래근, 앞정강근, 큰볼기근, 중간볼기근, 장딴지근, 가자미근은신발을착용한조건이맨발보다평균적으로다소낮았다. Sato et al. [28] 는신발을착용한것과맨발인조건에서스쿼트동작을실시하여관절의각도를비교한결과, 신발을착용한조건 (88.32 ) 이맨발인조건 (81.33 ) 보다스쿼트동작의무릎의굴곡각도가더컸다고하였다 [28]. 한편, Caterisano et al. [40] 는스쿼트의동작깊이에따른주요하체부위의근활성도연구에서스쿼트동작깊이에따라대퇴직근의근활성도의차이를보고하였으며 [40] 맨발에서상대적으로작은무릎각도는스쿼트의동작시앉은자세에서깊이의차이를유발하며따라서상대적으로대퇴부후면 (Hamstrings) 보다대퇴부앞면 (Quadriceps) 이보다활성화되어하지근육각부분의활성도차이를유발하고이러한차이가본연구에서맨발을착용한조건에서대퇴부앞면의활성화에더영향을미친요인으로사료된다. 결론다양한형태의하체근력훈련을실시하는무도선수들을대상으로맨발인조건과신발을착용한조건에서하지근기능과평형성을비교평가한결과, 모든변인에서맨발인경우가하지근기능과평형성이향상된것으로나타났다. 본연구로인해최대근력향상훈련을위한 1RM 훈련시맨발인조건하에서의트레이닝은선수들에게보다높은부하자극을주는데이용가능하며, 선수들의무릎손상등하지손상과관련하여재활초기관절의안정성향상을위한지침으로활용될수있을것으로보인다. 한편본연구는단발적인비교실험이기때문에맨발을이용한트레이닝의효과를검증하기위해서는일정한트레이닝기간을거쳐맨발트레이닝이신발을착용한트레이닝보다최대근력을포함한근기능과평형성을향상을시킬수있는지에대해검증할수있는후속연구가필요할것으로사료된다. Conflicts of Interest The authors declare no conflict of interest. References 1. McBride JM, Triplett-McBride T, Davie A, Newton RU. A Comparison of Strength and Power Characteristics Between Power Lifters, Olympic Lifters, and Sprinters. J Strength Cond Res. 1999; 13(1):58-66. 2. Duchateau J, Hainaut K. Mechanisms of muscle and motor unit adaptation to explosive power training. Strength and power in sport, 2003, p 315. 3. Stone MH, O'bryant HS, Mccoy L, Coglianese R, Lehmkuhl M, Schilling B. Power and maximum strength relationships during performance of dynamic and static weighted jumps. J Strength Cond Res. 2003; 17(1):140-147. 4. Baker DG, Newton RU. Comparison of lower body strength, power, acceleration, speed, agility, and sprint momentum to describe and compare playing rank among professional rugby league players. J Strength Cond Res. 2008; 22(1):153-158. 5. Prue P, McGuigan MR, Newton RU. Influence of strength on magnitude and mechanisms of adaptation to power training. Med Sci Sports Exerc. 2010; 42(8):1566-1581. 6. Ryan AS, Ivey FM, Hurlbut DE, et al. Regional bone mineral density after resistive training in young and older men and women. Scand J Med Sci Sports. 2004; 14(1):16-23. 7. Almstedt HC, Canepa JA, Ramirez DA, Shoepe TC. Changes in bone mineral density in response to 24 weeks of resistance training in college-age men and women. J Strength Cond Res. 2011; 25(4):1098-1103. 8. Alcaraz PE, Sánchez-Lorente J, Blazevich AJ. Physical performance and cardiovascular responses to an acute bout of heavy resistance circuit training versus traditional strength training. J Strength Cond Res. 2008; 22(3):667-671. 9. Cho HC, Kim YH, Kim JP et al. The Correlation of BMD, Isokinetic Muscle Strength and anaerobic power on Body Parts in Combat Sports Athlete. J Korean Alliance Martial Arts. 2011; 13(3):175-186. 10. Zatsiorsky VM, Kraemer WJ. Science and practice 62 The Asian Journal of Kinesiology
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