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        검색결과 20

        1.
        2024.08 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Background: The peroneus longus (PL) and peroneus brevis (PB) function as the primary muscles of eversion, a movement closely associated with tibial external rotation for ankle mortise stability. Ankle motion and tibial rotation vary based on different ankle and knee positions. Objects: This study aimed to investigate the PL, PB, and biceps femoris (BF) muscle activation and eversion strength during side-lying isometric eversion exercise based on different ankle positions (neutral [N] and plantarflexion [PF]) and knee positions (90° flexion [KF] and extension [KE]). Methods: Thirty healthy adults with an Ankle Joint Functional Assessment Tool score of ≥ 22 were recruited (mean age = 24.8 ± 3.1 years). Maximal isometric eversion strength and submaximal muscle activation of the PL, PB and BF were measured during isometric eversion exercise in side-lying. A 2 × 2 repeated measures analysis of variance was performed to investigate differences in muscle activation and strength. Results: The PL and PB muscle activation showed significant main effects with the knee and ankle positions (p < 0.05); activation was greater in the KE and PF positions than in the KF and N positions. The BF muscle activation showed a significant interaction effect with knee and ankle positions, which was greater in knee extension and ankle plantarflexed (KEPF) position than in knee flexion and ankle plantarflexed (KFPF) position (p < 0.05). Eversion strength showed a significant main effect only in ankle position (p < 0.05) and was greater in the N position than in the PF position. Conclusion: The results of this study indicate that the KEPF position can be recommended to facilitate contraction of the PL and PB during side-lying eversion exercise. Furthermore, the effects of the knee-ankle positions should be considered for measuring ankle eversion strength and implementing the isometric submaximal side-lying eversion exercise.
        4,000원
        2.
        2023.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Background: Proprioception in the ankle joint is important for maintaining balance. There is a correlation between joint position sense (JPS), balance and ankle dorsiflexion range of motion (DF-ROM). Objectives: The purpose of this study was to compare the effects of talocrural joint mobilization (TJM) and muscle energy technique (MET) of plantar flexor muscle (PF) on improving joint position sense (JPS) and static balance. Design: Cross-over randomized trial research. Methods: Sixteen participants (male 10, female 6; 20’s of their age) without ankle instability were recruited. In a randomized, three conditions, no intervention, talocalcaneal mobilization, and PF-MET were all applied to 16 participants. For TJM, the Kaltenborn grade 3 joint gliding method, in which the talus moves posteriorly perpendicular to the tacrocrural joint plane, were used. In the PF-MET, MET method were applied gastrocnemius muscle and soleus muscle with 25% of 1 Repeat Maximum of each muscle. The all participants performed PF-MET and TJM for 18 minutes. DF-ROM measured the weightbearing lunge test. JPS measured using the active joint angle reproduction test. Static balance was measured displacement of center of pressure parameter. Results: PF-MET and TJM had significant differences in DF-ROM and AP displacements. PF-MET significantly increased at 5° and 15° of plantar flexion and 5° of dorsiflexion, and COP velocity significantly decreased in JPS compared to TJM. Conclusion: PF-MET and TJM are effective in increasing DF-ROM. However, PF-MET has a more positive effect on improving JPS and static balance than on talocrural joint mobilization.
        4,000원
        3.
        2022.05 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Background: During postural control, older adults are more dependent on proprioception than are young adults. Ankle proprioception, which plays an important role in maintaining postural balance, decreases with age. Published studies are insufficient to establish a significant age difference in postural sway resulting from the known age-related decrease in ankle proprioception and do not examine various detailed test conditions. Objects: The present study aimed to compare ankle proprioception between older and younger groups along dimensions of position vs. force proprioception and dorsiflexion vs. plantarflexion. The present study also aimed to compare postural sway between young and older women during quiet standing under two sensory conditions. Methods: We recruited seven young women aged 21–24 and seven older women aged 60–63. Ankle proprioception was assessed as the accuracy of the joint position sense (JPS) and the force sense (FS). Postural sway was assessed using center-of-pressure measurements recorded during quiet standing under two sensory positions: eyes open and eyes closed with head tilted back. Results: Older women had lower JPS in dorsiflexion and lower FS in plantarflexion than did younger women. We found no significant age differences in JPS in plantarflexion or in FS in dorsiflexion. We observed a main effect of group on postural sway in two sway parameters out of three. We observed significant differences in JPS with dorsiflexion, and in FS with plantarflexion. Conclusion: Proprioception for ankle plantar flexor decreased more significantly with aging than did that for ankle dorsiflexor, accounting for the impaired postural balance observed in older women.
        4,000원
        4.
        2022.02 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Background: Bird dog exercise (BDE) is one of the lumbar stabilization exercises that rehabilitate low back pain by co-contraction of the local and global muscles. Previous studies have reported the effect of various type of BDEs (for example, practicing the exercises on various surfaces and changing the limb movement) for muscle co-contraction. Objects: This study aimed to investigate the effect of knee joint flexion position of the raised lower limb on abdominal and back muscle activity during BDE in patients with chronic low back pain (CLBP). Methods: Thirteen males participated in this study (age: 32.54 ± 4.48 years, height: 177.38 ± 7.17 cm). Surface electromyographic (SEMG) data of the internal abdominal oblique (IO), external abdominal oblique (EO), lumbar multifidus (MF), and thoracic part of the iliocostalis lumborum (ICLT) were collected in two knee joint flexion positions (90° flexion versus 0° flexion) during BDE. The SEMG data were expressed as a percentage of root mean square mean values obtained in the maximal voluntary isometric contraction. Results: Greater muscle activity of the IO (p = 0.001), MF (p = 0.009), and ICLT (p = 0.021) of the raised lower limb side and the EO (p = 0.001) and MF (p = 0.009) of the contralateral side were demonstrated in the knee joint flexion position compared to the knee joint extension position. Greater local/global activity ratios of the abdominal muscle (i.e., IO and EO) of the raised lower limb (p = 0.002) and the back muscle (i.e., MF and ICLT) of the contralateral side (p = 0.028) were also noted in the knee joint flexion position. Conclusion: BDE with a knee joint flexion position might be recommended as an alternative lumbar stabilization exercise to enhance muscle activity in both the raised lower limb and the contralateral sides of the trunk for individuals with CLBP
        4,000원
        5.
        2021.11 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Background: Individuals with scapular winging may have proprioceptive dysfunction which is important for motor control and causes shoulder instability. Reduced serratus anterior (SA) and lower trapezius (LT) muscle activity accompanied by over-active upper trapezius (UT), and pectoralis major (PM) may be contributing factors. Flexi-bar (FB) exercise may be used to increase joint position sense (JPS) and alter the target muscle activities. Objects: This study aimed to investigate the immediate effects of flexi-bar exercise prior to knee push-up plus (FPK) versus knee push-up plus (KPP) on JPS and muscle activity of SA, LT, UT, and PM in subjects with scapular winging. Methods: Eighteen subjects with scapular winging were recruited. JPS was investigated at baseline, after KPP and after FPK. Passive and active JPS errors were calculated by isokinetic equipment. Surface electromyography was used to record muscle activities during KPP and FPK. One-way repeated-measures analysis of variance and post hoc analyses were used to analyze the JPS error measured at baseline, after KPP and after FPK. Paired t-tests were used to compare muscle activities between KPP and FPK. Results: Passive JPS error was significantly decreased after KPP (p = 0.005) and after FPK (p = 0.003) compared to the baseline. Active JPS error was also significantly decreased after KPP (p = 0.016) and after FPK (p = 0.012) compared to the baseline. There was no significant difference in the passive and active JPS errors between KPP and FPK. SA activity during FPK was significantly increased (p = 0.024), and LT activity during FPK was significantly increased (p = 0.006). There were no significant differences in the UT and PM activity. Conclusion: FB might be recommended to immediately improve passive and active JPS and to selectively increase SA and LT muscle activities during KPP in individuals with scapular winging.
        4,000원
        6.
        2021.08 KCI 등재 구독 인증기관 무료, 개인회원 유료
        이 연구의 목적은 8주간의 플라이오메트릭 훈련이 대학 태권도 시범단의 순발력, 동적 평형성 및 관절 위치감각에 미치는 영향을 분석하고자 하였다. 태권도 시범 전공 대학생 20명을 훈련군 10명, 통제군 10명으로 분류한 후 운동군은 주 3회, 60분, 8주간 플라이오메트릭 훈련을 하였다. 측정 변인은 제자 리높이뛰기, 제자리멀리뛰기, 배근력, 동적 평형성 및 관절 위치감각으로 사전 사후 측정하였다. 연구 결과, 제자리높이뛰기와 멀리뛰기 및 배근력에서 유의한 운동의 효과가 있었다(p<.05). 동적 평형성은 후방 바깥 쪽과(p<.01) 후방 안쪽에서(p<.05) 유의한 운동의 효과가 있었다. 관절 위치감각은 왼발 15°와(p<.01) 45°에서는(p<.05) 운동군에서 유의한 효과가 있었다. 이상의 결과 8주간의 플라이오메트릭 훈련은 태권도 시범선수의 순발력과 동적 평형성 및 관절 위치감각에 긍정적인 영향을 미치는 것으로 나타났다.
        4,000원
        7.
        2021.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Background: This study evaluated the effectiveness of upper thoracic manipulation (UTM) and proprioceptive training versus proprioceptive training alone on forward head posture (FHP) and cervicocephalic joint position sense (CJPS) in asymptomatic university students during a short interval of time. Objectives: To evaluate whether the suggested combination would provide greater benefit, and be superior to proprioceptive training alone in improving proprioceptive acuity and head posture. Design: A single-blind randomized controlled trial. Methods: Thirty-three university student volunteers with asymptomatic FHP were recruited. Subjects were randomly assigned to a manipulation group (n=16) receiving UTM combined with proprioceptive training or a proprioception group (n=17) receiving proprioceptive training only. The intervention period lasted 5 weeks in total, and consisted of one 15 to 20-minute session per week. FHP and CJPS were assessed before and after the intervention. Results: A significant pre- to post-intervention decrease in FHP and joint position error was identified in both groups (P<.05). Subjects in the manipulation group demonstrated greater improvements in CJPS and head posture compared to the proprioception group (P<.05). Conclusion: These findings support employing either intervention for treating asymptomatic students with FHP. However, the addition of UTM to proprioceptive training was more effective than proprioceptive training alone in reducing joint position errors and improving head posture.
        4,000원
        8.
        2019.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Background: Measurement of passive ankle dorsiflexion range of motion (ADROM) is often part of a physical therapy assessment. Objects: The objective of this study was to identify the effects of subtalar joint neutral position (SJNP) on passive ADROM according to knee position in young adults. Methods: We recruited 14 young adult participants for this study. Two examiners used a universal goniometer to measure passive ADROM with and without SJNP. Dorsiflexion force was applied to the forefoot until maximum resistance was reached in two knee positions (extension and 90˚ flexion) in the prone position. Subtalar joint position was also recorded at maximum ADROM. Passive ADROM was measured three times at different knee and subtalar joint positions, in random order. Two-way repeated-measures analysis of variance was used to compare the effects of subtalar joint and knee position on passive ADROM. Results: Passive ADROM was significantly lower with than without SJNP during both knee extension (mean difference: 7.4˚) and 90˚ flexion (mean difference: 16.9˚) (p<.01). Passive ADROM was significantly higher during 90˚ knee flexion than during knee extension both with (mean difference: 5.8˚) and without SJNP (mean difference: 15.2˚) (p<.01). The valgus position of the subtalar joint was significantly lower with than without SJNP during both knee extension (mean difference: 3.3˚) and 90˚ flexion (mean difference: 4.3˚) (p<.01). Conclusion: Our results indicate that the gastrocnemius may limit ankle dorsiflexion more than the soleus does. Greater dorsiflexion at the subtalar and midtarsal joints was observed during passive ADROM measurement without than that with SJNP; therefore, SJNP should be maintained for accurate measurement of ADROM.
        4,000원
        9.
        2018.03 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The purpose of this study is to investigate the effect of pelvic, Lumbar spine and Cervical spine manipulation on the joint position sense in normal adults. Thirty normal adults were divided into an experimental group of 15 subjects and a control group of 15 subjects. The experimental group was treated with pelvic, Lumbar spine and Cervical spine manipulation with massage, whereas the control group received only massage. Both groups were evaluated in terms of joint position errors (JPEs) using a digital dual clinometer before and after the experiment. The comparison of the JPEs of the experimental group and the control group before and after the experiment showed that the experimental group’s cervical spine results were significantly different in the flexion, left lateral flexion, and right rotation (p < .05) and lumbar spine results were significantly different in the flexion and extension (p < .05), but the control group’s results were not statistically significant in all items (p > .05). The pelvic, lumbar spine and cervical spine manipulation makes an effect on the joint position sense in normal adults. The findings of this study suggest that the pelvis, lumbar spine and cervical spine manipulation improve the motor ability in people with low joint position sense.
        4,000원
        10.
        2017.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The purpose of the study was to investigate the strength of sokinetic muscle by the position of a volleyball players. Analysis and comparison of shoulder dynamic stability will be conducted according to rotational movement of the shoulder during spiking and serving amongst the various positions. Fifty professional Korean female volleyball players (age: 20~30), all different positions – attacker (left and right), center, setter, and libero were The concentric peak torque, strength ration of the internal and external rotation of the shoulder girdle for both dominant and non-dominant arms. Firstly, there were significant differences found for the strength ratio between the setter and the other positions in the dominant arm. On a second note, there was a significant decrease in shoulder dynamic stabilization for both the attacker and center in the dominant arm. However, there were no significant differences for the setter or the libero. This study suggests that the isokinetic muscle strengths of the volleyball players are different from each other.
        4,000원
        11.
        2015.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The purpose of this study was to investigate the effect of multi joint-joint position sense (MJ-JPS) training on joint position sense, balance, and gait ability in stroke patients. A total of 18 stroke patients participated in the study. The subjects were allocated randomly into two groups: an experimental group and a control group. Participants in the experimental group received MJ-JPS training (10 min) and conventional treatment (20 min), but participants in the control group only received conventional treatment (30 min). Both groups received training for five times per week for six weeks. MJ-JPS is a training method used to increase proprioception in the lower extremities; as such, it is used, to position the lower extremities in a given space. MJ-JPS measurement was captured via video using a Image J program to calculate the error distance. Balance ability was measured using Timed Up and Go (TUG) and the Berg Balance Scale (BBS). Gait ability was measured with a 10 m walking test (10MWT) and by climbing four flights of stairs. The Shapiro-Wilk test was used to assess normalization. Within-group differences were analyzed using the paired t-test. Between-group differences were analyzed using the independent t-test. The experimental group showed a significant decrease in error distance (MJ-JPS) compared to the control group (p<.05). Both groups showed a significant difference in their BBS and 10MWT results (p<.05). The experimental group showed a significant decrease in their TUG and climbing results (p<.05), but the control group results for those two tasks were not found to be significant (p>.05). There was significant difference in MJ-JPS and by climbing four flights of stairs on variation of pre and post test in between groups (p<.05), but TUG and BBS and 10MWT was no significantly (p>.05). We suggest that the MJ-JPS training proposed in this study be used as an intervention to help improve the functional activity of the lower extremities in stroke patients.
        4,000원
        12.
        2015.03 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The purpose of this study was to investigate the effects of joint position on the distraction distance in patients with adhesive capsulitis of glenohumeral joint. The study was conducted upon 20 adults in their 40's with the findings of adhesive capsulitis of glenohumeral joint. These subjects were subdivided into 3 groups, which were a group with neutral position(n=7), second group with resting position(n=7) and third group with end-range position( n=6). After having the subject wearing sleeveless shirts exposing armpit and lying straight on the plinth, a physical therapist with OMT qualification pulled glenohumeral joint at the Grade Ⅲ of Kaltenborn-Evjenth traction; and the distance between glenoid fossa and humeral head was measured with ultrasound. Following the application of traction, the group with resting position(.67±0.29) exhibited the longest distance between humeral head and glenoid fossa, and it was followed by neutral position(.50±0.25) and end-range position(.35±.21) in this order. From the comparison of these groups, there was no significant difference in distraction distance between resting position and neutral position; and there was again no significant difference in distraction distance between end-range position and neutral position. However, there was a significant difference in distraction distance between end-range position and resting position(p<.05). Upon application of the Grade Ⅲ of Kaltenborn-Evjenth traction, it was evident that the distance between humeral head and glenoid fossa can be varied depending on the location of the joint.
        3,000원
        13.
        2013.10 KCI 등재 구독 인증기관 무료, 개인회원 유료
        PURPOSES : The purpose of this study is to investigate the optimal joint positions which can minimize distresses of concrete pavement containing box culvert with horizontally skewed angles. METHODS : The concrete pavement containing the box culvert with different skewed angles and soil cover depths was modeled by 3 dimensional finite element method. The contact boundary condition was used between concrete and soil structures in addition to the nonlinear material property of soil in the finite element model. A dynamic analysis was performed by applying the self weight of pavement, negative temperature gradient of slab, and moving vehicle load simultaneously. RESULTS : In case of zero skewed angle (0˚), the maximum tensile stress of slab was the lowest when the joint was positioned directly over side of box culvert. In case there was a skewed angle, the maximum tensile stress of slab was the lowest when the joint passed the intersection between side of the box culvert and longitudinal centerline of slab. The magnitude of the maximum tensile stress converged to a constant value regardless the joint position from 3m of soil cover depth at all of the horizontally skewed angles. CONCLUSIONS : More reasonable and accurate design of the concrete pavement containing the box culvert can be possible based on the research results.
        4,000원
        14.
        2012.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The aim of this study was to examine the effects of repeated passive movement (RPM) of different velocities on the improvement of knee joint position sense (JPS) in post-stroke patients with hemiplegia, thereby investigate the possibility of clinical application in the initial stage of rehabilitation for patients with post-stroke hemiplegia. Thirteen hemiplegic patients participated in this study. For the subjects' knee JPS tests, a passive angle reproduction test and an active angle reproduction test were performed prior to and after the intervention, which involved 30 repetitions of passive full-range-of-motion flexion and extension exercise of the knee joints at randomized degrees of , , and . Paired t-test analysis was done in order to compare changes in the pre- and post-intervention knee JPS. One-way repeated analysis of variance was used in order to compare changes in JPS after intervention at three different movement velocities. The level of significance was set at .05. The result was that the subjects' post-intervention knee JPS significantly improved after the RPM exercise at a and a relative to the RPM exercise (p<.05). JPS changes with RPM intervention at the rapid velocity of were most increased, suggesting the most effective enhancement in knee JPS is with intervention at the velocity (p<.05). Therefore, RPM intervention at a half or higher velocity improved stroke patients' knee JPS. During the initial stage of rehabilitation for patients with post-stroke hemiplegia, the efficient application of the RPM exercise at a half or higher velocity will be possible.
        4,000원
        15.
        2012.04 KCI 등재 구독 인증기관 무료, 개인회원 유료
        지중구조물 주위는 다짐이 잘 되지 않아 지반이 장기 침하하므로 콘크리트 포장 하부에 공동이 발생하기 쉬우며, 이로 인해 지지력이 저하되기 쉽다. 여기에 하중이 가해지면 설계 시 기대한 것보다 큰 응력이 도입되어 포장에 파손이 발생하고 수명이 감소하게 된다. 본 논문에서는 한국도로공사 시험도로의 박스형 암거 상부 콘크리트 포장 슬래브의 파손을 조사하였다. 토피고가 다른 상행선과 하행선의 암거 위치에 발생한 슬래브의 횡방향 균열을 비교하였다. 시험도로의 횡방향 균열을 검증하기 위해 토피고가 없는 박스형 암거와 콘크리트 포장을 유한요소 방법으로 모형화하고 해석하였다. 포장의 자중을 고려하고 시험도로가 위치한 경기도 여주 지역 콘크리트 슬래브의 온도구배를 적용한 후 윤하중을 재하하였다. 각 하중조합에 대해 최대인장 응력이 발생하는 위치와 이때의 윤하중 위치를 찾아냈다. 이를 통해 최대인장응력을 감소시킬 수 있는 줄눈 위치를 찾아내고 암거 크기 별로 상부에 위치하는 슬래브의 적정 길이를 제안하였다.
        4,000원
        17.
        2009.05 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The purposes of this study were to compare abductor hallucis (AbdH) muscle activity during toe curl exercise according to position of interphalangeal joint (IPJ). Fifteen healthy subjects with neutral foot were recruit for this study. All subjects performed toe curl exercise with towel while maintaining the IPJ in flexion (condition 1) and extension (condition 2). Toe curl exercise with towel was perform three trials for five second periods in each condition. Surface electromyography (EMG) activities were recorded from three muscles (AbdH, tibialis anterior, peroneous longus) in each condition. EMG activity was normalized to the value of maximal voluntary isometric contraction (%MVIC). The EMG activities acoording to position of IPJ were compared using a paired t-test. This study showed that the EMG activity of AbdH during toe curl exercise with IPJ extension significantly increased compared to those during toe curl exercise with IPJ flexion (p<.05). However, the EMG activity of tibialis anterior and peroneus longus were not significantly different between the conditions (p>.05). These results suggest that toe curl exercise with towel must be performed with extension of IPJ in order to strengthen intrinsic muscle in subjects with overuse injuries related to excessive pronation.
        4,000원
        18.
        2007.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The purpose of this study was to compare the joint position sense at the knee joint at 3 different surface conditions by using the active knee joint angle reproduction test in the standing position. Twenty healthy volunteers (10 males and 10 females) age 20~29 years were recruited for this study. The knee joint position senses were assessed at three different surface conditions: on the floor (stable condition), TOGU (soft condition), and seat fit (unstable condition) in a closed kinetic chain. Testing orders were selected randomly. The absolute angle error was defined as the absolute difference between target angles (30°~45° knee flexion) and subject perceived angle of the knee flexion. One way ANOVA was used to compare the absolute angle of error among 3 different conditions. The Independent t-test was used to compare the absolute angle of error between male and female. The error angles were significantly different among surface conditions (1.3°±1.2° for the floor, 2.1°±0.9° for the TOGU, and 4.4°±1.8° for the seat fit, p<.05). There was no significant difference in error angle between male and female. In conclusion, the joint position sense of the knee joint in the closed kinetic chain decreased at unstable surface conditions. The result of this study indicates that surface conditions should be considered when assessing and training the joint position sense of the knee joint in clinical setting.
        4,000원
        19.
        2003.11 KCI 등재 구독 인증기관 무료, 개인회원 유료
        본 연구의 목적은 운동강도(최대근수축의 10, 30, 50, 70%)에 따라 유발되는 국소적인 근피로가 슬관절의 위치감각 인지에 미치는 영향을 연구함으로써 근력강화의 운동치료적 효과와 운동학습과 관련된 효과를 동시에 만족시키는 최적의 운동강도를 제시하는 것이었다. 대상자는 건강한 성인여자 40명이었다. 청각을 통한 위치감각 정보를 제공하는 장치와 원판 각도계가 부착된 등속성 Cybex를 사용하였다. 근피로의 상태를 확인하기 위해서 근전도를 이용하여 주파
        4,000원
        20.
        2011.08 KCI 등재 서비스 종료(열람 제한)
        A simplified linearized dynamic equation for the propulsion force generation of an Ostraciiform fish robot with elastically jointed double caudal fins is derived in this paper. The caudal fin is divided into two segments and connected using an elastic joint. The second part of the caudal fin is actuated passively via the elastic joint connection by the actuation of the first part of it. It is demonstrated that the derived equation can be utilized for the design of effective caudal fins because the equation is given as an explicit form with several physical parameters. A simple Ostraciiform fish robot was designed and fabricated using a microprocessor, a servo motor, and acrylic plastics. Through the experiment with the fish robot, it is demonstrated that the propulsion force generated in the experiment matches well with the proposed equation, and the propulsion speed can be greatly improved using the elastically jointed double fins, improving the average speed more than 80%. Through numerical simulation and frequency domain analysis of the derived dynamic equations, it is concluded that the main reason of the performance improvement is resonance between two parts of the caudal fins.