• 한국전문물리치료학회지
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• 제8권2호
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• pp.41-54
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• 2001

Fatigue is the decline in force produced as a result of prolonged muscle activity. Localized muscle fatigue can be identified by a shift toward low in the frequency components of the EMG signal, typically represented by a fall in the median frequency. Previous studies show that a shortened muscle develops a higher fatigue than elongated muscles. The purpose of this study was to investigate the time-related change of median frequency and torque during maximal isometric back extension exercises at different exercise angles ($0^{\circ}$, $12^{\circ}$, $36^{\circ}$, $72^{\circ}$). Twenty healthy subjects (mean age = $24.35{\pm}2.70$) were evaluated in this study. Median frequency was extracted from the EMG signals by fast Fourier transform (FFT). Initial median frequency and the slope of median frequency change over time were computed from linear regression analysis. Pearson's product moment correlation was used to quantify the relationship between slope of median frequency and torque. The results were as follows: 1) Significant differences in y-intercepts of torque regression equation with respect to exercise angle were shown. However, there were no differences in the slopes of the median frequency and torque, and y intercept of the median frequency among exercise angles. 2) There was no significant correlation between slope of median frequency and torque. 3) But there was moderate correlation between median frequency and torque at each exercise angle. In conclusion, the exercise angle during maximal isometric back extension exercise is not a direct effect on slope of median frequency and torque. But results showed that median frequency and torque shift were highly correlated in all subjects.

• International Journal of Contents
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• 제10권3호
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• pp.90-95
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• 2014

The purpose of this study was to analyze the changes in muscle fatigue by using electromyography (EMG) measurements of the median frequency of shoulder muscles of patients who underwent rotator cuff repair, and to provide basic data for efficient exercise methods during rehabilitation after the repair. In the study, 24 male and 8 female patients who underwent rotator cuff repair performed continuous passive shoulder joint motion for 3 weeks and the median frequency of their shoulder muscles before and after the repair were compared using measurements by EMG. The infraspinatus, supraspinatus, and serratus anterior muscles showed significant differences in the changes in the median frequency before and after the repair. Significant differences were also found in the median frequency of the three muscles both before and after the repair. Additionally, the middle deltoid muscle had a lower median frequency than the supraspinatus muscle before the repair and the infraspinatus muscle had a lower median frequency than the middle deltoid muscle after the repair. It is expected that these results will serve as important data in developing rehabilitation exercise programs for the infraspinatus, supraspinatus, and serratus anterior muscles by compensating the middle deltoid muscle with the lowest muscle fatigue after the rotator cuff repair erase.

• 한국안전학회지
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• 제15권1호
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• pp.153-160
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• 2000

Occupational cumulative traumas (CTDs) are becoming one of leading ailments in industrialized worl $d^{(1.2)}$. The degree of muscle fatigue is important parameter to understand cause of occupational cumulative trauma disorders. To quantify degree of muscle fatigue, muscle EMG activity was measured during isometric and dynamic contractions(repetitive concentric/eccentric muscle contraction) and its analyzed data, such as RMS, median frequency, and median power were compared when the muscle was fresh and exhausted. When muscle become fatigue, it was observed that median frequency decreased and median power and RMS increased However, based on overall prolonged observation, median frequency increased and median power and RMS decreased. Therefore it was concluded that shifting patterns of RMS, median frequency, and median power values can be used as parameter to evaluate degree of muscle fatigue even in dynamic muscle contraction.

• 한국전문물리치료학회지
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• 제10권3호
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• pp.141-149
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• 2003

Median frequency can be regarded as a valid indicator of local muscle fatigue. As local muscle fatigue develops, the muscle fiber conduction velocity decreases, the fast twitch fibers are recruited less, and consequently the median frequency shifts toward the lower frequency area. The aim of this study was to test the characteristics of the median frequency according to exercise load (30% and 60% of MVC on the biceps brachii, 40% and 80% of MVC on the vastus lateralis) during the fatiguing isometric exercise. Thirteen healthy male volunteer students of Yonsei University were recruited. After the testing maximal voluntary isometric contraction, three variables (initial median frequency, regression slope, fatigue index) from the regression line of MDF data were measured in each exercise load. The results showed that the regression slope and fatigue index were significantly different for the biceps brachii, but not for the vastus lateralis initial MDF was not significant difference according to the exercise load on both muscles. The regression slope and fatigue index could monitor physiologic muscle change during fatiguing isometric exercise. The results showed that two MDF variables reflect the local muscle fatigue according to the exercise load.

• 한국정보전자통신기술학회논문지
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• 제3권1호
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• pp.8-12
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• 2010

본 연구에서는 t-test와 ANOVA를 이용하여 근전도의 중앙주파수 추출을 위한 AR모델 차수결정 및 중앙주파수 비교에 관한 연구이다. 근전도의 근피로와 관계된 특징인자인 영교차율 및 저대역에너지, 중앙주파수를 추출하여 근피로에 이를 때까지의 변화를 평가해 봄으로써 근피로 정도나 시점까지의 변화 정도를 비교 및 고찰하였다.

• Communications for Statistical Applications and Methods
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• 제11권3호
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• pp.513-518
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• 2004

The well-known mode-mean-median inequality for the unimodal population distribution does not always hold for the frequency distribution. But many elementary statistics text books just mention that the relative location of the mean and median can be used to determine whether a distribution is positively or negatively skewed. In this paper we introduce the method generating data that is positively skewed but mean

• 대한의용생체공학회:의공학회지
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• 제24권3호
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• pp.175-181
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• 2003

근피로 연구는 주로 등척성(isometric)운동에서 수행되었고 등장성(isotonic)운동에서 얻은 근전도 신호는 통제하기 힘든 잡음이 많아 등척성운동에서 사용된 주파수분석기법을 동일하게 적용하였을 때 신뢰할만한 중앙주파수 자료와 근피로 판정용 변수를 구하는데 어려움이 있었다 이에 본 연구에서는 등장성운동에서 측정한 근전도신호의 중앙주파수 검출방법에 따른 근피로 판정 변수들의 차이를 비교해 보고자 하였다 이를 위해 동일한 근전도신호를 가지고 FFT 수행간격과 연속적인 FFT구간의 중첩비율을 다르게 하여 중앙주파수를 검출하고 이들의 선형회귀직선을 구하여 회귀직선상의 변수인 초기중앙주파수, 기울기. 근피로지수를 비교한 결과, 초기중앙주파수의 경우 FFT 수행간격이 넓을수록 조금씩 상승하는 것으로 나타났고, 기울기의 경우 FFT 수행간격이 넓을수록 중첩구간이 적을수록 기울기의 감소경향이 뚜렷하게 나타났다. 근피로지수의 경우는 특정 FFT 수행간격에서 가장 높은 수치를 나타냈다

• 대한의용생체공학회:의공학회지
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• 제23권1호
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• pp.9-16
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• 2002

국부적 근 피로는 근전도 신호의 저주파역으로의 천이, 특히 중앙주파수의 감소로 특징된다. 여러 운동각도(0$^{\circ}$, 12$^{\circ}$, 36$^{\circ}$, 72$^{\circ}$)에서 등척성 요추신전운동을 수행하는 동안 근 피로에 따른 근전도 신호의 중앙주파수와 토크의 특성을 살펴보고자 총 20명 (평균 연령 24.35$\pm$2.70세)의 건강i한 피검자를 대상으로 본 실험연구를 수행하였다. 근전도 신호로부터 FFT를 사용하여 중앙주파수를 추출하였으며 선형회귀분석을 통해서 시간에 따른 초기중앙주파수의 초기값과 기울기를 계산하였다. 중앙주파수의 기울기와 토크의 기울기에 대한 상관관계를 정량화하기 위해서 피어슨 상관계수를 적용하였다 중앙주파수의 기울기(p〈0.656)나 v-절편(p〈0.609), 피로지수(p〈0.555)에서는 요추의 각도 타이에 영향을 받지 않아 유의한 차이가 없었으며. 토크의 기울기. 피로지수 역시 유의한 차이가 없었으나, 토크의 ｙ-절편에서는 차이(p〈0.04)가 나타나서, 근육의 길이 증가와 자세변화가 토크에 영향을 미침을 알 수 있었다. 또한, 개인간의 중앙주파수와 토크의 기울기에는 상관관계가 낮았으나, 개인 내에서 중앙주파수와 토크의 시계열 변화에는 유의한 상관관계(0.682)가 있음을 알 수 있었다.

• 대한전기학회논문지:시스템및제어부문D
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• 제55권7호
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• pp.344-351
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• 2006

The fatigue of back muscle in the repetitive lifting motion was studied using multiple parameters(FFT_MDF, RMS, 2C, NT) in this study. Recent developments in the time-frequency analysis procedures to compute the IMDF(instantaneous median frequency) were utilized to overcome the nonstationarity of EMG signal using Cohen-Posch distribution. But the above method has a lot of computation time because of its complexity. So, in this study, FFT_MDF(median frequency estimation based on FFT) algorithm was used for median frequency estimation of back muscle EMG signal during muscle work in uniform velocity portion of lumbar movement. The analysis period of EMG signal was determined by using the run test and lumbar movement angle in dynamic task, such as lifting. Results showed that FFT_MDF algorithm is well suited for the estimation of back muscle fatigue from the view point of computation time. The negative slope of a regression line fitted to the median frequency values of back muscle EMG signal was taken as an indication of muscle fatigue. The slope of muscle fatigueness with FFT_MDF method shows the similarity of 77.8% comparing with CP_MDF(median frequency estimation based on Cohen Posch distribution) method.

• 대한의용생체공학회:의공학회지
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• 제33권3호
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• pp.135-140
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• 2012

Previous investigators have shown that the frequency compression is related to the muscle fatigue and the decreasing conduction velocity of muscle fibers. The aim of the present study was to investigate the relationship between endurance times and frequency parameters such as mean power frequency and median frequency in the surface EMG signal during isotonic contractions. Eight healthy subjects performed voluntary isotonic contractions of biceps Brachii muscle until their endurance times which were determined when the subject could no longer follow the contraction cycle. The regressive slopes of mean power frequency and median frequency were used to describe the frequency compression of the surface EMG signal, and to test the predictability of endurance time. As results of experiment, significant correlations were found between endurance time and the regressive slopes of mean power frequency and mean frequency computed over 50%Tend of endurance time.