Changes In Median Frequency Research Articles

Myoelectric manifestations of fatigue of the finger flexor muscles and endurance capacity in experienced versus intermediate climbers during suspension tasks

ABSTRACT Climbing is a physically demanding discipline, placing significant loads on the finger flexors. Notwithstanding the documented greater endurance capacity of experienced climbers, the mechanisms explaining these training-induced adaptations remain unknown. We therefore investigate whether two non-competing strategies – muscle adaptation and alternate muscle recruitment – may explain the disparity in endurance capacity in participants with different climbing experience. We analysed high-density surface electromyograms (EMGs) from 38 Advanced and Intermediate climbers, during suspension exercises over three different depths (15, 20, 30 mm) using a half-crimp grip position. From the spatial distribution of changes in MeDian Frequency and Root Mean Square values until failure, we assessed how much and how diffusely the myoelectric manifestations of fatigue took place. Advanced climbers exhibited greater endurance, as evidenced by significantly longer failure time (p < 0.009) and lower changes in MDF values (p < 0.013) for the three grip depths. These changes were confined to a small skin region (nearly 25% of the grid size), centred at variable locations across participants. Moreover, lower MDF changes were significantly associated with longer suspension times. Collectively, our results suggest that muscle adaptation rather than load sharing between and within muscles is more likely to explain the improved endurance in experienced climbers.

Comments on: Electromyographic signature of isometric squat in the highest refuge in Europe.

We read the comment by Šarabon and Sašek (Eur J Transl Myol 11846, 2023 doi: 10.4081/ejtm.2023.11846) on our study on the electromyographic results during squat at high-altitude. Their highlighting of the factors that may have biased our results is commendable, despite they criticized our work as if it were a controlled laboratory study. We considered the limitations and argued our interpretation with caution. We found no changes in median frequency, frequency's slope and conduction velocity of EMG signals at high altitude, and a slight decrease of root mean square. We argued that our results may have been due to a preventative mechanism that compensates for relatively greater effort during a fatiguing strength test involving large muscle masses, or to cumulative exertional stress on the muscles. The authors of the comment themselves somehow agree with these interpretations. Guidelines for collecting, reporting and interpreting data from EMG to obtain original information on the neuromuscular system should be integrated with the effort to maintain as much as possible those field conditions that offer unique opportunities.

Electromyographic signature of isometric squat in the highest refuge in Europe.

Reports of electromyography during hypoxic exercise are contrasting, due to protocol and muscle diversity. This work aimed to investigate alterations in muscle activation and myoelectrical fatigue during exercise at high-altitude in those muscles primarily involved in trekking. Twelve young adults balanced by gender and age were tested at low (1,667 m) and high (4,554 m, "Capanna Margherita", Italy) altitude, during an isometric squat lasting 60 seconds. High-density surface electromyography was performed from the quadriceps of right limb. The root mean square (RMS), median frequency with its slope, and muscle fiber conduction velocity (MFCV) were computed. Neither males nor females showed changes in median frequency (Med: 36.13 vs 35.63 Hz) and its slope (Med: -9 vs -12 degree) in response to high-altitude trekking, despite a great inter-individual heterogeneity, nor differences were found for MFCV. RMS was not significantly equivalent, with greater values at low altitude (0.385 ± 0.104 mV) than high altitude (0.346 ± 0.090 mV). Unexpected results can be due either to a postural compensation of the whole body compensating for a relatively greater effort or to the inability to support muscle activation after repeated physical efforts. Interesting results may emerge by measuring simultaneously electromyography, muscle oxygenation and kinematics comparing trekking at normoxia vs hypoxia.

The relationship between visual impairments and activity of the neck/shoulder muscles among surgeons during simulated surgical tasks.

Minimally Invasive Surgery (MIS) has an impact on surgeons' musculoskeletal and visual systems. However, the relationship between visual symptoms and musculoskeletal problems is not well understood. This study used surface electromyography (sEMG) to examine changes in fatigue of the neck/shoulder muscles among surgeons with visual impairments when performing simulated surgical tasks in 2D and 3D viewing modes. Cross-sectional laboratory study. Changes in median frequency (MDF, an indicator of muscle fatigue) were examined in 17 experienced gynaecologists. Four simulated surgical laparoscopy tasks were performed in 2D and 3D viewing modes. The MDF of three neck/shoulder muscles (cervical erector spinae, [CES], upper trapezii [UT], and anterior deltoids [AD]) were examined bilaterally. Visual parameters (accommodation, convergence, and stereoacuity) were measured prior to commencement. There was a downward shift of MDF from simple to more complex tasks for the right and left CES and AD muscles but not the UT, which was consistent for surgeons with mild accommodation/convergence impairment and/or good stereoacuity. There were significant differences in the level of muscle fatigue of the neck/shoulder muscles according to the severity of visual impairment, muscle side, task and surgical performance level. The results show a relationship between the degree of visual impairments and muscle fatigue of the neck/shoulder muscles among MIS surgeons. These findings have important implications in understanding the concurrence of musculoskeletal problems and visual symptoms.

Immediate and Delayed Effects of Cupping Therapy on Reducing Neuromuscular Fatigue.

Cupping therapy has been popular in elite athletes in recent years. However, the effect of cupping therapy on reducing muscle fatigue has not been investigated. The purpose of this study was to investigate the immediate and delayed effects of cupping therapy on reducing biceps brachii fatigue during biceps curls. Twelve healthy untrained participants were recruited for this repeated-measures study. Cupping therapy (–300 mmHg pressure for 5 min) and sham control (no negative pressure for 5 min) were applied after biceps fatigue induced by performing repeated biceps curls at 75% of the 10 repetitions of maximum of the non-dominant hand. Surface electromyography (EMG) with spectral analyses [mean frequency (MNF), median frequency (MDF), and spectral moments ratio (SMR)] were used to assess muscle fatigue during the fatigue task. EMG signals during the first 10 repetitions and the last 10 repetitions of biceps curls were used to assess neuromuscular fatigue. There were significant decreases in MNF and MDF and a significant increase in SMR immediately and 24 h after the sham control (no intervention). When comparing the MNF, MDF, and SMR after cupping therapy to the sham control, there was no significant immediate effect on reducing muscle fatigue. However, there was a significant delayed effect on improving recovery following fatigue for the cupping therapy compared to the sham control (MNF changes: sham 0.87 ± 0.02 vs. cupping 0.91 ± 0.02, p < 0.05; MDF changes sham: 0.85 ± 0.03 vs. cupping: 0.91 ± 0.02, p < 0.05; SMR changes: sham 1.89 ± 0.15 vs. cupping 1.58 ± 0.13, p < 0.05). The findings of this study demonstrate that there is a time effect of cupping therapy for reducing muscle fatigue. Cupping therapy is effective on reducing biceps brachii muscle fatigue after 24 h.

Changes in muscle activity with exercise-induced fatigue in Thoroughbred horses

Understanding the effects of fatigue can provide guidance for training regimens and injury prevention. We have previously reported that the integrated-electromyogram (iEMG) values of the M. gluteus medius and brachiocephalicus decreased with exercise-induced fatigue, whereas those of the M. longissimus dorsi and infraspinatus were not affected. We hypothesised that exercise-induced fatigue would decrease the activities of the muscles associated with propulsive force but not associated with joint stabilisation. Surface EMG recordings of the forelimb muscles (M. triceps brachii, common digital extensor, ulnaris lateralis), and hindlimb muscles (M. semitendinosus, extensor digitorum longus, extensor digitorum lateralis and flexor digitorum lateralis) were conducted on eight Thoroughbreds. Horses galloped on a treadmill (grade, 3%) at a constant speed (12.6-14.8 m/s) until they could not maintain their position with minimal human encouragement (~5 min). The stride frequency, iEMG for a stride and median frequency during muscle discharge were calculated every 30 s. These parameters were compared between the start and end of the test phase for the leading and trailing limbs. The stride frequency (P&lt;0.01) and iEMG values of the M. semitendinosus in both the leading (P&lt;0.01) and trailing limbs (P&lt;0.05) and those of the M. extensor digitorum longus in the trailing limbs (P&lt;0.05) significantly decreased at the end of the test. No median frequency changes were observed in the assessed muscles. Although muscular fatigue itself was not detected, observed fatigue caused by high-intensity exercise resulted in inability to maintain speed, which was associated with decreased iEMG values in the hip extensor muscles that generate propulsive force. In contrast, almost all muscles that stabilise joints were unaffected by fatigue. One exception was the decreased muscle activity observed in the M. extensor digitorum longus of the trailing limb, which may suggest unstable ground contact. Muscle activity changes with fatigue might be associated with muscle functions.

Is the timed loaded standing test a valid measure of back muscle endurance in people with vertebral osteoporosis?

The TLS test is suggested as a measure of back muscle endurance for patients with vertebral osteoporosis. However, to date, no study has demonstrated that TLS does measure back extensor or erector spinae (ES) muscle endurance. We used surface electromyography (sEMG) to investigate the performance of the thoracic ES muscles during TLS. Thirty-six people with vertebral osteoporosis with a mean age of 71.6 (range 45-86) years participated. sEMG recordings were made of the ES at T3 and T12 bilaterally during quiet standing (QS) and TLS. The relative (%) change in sEMG amplitude between conditions was compared. Fatigue was evaluated by analysing the change in median frequency (MF) of the sEMG signal during TLS, and the correlation between maximal TLS time and rate of MF decline was examined. Activity in the ES increased significantly during TLS at all electrode locations. During TLS, the MF declined at a mean rate of -24.2% per minute (95% C.I. -26.5 to -21.9%). The MF slope and test time were strongly correlated (r2 = 0.71), and at test end, the final MF dropped to an average 89% (95% C.I. 85 to 93%) of initial MF. Twenty-eight participants (78%) reported fatigue was the main reason for stopping, and for eight (22%), it was pain. This study demonstrates that TLS challenges the ES muscles in the thoracic region and results in ES fatigue. Endurance time and the point at which the TLS test ends are strongly related to ES fatigue.

Deficit of entropy modulation of the EEG in schizophrenia associated to cognitive performance and symptoms. A replication study

Spectral entropy (SE) is a measurement from information theory field that provides an estimation of EEG regularity and may be useful as a summary of its spectral properties. Previous studies using small samples reported a deficit of EEG entropy modulation in schizophrenia during cognitive activity. The present study is aimed at replicating this finding in a larger sample, to explore its cognitive and clinical correlates and to discard antipsychotic treatment as the main source of that deficit. We included 64 schizophrenia patients (21 first episodes, FE) and 65 healthy controls. We computed SE during performance of an odd-ball paradigm, at the windows prior (−300 to 0ms) and following (150 to 450ms) stimulus presentation. Modulation of SE was defined as the difference between post- and pre-stimulus windows. In comparison to controls, patients showed a deficit of SE modulation over frontal and central regions, also shown by FE patients. Baseline SE did not differ between patients and controls. Modulation deficit was directly associated with cognitive deficits and negative symptoms, and inversely with positive symptoms. SE modulation was not related to antipsychotic doses. Patients also showed a smaller change of median frequency (i.e., smaller slowing of oscillatory activity) of the EEG from pre- to post-stimulus windows. These results support that a deficit of fast modulation contributes to cognitive deficits and symptoms in schizophrenia patients.

An empirical profile of VLF triggered emissions

AbstractThe Siple Transmitter Experiment operated from 1973 to 1988 and generated a wealth of observations of nonlinear wave‐particle interactions including extensive recordings of triggered emissions generated by VLF signals injected into the magnetosphere from the transmitter at Siple Station, Antarctica. Due to their complex appearance and immensely varied behavior, triggered emissions remain poorly described and understood. This work provides a comprehensive statistical description of observed triggered emissions and establishes statistical bounds on triggered emission type (fallers, risers, and positive and negative hooks) and behavior (frequency changes between 1 kHz and 2.5 kHz with initial sweep rates between −2.5 kHz/s and 2.5 kHz/s, with risers undergoing a median frequency change of 556 Hz and fallers a median frequency change of −198 Hz). The statistical study also reveals an apparent dependence of the triggered emission behavior on the transmitted signal itself. Long tones and rising ramps generate more risers and positive hooks, while short tones and falling ramps produce more fallers and negative hooks. Triggered emissions also appear to favorably initiate with sweep rates similar to that of the triggering element, with the 1 kHz/s rising ramps triggering initial risers with a median sweep rate of 1.03 kHz/s and −1 kHz/s triggering initial fallers with a median sweep rate of −0.73 kHz/s. These results improve observations of wave modification resulting from wave‐particle interactions in the radiation belts and can be used to validate numerical simulations of triggered emissions.

Verification of anti-fatigue effect of anserine by angle fatigue indicator based on median frequency changes of electromyograms

Objective: Anserine, which is abundant in avian species and in a wide range of fish such as bonito and tuna, is reported to have anti-fatigue effect. Although chicken soup and bonito soup is traditionally used to recover from physical fatigue, it is generally difficult to verify the effect in humans. This study was to directly demonstrate the anti-fatigue effect of oceanic anserine in humans. Methods: Edible-grade anserine was purified from fish extract with food-grade reagents. Subjects were 17 healthy male volunteers (35.5 ± 5 yr., 75.5 ± 5.0 kg). Each subject performed the isometric exercise tolerance test (ETT) on the rectus femoris muscle twice (Ex_1, Ex_2) both for anserine and water conditions on a different day. Median frequency changes (MDF) during ETTs were calculated and regression curves were calculated over a frequency range of 21-214 Hz. The difference, or angle, between the slopes of Ex_1 and Ex_2 MDF regression curves, which corresponds to the degree of fatigue, was defined as an angle fatigue index and compared between anserine and water intake conditions.Results: MDF decreased during ETTs in most patients and the slopes of regression curves were larger in Ex_2 than in Ex_1. Angle fatigue index for water (control) was significantly larger than that for anserine (p&lt;0.01, paired t-test, n=17). The result indicates that anserine have an anti-fatigue effect on skeletal muscle in humans. Conclusions: We proposed the angle fatigue index as a touchstone of the muscle fatigue. The index indicates that anserine is effective to reduce the muscle fatigue in humans.Keywords: anserine, muscle fatigue, electromyogram, median frequency power, MDF angle

스트레칭의 유형에 따른 근활성도 및 최대 수의적 등척성 수축력의 유지기간 비교

본 연구는 넙다리곧은근에 적용한 정적 및 탄성적 스트레칭의 유지기간을 알아보기 위하여 남성 22명을 대상으로 정적 스트레칭 군 11명과 탄성적 스트레칭 군 11명을 스트레칭 적용 전, 적용 후 30초, 1분 후, 3분 후, 5분 후, 10분 후에 중앙주파수 및 최대 수의적 등척성 수축력의 변화를 분석하였다. 중앙주파수는 시간에 따른 변화와 군 간에서 유의한 차이를 보였다. 정적 스트레칭군과 탄성적 스트레칭군 모두에서 3분후까지 감소되었다가 증가되었다. 최대 수의적 등척성 수축력은 시간에 따른 변화와 군 간에서도 유의한 차이를 보였다. 정적 스트레칭군은 3분후까지 감소되었다가 그 이후부터 증가되었으며, 탄성적 스트레칭군은 5분후까지 감소되었다가 증가되었다. 결론적으로 스트레칭 적용 후 시간에 따라 변화를 보였으며, 정적 스트레칭보다 탄성적 스트레칭의 효과가 조금 더 길게 유지되는 것을 알 수 있었다. This study selected 22 male subjects to examine the maintenance period of static and ballistic stretching applied to rectus femoris, divided them into 11 static stretching group and 11 ballistic stretching group and analyzed changes in median frequency and in maximal voluntary isometric contraction before stretching and at 30 sec, 1 min, 3 min, 5 min, and 10 min after stretching. Median frequency showed significant differences in changes according to time and groups after the test of main effects. It was reduced after 3 min. in both static stretching and ballistic stretching groups and then increased again. Maximal voluntary isometric contraction showed significant differences in changes according to time and groups from the results of the main effect test. Static stretching group was reduced at 3 min after the experiment and then increased after that and ballistic stretching group was reduced at 5 min after the experiment and then increased again. In conclusion, changes were shown according to time after stretching and the effects of ballistic stretching were maintained a little longer than those of static stretching.

Neuromuscular response to varying pressures created by tightness of restriction cuff

Variation in regional body composition between genders may change the degree of pressure created by the tightness of cuff used during blood flow restriction training resulting in changes in the level of neuromuscular activation. This study investigates the effects of tightness of cuff and skin and subcutaneous fat thickness on electromyography (EMG) amplitude (RMS) and median frequency (MDF) during exercises and strength testing. Subjects performed knee-extension exercises with varying tightness of cuff while using EMG to measure changes in neuromuscular response. EMG RMS was significantly affected by tightness of cuff and skin and subcutaneous fat thickness. The strongest individual variable for the changes in MDF was also skin and subcutaneous-fat thickness. The changes in EMG response due to tightness of cuff and the effect of skin and subcutaneous fat thickness on tightness of cuff prove the importance of details on BFR protocol and leg composition on neuromuscular function during BFR exercises.

Muscle fatigue during repetitive voluntary contractions: A comparison between children with cerebral palsy, typically developing children and young healthy adults

AimTo combine peak torque and EMG analyses to investigate the hypothesis that 1) children with cerebral palsy (CP) have lower muscle fatigability than typically developing children (TD) and whether 2) muscle fatigue correlates with muscle strength. MethodsSeven CP children, eight TD children and ten young healthy adults (YHA) performed an all-out fatigue test of 35 maximal concentric knee extension and flexion contractions on an isokinetic dynamometer. Angular velocity was set at 60°/s. Peak torque (PT) was determined per repetition and either normalized to bodyweight or maximum voluntary torque. Surface-EMG of quadriceps and hamstring muscles was measured to obtain changes in median frequency (EMG-mf) and smooth rectified EMG amplitude per contraction. ResultsDecline in PT differed between all groups for extensors and flexors, where YHA showed the largest decline and CP children the smallest decline over the course of the test. YHA showed a larger decline in EMG-mf of all quadriceps and hamstrings than TD and CP children, while TD children showed a larger decline in EMG-mf of m.rectus femoris and m.vastus lateralis than CP children. InterpretationResults confirm that children with CP show lower fatigability than TD children and that the lower fatigability coincides with lower maximal muscle strength.

Spectral properties of surface electromyogram signal and change in muscle conduction velocity during isometric muscle contraction

It is well known that there is a change in the spectrum of surface electromyogram (sEMG) with the onset of muscle fatigue. This change has largely been attributed to the change in muscle conduction velocity. We have investigated this theory by using our previously developed sEMG model with the various neuromuscular parameters. The change of spectrum of the experimental results has been compared with simulated sEMG in response to the change in muscle conduction velocity using similar conditions. In this study, the designed model implemented the change in the muscle conduction velocity (\(\Delta v\)) as a parameter to simulate the sEMG. The shift in spectrum was identified by computation of the median frequency (MDF) of the sEMG before and after the implementation of the rate of the slow down (RS or \(\Delta v\)) parameter in the model. The results based on the simulation of the model show that the rate of change in MDF was consistent in all levels of contractions and it is not same with experimental conditions. The results also suggest that the large change in MDF in the simulated sEMG than in experimental conditions may be attributable to other factors such as change in the recruitment pattern and the level of contraction not only due to the change in the muscle conduction velocity (\(\Delta v\)).

Divergent muscle fatigue during unilateral isometric contractions of dominant and non-dominant quadriceps

ObjectivesWe examined mechanical and electromyographic responses of unilateral dominant and non-dominant m. quadriceps femoris during fatiguing submaximal isometric contractions and early recovery. DesignWithin subjects randomized. MethodsHealthy males (n=18, age: 20±2yr, height: 181±7cm, and body mass: 79.4±10.5kg) attended two sessions. Leg dominance was based on the preferred kicking leg. Maximal voluntary isometric force, endurance time and force fluctuations during a 20%MVIF until exhaustion were measured simultaneously with surface electromyography (EMG) of m.vastus lateralis and m.vastus medialis at a knee angle of 90° as well as the MVIF 20s after exhaustion (early recovery). ResultsThe maximal voluntary isometric force of dominant m. quadriceps femoris was 4.6% higher (D: 749±178N, ND: 716±184N, and P=0.01). The m. quadriceps femoris of both legs had similar endurance times during the 20%MVIF (D: 367±157s, ND: 381±153s, and P=0.40). Force fluctuations during the 20%MVIF increased over time (two-way ANOVA, P<0.05) with no differences between legs at comparable time points. Changes in median frequency and root mean square of m.vastus lateralis and m.vastus medialis during the 20%MVIF were similar for both legs. However, after the 20%MVIF, early recovery, quantified by the fatigue index, showed larger force loss for dominant m. quadriceps femoris (D: 39.9±15.7%, ND: 34.8±16.0%, and P<0.05). ConclusionsMuscle fatigue that develops during submaximal sustained isometric contractions may not be accurately quantified by force loss soon after exhaustion. The present study has implications for unilateral studies to examine mechanisms of muscle fatigue.

A study of median frequencies of skeletal muscle undergoing Tuina intervention in patients with chronic fatigue syndrome

To study the changes in median frequency (MF) from a surface electromyogram of skeletal muscles and functional assessment of chronic illness therapy (FACIT) figure scale scores for patients with chronic fatigue syndrome (CFS) before and after Tuina treatment. A controlled clinical trial was adopted. Thirty-two patients suffering from CFS were enrolled according to the inclusion criteria from outpatient department of Shanghai Yueyang Hospital of Integrated Chinese and Western Medicine in China; thirty normal people whose gender, age, height and body mass were concordant with the CFS patients were selected as the normal group. Surface electromyography was used to detect the median frequency (MF) of biceps, quadriceps, and waist and back muscle before and after a 20-day course of treatment. CFS patients also were asked to fill out the figure scale of FACIT to evaluate the degree of fatigue. There was no significant difference in surface electromyography MF of myoelectric signal of biceps and quadriceps between CFS and normal person; however, the waist and back muscle MF of the normal person was significantly lower than that of the CFS patients. Before and after treatment, there were no obvious changes in the MF of myoelectric signals of all muscles. Tuina significantly decreased the scale score of FACIT. Tuina can improve the symptom of patients with CFS.

Back extensor muscle fatigue at submaximal workloads assessed using frequency banding of the electromyographic signal

Background Changes in the mean or median frequency of the electromyographic (EMG) power spectrum are often used to assess skeletal muscle fatigue. A more global analysis of the spectral changes using frequency banding may provide a more sensitive measure of fatigue than changes in mean or median frequency. So, the aim of the present study was to characterize changes in different power spectrum frequency bands and compare these with changes in median frequency. Methods Twenty male subjects performed isometric contractions of the back muscles in an isometric dynamometer at 30%, 40%, 50% and 60% of maximum voluntary contraction. During each contraction, surface EMG signals were recorded from the right and left longissimus thoracis muscles, and endurance time was measured. The EMG power spectra were divided into four frequency bands (20–50 Hz; 50–80 Hz; 80–110 Hz; 110–140 Hz) and changes in power in each band with fatigue were compared with changes in median frequency. Findings The percentage changes in 20–50 Hz band were greater than in all other and the rate of change in power, indicated by the slope, was also greatest in 20–50 Hz band. Also, 20–50 Hz band had a greater change in power than the median frequency. Interpretation Power in the low frequency part of the EMG power spectrum increases with fatigue in a load-dependent manner. The rate of change in low frequency power may be a useful indicator of fatigue rate or “fatigability” in the back muscles. Also, changes in low frequency power are more evident than changes in the median frequency.

Effect of Botulinum Toxin on Pressure Pain Threshold and EMG Power Spectrum of Masseter Muscle During Sustained Fatiguing Contraction

The aims of this study were to test the effect of botulinum toxin on a reversible, prolonged, experimental pain and on muscle fatigue in human masseter muscle, both caused by a sustained clench. The masseter muscles were injected with botulinum toxin in 19 subjects and with isotonic saline in 16 subjects. We measured electromyographic activity at maximum voluntary contraction, pressure pain threshold before and after a 70% maximum voluntary contraction clench sustained to pain tolerance, and the median frequency of the electromyographic power spectrum during that clench at baseline and at 1, 2, and 3 mos after botulinum toxin or saline injection. After botulinum toxin injection, the botulinum toxin group had a reduced maximum voluntary contraction for the ensuing 3 mos and smaller decreases in pressure pain threshold from before to after the sustained clench. Also, the change in median frequency from before to after the sustained clench did not significantly differ during the postinjection sessions. However, postinjection, preclench median frequency was lower in the group injected with botulinum toxin. We interpret the reduced change in pressure pain threshold with botulinum toxin as a clinically modest but statistically significant analgesic effect on this model of acute muscle pain.

Differentiation of power and endurance athletes based on their muscle fatigability assessed by new spectral electromyographic indices

The aim of this study was to differentiate between endurance and power athletes based on electromyographic (EMG) data analysed using new spectral indices. Nine endurance and six strength athletes were recruited to complete sets of knee extension repetitions (15 per set) until exhaustion, with each set followed by a maximal voluntary isometric knee extensor contraction. Peripheral muscle fatigue of the vastus lateralis, vastus medialis, and rectus femoris (bilaterally) was quantified by the changes in median frequency of the EMG power spectrum and a new spectral EMG fatigue index. Cluster analysis of the fatigue indices differentiated athletes into two groups: endurance (fatigue resistant) and strength (faster fatigue), whereas cluster analysis of the median EMG power spectrum frequency produced six indistinct groups. The average fatigue index for the quadriceps group increased across repetitions by 40 ± 24% in the endurance group and by 184 ± 12% in the strength group. The decrease in peak force and power across repetitions, and the rate of force decrease during maximal voluntary contraction per set, were significantly smaller for the endurance than for the strength group. The new spectral EMG indices effectively discriminated between strength and endurance athletes, thus providing a useful functional index that could be applied to track training adaptations as well as potentially talent identification.

하지 자세가 근전도, 심박수 그리고 불편도에 미치는 영향분석

Repetitive movement, inadequate working posture, overuse of force, physical contact with sharp edge, vibration and temperature were well known risk factors of WMSDs (Work-related Musculoskeletal Disorders). Many researchers have investigated the relationship between inadequate working postures and incidences of WMSDs of the upper extremities, whereas relatively few researchers have tried to evaluate workload associated with the lower-body postures. The effects of lower-limb postures including various knee flexion angles on the subjective discomfort, heart rate and EMG of lower-limb muscles were investigated in this study. Thirty graduate students were asked to maintain thirteen different body postures, and heart rate and EMG data of five muscle groups (electro spine, biceps femoris, vastus medialis, gastrocnemius and tibialis anterior) from each posture were collected during fifteen minutes sustaining tasks. All participants were also asked to report their discomfort ratings of body parts. Results showed that high subjective discomfort ratings and heart rates were reported at the postures of knee angles of and , whereas low discomfort ratings were founded at the postures of chair heights with 20cm, 40cm, and sitting with crossed legged. The change of median frequency for each muscle group during fifteen minutes tasks was investigated for each body posture to evaluate the relationship between muscle fatigue and body posture. It was found that the trends of changes of median frequency were different based on muscle group as well as lower-limb body posture from this study.