Muscle Fatigue Index Research Articles

DETERMINATION OF EPOCH LENGTH AND REGRESSION MODEL FOR 15-SECOND SEGMENT OF SEMG SIGNAL USED IN JOINT ANALYSIS OF ELECTROMYOGRAPHY SPECTRUM AND AMPLITUDE

Regression model is one of the techniques employed in Joint Analysis of Electromyography Spectrum and Amplitude (JASA) to investigate the behaviour of muscle fatigue indices. However, the analysis of the electromyography signal is influenced by the epoch length and regression model used. To meaningfully describe the behaviour of fatigue indices, this study was conducted to determine the appropriate epoch length and regression model for 15-second segment of electromyography signal. Ten subjects participated in this study. With their right forearm and upper arm formed an angle of 90 degree, the subjects were asked to hold a 2-kg dumbbell and stayed in that position for 2 minutes. Surface electromyography (sEMG) was used to record the signal from the biceps brachii muscle. Two fatigue indices were extracted: Root Mean Square (RMS) and Mean Frequency (MNF). The 120-second sEMG signal from each subject was then sliced into 8 segments (15 seconds each). In each segment, the effect of different epoch lengths (1-second, 3-second, and 5-second) was studied. Standard Error Estimate (SEE) was used to decide the suitable epoch length. The 3-second and 5-second epoch lengths were found to fit the regression model better (smaller SEE value). When 3-second and 5-second epoch lengths were applied in different regression models (linear and polynomial), polynomial regression was found to better estimate the behaviour of the fatigue indices (higher correlation coefficient). This study concludes that 3-second and 5-second epoch length can fit the polynomial regression well. However, fatigue behaviour (pattern of changes in fatigue indices) for every 15-second segment of sEMG signal is better described by JASA using polynomial regression with 3-second epoch length.

FACTOR STRUCTURE OF PARAMETERS OF EX VIVO MUSCLE GASTROCNEMIUS MEDI-ALIS ISOMETRIC CONTRACTION IN LABORATORY RATS WITH ACUTE PELVIC LIMB ISCHEMIA

Two factors that affect the own muscle contractile ability in isometric mode in rats with acute shim ischemia (1, 3 and 6 h), reproduced by compression of artery femoralis occlusion, were found by the application of method of analysis of the principal components, method of orthogonal rotation of factors in two-dimensional space varimax and scree plot criterion. Tetanic contraction of the muscle was recorded by the strain gauge method for 60 minutes. The muscle was irritated through rectangular pulses (voltage 2 V, 0.2 ms duration, frequency 50 Hz), which were formed in 12 cyclical stimulus patterns 3 sec duration and 5 min period. It was found that the first factor was loaded by variables that characterize the biomechanical muscle contraction properties: muscle strength, the time to peak tension, fusion index, muscle contraction and half-relaxation time, muscle strength increase during tetanic contraction and its reduction during tetanic half-relaxation, and the second factor - muscle fatigue index. The conclusion about the dependence of own ischemic muscle contractile ability in rats on variables of the first factor and influence of fatigue as a secondary factor was made.

Assessment of Muscle Fatigue during Prolonged, Moderate-Intensity Cycling Across Two Age Groups

PURPOSE: To examine the progression of muscle fatigue in lower limb muscles during a prolonged, moderate-intensity cycling protocol and compare adults of two age groups. METHODS: Eighteen male, healthy, novice cyclists, with no history of joint problems, participated in this study and were divided into two groups of young (Y; n=12; age= 22±2 yrs.) and old (O; n=6; age=53±3 yrs.). All participants signed an informed consent, prior to the beginning of the study. After a 2-min warm up, participants engaged in continuous cycling for 30 minutes at a constant workload of 50 W and a cadence of 60 rpm. Cycling period was followed by a 5-min cool-down. During cycling, ten 30-sec epochs of EMG data were collected at 3-min intervals from rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and gastrocnemius medialis (GT) of the right leg. Kinematics of the pedal were recorded and synchronized with the EMG data. Median frequency (MDF) of the power spectrum was utilized as an indicator of muscle fatigue. Linear regression was performed on all MDF values of each participant. T-tests were used to compare the regression slopes between the two groups and to determine the presence of sustained muscle fatigue. An ANOVA with repeated measures was used to compare the progression of transient fatigue between the two groups across all epochs. RESULTS: Occurrence of sustained muscle fatigue was not statistically significant (p>0.05) in any of the muscles. The young group showed trends of sustained fatigue by exhibiting negative average slopes for the RF (-0.14±0.77), BF (-0.14±0.78), and GT (-0.28±1.16) muscles. Whereas the older group only showed a negative average slope for the RF muscle (-0.18±0.71). Average MDF of both groups exhibited non-monotonic changes across epochs in all muscles. The transient fatigue and recovery periods appeared more frequently in older adults, compared to young; however, no significant difference (p>0.05) was observed between the two groups in any of the muscles. CONCLUSIONS: None of the groups exhibited significant emergence of transient or sustained muscle fatigue throughout the cycling session. The employed prolonged, moderate-intensity cycling exercise satisfies the ACSM guidelines for maintaining a daily dose of exercise, making it an ideal physical activity alternative for older populations.

Potential of M-Wave Elicited by Double Pulse for Muscle Fatigue Evaluation in Intermittent Muscle Activation by Functional Electrical Stimulation for Motor Rehabilitation.

Clinical studies on application of functional electrical stimulation (FES) to motor rehabilitation have been increasing. However, muscle fatigue appears early in the course of repetitive movement production training by FES. Although M-wave variables were suggested to be reliable indices of muscle fatigue in long lasting constant electrical stimulation under the isometric condition, the ability of M-wave needs more studies under intermittent stimulation condition, because the intervals between electrical stimulations help recovery of muscle activation level. In this paper, M-waves elicited by double pulses were examined in muscle fatigue evaluation during repetitive movements considering rehabilitation training with surface electrical stimulation. M-waves were measured under the two conditions of repetitive stimulation: knee extension force production under the isometric condition and the dynamic movement condition by knee joint angle control. Amplitude of M-wave elicited by the 2nd pulse of a double pulse decreased during muscle fatigue in both measurement conditions, while the change in M-waves elicited by single pulses in a stimulation burst was not relevant to muscle fatigue in repeated activation with stimulation interval of 1 s. Fatigue index obtained from M-waves elicited by 2nd pulses was suggested to provide good estimation of muscle fatigue during repetitive movements with FES.

Effect of thigh muscle fatigue on the biomechanical factors of the lower limbs when walking in a squatted position.

[Purpose] The purpose of this study was to compare and analyze the effects of thigh muscle fatigue caused by walking in a squatted position on biomechanical factors, to evaluate the risk of a job performed sitting in a squatted position for a long period of time. [Subjects and Methods] Eighteen right foot dominant women without any injuries in their joints and body in the last 6 months were selected. They walked in a squatted position, and then muscle fatigue was induced by using an isokinetic muscular function measuring device (CSMI, USA). After the CSMI measurement, the participants performed walking in a squatted position again. [Results] After inducing thigh muscle fatigue, the knee joint maximum adduction moment significantly increased and the required duration was reduced. The muscle fatigue index was positively correlated with adduction moment and negatively with the duration. It influenced the changes of maximum adduction moment; 55.0% of the adduction moment change was explained by the degree of fatigue. [Conclusion] A quantitative analysis of working in a squatted position was performed. The thigh muscle fatigue index negatively the knee joint during walking in a squatted position. Therefore, this experiment can be used as an ergonomic analysis tool of general farm work.

Muscular fatigue detection using sEMG in dynamic contractions.

In this work we have studied different indicators of muscle fatigue from the electrical signal produced by the muscles when contract (sEMG or EMG: surface electromyography): Mean Frequency of the power spectrum (MNF), Median Frequency (Fmed), Dimitrov Spectral Index (FInsm5), Root Mean Square (RMS), and Zerocrossing (ZC). The most reliable features are selected to develop a detection algorithm that estimates muscle fatigue. The approach used in the algorithm is probabilistic and is based on the technique of Gaussian Mixture Model (GMM). The system is divided into two stages: training and validation. During training, the algorithm learns the distribution of data regarding fatigue evolution; after that, the algorithm is validated with data that have not been used to train. Therefore, two experimental sessions have been performed with 6 healthy subjects for biceps.

Reduced Radial Displacement of the Gastrocnemius Medialis Muscle After Electrically Elicited Fatigue.

Assessments of skeletal-muscle functional capacity often necessitate maximal contractile effort, which exacerbates muscle fatigue or injury. Tensiomyography (TMG) has been investigated as a means to assess muscle contractile function after fatigue; however, observations have not been contextualized by concurrent physiological measures. To measure peripheral-fatigue-induced alterations in mechanical and contractile properties of the plantar-flexor muscles through noninvasive TMG concurrently with maximal voluntary contraction (MVC) and passive muscle tension (PMT) to validate TMG as a gauge of peripheral fatigue. Pre- and posttest intervention with control. University laboratory. 21 healthy male volunteers. Subjects' plantar flexors were tested for TMG parameters, along with MVC and PMT, before and after either a 5-min rest period (control) or a 5-min electrical-stimulation intervention (fatigue). Temporal (contraction velocity) and spatial (radial displacement) contractile parameters of the gastrocnemius medialis were recorded through TMG. MVC was measured as an indicator of muscle fatigue, and PMT was measured to assess muscle stiffness. Radial displacement demonstrated a fatigue-associated reduction (3.3 ± 1.2 vs 4.0 ± 1.4 mm, P = .031), while contraction velocity remained unaltered. In addition, MVC significantly declined by 122.6 ± 104 N (P < .001) after stimulation (fatigue). PMT was significantly increased after fatigue (139.8 ± 54.3 vs 111.3 ± 44.6 N, P = .007). TMG successfully detected fatigue, evident from reduced MVC, by displaying impaired muscle displacement accompanied by elevated PMT. TMG could be useful in establishing skeletal-muscle fatigue status without exacerbating the functional decrement of the muscle.

Changes In Select Emg Parameters During An Agility Test Performed To Fatigue.

PURPOSE: To determine the effect of fatigue (FAT) on the mean median frequency (MF) and peak amplitude (PA) of select muscles. METHODS: Surface EMG of the vastus medialis (VM), vastus lateralis (VL), semitendinosus (ST) and biceps (BF) and rectus femoris (RF) were recorded at 4800Hz in 16 female, DI soccer players (19.7 ± 1.1 yrs), during an agility test. Subjects completed 4 trials of the test, alternating sides. Rest between trials ensured non-FAT. Subjects then ran trials starting every 30s, alternating sides, until a 5% decrement in their non-FAT times occurred on 2 successive runs. Two trials from each side were then run and recorded as the FAT trials. For each muscle, the EMG data were band pass filtered. The MF of a 107 ms moving window was calculated using a time-frequency analysis based on power spectra estimation (short-time Fourier transform) for each muscle, for each trial. The mean MF for the trial was determined using the obtained MFs. The mean PA for each muscle was determined by dividing the trial into 107 ms windows obtaining the PA of the window and then obtaining the mean of the individual PAs. The average MFs and PAs for each trial were grouped into 3 trial periods: the first 4 non-FAT, 4 middle and the last 4 FAT trials. Linear mixed models, with trial period as a repeated factor, were used to test for differences in average MF and PA between trial periods. RESULTS: For all 5 muscles for both legs, there was a significant difference in average MF and PA across trial periods (p <0.001). Pairwise comparisons showed a significant decrease for both the MF and PA from the non-FAT trials to the middle trials on all muscles for both legs (p <0.001). Significant decreases from middle trials to FAT trials were noted for all muscles for both legs for PA (p <0.05) except the left BF, while for MF, significant differences were noted for the right RF and VL, and the left VM, RF, and VL (p-<0.01). Across all muscles MF decreased 7.6% from the non-FAT to middle trials and decreased another 3.1% from middle to FAT trials. Similarly, across all muscles PA decreased 17.5% from the non-FAT to middle trials and further decreased 16.9% from middle to FAT trials. CONCLUSIONS: In the current testing paradigm, during a dynamic task in which performance decreases overtime, a decrease in the average MF and PA are potential indicators of muscle fatigue.

Electrophysiological characteristics according to activity level of myofascial trigger points

[Purpose] This study compared the differences in electrophysiological characteristics of normal muscles versus muscles with latent or active myofascial trigger points, and identified the neuromuscular physiological characteristics of muscles with active myofascial trigger points, thereby providing a quantitative evaluation of myofascial pain syndrome and clinical foundational data for its diagnosis. [Subjects] Ninety adults in their 20s participated in this study. Subjects were equally divided into three groups: the active myofascial trigger point group, the latent myofascial trigger point group, and the control group. [Methods] Maximum voluntary isometric contraction (MVIC), endurance, median frequency (MDF), and muscle fatigue index were measured in all subjects. [Results] No significant differences in MVIC or endurance were revealed among the three groups. However, the active trigger point group had significantly different MDF and muscle fatigue index compared with the control group. [Conclusion] Given that muscles with active myofascial trigger points had an increased MDF and suffered muscle fatigue more easily, increased recruitment of motor unit action potential of type II fibers was evident. Therefore, electrophysiological analysis of these myofascial trigger points can be applied to evaluate the effect of physical therapy and provide a quantitative diagnosis of myofascial pain syndrome.

Four-Month Course of Soluble Milk Proteins Interacts With Exercise to Improve Muscle Strength and Delay Fatigue in Elderly Participants

BackgroundThe benefit of protein supplementation on the adaptive response of muscle to exercise training in older people is controversial. ObjectiveTo investigate the independent and combined effects of a multicomponent exercise program with and without a milk-based nutritional supplement on muscle strength and mass, lower-extremity fatigue, and metabolic markers. DesignA sample of 48 healthy sedentary men aged 60.8 ± 0.4 years were randomly assigned to a 16-week multicomponent exercise training program with a milk-based supplement containing, besides proteins [total milk proteins 4 or 10 g/day or soluble milk proteins rich in leucine (PRO) 10 g/day], carbohydrates and fat. Body composition, muscle mass and strength, and time to task failure, an index of muscle fatigue, were measured. Blood lipid, fibrinogen, creatine phosphokinase, glucose, insulin, C-reactive protein, interleukin-6, tumor necrosis factor-α soluble receptors, and endothelial markers were assessed. ResultsBody fat mass was reduced after the 4-month training program in groups receiving 10 g/day of protein supplementation (P < .01). The training program sustained with the daily 10 g/day PRO was associated with a significant increase in dominant fat free mass (+5.4%, P < .01) and in appendicular muscle mass (+4.5%, P < .01). Blood cholesterol was decreased in the trained group receiving 10 g/day PRO. The index of insulin resistance (homeostasis model assessment–insulin resistance) and blood creatine phosphokinase were reduced in the groups receiving 10 g/day PRO, irrespective of exercise. The inflammatory and endothelial markers were not different between the groups. Training caused a significant improvement (+10.6% to 19.4%, P < .01) in the maximal oxygen uptake. Increased maximum voluntary contraction force was seen in the trained groups receiving 10 g/day of proteins (about 3%, P < .05). Time to task failure was improved in the trained participants receiving a 10 g/day supplementation with PRO (P < .01). ConclusionsSoluble milk proteins rich in leucine improved time to muscle failure and increase in skeletal muscle mass and strength after prolonged multicomponent exercise training in healthy older men.

Assessment of Muscle Endurance of the Knee Extensor Muscles in Adolescents With Spastic Cerebral Palsy Using a Submaximal Repetitions-to-Fatigue Protocol

ObjectiveTo compare muscle endurance in adolescents with spastic cerebral palsy (CP) with typically developing (TD) peers using a submaximal repetitions-to-fatigue (RTF) protocol. DesignCross sectional. SettingHuman motion laboratory. ParticipantsAdolescents with spastic CP (n=16; Gross Motor Function Classification System levels I or II) and TD adolescents (n=18) within the age range of 12 to 19 years old. InterventionsNot applicable. Main Outcome MeasuresEach participant performed 3 RTF tests at different submaximal loads, ranging from 50% to 90% of their maximal voluntary knee extension torque. The relation between the number of repetitions (repetition maximum [RM]) and imposed submaximal relative (percent of maximal voluntary torque [%MVT]) and absolute (Nm/kg) torque was quantified. To compare adolescents with CP with TD adolescents, a mixed linear model was used to construct load endurance curves. Surface electromyography of quadriceps muscles was measured to assess changes in normalized amplitude and median frequency (MF) as physiological indicators of muscle fatigue. ResultsAdolescents with CP showed a larger decrease in %MVT per RM than TD adolescents (P<.05). TD adolescents showed substantial higher absolute (Nm/kg) load endurance curves than adolescents with CP (P<.001), but they did not show a difference in slope. Electromyographic normalized amplitude increased significantly (P<.05) in the quadriceps muscles in all tests for both groups. Electromyographic MF decreased significantly (P<.05) in tests with the low and medium loads. Electromyographic responses did not differ between groups, indicating that similar levels of muscle fatigue were reached. ConclusionsAdolescents with CP show slightly lower muscle endurance compared with TD adolescents on a submaximal RTF protocol, which is in contrast with earlier findings in a maximal voluntary fatigue protocol. Accordingly, adolescents with CP have a reduced capacity to endure activities at similar relative loads compared with TD adolescents.

Efficacy of pre-exercise low-level laser therapy on isokinetic muscle performance in individuals with type 2 diabetes mellitus: study protocol for a randomized controlled trial

BackgroundType 2 diabetes, also known non-insulin-dependent diabetes, is the most prevalent type of the disease and involves defects in the secretion and action of insulin. The aim of the proposed study is to evaluate the efficacy of pre-exercise low-level laser therapy (LLLT) on muscle performance of the quadriceps femoris in individuals with type 2 diabetes.Methods/DesignA double-blind, randomized, controlled clinical trial will be carried out in two treatment phases. In the first phase, quadriceps muscle performance will be evaluated using an isokinetic dynamometer and the levels of creatine kinase and lactate dehydrogenase (biochemical markers of muscle damage) will be determined. The participants will then be allocated to four LLLT groups through a randomization process using opaque envelopes: Group A (4 Joules), Group B (6 Joules), Group C (8 Joules) and Group D (0 Joules; placebo). Following the administration of LLLT, the participants will be submitted to an isokinetic eccentric muscle fatigue protocol involving the quadriceps muscle bilaterally. Muscle performance and biochemical markers of muscle damage will be evaluated again immediately after as well as 24 and 48 hours after the experimental protocol. One week after the last evaluation the second phase will begin, during which Groups A, B and C will receive the LLLT protocol that achieved the best muscle performance in phase 1 for a period of 4 weeks. At the end of this period, muscle performance will be evaluated again. The protocol for this study is registered with the World Health Organization under Universal Trial Number U1111-1146-7109.DiscussionThe purpose of this randomized clinical trial is to evaluate the efficacy of pre-exercise LLLT on the performance of the quadriceps muscle (peak torque, total muscle work, maximum power and fatigue index – normalized by body mass) in individuals with DM-2. The study will support the practice of evidence-based to the use of LLLT in improving muscle performance in Individuals with DM-2. Data will be published after the study is completed.

Wide-pulse-high-frequency neuromuscular stimulation of triceps surae induces greater muscle fatigue compared with conventional stimulation

We compared the extent and origin of muscle fatigue induced by short-pulse-low-frequency [conventional (CONV)] and wide-pulse-high-frequency (WPHF) neuromuscular electrical stimulation. We expected CONV contractions to mainly originate from depolarization of axonal terminal branches (spatially determined muscle fiber recruitment) and WPHF contractions to be partly produced via a central pathway (motor unit recruitment according to size principle). Greater neuromuscular fatigue was, therefore, expected following CONV compared with WPHF. Fourteen healthy subjects underwent 20 WPHF (1 ms-100 Hz) and CONV (50 μs-25 Hz) evoked isometric triceps surae contractions (work/rest periods 20:40 s) at an initial target of 10% of maximal voluntary contraction (MVC) force. Force-time integral of the 20 evoked contractions (FTI) was used as main index of muscle fatigue; MVC force loss was also quantified. Central and peripheral fatigue were assessed by voluntary activation level and paired stimulation amplitudes, respectively. FTI in WPHF was significantly lower than in CONV (21,717 ± 11,541 vs. 37,958 ± 9,898 N·s P<0,001). The reductions in MVC force (WPHF: -7.0 ± 2.7%; CONV: -6.2 ± 2.5%; P < 0.01) and paired stimulation amplitude (WPHF: -8.0 ± 4.0%; CONV: -7.4 ± 6.1%; P < 0.001) were similar between conditions, whereas no change was observed for voluntary activation level (P > 0.05). Overall, our results showed a different motor unit recruitment pattern between the two neuromuscular electrical stimulation modalities with a lower FTI indicating greater muscle fatigue for WPHF, possibly limiting the presumed benefits for rehabilitation programs.

High‐pass‐filter cut‐offs optimization of the filter‐based fatigue index during dynamic contractions

) havea relatively low sensitivity under dynamic exercise condi-tions. Various muscle fatigue indices have been attemptedto overcome this problem [1,2]. However, their methodsrequired large amounts of computation and had limitationsin time-frequency resolution [3]. Kim et al. introduced theuse of a filter-based fatigue index (FI

미세전류 자극이 척주세움근의 피로지수에 미치는 영향

본 연구는 단시간 들기 내리기 작업을 실시한 누적피로 대상자에게 미세전류자극 및 휴식을 적용하여 피로 지수에 미치는 영향을 비교하였다. 2012년 12월부터 2013년 2월까지 S대학에서 연구가 진행되었으며, 말초질환 및 근골격계 질환이 없고 오른손을 사용하는 20대의 신체 건강한 남자 22명을 대상자로 선정하였다. 모든 대상자는 10 kg 상자를 15분 동안 들기 내리기를 100회 실시한 직후, 표면근전도기를 이용한 근피로지수(Median Frequency : MF)와 혈액피로지수(Creatine Kinase Lactate : CK, Lactate Dehydrogenase : LDH)를 측정하였다. 두 그룹으로 나누어 실험군에는 미세전류자극을 대조군에는 휴식을 각각 20분간 중재하였다. 중재 후, 근피로지수와 혈액피로지수를 측정하여 누적 피로지수의 변화를 비교하였다. 그 결과 휴식그룹의 왼쪽 척주세움근 피로지수를 제외한 두 그룹 모두에서 중재방법 적용 전보다 적용 후 유의한 누적피로의 감소(p<.05)가 있었고, 미세전류의 자극은 휴식과 비교했을 때, 근피로지수의 유의한 감소(p<.05)를 보였지만, 혈액피로지수는 차이가 없었다. 본 연구의 결과를 토대로 미세전류자극은 반복적인 들기와 내리기 작업 종사자들의 근피로회복에 도움이 될 것이라 사료되며, 장시간 피로지수 추적조사 및 중재 적용시간에 따른 피로회복의 상관관계 대한 추가적인 연구가 필요하다. This study aimed to compare the effects of microcurrent stimulation and rest on the fatigue index by applying both to subjects who had accumulated fatigue after performing short-duration physical activity. The experiment was performed at S University from December 2012 to February 2013, on 22 healthy men in their 20s, who were right-handed, and without peripheral or musculoskeletal diseases. All subjects lifted a 10-kg box lift and lower 100 times in 15 minutes. Immediately after that, muscle fatigue index (Median Frequency: MF) and blood fatigue index (Creatine Kinase Lactate: CK, Lactate Dehydrogenase: LDH) were measured by using surface electromyography. The subjects were divided into two groups, and microcurrent stimulation and rest were mediated to the experimental and control groups, respectively, for 20 minutes. After intervention, muscle fatigue index and blood fatigue index were measured and the changes in the accumulated fatigue index were compared. Both groups manifested significantly decreased cumulative fatigue after applying the mediation compared to the pre-intervention level (p < .05), the only exception being the fatigue index of the left erector spinae in the rest group. Compared to the rest group, the microcurrent stimulation group showed a significant decrease in muscle fatigue index (p < .05) but no significant differences were found in the blood fatigue index. Given the results of this study, microcurrent stimulation is considered to be helpful in muscle fatigue recovery for workers who have to perform repetitive movements lifting weights, and additional studies on the correlations of the fatigue recovery with respect to the long-term follow-up of fatigue index and mediation time are necessary.

Relationship between CNTF gene polymorphism and athletes training adaptation of muscle tissue

To explore the relationship between CNTF gene polymorphism and athletes training adaptation of muscle tissue. A total of 215 new students without a training history CNTF genotype were recruited from a sports college. During training, the changes in test object biceps muscle belly cross-sectional area, muscle fatigue and muscle damage related biochemical indices were detected. And the impact of gene polymorphism was analyzed on the detection results. After training, biceps brachii muscle cross-sectional areas showed different degrees of growth and the GG gene type growth was greater than other genotypes (P < 0.05) . At post-training physical examination, all subjects of muscle fatigue and muscle damage index were higher than those of the control group, but no obvious difference existed between examination groups.In basic training at the end of physical examination, the related indices of each group were higher than those of the control group, but the values of lactic acid, blood urea nitrogen and serum CK value were lower for object type GG than those for the other groups [ (234.7±57.5) vs (84.7±24.7) U, (5.8±0.8) vs (4.3±0.6) mmol/L, (271.5±98.7) vs (59.2±35.6) U] (P < 0.05). During training, muscle cross-sectional area of GG genotype grows more while the serum levels of muscle injury are significantly lower than those of other groups. In summary, GG genotype has better muscle training adaptation than GA and AA.

Possibility of intrinsic muscle contractile properties in force summation and postactivation potentiation as indices of maximal muscle strength and muscle fatigue

We investigated whether intrinsic muscle contractile properties in force summation and postactivation potentiation (PAP) can be used as indices of maximal muscle strength and muscle fatigue. Twelve men participated in this study. The maximum voluntary contraction torque (MVC), torque evoked by several stimulations in the tibialis anterior (TA) muscle, force summation parameters, and PAP were evaluated with the progression of fatigue. The force summation parameters were evaluated with respect to responses of single, double, and triple stimulations. The percent decreases in the evoked torque parameters with or without PAP were greater than those during MVC. Force summation parameters were significantly related to MVC and fatigue resistance. Intrinsic muscle contractile properties with or without PAP in the TA overestimate fatigue during MVC. However, force summation parameters can be used as indices of maximal muscle strength with or without fatigue and fatigue resistance capacity.

Mean and Median Frequency of EMG Signal to Determine Muscle Force based on Time-Dependent Power Spectrum

The analysis of EMG signals can be generally divided into three main issues, i.e., muscle force, muscle geometry and muscle fatigue. Recently, there are no universal indices that can be applied for all issues. In this paper, we modify the global fatigue indices, namely mean frequency (MNF) and median frequency (MDF), to be used as a muscle force and fatigue index. Due to a drawback of MNF and MDF that it has a non-linear relationship between muscle force and feature value, especially in large muscles and in cyclic dynamic contractions. A time-dependence of MNF and MDF (TD-MNF and TD-MDF) is computed for dynamic contractions. Subsequently, a slope of the regression line that fits maximum values of MDF (and MNF) during a number of cyclic contractions is used as a fatigue index. To be additionally used as a muscle force index, some suitable ranges of TD-MNF and TD-MDF should be selected and five effective statistical parameters including mean, median, variance, root mean square and kurtosis, were applied to the selected range. From the experiments, the performance of TD-MNF is definitely better than that of TD-MDF. The results showed that mean and median features of the selected TD-MNF series have a better linear relationship with muscle force (load level) compared to the traditional methods and have a significant difference (p<0.001) between feature values for different loading conditions. Moreover, there is a certain pattern of TD-MNF for all trials and subjects that has not been found in traditional MNF. TD-MNF is optimized when an overlapping consecutive window method is performed with a 384-sample window-size and a 192-sample window-increment. In total, mean and median features of the selected TD-MNF series can be used as a muscle force and fatigue index. In future works, the proposed method can be used instead of using multiple features for the EMG signal analysis.

축구선수의 진행형 요부안정화운동이 복횡근 두께와 하지근육 피로지수에 미치는 영향

This study aimed to assess the effects of progressive lumbar stability exercises and lumbar stability exercises on changes in the transversus abdominis muscle thickness and lower extremity muscle fatigue index in soccer players. Ten subjects were assigned to undergo training in each of the 2 groups, namely, the progressive lumbar stability exercise group and lumbar stability exercise group. Each intervention session lasted for 30 min, and 4 sessions were conducted in a week for 6 weeks for soccer players of S. University in Jeonnam, Korea. Changes in the transversus abdominis muscle thickness and lower extremity muscle fatigue index were measured using ultrasound and surface electromyogram. The results of the ultrasound measurement for the transversus abdominis muscle thickness indicated that progressive lumbar stability exercises were more effective than lumbar stability exercises. The results of the lower extremity muscle fatigue index measurements using surface electromyogram indicated that the fatigue index decreased in the progressive lumbar stability exercise group. Progressive lumbar stability exercise is believed to have put more workload during the shaking of the limbs, leading to increased stability and increased efficiency of the lower extremity muscle, thereby decreasing the fatigue index. Therefore, progressive lumbar stability exercises can be an effective measure for preventing injuries and improving the game performance of sports players by increasing the transversus abdominis muscle thickness and decreasing the lower extremity muscle fatigue index.

Transgenic overexpression of heat shock protein 72 in mouse muscle protects against exhaustive exercise-induced skeletal muscle damage

Lifelong overexpression of heat shock protein (HSP) 72 in skeletal muscle is known to protect against age-related oxidative stress and muscle damage. This study aimed to ascertain whether exhaustive exercise (EE)-induced muscle fatigue and damage can be prevented by lifelong overexpression of HSP72 in skeletal muscle. Transgenic mice heterozygous for the porcine HSP70.2 gene ([+]HSP72) and transgene-negative littermate controls ([-]HSP72) were subjected to an EE protocol. Mice were randomly divided into four groups: sedentary [-]HSP72, sedentary [+]HSP72, EE [-]HSP72, and EE [+]HSP72. Animals were killed 82 minutes after the start of EE to determine muscular levels of HSP72, serum levels of superoxide dismutase (SOD, an antioxidant enzyme) and lactate (an indicator of muscle fatigue), muscular levels of matrix metalloproteinase (an indicator of inflammatory myopathies), and muscular damage. During the test, the latency value for the occurrence of EE was 79-85 minutes and 100-110 minutes for [-]HSP72 and [+]HSP72 mice, respectively. After EE, [+]HSP72 mice had significantly higher serum SOD and significantly lower serum lactate, muscular matrix metalloproteinase or myeloperoxidase activity, and muscle damage compared to [-]HSP72 mice. The results suggest that HSP72 overexpression in skeletal muscle may improve muscle fatigue and damage in EE by reducing oxidative damage and phagocytic infiltration, at least in mice.