Research Paper: Evaluation of Electromyographic Activity of Upper Trapezius Muscle Fatigue in Patients with Latent Myofascial Trigger Point: A Randomized Control Trial (original) (raw)
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2018
Introduction: Latent Myofascial Trigger Points (LMTrPs) are defined as certain pain-free hyperirritable spots in a taut band of muscle, which lead to alternation in muscle activation pattern in both loaded and unloaded conditions. Fatigue can alter the stability of the cervical spine because of transferring loads to the passive connective tissues and also increasing muscle activity. Few studies have investigated the effects of fatigue on the parameters of the upper trapezius muscle as a more common muscle to MTrPs. This study attempts to examine the electromyographic activity of the upper trapezius muscle fatigue during shoulder elevation.Materials and Methods: Thirty-six right-handed subjects without upper extremity disorders took part in this study. The highest measured force level was assumed to be the Maximal Voluntary Contraction (MVC) of the trapezius. A sustained submaximal contraction of the trapezius was performed. The subjects were asked to sustain a unilateral (80%) MVC isometric shoulder elevation until the force gauge monitor showed (50%) of MVC in at least three minutes.Results: The Root Mean Square (RMS norm) of the sustained trapezius contractions showed differences between the groups. The Myocardial Depressant Factor (MDF) parameters of the left and right sides of both healthy subjects and patients were significantly different (P<0.001).Conclusion: The increase in RMS is related to the recruitment of additional motor units and also an increased firing rate. These are necessary to compensate for the loss of force. This accumulation also inhibits the excitability of the muscle membrane, thereby causing a decrease in the firing rate and, consequently, a decrease in Median Frequency (MF).
Journal of Electromyography and Kinesiology, 2009
Two physiological factors are assumed in this paper to mainly determine the myoelectric manifestations of fatigue: 1) the decrease of the conduction velocity (CV) of motor unit action potentials (MUAP) (peripheral fatigue), and 2) the increase of MU synchronization by the central nervous system (central fatigue). To describe separately the peripheral and central components of 5 the myoelectric manifestations of fatigue, we investigated the following indexes: 1) mean spectral frequency -MNF, 2) median spectral frequency -MDF, 3) root mean square -RMS, 4) average rectified value -ARV, 5) estimation of muscle fiber conduction velocity -ECV, 6) percentage of determinism -%DET , 7) spectral indexes defined as the ratio between signal spectral moments -FI k , 8) MNF estimated by autoregressive analysis -MNF AR , 9) MNF estimated by Choi-Williams 10 time-frequency representation -MNF CWD , 10) MNF estimated by continuous wavelet transform -MNF CWT , 11) signal entropy -S, 12) fractal dimension -FD. The indexes were tested with a set of synthetic EMG signals, with different CV distribution and level of MU synchronization. The indexes were calculated on epochs of 0.5 s. It was observed that ECV is uncorrelated with the level of simulated synchronization (promising index of peripheral fatigue). On the other hand FD was the 15 index least affected by CV changes and most related to the level of synchronism (promising index of central fatigue). A representative application to some experimental signals from vastus lateralis muscle during an isometric endurance test supported the results of the simulations. The vector (ECV, FD) is suggested to provide selective indications of peripheral and central fatigue. The description of EMG fatigue by a bi-dimensional vector opens new perspectives in the assessment of 20 muscle properties, with potential application in both clinical and sport sciences. Dedering A, Roos af Hjelmsater M, Elfving B, Harms-Ringdahl K, Nemeth G. Between days 25 reliability of subjective and objective assessments of back extensor muscle fatigue in subjects without lower back pain, J Electromyogr Kinesiol, 2000. 10: 151-158 Dimitrov GV, Arabadzhiev TI, Hogrel JY, Dimitrova NA.
Low-threshold motor unit activity during a 1-h static contraction in the trapezius muscle
International Journal of Industrial Ergonomics, 2002
Many workers, including computer workers, with repetitive or monotonous work tasks develop work-related shoulder myalgia, even from work with low muscle activity. The Cinderella hypothesis postulates that low-threshold motor units (MUs) which are first recruited also are the first ones to be at risk for selective fibre injuries in a sustained activation of the muscle due to long-duration activation. The validity of the Cinderella hypothesis demands that there exist MUs which can be active for long times. MU firing patterns were examined in the trapezius muscle on 8 healthy subjects during 60 min of static isometric contraction corresponding to approximately 5% of maximal voluntary electrical activity. In 3 out of 8 subjects, MUs were found that were continuously active throughout the 60-min measurement, with the exception of a few 1-3 s interruptions coinciding with surface electromyographic dips in two of these subjects. Indications of MU substitution were also found in all subjects. Thus, it seems to be possible for some low-threshold MUs to be continuously active, while substitution occur among others. The results support the Cinderella hypothesis for fibre injuries in low-threshold MUs exposed to long-term muscle activations.
European Journal of Applied Physiology, 2006
The aim of the present study was to investigate the extent to which work-related muscular disorders of the upper trapezius affect the activity of other pain-free muscles, in particular in the biceps brachii. Two groups of female subjects (age >43 years) participated in the study: seven affected subjects with self-reported disorders in the shoulder/neck region (cases) and nine healthy subjects (control group). Multi-channel electromyography (EMG) and force were recorded during maximum voluntary contractions (MVC) and during 6 min sustained contractions (at 30% MVC) of the upper trapezius and biceps brachii on the dominant side. From the EMG signals, the root mean square (RMS), median frequency (MDF) and single motor unit (MU) conduction velocity (CV) were estimated. From the force signal, the coefficient of variation was calculated. All data are presented as mean values and standard deviation. Differences between the cases and controls were found in the MVC force of the upper trapezius, which was lower in cases [253 (70) N] than in controls [357 (75) N], while the coefficient of variation of force during the sustained contraction was increased [cases 5.5 (2.2); controls 4.1 (1.9)]. The RMS (normalized to the RMS at MVC) during the 6 min sustained contractions was significantly lower in the cases than in the controls for both the upper trapezius and the biceps brachii. A tendency towards a smaller increase in the RMS with fatigue was only found in the trapezius muscle [slope: cases 6.5 (14.1) %/min, controls 10.2 (12.9) %/min]. No differences were found between the two subject groups with respect to the MDF and single MU CV in both muscles. While the lower RMS for the trapezius muscles of the cases may reflect changes at the local level, as well as in motor control, the lower biceps activity indicates a change in the central control strategies of the primarily unaffected muscle. Indications for a changed fatigability of the muscle were only found in the trapezius.
Human muscle fatigue: frequency dependence of excitation and force generation
The Journal of physiology, 1988
1. Human adductor pollicis was fatigued using intermittent trains of programmed stimulation at 1, 10, 20, 50, 100 and 1 Hz, during activity with and without circulatory occlusion, to investigate the relationships between force generation, excitation and maximal relaxation rate (MRR). 2. The relationship between force generation and excitation was markedly dependent on stimulation frequency. Force loss was greatest at low frequencies, with little reduction in excitation, but as frequency increased force was well maintained despite marked loss of excitation. 3. Changes in MRR during activity and recovery were independent of stimulation frequency. 4. Marked increases of force at 1 Hz (pre-tetanic) and 10 Hz occurred, with little reduction in excitation, during activity with and without circulatory occlusion. This may be due to post-tetanic potentiation in addition to slowing of relaxation (MRR). 5. At high frequency a 'safety factor' may thus operate to maintain force, despite ...
The investigation of median frequency changes in paraspinal muscles following fatigue
Objectives: There are two sub systems of paraspinal muscles, the global-mobilizing system and the local stabilizing system. The multifidus muscles are assigned to the local system and stabilize the joints. In contrast, the longissimus muscles are assigned to the global system and force exertion. This study aimed to investigate the median frequency changes in mobilizing and stabilizing muscles following fatigue. Method: A cross sectional study was designed. sEMG measurements were recorded from twenty participants following a fatigue protocol in B200 dynamometer. Participants performed dynamic trunk fl exion-extension against a moderate resistance while standing in a static dynamometer until they could no longer performs the task because of fatigue. Results: Statistical analyses showed significant differences between median frequencies pre and post fatigue (p<0.05). Median frequency of the right and left multifudus muscles reduced from "99.12 and 93.2" to "86.55 and 85.85" respectively. Also Median frequency of the right and left longissimus reduced from "76.54 and 76.82" to "66.43 and 68.55" respectively. Conclusion: Median frequency shift toward low values following fatigue in global and local paraspinal muscles was seen. However, median frequency values for the local stabilizer muscle were higher than median frequency values for the global muscles.
European Journal of Applied Physiology and Occupational Physiology, 1991
A comparison of the mean power frequency (MPF) and the root mean square amplitude (rms) of the myo-electric signal of two agonist muscles [triceps brachii (fast; TB) and anconeus (slow; ANC)] has been made during repeated intermittent static contractions. Subjects were asked to maintain different extension torques at 50% of maximal voluntary contraction until this could no longer be maintained (endurance time). The interval between successive contractions was kept constant at 3 min. During the first six successive contractions, a decrease in MPF and an increase in rms were most pronounced, ANC and TB MPF recovered with subsequent overshoot. A marked decline in endurance time was also seen. The increase in rms was greater for TB than for ANC when the decrease in MPF was greater for ANC than for TB. The differences in power spectrum density function upper frequencies of the two muscles could explain the greater decrease of MPF in ANC. Our data would suggest a greater fatigability in TB relative to ANC. On and after the seventh contraction, a steady-state in duration, muscle temperature, MPF and rms was reached. These results suggested that a slow (ANC) and a fast (TB) muscle acted in a similar way during intermittent static contractions, when the intervening rest was not long enough to allow full recovery of the muscles.