Detection of surface electromyography recording time interval without muscle fatigue effect for biceps brachii muscle during maximum voluntary contraction

The effects of fatigue on maximum voluntary contraction (MVC) parameters were examined by using force and surface electromyography (sEMG) signals of the biceps brachii muscles (BBM) of 12 subjects. The purpose of the study was to find the sEMG time interval of the MVC recordings which is not affected by the muscle fatigue. At least 10 s of force and sEMG signals of BBM were recorded simultaneously during MVC. The subjects reached the maximum force level within 2 s by slightly increasing the force, and then contracted the BBM maximally. The time index of each sEMG and force signal were labeled with respect to the time index of the maximum force (i.e. after the time normalization, each sEMG or force signal’s 0 s time index corresponds to maximum force point). Then, the first 8 s of sEMG and force signals were divided into 0.5 s intervals. Mean force, median frequency (MF) and integrated EMG (iEMG) values were calculated for each interval. Amplitude normalization was performed by dividing the force signals to their mean values of 0 s time intervals (i.e. ?0.25 to 0.25 s). A similar amplitude normalization procedure was repeated for the iEMG and MF signals. Statistical analysis (Friedman test with Dunn’s post hoc test) was performed on the time and amplitude normalized signals (MF, iEMG). Although the ANOVA results did not give statistically significant information about the onset of the muscle fatigue, linear regression (mean force vs. time) showed a decreasing slope (Pearson-r = 0.9462, p < 0.0001) starting from the 0 s time interval. Thus, it might be assumed that the muscle fatigue starts after the 0 s time interval as the muscles cannot attain their peak force levels. This implies that the most reliable interval for MVC calculation which is not affected by the muscle fatigue is from the onset of the EMG activity to the peak force time. Mean, SD, and range of this interval (excluding 2 s gradual increase time) for 12 subjects were 2353, 1258 ms and 536–4186 ms, respectively. Exceeding this interval introduces estimation errors in the maximum amplitude calculations of MVC–sEMG studies for BBM. It was shown that, simultaneous recording of force and sEMG signals was required to calculate the maximum amplitude of the MVC–sEMG more accurately.     

An investigation of the simultaneously recorded occlusal contact and surface electromyographic activity of jaw-closing muscles for patients with temporomandibular disorders and a scissors-bite relationship

Surface electromyographic (SEMG) activity of the masseter and anterior temporalis (TA) muscles has been reported to be associated with occlusion and orofacial pain. However, our recent report did not reveal an association between the side of orofacial pain and the side showing higher or lower level of SEMG activity of masseter or TA. The present purpose was to re-test this association in patients who had unilateral scissors-bite relationship. Thirty-two unilateral scissors-bite femalepatients complaining of unilateral orofacial pain (n = 15) or TMJ sounds (n = 17) were enrolled to simultaneously record contacts, force distribution of occlusion, and SEMG activity of masseter and TA during centric maximal voluntary clenching (MVC). The results indicated that neither orofacial pain nor the TMJ sounds had an association with the masseter’s SEMG values, while scissors-bite had (P < 0.05). A lower SEMG value for masseter was found on the scissors-bite side where there was a smaller number of contacts and a lower biting force distribution (P < 0.05). No such association was revealed in TA. In conclusion, in patients with unilateral TMD symptom(s) and scissors-bite, the jawclosing muscles’ SEMG activity during centric MVC was associated with the scissors-bite rather than the symptoms of orofacial pain or TMJ sounds.     

Intramuscular fine-wire electromyography during cycling: Repeatability,normalisation and a comparison to surface electromyography

This study investigated (a) the feasibility and repeatability of intramuscular fine-wire electromyographic (fEMG) recordings from leg muscles during the repetitive, high-velocity cycling movement, (b) the influence of amplitude normalization technique on repeatability and statistical sensitivity, (c) the influence of test-retest interval duration on repeatability, and (d) differences between fEMG and surface EMG (sEMG) recordings of cycling. EMG activity of leg muscles was recorded using surface and fine-wire electrodes during one (n = 12, to investigate statistical sensitivity and compare sEMG and fEMG) or two sessions (T1 and T2, 5–20 days apart, n = 10, to investigate repeatability). fEMG recordings were feasible and there was high repeatability of fEMG recordings normalised to maximum measured EMG amplitude (MAX); mean coefficients of multiple correlation (CMC) ranged from .83 ± .13 to .88 ± .07. Data normalised to maximal (MVC) or submaximal contractions (sMVC) were less repeatable (p < .01). Statistical sensitivity was also greatest for data normalised to MAX (p < .01). Repeatability of fEMG increased with greater test-retest intervals (p < .01). The global pattern of muscle recruitment was consistent between sEMG and fEMG but sEMG recordings were characterized by additional myoelectric content. These findings support and guide the use of fEMG techniques to investigate leg muscle recruitment during cycling.     

Multi-channel electromyography during maximal isometric and dynamic contractions

Motor unit behavior differs between contraction types at submaximal contraction levels, however is challenging to study during maximal voluntary contractions (MVCs). With multi-channel surface electromyography (sEMG), mean physiological characteristics of the active motor units can be extracted. Two 8-electrode sEMG arrays were attached on biceps brachii muscle (one on each head) to examine behavior of sEMG variables during isometric, eccentric and concentric MVCs of elbow flexors in 36 volunteers.On average, isometric (364 ± 88 N) and eccentric (353 ± 74 N) MVCs were higher than concentric (290 ± 73 N) MVC (p < 0.001). Mean muscle fiber conduction velocity (CV) was highest during eccentric MVC (4.42 ± 0.49 m/s) than concentric (4.25 ± 0.49 m/s, p < 0.01) and isometric (4.14 ± 0.45 m/s, p < 0.001) MVCs. Furthermore, eccentric MVC showed lower sEMG amplitude at the largest elbow joint angles (120–170°) and higher CV at the smallest (70–150°) elbow joint angles (p < 0.05–0.001) than concentric MVC.The differences in CV and sEMG amplitude between the MVCs suggest that the control strategy of motor units differs between the contraction types during MVCs, and is dependent on the muscle length between the dynamic MVCs.     

Tennis players show a lower coactivation of the elbow antagonist muscles during isokinetic exercises

PurposePrevious studies have suggested that muscle coactivation could be reduced by a recurrent activity (training, daily activities). If this was correct, skilled athletes should show a specific muscle activation pattern with a low level of coactivation of muscles which are typically involved in their discipline. In particular, the aim of this study was to verify the hypothesis that the amount of antagonist activation of biceps brachii (BB) and triceps brachii (TB) is different between tennis players and non-players individuals during maximal isokinetic contractions.MethodsTen young healthy men and eight male tennis players participated in the study. The surface electromyographic signals (sEMG) were recorded from the BB and TB muscles during three maximal voluntary isometric contractions (MVC) of elbow flexors and extensors and a set of three maximal elbow flexions and extensions at 15°, 30°, 60°, 120°, 180° and 240°/s. Normalized root mean square (RMS) of sEMG was calculated as an index of sEMG amplitude.ResultsAntagonist activation (%RMSmax) of TB was significantly lower in tennis players (from 14.0 ± 7.9% at MVC to 16.3 ± 8.9% at 240°/s) with respect to non-players (from 27.7 ± 19.7% at MVC to 38.7 ± 17.6% at 240°/s) at all angular velocities. Contrary to non-players, tennis players did not show any difference in antagonist activation between BB and TB muscles.ConclusionsTennis players, with a constant practice in controlling forces around the elbow joint, learn how to reduce coactivation of muscles involved in the control of this joint. This has been shown by the lower antagonist muscular activity of triceps brachii muscle during isokinetic elbow flexion found in tennis players with respect to non-players.     

Surface electromyograph activity of submental muscles during swallowing and expiratory muscle training tasks in Huntington’s disease patients

IntroductionHuntington’s disease (HD) patients have difficulty in swallowing, leading to aspiration pneumonia, which is a major cause of death. It seems possible that submental muscles that are crucial for preventing an escape of a bolus into the airway, are affected by HD, but no previous studies have investigated this.ObjectiveTo assess surface electromyograph (sEMG) activity of submental muscles during swallowing and expiratory muscle training (EMT) tasks in HD patients in comparison to healthy volunteers.MethodssEMG activities of submental muscles during saliva, water swallowing, EMT tasks performed at 25% and 75% of maximum expiratory pressure were recorded and normalised by the sEMG activity during an effortful swallow in 17 early to mid stage HD patients and 17 healthy volunteers.ResultssEMG activity was greater (p < 0.05) during EMT tasks than saliva and water swallowing, but was not significantly different between groups for saliva, water swallowing and EMT at 25%. HD patients had lower sEMG activity for EMT at 75% (p < 0.05).ConclusionDecreases in submental muscle activity were not evident in HD patients except during EMT at 75%. This suggests that relative submental muscle weakness is observed only during a high intensity task in early to mid stage HD patients.     

Surface electromyographic measurements on land prior to and after 90 min of submersion (swimming) are highly reliable

The purpose of this study was to investigate the reliability of surface electromyography (sEMG) measurements after submersion (swimming) for 90 min. Isometric maximal voluntary contractions (MVC) on land and in water were collected from eight muscles on the right side of the body in 12 healthy participants (6 women and 6 men). Repeated measures analyses of variance (general linear model ANOVA) showed no significant differences in the peak amplitude MVC scores between land pre and post measurements for all muscles, p > .05. The mean of the Intraclass correlation coefficient (1, 1) for land pre and land post was .985 with (95% Cl = .978–.990), for land pre and water pre .976 (95% Cl = .964–.984) and for land pre and post, water pre and post .981 (95% Cl = .974–.987). Measuring sEMG on land before and after a prolonged submersion is highly reliable without additional waterproofing when using electrodes with 57 mm diameter.     

Changes in EMG activity during clenching in chronic pain patients with unilateral temporomandibular disorders

The study assessed the differences in electromyographic (EMG) activity recorded during clenching in women with chronic unilateral temporomandibular disorders (TMDs) as compared to control subjects. Seventy-five full dentate, normo-occlusion, right-handed, similarly aged female subjects were recruited. Twenty five subjects presented with right side TMD, 25 presented with left side TMD and 25 pain-free control subjects participated. Using integrated surface EMG over a 1 s contraction, the anterior temporalis and masseter muscles were evaluated bilaterally while subjects performed maximum voluntary clenching. Lower EMG activation was observed in patients with TMD as compared to control subjects (temporalis: 195.74 ± 18.57 vs. 275.74 ± 22.11, P = 0.011; masseters: 151.09 ± 17.37 vs. 283.29 ± 31.87, P < 0.001). An asymmetry index (SAI) was calculated to determine ratios of right to left sided activation. Patients with right-sided TMD demonstrated preferential use of their left-sided muscles (SAI ?5.35 ± 4.02) whereas patients with left-sided TMD demonstrated preferential use of their right-sided muscles (SAI 6.95 ± 2.82), (P = 0.016). This unilateral reduction in temporalis and masseter activity could be considered as a specific protective functional adaptation of the neuromuscular system due to nociceptive input. The asymmetry index (SAI) may be a useful measure in discriminating patients with right vs. left-sided TMD.     

Innervation zone shift at different levels of isometric contraction in the biceps brachii muscle

Experiments were carried out to examine whether innervation zone (IZ) location remains stable at different levels of isometric contraction in the biceps brachii muscle (BB), and to determine how the proximity of the IZ affects common surface electromyography (sEMG) parameters. Twelve subjects performed maximal (MVC) and submaximal voluntary isometric contractions at 10%, 20%, 30%, 40%, 50% and 75% of MVC. sEMG signals were recorded with a 13 rows × 5 columns grid of electrodes from the short head of BB. The IZ shifted in the proximal direction by up to 2.4 cm, depending upon the subject and electrode column. The mean shift of all the columns was 0.6 ± 0.4 cm (10% vs. 100% MVC, P < 0.001). This shift biased the average values of mean frequency (+21.8 ± 9.9 Hz, P < 0.001), root mean square (?0.16 ± 0.15 mV, P < 0.05) and conduction velocity (?1.15 ± 0.93 m/s, P < 0.01) in the channels immediately proximal to the IZ. The shift in IZ could be explained by shortening of the muscle fibers, and thus lengthening of the (distal) tendon due to increasing force. These results underline the importance of individual investigation of IZ locations before the placement of sEMG electrodes, even in isometric contractions.     

Characteristics of EMG frequency bands in temporomandibullar disorders patients

The aim of the present study was to determine whether any specific frequency bands of surface electromyographic (sEMG) signals are more susceptible to alterations in patients with temporomandibular disorders (TMD), when compared with healthy subjects. Twenty-seven healthy adults (19 women and eight men; mean age: 23 ± 6.68 years) and 27 TMD patients (20 women and seven men; mean age: 24 ± 5.89 years) voluntarily participated in the experiment. sEMG data were recorded from the right and left masseter muscles (RM and LM) and the right and left anterior temporalis muscles (RT and LT) as the participants performed tests of chewing (CHW) and maximal clenching effort (MCE). Frequency domain analysis of the sEMG signal was used to analyze differences between TMD patients and healthy subjects in relation to the Power Spectral Density Function (PSDF). The analysis focused on the median frequency (MDF) of the sEMG signal and PSDF frequency bands after the EMG spectrum was divided into twenty-five frequency band of 20 Hz each. The Mann-Whitney test was used to compare MDF between TMD patients and healthy subjects and the frequency bands were analyzed using three-way ANOVA with three factors: frequency band, muscle and group. The results of the analysis confirmed that the median frequency values in TMD patients were significantly higher (p < 0.05) than those recorded for healthy subjects in the two experimental conditions (MCE and CHW), for all of the muscles assessed (RM, LM, RT and LT). In addition, frequency content between 20 and 100 Hz of the normalized PSDF range was significantly lower (p < 0.05) in TMD patients than in healthy. This study contributes to quantitatively identify TMD dysfunctions, by non-invasive sEMGs; this assessment is clinically important and still lacking nowadays.     

Effect of bolus hardness on the chewing pattern and activation of masticatory muscles in subjects with normal dental occlusion

The aim of the study was to evaluate the effect of bolus hardness on the kinematic of mastication and jaw-elevator muscle activity in subjects with normal dental occlusion and function. The mandibular motion and the surface EMG envelope of the masseter and temporalis anterior muscles were assessed in twelve subjects during mastication of a soft and hard bolus of the same size. When chewing the hard bolus, the chewing pattern in the frontal plane was significantly higher and wider, with smaller closure angle and higher peak velocity than when chewing the soft bolus. EMG peak amplitude of both the masseter and anterior temporalis muscles was higher for the side of the bolus but the contralateral side increased its activity significantly more than the ipsilateral side when the hardness of the bolus increased (for the masseter, mean ± SD: 130.4 ± 108.1% increase for the contralateral side and 29.6 ± 26.9% for the ipsilateral side). Moreover, the peak EMG activity for both muscles occurred more distant from the closure point with hard bolus. The increased activity of the contralateral side may help maintaining the mandibular equilibrium, with indirect participation to the power stroke generated by the chewing-side masseter. The results provide kinematic and EMG adaptations to bolus hardness in healthy subjects and can be used as normative data in the development of methods for early diagnosis of impaired chewing function.     

The minimum number of contractions required to examine the EMG amplitude versus isometric force relationship for the vastus lateralis and vastus medialis

Studies have demonstrated that the electromyographic (EMG) amplitude versus submaximal isometric force relationship is relatively linear. The purpose of this investigation was to determine the minimum number of contractions required to study this relationship. Eighteen men (mean age = 23 years) performed isometric contractions of the leg extensors at 10–90% of the maximum voluntary contraction (MVC) in 10% increments while surface EMG signals were detected from the vastus lateralis and vastus medialis. Linear regression was used to determine the coefficient of determination, slope coefficient, and y-intercept for each muscle and force combination with successively higher levels included in the model (i.e., 10–30%, … 10–90% MVC). For the slope coefficients, there was a main effect for force combination (P < .001). The pairwise comparisons showed there was no difference from 10–60% through 10–90% MVC. For the y-intercepts, there were main effects for both muscle (vastus lateralis [4.3 μV RMS] > vastus medialis [−3.7 μV RMS]; P = .034) and force combination (P < .001), with similar values shown from 10–50% through 10–90% MVC. The linearity of the absolute EMG amplitude versus isometric force relationship for the vastus lateralis and vastus medialis suggests that investigators may exclude high force contractions from their testing protocol.     

Mandibular kinematics and masticatory muscles EMG in patients with short lasting TMD of mild-moderate severity

Mandibular kinematic and standardized surface electromyography (sEMG) characteristics of masticatory muscles of subjects with short lasting TMD of mild-moderate severity were examined.Volunteers were submitted to clinical examination and questionnaire of severity. Ten subjects with TMD (age 27.3 years, SD 7.8) and 10 control subjects without TMD, matched by age, were selected.Mandibular movements were recorded during free maximum mouth opening and closing (O–C) and unilateral, left and right, gum chewing. sEMG of the masseter and temporal muscles was performed during maximum teeth clenching either on cotton rolls or in intercuspal position, and during gum chewing. sEMG indices were obtained. Subjects with TMD, relative to control subjects, had lower relative mandibular rotation at the end of mouth opening, larger mean number of intersection between interincisal O–C paths during mastication and smaller asymmetry between working and balancing side, with participation beyond the expected of the contralateral muscles (P < 0.05, t-test). Overall, TMD subjects showed similarities with the control subjects in several kinematic parameters and the EMG indices of the static test, although some changes in the mastication were observed.     

Myoelectric manifestations of fatigue in vastus lateralis,medialis obliquus and medialis longus muscles

The purpose of this study was to determine whether surface electromyography (EMG) assessment of myoelectric manifestations of muscle fatigue is capable of detecting differences between the vastus lateralis and medialis muscles which are consistent with the results of previous biopsy studies. Surface EMG signals were recorded from the vastus medialis longus (VML), vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles during isometric knee extension contractions at 60% and 80% of the maximum voluntary contraction (MVC) for 10 s and 60 s, respectively. Initial values and rate of change of mean frequency (MNF), average rectified value (ARV) and conduction velocity (CV) of the EMG signal were calculated. Comparisons between the two force levels revealed that the initial values of MNF for the VL muscle were greater at 80% MVC compared to 60% MVC (P < 0.01). Comparisons between the vasti muscles demonstrated lower initial values of CV for VMO compared to VL at 60% MVC (P < 0.01) and lower than VML and VL at 80% MVC (P < 0.01). In addition, initial values of MNF were higher for VL with respect to both VML and VMO at 80% MVC (P < 0.01) and initial estimates of ARV were higher for VMO compared to VML at both force levels (P < 0.01 at 60% MVC and P < 0.05 at 80% MVC). For the sustained contraction at 80% MVC, VL demonstrated a greater decrease in CV over time compared to VMO (P < 0.05).These findings suggest that surface EMG signals and their time course during sustained isometric contractions may be useful to non-invasively describe functional differences between the vasti muscles.     

Muscular activity during isometric incisal biting

This study attempted to estimate TMJ loading during incisal loading using a custom load-cell device and surface electromyographic (sEMG) recordings of the main jaw closers to assess the outcome correlation. Study participants were 23 healthy volunteers. The incisal loads having submaximal and mean intensity were recorded using a calibrated electronic load cell; simultaneously, surface electromyography (sEMG) of the right and left masseter and temporalis muscles was recorded. Readings of the resting, clenching in maximal and submaximal intercuspal positions and mean (50%) incisal loads were recorded. Clenching sEMG activity was used as a reference for normalization. The mean (SD) submaximal incisal load recorded was 498 (305.78) N, and the mean at 50% of the submaximal load was 268.93 (147.37) N. Mean (SD) sEMG activity during submaximal clenching was 141.23 (87.76) μV, with no significant differences between the four muscles. During submaximal voluntary incisal loading, the normalized mean sEMG activity was 49.99 (34.54) µV %, and 27.17(15.29) µV % during mean (50%) effort. The incisal load was generated mainly by the masseter muscles, as these showed a positive correlation during mean but not during submaximal effort. In the edge-to-edge jaw position, the mean incisal load effort seems to be physiological, but excessive TMJ loads can be expected from chronic or excessive incisal loading. In conclusion, incisal loads require the activity of the masseter muscles, which show a positive correlation between sEMG activity and effective incisal loads during mean, but not during submaximal, effort, and the masseter muscles are dominant over the temporalis muscles during submaximal incisal biting.     

Neuromuscular fatigue following low-intensity dynamic exercise with externally applied vascular restriction

This study investigated neuromuscular fatigue following low-intensity resistance exercise with vascular restriction (VR) and without vascular restriction (control, CON). Fourteen males participated in two experimental trials (VR and CON) each separated by 48 h. Each participant performed two isometric maximum voluntary contractions (MVCs) before and after five sets of 20 dynamic constant external resistance leg extension exercises (DCER-EX) at 20% of one-repetition maximum (1-RM). The participants were asked to lift (1.5 s) and lower (1.5 s) the load at a constant velocity. Surface electromyography (EMG) was recorded from the vastus lateralis during MVC and DCER-EX. Twitch interpolation was used to assess the percent of maximal voluntary activation (%VA) during the MVC. During performing five sets of 20 DCER-EX, the increases (p < 0.05) in EMG amplitude and decreases (p < 0.05) in EMG mean power frequency were similar for both VR and CON. However, there were significant differences between VR and CON for MVC force, %VA, and potentiated twitch force and significant interactions for EMG amplitude. VR decreased MVC force, %VA, potentiated twitch force, and EMG amplitude more than CON. Our findings suggest that the VR-induced fatigue may have been due to a combination of peripheral (decreases in potentiated twitch) and central (decreases in %VA and EMG amplitude) fatigue.     

Correlation between long-term in vivo amalgam restorations and the presence of heavy elements in the dental pulp

ProjectTo measure the levels of heavy metals (Hg, Sn) in the dental pulp and blood samples of patients with long-term amalgam restorations.Procedure12 amalgam restored and 12 non-restored, sound teeth were chosen and access cavity preparation to the pulp chamber was made. The contents were transferred and dissolved in 5 mL of concentrated nitric acid followed by placement in an oven at 180 °C for tissue digestion. After cooling the tubes each digested sample was transferred to an atomic absorption system to measure the levels of heavy metals. The blood samples of five patients in each group were randomly analyzed to determine the levels of these heavy metals in the blood and if there were a correlation between these levels in blood and pulp. Data were analyzed by t-test at a P < 0.05 level of significance.ResultsNo significant difference was seen between the levels of Hg and Sn in pulp tissues (P > 0.05); however, the blood analysis showed higher level of Hg amalgam group (P = 0.009). The analysis between the pulp and blood samples showed positive correlations for both Hg and Sn elements in dental pulp and the blood (P = 1.000) (P = 0.900).ConclusionsThe long-term presence of dental amalgam (at least 5 years) did not result in any remarkable changes in the levels of mercury and tin in the pulp tissue; however, there were increases in the level of mercury in the blood circulation even five years following the placement of the restoration.     

The effect of perspiration on the sEMG amplitude and power spectrum

Sweat accumulation underneath surface EMG (sEMG) electrodes is a common problem in workplace studies which compromises electrode adherence to the skin as well as signal fidelity. In this study, the effect of sweat accumulation on signal amplitude and mean frequency (MF) was examined to determine if the sEMG signal becomes altered through the sweat layer and whether this effect can be avoided by interrupting the pool of sweat using a thin strip of medical adhesive between the electrode snaps. Nine males performed a maximum, isometric contraction of their right quadriceps as sEMG was collected. Skin conditions under the electrode were dry and wet in incremental layers of 0.02 mm of artificial sweat. The results demonstrated that sweat accumulation under sEMG electrodes dampens the amplitude of the EMG signal in a predictable way (r = .88 and .97 for double and single snap electrodes, respectively) with almost 2% and 3% deterioration for every 0.02 mm of sweat depending on the type of electrode used. The medical adhesive proved to be highly effective at preventing amplitude deterioration indicating that signal shunting can be prevented. MF was not influenced by sweat accumulation even under the extreme wet condition.     

Contraction intensity and sex differences in knee-extensor fatigability

Females are less fatigable than males during isometric contractions across various muscles and intensities. However, sex differences in knee-extensor fatigability remain relatively unexplored. Purpose: To determine the sex difference in performance fatigability for intermittent, isometric contractions of the knee-extensor muscles. Methods: Eighteen participants (10 males, 8 females) performed intermittent, isometric, knee-extensor contractions at 30% of their maximal voluntary force (MVC) for 30 min and in a separate session at 50% MVC until task-failure. During both fatiguing protocols a MVC was performed every 60 s and electromyography (EMG) was recorded during all contractions. Results: At task completion males had a larger reduction in MVC force for the 30% MVC task (−32 ± 15% vs. −15 ± 16%, P = 0.042) and the 50% MVC task (−34 ± 8% vs. −24 ± 1%, P = 0.045). Furthermore, for the 50% MVC task, females had a longer task duration (937 ± 525 s vs. 397 ± 153 s, P = 0.007). The rise in EMG activity and force fluctuations were more rapid for the males than females (P < 0.05). When participants were matched for strength post hoc (n = 10), a sex difference in fatigability for both tasks was still evident. Conclusions: Females were less fatigable than males during intermittent, isometric, knee-extensor contractions at moderate relative forces and this difference was independent of strength.     

Micro movements of the upper limb in fibromyalgia: The relation to proprioceptive accuracy and visual feedback

The purpose of this study was to explore the role of visual and proprioceptive feedback in upper limb posture control in fibromyalgia (FM) and to assess the coherence between acceleration measurements of upper limb micro movements and surface electromyography (sEMG) of shoulder muscle activity (upper trapezius and deltoid). Twenty-five female FM patients and 25 age- and sex-matched healthy controls (HCs) performed three precision motor tasks: (1) maintain a steady shoulder abduction angle of 45° while receiving visual feedback about upper arm position and supporting external loads (0.5, 1, or 2 kg), (2) maintain the same shoulder abduction angle without visual feedback (eyes closed) and no external loading, and (3) a joint position sense test (i.e., assessment of proprioceptive accuracy). Patients had more extensive increase in movement variance than HCs when visual feedback was removed (P < 0.03). Proprioceptive accuracy was related to movement variance in HCs (R ⩾ 0.59, P ⩽ 0.002), but not in patients (R ⩽ 0.25, P ⩾ 0.24). There was no difference between patients and HCs in coherence between sEMG and acceleration data. These results may indicate that FM patients are more dependent on visual feedback and less reliant on proprioceptive information for upper limb posture control compared to HCs.