Muscle activation characteristics associated with differences in physiological tremor amplitude between the dominant and non-dominant hand

The aim of this study was to assess differences in physiological tremor amplitude of the hand between the dominant and non-dominant side of right-handed individuals. Mechanical loading of the hand and frequency analysis were used in an attempt to identify the physiological mechanisms involved in observed differences. Seventeen healthy right-handed adults participated in a single session where physiological tremor of the outstretched left and right hands was recorded under different loading conditions (0 g up to 5614 g). Physiological tremor amplitude was quantified through accelerometry and electromyographic (EMG) signals of wrist extensor and flexor muscles were also recorded. The main findings were: ～30% greater amplitude of fluctuations in acceleration for the non-dominant compared with the dominant hand, no difference in the frequency content of acceleration or demodulated EMG signals between dominant and non-dominant sides across all loads, and condition-dependent associations between the amplitude of fluctuations in acceleration and EMG amplitude and frequency content. These associations suggest a potential role of central modulation of neural activity to explain dominance-related differences in physiological tremor amplitude of the hand.     

The impact of localized fatigue on contralateral tremor and muscle activity is exacerbated by standing posture

Physiological tremor is an inherent feature of the motor system that is influenced by intrinsic (neuromuscular) and/or extrinsic (task) factors. Given that tremor must be accounted for during the performance of many fine motor skills; there is a requirement to clarify how different factors interact to influence tremor. This study was designed to assess the impact localized fatigue of a single arm and stance position had on bilateral physiological tremor and forearm muscle activity. Results demonstrated that unilateral fatigue produced bilateral increases in tremor and wrist extensor activity. For example, fatigue resulted in increases in extensor activity across both exercised (increased 8–10% MVC) and the non-exercised arm (increased 3–7% MVC). The impact of fatigue was not restricted to changes in tremor/EMG amplitude, with altered hand–finger coupling observed within both arms. Within the exercised arm, cross-correlation values decreased (pre-exercise r = 0.62–0.64; post-exercise r = 0.37–0.43) while coupling increased within the non-exercised arm (pre-exercise r = 0.51–0.55; post-exercise r = 0.62–0.67). While standing posture alone had no significant impact on tremor/EMG dynamics, the tremor and muscle increases seen with fatigue were more pronounced when standing. Together these results demonstrate that the combination of postural and fatigue factors can influence both tremor/EMG outputs and the underlying coordinative coupling dynamics.     

Neuromuscular fatigue during maximal concurrent hand grip and elbow flexion or extension.

The objective was to investigate muscle fatigue measuring changes in force output and force tremor and electromyographic activity (EMG) during two sustained maximal isometric contractions for 60s: (1) concurrent hand grip and elbow flexion (HG and EF); or (2) hand grip and elbow extension (HG and EE). Each force tremor amplitude was decomposed into four frequency bands (1-3, 4-10, 11-20, and 21-50Hz). Surface EMGs were recorded from the flexor digitorum superficialis (FDS), extensor digitorum (ED), biceps brachii (BB) and lateral head of triceps brachii (TB). The HG and EF forces for the HG and EF and the HG force for the HG and EE declined rapidly, whereas the EE force remained almost constant near to the initial value for the first 40s and then declined. The decrease in EMG amplitude was observed not for the FDS muscle but for the ED muscle. The HG tremor amplitude for each frequency band showed similar decreasing rate, whereas the decreases in EF and EE tremor amplitudes for the lower band (below 10Hz) were slower than those for the higher band (above 11Hz). The neuromuscular mechanisms underlying muscle fatigue during sustained maximal concurrent contractions of hand grip and elbow flexion or extension are discussed.     

Suppression of Enhanced Physiological Tremor via Stochastic Noise: Initial Observations

Enhanced physiological tremor is a disabling condition that arises because of unstable interactions between central tremor generators and the biomechanics of the spinal stretch reflex. Previous work has shown that peripheral input may push the tremor-related spinal and cortical systems closer to anti-phase firing, potentially leading to a reduction in tremor through phase cancellation. The aim of the present study was to investigate whether peripherally applied mechanical stochastic noise can attenuate enhanced physiological tremor and improve motor performance. Eight subjects with enhanced physiological tremor performed a visuomotor task requiring the right index finger to compensate a static force generated by a manipulandum to which Gaussian noise (3–35 Hz) was applied. The finger position was displayed on-line on a monitor as a small white dot which the subjects had to maintain in the center of a larger green circle. Electromyogram (EMG) from the active hand muscles and finger position were recorded. Performance was measured by the mean absolute deviation of the white dot from the zero position. Tremor was identified by the acceleration in the frequency range 7–12 Hz. Two different conditions were compared: with and without superimposed noise at optimal amplitude (determined at the beginning of the experiment). The application of optimum noise reduced tremor (accelerometric amplitude and EMG activity) and improved the motor performance (reduced mean absolute deviation from zero). These data provide the first evidence of a significant reduction of enhanced physiological tremor in the human sensorimotor system due to application of external stochastic noise.     

Frequency and displacement amplitude relations for normal hand tremor.

Spectral analysis of hand tremor records obtained from normal subjects during continuous extension of the hand for 15-45 min revealed that the root-mean-square (rms) displacement amplitude of the tremor increased from control levels of about 30 mum to levels on the order of 100-1,000 times control. Associated with this increase in the displacement was a systematic decrease in the hand tremor frequency from control values of 8-9 Hz to values of 4-6 Hz. Spectral analysis of demodulated extensor EMG records indicated a consistent relation between EMG modulation amplitude at the tremor frequency and the tremor displacement amplitude for tremor records with rms displacement above about 100 mum. No consistent relation was found between these two variables for tremor records with displacements below 100 mum. Consideration of both mechanical and neural reflex effects indicated that a viscoelastic-mass mechanism primarily determined the small-amplitude (less than 100 mum) tremors, while the large displacement tremors may have involved both mechanical and neural feed back factors.     

Force depression in human quadriceps femoris following voluntary shortening contractions.

The purpose of this study was to investigate whether the isometric muscle force, redeveloped following maximal-effort voluntary shortening contractions in human skeletal muscle, is smaller than the purely isometric muscle force at the corresponding length. Isometric knee extensor moments, surface electromyographic (EMG) signals of quadriceps femoris, and interpolated twitch moments (ITMs) were measured while 10 subjects performed purely isometric knee extensor contractions at a 60 degrees knee angle and isometric knee extensor contractions at a 60 degrees knee angle preceded by maximal-effort voluntary shortening of the quadriceps muscles. It was found that the knee extensor moments were significantly decreased for the isometric-shortening-isometric contractions compared with the isometric contractions for the group as a whole, whereas the corresponding EMG and ITM values were the same. This study is the first to demonstrate force depression following muscle shortening for voluntary contractions. We concluded that force depression following muscle shortening is an actual property of skeletal muscle rather than a stimulation artifact and that force depression during voluntary contraction is not accompanied by systematic changes in muscle activation as evaluated by EMG and ITM.     

女子拳击运动员上肢和腰部肌肉力量训练的肌电分析

目的：利用肌电指标分析拳击运动员上肢和腰部肌肉力量训练效果。方法：用Mega公司的ME6000肌电图仪记录分析10名女子拳击运动员上臂肱二头肌（主动肌）与肱三头肌（拮抗肌）、前臂屈肌（主动肌）与伸肌（拮抗肌）和腰部肌群的运动诱发肌电,规定运动为手持2.5 kg的哑铃负荷进行直拳空击运动直至局部肌肉力竭。结果：直拳空击运动至局部肌肉力竭过程中,上肢拮抗肌的中位频率（MF）下降幅度和速度大于相对应的主动肌,且从肌群作功来看,主动肌作功百分比较拮抗肌大。其中9名普通运动员腰肌的肌电频率（MF）均值较1名指定样本世界冠军的下降缓慢,而且其作功百分比都较小。结论：通过对普通女子拳击运动员上肢和腰部肌群肌电指标测试与世界冠军的比较分析,提示本研究中所测普通拳击运动员拮抗肌和腰部肌肉力量训练不足,有待加强该部肌肉的力量训练。     

The effect of changes in joint angle on the characteristics of physiological tremor

IntroductionPhysiological tremor, as a whole, can be influenced by changes in muscle activity. However, the origin of low-frequency physiological tremor oscillations has yet to be conclusively determined. It is possible that by experimentally manipulating muscular activity, a better determination of the origin of those low-frequency oscillations can be achieved. It was demonstrated that changes in joint angle modify characteristics of muscular activity. As such, we hypothesize that changes in wrist-joint angle will alter the characteristics of low-frequency physiological tremor oscillations.ObjectiveAssess the influence of changes in joint angle of the wrist on characteristics of physiological finger tremor.MethodsPhysiological finger tremor was recorded (n = 25) using a laser displacement system while the arm and hand were supported. The relative angle between the dorsum of the hand and the forearm was altered between conditions (135°, 180°, 225° and 270°), while the hand and the finger remained parallel to the ground. EMG of the extensors and flexors were also recorded.ResultsTremor amplitude was significantly altered by changes in wrist-joint angle. This was especially the case for lower frequency oscillations. In addition, electromyography properties of forearm muscles were also significantly modified by changes in wrist-joint angles.ConclusionsThis study demonstrates that changes in wrist-joint angle modify the characteristics of physiological finger tremor. This should be taken into account when interpreting tremor data as well as when developing tools to minimize tremor.     

Analyzing the dynamics of hand tremor time series

We investigate physiological, essential and parkinsonian hand tremor measured by the acceleration of the streched hand. Methods from the theory of dynamical systems and from stochastics are used. It turns out that the physiological tremor can be described as a linear stochastic process, and that the parkinsonian tremor is nonlinear and deterministic, even chaotic. The essential tremor adopts a middle position, it is nonlinear and stochastic.     

On the reflex coactivation of ankle flexor and extensor muscles induced by a sudden drop of support surface during walking in humans.

Recent studies have revealed that the stretch reflex responses of both ankle flexor and extensor muscles are coaugmented in the early stance phase of human walking, suggesting that these coaugmented reflex responses contribute to secure foot stabilization around the heel strike. To test whether the reflex responses mediated by the stretch reflex pathway are actually induced in both the ankle flexor and extensor muscles when the supportive surface is suddenly destabilized, we investigated the electromyographic (EMG) responses induced after a sudden drop of the supportive surface at the early stance phase of human walking. While subjects walked on a walkway, the specially designed movable supportive surface was unexpectedly dropped 10 mm during the early stance phase. The results showed that short-latency reflex EMG responses after the impact of the drop (<50 ms) were consistently observed in both the ankle flexor and extensor muscles in the perturbed leg. Of particular interest was that a distinct response appeared in the tibialis anterior muscle, although this muscle showed little background EMG activity during the stance phase. These results indicated that the reflex activities in the ankle muscles certainly acted when the supportive surface was unexpectedly destabilized just after the heel strike during walking. These reflex responses were most probably mediated by the facilitated stretch reflex pathways of the ankle muscles at the early stance phase and were suggested to be relevant to secure stabilization around the ankle joint during human walking.     

Control of single-joint movements with a reversal.

We studied the kinematic and electromyographic (EMG) patterns during single-joint elbow flexion movements with a reversal and tested two hypotheses. First, that the amplitude of the second phase of the movement (M(2)) will be controlled by two different means, a drop in the second flexor burst for a small M(2) and an increase in the integral of the extensor burst for larger M(2). Second, based on the muscle stretch-shortening cycle (SSC), that movements reversing without a delay will show a larger extensor burst, as compared to movements that reverse after a delay. Changes in EMG patterns with M(2) amplitude supported the first hypothesis and could be interpreted within the framework of the equilibrium-point hypothesis. The observations also corroborate a hypothesis that discrete movements represent outcomes of an oscillatory control process stopped at a particular phase. In Experiment-2, even the shortest delay at the target led to a significantly larger extensor burst. However, there were no differences in the peak velocity of M2 with and without the delay. These observations do not support a major role of stretch reflexes in the SSC effects during such movements. However, they are compatible with the idea of peripheral factors, such as peripheral muscle and tendon elasticity, playing a major potentiating role in the SSC.     

蹲跳、反向跳和下落跳的膝关节屈伸肌群肌电信号分析

目的：通过观察肌电图（EMG）的变化,了解运动员与普通中学生在纵跳过程中,膝关节屈伸肌群工作特点,为运动员科学选材提供依据。方法：30名男女青少年运动员和30名男女普通中学生进行各种形式纵跳（蹲跳、反向跳、下落跳）,测试膝关节屈伸肌群的EMG变化情况。结果：主动肌（股外肌）EMG的变化存在性别差异,随着下肢工作强度的增加,男运动员积分肌电图（iEMG)和平均功率频率（Fmean)均没有显著变化,女运动员iEMG增加,Fmean没有显著变化,对抗肌（股二头肌）,随着下肢工作强度的增加。青少年运动员EMG活动变化较小,而普通中学生的EMG活动明显增加。结论：在增加工作负荷的过程中,男运动员膝关节伸肌群以提高效率为主,女运动员以提高肌肉的募集数量为主;运动员的对抗肌协调水平高于普通中学生。     

Application of singular spectrum-based change-point analysis to EMG-onset detection

While many approaches have been proposed to identify the signal onset in EMG recordings, there is no standardized method for performing this task. Here, we propose to use a change-point detection procedure based on singular spectrum analysis to determine the onset of EMG signals. This method is suitable for automated real-time implementation, can be applied directly to the raw signal, and does not require any prior knowledge of the EMG signal’s properties. The algorithm proposed by Moskvina and Zhigljavsky (2003) was applied to EMG segments recorded from wrist and trunk muscles. Wrist EMG data was collected from 9 Parkinson’s disease patients with and without tremor, while trunk EMG data was collected from 13 healthy able-bodied individuals. Along with the change-point detection analysis, two threshold-based onset detection methods were applied, as well as visual estimates of the EMG onset by trained practitioners. In the case of wrist EMG data without tremor, the change-point analysis showed comparable or superior frequency and quality of detection results, as compared to other automatic detection methods. In the case of wrist EMG data with tremor and trunk EMG data, performance suffered because other changes occurring in these signals caused larger changes in the detection statistic than the changes caused by the initial muscle activation, suggesting that additional criteria are needed to identify the onset from the detection statistic other than its magnitude alone. Once this issue is resolved, change-point detection should provide an effective EMG-onset detection method suitable for automated real-time implementation.     

Eccentric exercise increases EMG amplitude and force fluctuations during submaximal contractions of elbow flexor muscles.

The purpose of this study was to determine the effect of eccentric exercise on the ability to exert steady submaximal forces with muscles that cross the elbow joint. Eight subjects performed two tasks requiring isometric contraction of the right elbow flexors: a maximum voluntary contraction (MVC) and a constant-force task at four submaximal target forces (5, 20, 35, 50% MVC) while electromyography (EMG) was recorded from elbow flexor and extensor muscles. These tasks were performed before, after, and 24 h after a period of eccentric (fatigue and muscle damage) or concentric exercise (fatigue only). MVC force declined after eccentric exercise (45% decline) and remained depressed 24 h later (24%), whereas the reduced force after concentric exercise (22%) fully recovered the following day. EMG amplitude during the submaximal contractions increased in all elbow flexor muscles after eccentric exercise, with the greatest change in the biceps brachii at low forces (3-4 times larger at 5 and 20% MVC) and in the brachialis muscle at moderate forces (2 times larger at 35 and 50% MVC). Eccentric exercise resulted in a twofold increase in coactivation of the triceps brachii muscle during all submaximal contractions. Force fluctuations were larger after eccentric exercise, particularly at low forces (3-4 times larger at 5% MVC, 2 times larger at 50% MVC), with a twofold increase in physiological tremor at 8-12 Hz. These data indicate that eccentric exercise results in impaired motor control and altered neural drive to elbow flexor muscles, particularly at low forces, suggesting altered motor unit activation after eccentric exercise.     

Corticomuscular Transmission of Tremor Signals by Propriospinal Neurons in Parkinson's Disease

Cortical oscillatory signals of single and double tremor frequencies act together to cause tremor in the peripheral limbs of patients with Parkinson''s disease (PD). But the corticospinal pathway that transmits the tremor signals has not been clarified, and how alternating bursts of antagonistic muscle activations are generated from the cortical oscillatory signals is not well understood. This paper investigates the plausible role of propriospinal neurons (PN) in C3–C4 in transmitting the cortical oscillatory signals to peripheral muscles. Kinematics data and surface electromyogram (EMG) of tremor in forearm were collected from PD patients. A PN network model was constructed based on known neurophysiological connections of PN. The cortical efferent signal of double tremor frequencies were integrated at the PN network, whose outputs drove the muscles of a virtual arm (VA) model to simulate tremor behaviors. The cortical efferent signal of single tremor frequency actuated muscle spindles. By comparing tremor data of PD patients and the results of model simulation, we examined two hypotheses regarding the corticospinal transmission of oscillatory signals in Parkinsonian tremor. Hypothesis I stated that the oscillatory cortical signals were transmitted via the mono-synaptic corticospinal pathways bypassing the PN network. The alternative hypothesis II stated that they were transmitted by way of PN multi-synaptic corticospinal pathway. Simulations indicated that without the PN network, the alternating burst patterns of antagonistic muscle EMGs could not be reliably generated, rejecting the first hypothesis. However, with the PN network, the alternating burst patterns of antagonist EMGs were naturally reproduced under all conditions of cortical oscillations. The results suggest that cortical commands of single and double tremor frequencies are further processed at PN to compute the alternating burst patterns in flexor and extensor muscles, and the neuromuscular dynamics demonstrated a frequency dependent damping on tremor, which may prevent tremor above 8 Hz to occur.     

Cholinergic mechanism controlling the response gain of forelimb extensor muscles to sinusoidal stimulation of macular labyrinth and neck receptors

The multiunit EMG activity of the triceps brachii was recorded in precollicular decerebrate cats during roll tilt of the animal or neck rotation at the frequencies of 0.026-0.15 Hz and at the peak amplitude of 10 degrees, leading to selective stimulation of labyrinth or neck receptors. The first harmonic component of the EMG responses to labyrinth stimulation was characterized by an increased activity during side-down tilt of the animal and a decreased activity during side-up tilt; however, just the opposite changes were elicited for the same directions of neck rotation. The peak of the responses was closely related to the extreme animal or neck displacement, thus being attributed to stimulation of position-sensitive macular labyrinth and receptors. Moreover, the modulation as well as the gain of the EMG responses were small in amplitude. Intravenous injections of an anticholinesterase at a dose which in some instances slightly decreased the extensor tonus as well as the background activity of the triceps brachii (eserine sulphate, 0.05-0.075 mg/kg), greatly enhanced the response gain of this extensor muscle to animal tilt or neck rotation at the parameters reported above. This finding was also observed in the absence of any decrease in spontaneous EMG activity of the extensor muscle after injection of the anticholinesterase. In no instance did the phase angle of the response change following these injections. The increased gain of the EMG response of the forelimb extensor muscle to sinusoidal stimulation of labyrinth and neck receptors was first observed 5-10 min after the injection and reached the highest value in about one hour. This effect, was not only time-dependent, but also state-dependent. In fact, the increase in response gain described above either did not occur or was negligible during the sudden recovery of the extensor rigidity which occurred either spontaneously or after somatosensory stimulations. The effects elicited by eserine sulphate were reversed within seconds by a 0.1-0.5 mg/kg dose of atropine sulphate, an anticholinergic drug. It is postulated that for the same labyrinthine or neck signal giving rise to excitatory vestibulospinal volleys acting on extensor motoneurons, the amplitude of the EMG modulation of limb extensor muscles depends on the activity of a cholinergic system.(ABSTRACT TRUNCATED AT 400 WORDS)     

Nonlinear smooth orthogonal decomposition of kinematic features of sawing reconstructs muscle fatigue evolution as indicated by electromyography

Tracking or predicting physiological fatigue is important for developing more robust training protocols and better energy supplements and/or reducing muscle injuries. Current methodologies are usually impractical and/or invasive and may not be realizable outside of laboratory settings. It was recently demonstrated that smooth orthogonal decomposition (SOD) of phase space warping (PSW) features of motion kinematics can identify fatigue in individual muscle groups. We hypothesize that a nonlinear extension of SOD will identify more optimal fatigue coordinates and provide a lower-dimensional reconstruction of local fatigue dynamics than the linear SOD. Both linear and nonlinear SODs were applied to PSW features estimated from measured kinematics to reconstruct muscle fatigue dynamics in subjects performing a sawing motion. Ten healthy young right-handed subjects pushed a weighted handle back and forth until voluntary exhaustion. Three sets of joint kinematic angles were measured from the right upper extremity in addition to surface electromyography (EMG) recordings. The SOD coordinates of kinematic PSW features were compared against independently measured fatigue markers (i.e., mean and median EMG spectrum frequencies of individual muscle groups). This comparison was based on a least-squares linear fit of a fixed number of the dominant SOD coordinates to the appropriate local fatigue markers. Between subject variability showed that at most four to five nonlinear SOD coordinates were needed to reconstruct fatigue in local muscle groups, while on average 15 coordinates were needed for the linear SOD. Thus, the nonlinear coordinates provided a one-order-of-magnitude improvement over the linear ones.     

Low-level activity of the trunk extensor muscles causes electromyographic manifestations of fatigue in absence of decreased oxygenation

This study was designed to determine whether trunk extensor fatigue occurs during low-level activity and whether this is associated with a drop in muscle tissue oxygenation. Electromyography (EMG) feedback was used to impose constant activity in a part of the trunk extensor muscles. We hypothesized that electromyographic manifestations of fatigue and decreased oxygenation would be observed at the feedback site and that EMG activity at other sites would be more variable without fatigue manifestations. Twelve volunteers performed 30-min contractions at 2% and 5% of the maximum EMG amplitude (EMGmax) at the feedback site. EMG was recorded from six sites over the lumbar extensor muscles and near-infrared spectroscopy was used to measure changes in oxygenation at the feedback site (left L3 level, 3 cm paravertebral). In both conditions, mean EMG activity was not significantly different between electrode sites, whereas the coefficient of variation was lower at the feedback site compared to other recording sites. The EMG mean power frequency (MPF) decreased consistently at the feedback site only. At 5% EMGmax, the decrease in MPF was significant at the group level at all sites ipsilateral to the feedback site. These results suggest that the limited variability of muscle activity at the EMG feedback site and at ipsilateral locations enhances fatigue development. No decreases in tissue oxygenation were detected. In conclusion, even at mean activity levels as low as 2% EMGmax, fatigue manifestations were found in the trunk extensors. These occured in absence of changes in oxygenation of the muscle tissue.     

肌肉萎缩引起肌电功率谱变化的理论和实验研究

为了通过肌电分析实现肌肉萎缩的无创检测,建立了一种数学模型研究肌肉萎缩后,其肌电信号功率谱的相应变化,并用大鼠的后肢卸载肌肉萎缩实验模型初步验证了数学模型分析的结论。该模型根据肌肉萎缩后肌纤维横截面积减小以及肌肉由于卸栽而出现持续性收缩的性质,采用中心导体模型及其电缆方程和肌电的线性系统模型建立起肌肉萎缩和生理肌电功率谱变化之间的数学关系。通过数字仿真和动物实验均发现了肌肉萎缩引起肌电幅度增加和功率谱高频成分降低的现象。结果表明数学模型和动物实验结果吻合,采用的数学模型能较好地阐述肌肉萎缩和肌电功率谱变化之间的关系。肌肉萎缩后肌电功率谱发生相应改变这一性质将为肌肉萎缩的无创检测提供一种新的方法。