Reliability of measures of quadriceps muscle function using magnetic stimulation

Introduction: Magnetic stimulation can be used to assess muscle function by calculating voluntary activation using an interpolated twitch during maximal voluntary contractions (MVCs) and control twitches to potentiated muscle. In this study we assessed the reliability of torque, electromyography (EMG), and voluntary activation variables. Methods: Fifteen men completed 5 testing sessions (2 familiarization and 3 reliability trials) to assess quadriceps femoris muscle function. Intra‐ and interday reliability levels of torque and EMG variables were estimated using typical error ± 90% confidence limits, expressed as percentage [coefficient of variation (CV)] and intraclass correlation coefficient. The smallest worthwhile change was calculated as 0.2 × between‐participant standard deviation. Results: Intra‐ and interday torque variables for MVC were reliable (CV < 4%, ICC 0.98, and CV < 5%, ICC 0.99, respectively). EMG variables were less reliable than torque variables, with CVs ranging from 7% to 18%. Conclusion: Magnetic stimulation of the femoral nerve is a reliable method for assessing muscle function. Muscle Nerve 53 : 770–778, 2016     

Strength training in old age: adaptation of antagonist muscles at the ankle joint

The purpose of this study was to determine whether strength training could reduce the deficit in plantarflexion (PF) maximal voluntary contraction (MVC) torque observed in previous studies in older subjects relative to young adults. Accordingly, the effects of a 6-month strength training program on the muscle and neural properties of the major muscle groups around the ankle were examined. PF and dorsiflexion (DF) isometric MVC torques were measured and surface electromyographic activity of the triceps surae and tibialis anterior muscles was recorded. The strength training program was very effective in improving strength in PF (+24.5%), and it thus reduced the DF-to-PF MVC torque ratio; in addition, it also induced gains in DF (+7.6%). Thus, there must be an improvement in ankle joint stability. In PF, gains were due particularly to a modification of the agonist neural drive; in DF, the gains appeared to be the consequence of a reduction in antagonist coactivation. Our findings indicate that the investigation of one muscle group should always be accompanied by examination of its antagonist muscle group.     

Human muscle fascicle behavior in agonist and antagonist isometric contractions

Introduction: The aim of this study was to compare, at a given level of electromyographic (EMG) activity, the behavior of dorsiflexor and plantarflexor muscles as assessed via their architecture (pennation angle and fiber length) during agonist or antagonist isometric contractions. Methods: Real‐time ultrasonography and EMG activity of gastrocnemius medialis (GM) and tibialis anterior (TA) muscles were obtained while young males performed ramp isometric contractions in dorsi‐ and plantarflexion. Results: For both muscles, at a similar level of EMG activity, fiber length was longer, and pennation angle was smaller, during antagonist than during agonist contractions. Conclusions: These results indicate that, at similar levels of EMG activity, GM and TA muscles elicit a higher mechanical output while acting as an antagonist. These findings have important implications for muscle function testing. They show that estimation of antagonistic force using the common method based on the EMG/net torque relationship yields underestimated values. Muscle Nerve 45: 92–99, 2012     

Electromyography and mechanomyography of elbow agonists and antagonists in Parkinson disease

The purpose of this study was to assess the electromyographic (EMG) and mechanomyographic (MMG) activities of agonist and antagonist muscles in Parkinson disease patients during maximal isometric elbow contraction in flexion and extension. Ten elderly females with Parkinson disease (average age 75 years) and 10 age‐matched healthy females were tested. The torque and the EMG and MMG signals from biceps brachii and triceps brachii were recorded during sustained maximal voluntary isometric contraction of the elbow flexors and extensors. There were no intergroup differences in the EMG and MMG activities of agonist and antagonist muscles or in torque. This might be because the Parkinson subjects were tested during their medication “ON” phase, or perhaps maximal isometric contraction (MVC) induced greater active muscle stiffness that affected the MMG signal. Muscle Nerve 40: 240–248, 2009     

Effect of moderate dehydration on torque,electromyography, and mechanomyography

The purpose of the present investigation was to test the hypotheses that the mechanomyographic (MMG) signal would be affected by hydration status due to changes in the intra- and extracellular fluid content (which could affect the degree of fluid turbulence), changes in the filtering properties of the tissues between the MMG sensor and muscle, and changes in torque production that may accompany dehydration. Ten subjects (age 22.5 +/- 1.6 years) were tested for maximal isometric (MVC), submaximal isometric (25, 50, and 75%MVC), and maximal concentric isokinetic muscle strength of the biceps brachii in either a euhydrated or dehydrated state while the electromyographic (EMG) and MMG signals were recorded. Separate three-way and two-way ANOVAs indicated no change in torque, EMG amplitude, EMG mean power frequency (MPF), MMG amplitude, and MMG MPF with dehydration. The lack of dehydration effect suggests that MMG may be more reflective of the intrinsic contractile processes of a muscle fiber (torque production) or the motor control mechanisms (reflected by the EMG) than the tissues and fluids surrounding the muscle fiber.     

Effect of diathermy on muscle temperature, electromyography, and mechanomyography

This study examined the effects of pulsed shortwave diathermy on intramuscular temperature, surface electromyography (EMG), and mechanomyography (MMG) of the vastus lateralis. Thirty-five men were assigned to diathermy (n = 13), sham-diathermy (n = 12), or control (n = 10) groups. Each subject performed isometric maximal voluntary contractions (MVCs) and incremental ramp contractions (10%-90% MVC) before and after treatment. Torque, intramuscular temperature, EMG, and MMG were recorded. Temperature for the diathermy group increased (P 相似文献   

Mechanomyographic and electromyographic responses to stimulated and voluntary contractions in the dorsiflexors of young and old men

The effect of age on mechanomyography (MMG) has not been examined for electrically evoked contractions. Similar to torque, we expected that postactivation potentiation of the MMG would differ between young and old subjects. Additionally, under voluntary conditions, we compared normalized MMG and electromyographic (EMG) signals in relation to torque, and expected that MMG, unlike EMG, would be affected by age. In 10 young and 10 old men, electrical stimulation was delivered before and after a 10-s maximal voluntary contraction (MVC) to assess potentiation of contractile (twitch torque; Pt), electrical (M-wave amplitude), and mechanical (MMG amplitude) properties of the dorsiflexors. Subsequently, subjects performed voluntary contractions at 20%, 40%, 60%, 80%, and 100% MVC for calculation of normalized MMG-torque and EMG-torque relationships. Following the MVC, Pt and evoked MMG were larger than at rest in both groups, but M-wave amplitude was unchanged. Twitch potentiation was greater in young than old, whereas evoked MMG was unaffected by age. Under voluntary conditions, values for MMG and EMG were similar between groups, except for greater MMG at MVC in young men. The shape of MMG and EMG relationships to torque was similar only in young men. Using the aging model, our results indicate that potentiation of the mechanical components (MMG) differ from those of twitch torque. Furthermore, the comparison of normalized voluntary MMG with age provides additional support for the concept of age-related motor unit remodeling.     

Activation deficit correlates with weakness in chronic stroke: Evidence from evoked and voluntary EMG recordings

ObjectiveTo use evoked (M-wave) and voluntary (during maximal voluntary contraction (MVC)) EMG recordings to estimate the voluntary activation level in chronic stroke.MethodsNine chronic hemiparetic stroke subjects participated in the experiment. M-wave (EMG_M-wave) and MVC (EMG_MVC) EMG values of the biceps brachii muscles were recorded.ResultsPeak torque was significantly smaller on the impaired than non-impaired side. EMG_M-wave was also significantly smaller on the impaired than non-impaired side. However, the normalized EMG_M-wave/Torque_MVC ratio was not significantly different between two sides. In contrast, both absolute EMG_MVC and normalized EMG_MVC/Torque_MVC were smaller on the impaired than non-impaired side. The voluntary activation level, EMG_MVC/M-wave, was also smaller on the impaired than non-impaired side. The voluntary activation level on the impaired side was highly correlated with weakness (R = 0.72), but very low (R = 0.32) on the non-impaired side.ConclusionCollectively, our findings suggest that both peripheral and central factors contribute to post-stroke weakness, but activation deficit correlates most closely with weakness as estimated from maximum voluntary torque generation.SignificanceThese findings serve to highlight the potential benefit from high-intensity exercises to enhance central activation for facilitation of motor recovery.     

Effect of static stretch training on neural and mechanical properties of the human plantar-flexor muscles

To determine the contributions of neural and mechanical mechanisms to the limits in the range of motion (ROM) about a joint, we studied the effects of 30 sessions of static stretch training on the characteristics of the plantar-flexor muscles in 12 subjects. Changes in the maximal ankle dorsiflexion and the torque produced during passive stretching at various ankle angles, as well as maximal voluntary contraction (MVC) and electrically induced contractions, were recorded after 10, 20, and 30 sessions, and 1 month after the end of the training program. Reflex activities were tested by recording the Hoffmann reflex (H reflex) and tendon reflex (T reflex) in the soleus muscle. Training caused a 30.8% (P < 0.01) increase in the maximal ankle dorsiflexion. This improved flexibility was associated (r(2) = 0.88; P < 0.001) with a decrease in muscle passive stiffness and, after the first 10 sessions only, with a small increase in passive torque at maximal dorsiflexion. Furthermore, both the H- and T-reflex amplitudes were reduced after training, especially the latter (-36% vs. -14%; P < 0.05). The MVC torque and the maximal rate of torque development were not affected by training. Although the changes in flexibility and passive stiffness were partially maintained 1 month after the end of the training program, reflex activities had already returned to control levels. It is concluded that the increased flexibility results mainly from reduced passive stiffness of the muscle-tendon unit and tonic reflex activity. The underlying neural and mechanical adaptation mechanisms, however, showed different time courses.     

Creatine supplementation does not alter neuromuscular recovery after eccentric exercise

Introduction: The purpose of this study was to investigate the effects of creatine (CR) supplementation on recovery after eccentric exercise (ECC). Methods: Fourteen men were assigned randomly to ingest 0.3 g/kg of CR or placebo (PL) before and during recovery (48 hours) from 6 sets of 8 repetitions of ECC. Maximal voluntary contraction (MVC), voluntary activation (VA), muscle thickness (MT), electromyography (EMG), contractile properties, and soreness were assessed. Results: MVC, evoked twitch torque, and rate of torque development decreased for both groups immediately after ECC and recovered at 48 hours. MT increased and remained elevated at 48 hours for both groups. Soreness increased similarly for both groups. EMG activation was higher for CR versus PL only at 48 hours. There were no group differences for torque, total work, or fatigue index during ECC. Conclusions: CR supplementation before and during recovery from ECC had no effect on strength, voluntary activation, or indicators of muscle damage. Muscle Nerve 54 : 487–495, 2016     

Effect of shoulder angle on the activation pattern of the elbow extensors during a submaximal isometric fatiguing contraction

The aim of this study was to examine the effect of shoulder angle on the electromyographic (EMG) activation pattern of the elbow extensors during a fatiguing contraction. Ten young men (23.5 ± 1.7) were tested on two occasions with the elbow angle at 90° and the shoulder at either 0° or 90° of flexion. EMG was recorded by fine wire electrodes inserted into the lateral, medial, and long heads of the triceps brachii and the anconeus. An EMG‐torque relationship was determined prior to a sustained isometric contraction at 20% of maximum voluntary contraction (MVC) until target failure. Endurance time was shorter, and postfatigue MVC torque was lower at 90° (40.4 ± 12.7 Nm) versus 0° (47.9 ± 14.7 Nm) of flexion. EMG activity of the long head during the final 10% of the fatiguing contraction was significantly greater at 90° versus 0° with no effect of shoulder angle on any other muscle portions. The findings suggest that measures from one muscle portion of the elbow extensors are not representative of the whole group, and the relative activation of the two‐joint long head was changed depending on shoulder angle during a fatigue task. Muscle Nerve, 2010     

Anodal Transcranial Direct Current Stimulation Alters Elbow Flexor Muscle Recruitment Strategies

BackgroundTranscranial direct current stimulation (tDCS) is known to reliably alter motor cortical excitability in a polarity dependent fashion such that anodal stimulation increases cortical excitability and cathodal stimulation inhibits cortical excitability. However, the effect of tDCS on agonist and antagonist volitional muscle activation is currently not known.ObjectiveThis study investigated the effect of motor cortical anodal tDCS on EMG/force relationships of biceps brachii (agonist) and triceps brachii (antagonist) using surface electromyography (EMG).MethodsEighteen neurologically intact adults (9 tDCS and 9 controls) participated in this study. EMG/force relationships were established by having subjects perform submaximal isometric contractions at several force levels (12.5%, 25%, 37.5%, and 50% of maximum).ResultsResults showed that anodal tDCS significantly affected the EMG/force relationship of the biceps brachii muscle. Specifically, anodal tDCS increased the magnitude of biceps brachii activation at 37.5% and 50% of maximum. Anodal tDCS also resulted in an increase in the peak force and EMG values during maximal contractions as compared to the control condition. EMG analyses of other elbow muscles indicated that the increase in biceps brachii activation after anodal tDCS was not related to alterations in synergistic or antagonistic muscle activity.ConclusionsOur results indicate that anodal tDCS significantly affects the voluntary EMG/force relationship of the agonist muscles without altering the coactivation of the antagonistic muscles. The most likely explanation for the observed greater EMG per unit force after anodal tDCS appears to be related to alterations in motor unit recruitment strategies.     

Contributing factors to muscle weakness in children with cerebral palsy

The aim of this study was to determine the extent of ankle muscle weakness in children with cerebral palsy (CP) and to identify potential causes. Maximal voluntary contractions of plantar (PF) and dorsiflexors (DF) were determined at optimal angles in knee flexion and extension in both legs of 14 children with hemiplegia (7 males, 7 females) and 14 with diplegia (8 males, 6 females). Their results were compared to 14 age- and weight-matched control participants (5 males, 9 females). Muscle cross-sectional areas of soleus, posterior, and anterior compartment muscles were determined from MRIs in 14 children with CP (eight diplegia, six hemiplegia) and 18 control children. Specific tension (torque/unit area) of PF and DF was determined from torque and cross-sectional area results. Muscle volumes of PF and DF were also determined in both legs of five control children and five with hemiplegia. Muscle EMG was recorded from soleus, medial gastrocnemius, and tibialis anterior during each maximal voluntary contraction. Mean amplitude was significantly reduced in PF and DF in both CP groups and significantly higher levels of coactivation of antagonists were found compared to control participants. Strength of PF and DF was significantly reduced in both CP groups, but more importantly the muscles were found to be weak based on significantly reduced specific tensions. The PF were most affected, particularly in the group with hemiplegia. It is believed that an inability to maximally activate their muscles contributed to this weakness. A combination of incomplete activation and high levels of PF coactivation are thought to have contributed to DF weakness.     

Relationship between electrical and vibratory output of muscle during voluntary contraction and fatigue

Measurements were done on the biceps muscles of 6 healthy volunteers to record simultaneously the surface electromyogram (EMG) and vibromyogram (VMG) by means of a piezoelectric device (accelerometer). The VMG is generated by mechanical waves due to the contraction mechanism and often measured as sound. The frequency spectrum and integrated value (IEMG and IVMG) of both signals were calculated. Both IEMG and IVMG showed a clear linear correlation with force, although at high forces, the variability of the VMG became rather high. Two series of experiments were performed to study the EMG and VMG changes in relation to changes induced by fatigue: (1) during constant force at 50% of the maximal voluntary contraction (MVC) and recovery; (2) for one 1 minute during declining force at MVC. The main finding was that the IVMG was related to the absolute force, irrespective of the fatigue state of the muscle. In contrast, the IEMG showed the well-known changes during fatigue, such as an increase during endurance. The spectral changes of the two measurements also showed a divergence. The spectra of the EMG shifted to lower frequencies in both fatigue protocols. In contrast, the spectra of the vibratory signal did not shift, except for several measurements at MVC. However, the shape did change to a somewhat flatter spectrum with less pronounced peaks. Possible explanations for this different behavior are discussed. It is concluded that the vibratory energy generated by the contraction mechanism is linearly related to force. Changes induced by fatigue do not alter this relationship: this contrasts with the behavior of the EMG.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence for strength imbalances as a significant contributor to abnormal synergies in hemiparetic subjects

Abnormal synergies in the paretic shoulder and elbow of hemiparetic subjects were quantified during maximal voluntary contractions (MVCs) in 27 subjects with a history of stroke and 8 age-matched control subjects. A six-axis load cell allowed simultaneous measurement of the primary torque the subject was attempting to maximize and the secondary torques at other joint actions. For example, during MVC of shoulder flexion, shoulder flexion is the primary torque and the secondary torques are internal/external rotation, abduction/adduction, and elbow flexion/extension. In general, the stroke subjects had increased secondary torques compared to controls, resulting in abnormal joint torque coupling within the set consisting of elbow flexion, internal rotation, adduction, shoulder flexion. Unlike previous studies, abnormal secondary torques in several cases were due to strength imbalances, which occur when the strength deficit for a particular joint action is greater than the strength deficit in the opposite joint action. This hypothesis was supported by electromyographic recordings and by the finding that subjects with larger strength imbalances tended to produce larger secondary torques. Possible mechanisms and consequences for rehabilitative treatments are discussed.     

The influence of prolonged vibration on motor unit behavior

Introduction: The purpose of this study was to determine the effects of vibration (VIB) on motor unit (MU) behavior of the vastus lateralis (VL) muscle during a 40% maximal voluntary contraction (MVC). Methods: Eleven healthy (age 21.3 ± 2.6 years) individuals participated in the study. Surface electromyography (EMG) data were recorded from the VL during isometric trapezoidal muscle contractions at 40% MVC. Firing events of single MUs and EMG amplitude were reported for the first, middle, and final seconds of a 12‐second steady force segment at 40% MVC. VIB was applied at 55 Hz to the patellar tendon for 15 minutes before and continued throughout the remainder of testing (VIB) or remained off (CON). Results: There were significant increases in MU firing rates during VIB in comparison to CON and no differences in EMG amplitude between VIB and CON. Conclusion: The VIB‐mediated reduction in muscle spindle function altered MU behavior at 40% MVC. Muscle Nerve 55 : 500–507, 2017     

肌电生物反馈治疗脑卒中患者运动功能障碍的疗效观察

目的观察在进行常规药物治疗的同时,早期使用肌电生物反馈疗法辅助治疗脑卒中患者运动功能障碍的疗效。方法对我科2008年5月至2010年1月收治的105例脑梗死及脑出血住院患者进行回顾性分析。其中治疗组55例住院期间使用肌电生物反馈疗法辅助治疗14d。对照组50例未做辅助治疗。两组患者于治疗前后进行简式Fugl—Meyer运动功能评定（FMA）并进行统计分析。结果两组运动功能恢复比较显示治疗组改善较对照组明显,统计学分析差异有显著性（P〈0．01）。结论本研究结果表明在进行常规药物治疗的同时,早期使用肌电生物反馈疗法辅助治疗脑卒中偏瘫患者有明显疗效,有利于患者运动功能的康复。     

Neuromuscular fatigue after low‐ and medium‐frequency electrical stimulation in healthy adults

Introduction: In this study we investigated fatigue origins induced by low‐frequency pulsed current (PC) and medium‐frequency current (MF) neuromuscular electrical stimulation (NMES) after a clinical‐like session. Methods: Eleven healthy men randomly underwent 2 NMES sessions, PC and MF, on quadriceps muscle (15‐minute duration, 6 seconds on and 18 seconds off). Maximal voluntary contraction (MVC), central activation ratio (CAR), vastus lateralis electromyographic activity (EMG), and evoked contractile properties were determined before and after the sessions. Evoked torque and discomfort during the sessions were also measured. Results: Both currents produced decreases in MVC, EMG, and evoked contractile properties after the sessions. No difference was found between currents for all variables (P > 0.05). Evoked torque during sessions decreased (P < 0.05). No difference was observed in mean evoked torque and discomfort (P > 0.05). Discussion: Both currents induced similar neuromuscular fatigue. Clinicians can choose either PC or MF and expect similar treatment effects when the goal is to generate gains in muscle strength. Muscle Nerve 58 : 293–299, 2018     

Increased H‐reflex excitability is not accompanied by changes in neural drive following 24 days of unilateral lower limb suspension

The purpose of this study was to determine whether the gain in soleus H‐reflex excitability induced by unilateral lower limb suspension (ULLS) is associated with changes in neural drive to the plantar flexor muscles. Six male subjects (23 ± 2 years, 187 ± 7 cm, 79 ± 9 kg) underwent 24 days of ULLS of the dominant limb. Plantar flexor maximal voluntary contraction (MVC) torque, activation capacity (twitch interpolation), soleus maximal electromyographic (EMG) activity, Hoffman (H)‐reflex, and the first volitional (V) wave normalized to the compound muscle action potential (M‐wave) were quantified before and after ULLS. Following ULLS, MVC torque decreased by 15% (P < 0.05). However, neither activation capacity nor EMG activity was significantly altered after the suspension. The V‐wave remained unchanged consistently after ULLS, whereas the H‐reflex increased significantly (+20%). Furthermore, there was no significant relationship between changes in H‐reflex and V‐wave over the ULLS period. These findings indicate that 24 days of ULLS can result in a substantial reduction of muscle strength without any apparent change in voluntary activation capacity. H‐reflex and V‐wave findings suggest that the spinal adaptations that underlie the unloading‐induced increase in resting soleus H‐reflex excitability did not significantly affect the efferent motor output to the plantar flexor muscles. Muscle Nerve, 2009     

Investigating the Effects of Peripheral Electrical Stimulation on Corticomuscular Functional Connectivity Stroke Survivors

Background: Electrical stimulation (ES) in the periphery can induce brain plasticity and has been used clinically to promote motor recovery in patients with central nervous system lesion. Electroencephalogram (EEG) and electromyogram (EMG) are readily applicable in clinical settings and can detect real-time functional connectivity between motor cortex and muscles with EEG–EMG (corticomuscular) coherence.

Objective: The purpose of this study was to determine whether EEG–EMG coherence can detect changes in corticomuscular control induced by peripheral ES.

Methods: Fifteen healthy young adults and 15 stroke survivors received 40-min electrical stimulation session on median nerve. The stimulation (1-ms rectangular pulse, 100 Hz) was delivered with a 20-s on–20-s off cycle, and the intensity was set at the subjects’ highest tolerable level without muscle contraction or pain. Both before and after the stimulation session, subjects performed a 20-s steady-hold thumb flexion at 50% maximal voluntary contraction (MVC) while EEG and EMG were collected.

Results: Our results demonstrated that after ES, EEG–EMG coherence in gamma band increased significantly for 22.1 and 48.6% in healthy adults and stroke survivors, respectively. In addition, after ES, force steadiness was also improved in both groups, as indicated by the decrease in force fluctuation during steady-hold contraction (?1.7% MVC and ?3.9%MVC for healthy and stroke individuals, respectively).

Conclusions: Our results demonstrated that EEG–EMG coherence can detect ES-induced changes in the neuromuscular system. Also, because gamma coherence is linked to afferent inputs encoding, improvement in motor performance is likely related to ES-elicited strong sensory input and enhanced sensorimotor integration.