Correlation between Elbow Flexor Muscle Strength and Needle Electromyography Parameters after Musculocutaneous Nerve Injury / 法医学杂志

OBJECTIVES@#To explore the changes of elbow flexor muscle strength after musculocutaneous nerve injury and its correlation with needle electromyography (nEMG) parameters.@*METHODS@#Thirty cases of elbow flexor weakness caused by unilateral brachial plexus injury (involving musculocutaneous nerve) were collected. The elbow flexor muscle strength was evaluated by manual muscle test (MMT) based on Lovett Scale. All subjects were divided into Group A (grade 1 and grade 2, 16 cases) and Group B (grade 3 and grade 4, 14 cases) according to their elbow flexor muscle strength of injured side. The biceps brachii of the injured side and the healthy side were examined by nEMG. The latency and amplitude of the compound muscle action potential (CMAP) were recorded. The type of recruitment response, the mean number of turns and the mean amplitude of recruitment potential were recorded when the subjects performed maximal voluntary contraction. The quantitative elbow flexor muscle strength was measured by portable microFET 2 Manual Muscle Tester. The percentage of residual elbow flexor muscle strength (the ratio of quantitative muscle strength of the injured side to the healthy side) was calculated. The differences of nEMG parameters, quantitative muscle strength and residual elbow flexor muscle strength between the two groups and between the injured side and the healthy side were compared. The correlation between elbow flexor manual muscle strength classification, quantitative muscle strength and nEMG parameters was analyzed.@*RESULTS@#After musculocutaneous nerve injury, the percentage of residual elbow flexor muscle strength in Group B was 23.43% and that in Group A was 4.13%. Elbow flexor manual muscle strength classification was significantly correlated with the type of recruitment response, and the correlation coefficient was 0.886 (P<0.05). The quantitative elbow flexor muscle strength was correlated with the latency and amplitude of CMAP, the mean number of turns and the mean amplitude of recruitment potential, and the correlation coefficients were -0.528, 0.588, 0.465 and 0.426 (P<0.05), respectively.@*CONCLUSIONS@#The percentage of residual elbow flexor muscle strength can be used as the basis of muscle strength classification, and the comprehensive application of nEMG parameters can be used to infer quantitative elbow flexor muscle strength.

Neural Adaptation Analysis of Muscle Isometric Maximum Voluntary Contraction Resistance Training at Different Joint Angles / 医用生物力学

Objective To study the characteristics of neural adaptation for resistance training of maximum voluntary contraction (MVC) of muscles at different joint angles. Methods Thirty healthy male college students were randomly divided into 3 groups, and each group was subjected to MVC isometric contraction resistance training at elbow joint angles of 45°, 90°, and 135°. Surface electromyography (sEMG) signals of the biceps brachii were measured before and after training, and the root mean square (RMS) and median frequency (MF) of the sEMG signals were also analyzed. ResultsThere were significant differences in normalized RMS of sEMG for the biceps brachii before and after training at 45°, 90°, and 135° elbow joints. Comparison of the RMS between different angles after training showed that 45° was significantly different from 90° and 135°. There were no significant differences between 90° and 135°. After training, no significant differences were found in normalized MF at all angles. Conclusions The RMS of sEMG shows angle-specific changes, while the MF of sEMG does not have angle-specific changes. When the biceps brachii is at the middle and large elbow joint angles, the neural adaptation effect produced by isometric resistance training is better.

The effect of carbohydrate mouth rinse in isometric hand grip performance / 体力科学

This study aimed to clarify the effects of carbohydrate mouth rinse on exercise performance. We examined the effect of mouth rinse on fatigability. Thirty healthy male college students completed three trials with non mouth rinse (CON), mouth rinse intervention of 6% glucose (GMR), and artificial sweetener (PLA). Handgrip exercise was performed as a fatigue task. The subjects performed a 10-seconds maximal voluntary contraction (MVC) followed by a 40% MVC rhythmic grasping movement for 14 per minutes, followed by a 4-seconds rest. This set of exercises was performed for a total of ten sets. Mouth rinse was performed from the 5th set to the 10th set. The subjects were divided into three groups: L, M, and S, according to the degree of decrease in MVC due to fatigue in CON. The effect was evaluated using the rate of change in MVC after the mouth rinse. The evaluation was performed for each trail and group. In the L group, mouth rinse significantly improved the rate of change of MVC compared with the other trials (GMR vs. CON: P = 0.002; PLA vs. CON: P = 0.042). A significant trend was observed in the M (GMR vs. CON: P = 0.062), but not in the S. In conclusion, the effects of mouth rinse differed depending on fatigability in isometric hand grip performance, with mouth rinse inhibiting the decrease of motor fatigue. In addition, it was suggested that the sweetness of carbohydrates may have an effect on mouth rinse.

Acute effects of maximal isometric muscle action of the elbow extensors on contralateral dynamic task of the elbow flexors: a pilot study

Aim: the aim was to investigate the influence of a maximal isometric muscle action of the elbow extensors on the contralateral dynamic task of the elbow flexors. Methods Seventeen recreationally trained men (23.3 ± 4.9 yrs, BMI: 24.8 ± 2.2 Kg/m²) underwent two randomized different testing sessions separated by one week. In the control session (CON) all subjects performed a maximum number of repetitions test (RMs) at 75%1RM using the right elbow flexors. The experimental session (EXP) was similar to the CON; however, all subjects were instructed to perform RMs at 75%1RM by using the right elbow flexors and maintaining the maximal voluntary contraction of the left elbow extensors during the test. RMs, rating of perceived exertion (RPE), and training volume (TV) were measured and compared between sessions. Results: The EXP showed a significant 10.4% increase on the RMs (13.8 vs. 12.5, p < lt; 0.001, d = 0.44) and 12.1% increase in TV (238.0 vs. 212.4 kg, p >lt; 0.001, d = 0.43) than CON. No differences were observed for RPE between sessions. Conclusion: The maximum voluntary contraction of the left elbow extensors increased the RMs of the contralateral elbow flexors, reflecting a higher TV, and no differences in the RPE. Our results suggest that the investigated method may be a viable and practical alternative to increase the acute strength performance of elbow flexors when using submaximal loads.(AU)

Cross-education after unilateral resistance training for forearm rotation / 中华物理医学与康复杂志

Objective To investigate the extent of cross-education between the pronation and supination muscles of the right and left forearms after unilateral isometric training.Methods Twenty healthy young girls were randomized into a training group and a control group using a random number table.The training group underwent isometric training of their right forearms for six weeks,while the control group continued ordinary life without exercises.Pronation peak torque (PPT) and supination peak torque (SPT) were assessed before and after the training for both groups.Results The differences in PPT or SPT between the training group and the control group were not significant before the training program.When the training had been completed,however,the average PPT and SPT on right side of those trained of course had increased significantly compared to before training or to the control group.More significantly,the average PPT and SPT on the left side in the training group were also significantly better than before training or in the control group after training.Conclusion Unilateral isometric training of the forearm pronation and supination muscles for six weeks can significantly increase muscle strength bilaterally,indicating good cross-education.

Inter-hand transfer of the effects of unilateral isometric resistance training for wrist flexion and extension / 中华物理医学与康复杂志

Objective To investigate the effects on one hand of training the other with isometric wrist extension and flexion training and its underlying mechanism.Methods Twenty healthy young girls were recruited and randomized into a training group and a control group with 10 subjects in each,using a random number table.The subjects in the training group were accepted isometric training of the wrist extensors and flexors on the right side once every other day,4 days a week for 6 weeks according to a pre-programmed protocol,while those in the control group had no intervention.Peak torque and surface electromyography (sEMG) were recorded and assessed before and after 6 weeks of training.Results In the training group,the average peak torque of right wrist flexion and extension were both significantly higher than before training (within-group comparison) and higher than in the control group (between-group comparison) after 6 weeks of training.The average peak torques of the left wrist in the training group in flexion and extension were (12.9±2.0) Nm and (6.4 ± 1.3) Nm after training,both significantly higher than before the training and stronger than the control group.In the sEMG traces during wrist extension,after training the ascend velocity of the right extensor carpi ulnaris and the integrated area of the left extensor carpi ulnaris in the training group were significantly smaller than before training and in the control group.Conclusion Unilateral isometric resistance training of the wrist muscles can transfer to the contralateral side,probably by altering muscle recruitment.

Evaluation on central and peripheral origin of muscle fatigue / 医用生物力学

atigue is a common phenomenon in many medical and neurologic diseases. Understanding the origins of fatigue in these diseases is of great guiding significance in developing targeted interventions for muscle fatigue. In this review, the central origin (including all the supraspinal and spinal physiological phenomena capable of inducing a decrease in motoneuron excitation) and the peripheral origin (including neuromuscular transmission, propagation of action potentials in muscle, excitation-contraction coupling) of muscle fatigue were summarized. The methods of assessing the central or peripheral origin of muscle fatigue were discussed, including the direct measurement (maximal voluntary contraction force, twitch force) and the indirect tests (twitch interpolation, electromyography, motor cortical stimulation).

EFFECT OF EXPERIMENTAL MUSCLE PAIN INDUCED BY INTRAMUSCULAR INJECTION OF HYPERTONIC SALINE ON MUSCLE FATIGUE DURING SUSTAINED MAXIMAL VOLUNTARY CONTRACTION / 体力科学

It has recently demonstrated that central fatigue during sustained maximal voluntary contraction (MVC) progresses faster in the presence of delayed onset muscle soreness due to eccentric contractions than in normal states (Endoh et al., 2005). However, it remains to be clarified whether these findings are related to muscle damage or muscle pain induced by eccentric contractions. The present study investigated which factor plays a more critical role in the earlier onset of central fatigue during sustained MVC with muscle pain induced by injecting hypertonic saline. Ten healthy male right-handed subjects (age, 21~32 yrs.) were asked to perform brief MVCs (~3 sec) before and after injection of isotonic saline (0.9%, 1.0 ml, ISO) or hypertonic saline (5.25%, 1.0 ml, HYP) into the left biceps brachii. The subjects then performed 1 min MVC (fatigue test) with isometric elbow flexion was done in ISO or HYP condition or intact control condition (CON). During these contractions, transcranial magnetic stimulation was delivered to the contralateral motor cortex to evaluate voluntary activation (VA), the motor evoked potential (MEP) and electromyographic (EMG) silent period (SP). Ratio of root mean square of the EMG and elbow flexion force (EMGrms/F) was also measured.The peak pain induced by the injection of HYP was significantly higher than that of ISO (p<0.01). There was no significant difference in either the maximum size of the M response or the twitch force between ISO and HYP (p>0.05). However, during the brief MVCs, both maximal force (p<0.01) and VA (p<0.05) for HYP were significantly decreased compared to those for ISO. During the fatigue test, although MVC, VA, MEP and SP were significantly altered (p<0.05~0.01), there was no significant difference among CON, ISO and HYP (p>0.05). There was no significant difference in EMGrms during the fatigue test (p>0.05).These results suggest that peripheral force-producing capacity remained intact after the injection of ISO and HYP during sustained MVC, and that progression of central fatigue during sustained MVC was less affected by the increased group III and IV afferent activity induced by HYP.

CENTRAL AND PERIPHERAL FATIGUE DURING SUSTAINED MAXIMAL VOLUNTARY CONTRACTIONS IN TRAINED AND UNTRAINED HUMAN SUBJECTS / 体力科学

The present study investigated how resistance training affects behaviors related to central and peripheral fatigue during a sustained maximal voluntary contraction (MVC) . The subjects were well-trained (TR, n=8) and sedentary untrained (UT, n=6) males. The subjects were asked to repetitively perform 3 sets of MVC (elbow flexion) for 1 min with a rest interval of 1 min. Transcranial magnetic stimulation (TMS) was delivered to the contralateral motor cortex to evoke the motor evoked potential (MEP) and electromyographic (EMG) silent period (SP) after the MEP. Ratio of root mean square (RMS) of the EMG and elbow flexion force (RMS/F) was also calculated.<BR>The time course of the decrease in elbow flexion force that was standardized with respect to the maximal value obtained at the beginning of the first MVC was almost identical in both TR and UT. At the end of the task, the elbow flexion force decreased to around 30 % of the initial value in both groups. Decrease in voluntary activation (VA) estimated by the increment of the force after TMS was significantly larger in UT (77.3%) than in TR (88.2%) at the end of the task. Although the increase in MEP during the first set was significantly greater in UT than in TR, elongation of SP was significantly larger in UT than in TR. Increase in RMS/F, which is a manifestation of peripheral fatigue, was significantly larger in TR than in UT.<BR>These results suggest that decrease in MVC in UT and in TR is respectively more attributable to central and peripheral fatigue, and that inhibitory inputs to motor cortex were larger in UT than in TR. It is concluded that expression of central and peripheral fatigue is affected by resistance training.

Features of surface myoelectric signals taken from the triceps brachii and biceps brachii of stroke patients / 中华物理医学与康复杂志

Objective To provide scientific evidence for the effectiveness of upper limb training after stroke.Methods Surface electromyograms (sEMGs) of the triceps braehii and biceps brachii were recorded in stroke patients during maximum isometric voluntary contraction (MIVC).A total of 18 patients with hemiparesis were studied.During the elbow's MIVC,flexor and extensor peak torque were measured,and sEMGs of the biceps and tri- ceps brachii were recorded.Results During MIVC,the biceps braehius of the intact side registered a stronger EMG than that of the affected side when the elbow flexed,but the differenees in the triceps braehii readings were not significant.The triceps bracbius of the intact side gave a stronger iEMG than the affected side when the elbow extend- ed,but the iEMG form the biceps brachius of the affeeted side was higher than that of the intact side.The co-contrac- tion ratio (CCR) of the triceps brachius on the affected side was higher than that of the intact side.Though there was a tendency for the CCR of the biceps brachius on the affected side to be higher than the intact side,any difference was not statistically significant.For both flexor and extensor MIVC,the peak torque on the affected side was lower than that of the intact side.Conclusions Elbow spastieity in hemiplegic patients is mainly attributable to the flexor muscles.In the rehabilitation of the upper limb after stroke,it is important when training extensor strength to inhibit co-contraction of the antagonistic muscle.

Maximum isometric voluntary contraction of ankle dorsiflexors and plantarflexors: comparison of surface electromyography between patients at the acute stage after stroke and age-matched healthy elderly / 中华物理医学与康复杂志

Objective To compare muscle function of the ankle dorsiflexors and plantarflexors between stroke patients at the acute stage and age-matched healthy elderly, in an attempt to gain insight for an early rehabilitation program after stroke. Methods Two groups of volunteers participated in the study. One group was 11 healthy elderly aged 62.3?5.7 years and the other was 12 patients with first ever stroke aged 66.6?8.3 years. During measurement, the leg being tested was positioned on a specially designed frame, with a load cell (force sensor) attached to the ball of the foot. Surface electrodes were applied on the skin of both anterior tibialis and gastrocnemius muscles for electromyography (EMG). Torque and integrated EMG during maximum isometric voluntary contraction (MIVC) of the ankle dorsiflexors and plantarflexors were recorded and analyzed. Results There were no significant differences in the MIVC of either ankle dorsiflexion or plantarflexion between the left and right sides of the healthy elderly. However, significant reduction in the ankle dorsiflexion and plantarflexion torques were found in the affected side of stroke patients(P

Mechanism for Slowing Surface Electromyography During Fatiguing Contraction Revealed by Superimposed M-Wave Analysis / 体力科学

We studied the mechanism for slowing surface electromyography (EMG) during fatiguing contraction using superimposed M-wave analysis. Seven healthy male subjects exerted 60% maximum voluntary contraction of isometric abductions in the left first dorsal interosseous muscle (FDI) until exhaustion. Simultaneously with voluntary contractions, the ulnar nerve was electrically stimulated at supramaximal intensity, and volitional EMG and superimposed M-waves were obtained. We examined the behavior of muscle fiber conduction velocity (MFCV) and median frequency (MDF) for both EMG, with the following results:<BR>1) MFCV calculated from volitional EMG of FDI was about 6 m/s during 60% MVC.<BR>2) The waveform of voluntary EMG detected from FDI slowed in all subjects during fatiguing contraction at 60% MVC, indicating fatigue had developed in the muscle.<BR>3) As fatigue progressed, the waveform of the superimposed M-wave tended to decrease in amplitude and increase in duration.<BR>4) As fatigue progressed, MDF and MFCV in volitional EMG decreased significantly (p<0.04) . The rate of change was larger in MDF than in MFCV (p<0.01) .<BR>5) As fatigue progressed, MDF and MFCV in the superimposed M-wave decreased significantly (p<0.01) . The rate of change was larger in NIDF than in MFCV (p<0.05) .<BR>These results suggested that MFCV and other peripheral factors affected the slowing of volitional EMG. Elongation of the depolarization zone in muscle fiber is proposed as a peripheral factor.

Effect of Voluntary Contraction in Motor Evoked Potential and Silent Period by Transcranial Magnetic Stimulation

OBJECTIVE: To determine the effects of the voluntary contraction of muscles and magnetic stimulation intensity on the motor evoked potential (MEP) and the silent period (SP). METHOD: We studied MEPs and SPs in opponens pollicis muscle in 30 healthy adults (male: 16, female: 14) while varying the amount of the voluntary contraction and the stimulation intensity. We analyzed MEPs and SPs in relation to sex, recording site, opposition power and height. RESULTS: 1) During the contraction, the latencies of MEP were significantly shorter than during the relaxation. 2) The amplitudes of MEP reached plateau at 30% of maximal voluntary contraction and increased with increment of stimulation intensity without limitation. The amplitudes of MEP of right hand were bigger than left hand. There were no significant differences according to sex and recording site. 3) The durations of SP were directly proportional to the degrees of voluntary contraction and the stimulation intensity. CONCLUSION: Transcranial magnetic stimulation should be performed under the same voluntary contraction and magnetic stimulation intensity.

Optimization of Facilitation Threshold in Transcranial Magnetic Stimulation

OBJECTIVES: To analyze the motor evoked potential (MEP) responses to a degree of voluntary contraction and stimulus intensity and to suggest the standardized optimal stimulation for MEP responses. METHODS: MEPs induced by a cortical stimulation were elicited at the thenar muscles in 15 normal subjects during the rest and gradual voluntary contraction, using the 10% of maximal voluntary contraction (MVC), 30%, 50%, and MVC. During rest and during each contraction, excitability threshold at rest (RET) and at contraction (CET) were determined. Consecutive stimuli were applied, according to the intensity of ratio increment (110% to 150% of excitation threshold). RESULTS: The RET showed a remarkable decrease (57.1+/-8.2% --> 47.4+/-8.7%) after the voluntary contraction (P<0.05). Shortening of latency reached the saturation level with 10% of MVC, irrespective of stimulus intensity. Amplitude reached a saturation level at 30% of MVC with 62.7% intensity of maximal output, which is equal to 140% intensity of its CET, and to 110% of RET. MEP amplitude at rest and at 10% of MVC were influenced by the excitation threshold (P<0.05), but those at above 30% of MVC were not related. CONCLUSION: The procedure for optimal facilitation for the MEPs is as follows; for minimal latency of MEPs, minimal contraction (10% of MVC) with RET intensity is enough. For maximal amplitude of MEPs, moderate contraction (30% MVC) with 110% intensity of RET is adequate.

Effect of Facilitation and Averaging on Side-to-Side H Reflex Amplitude Ratio

OBJECTIVES: To determine the effect of facilitation on H reflex side-to-side amplitude ratio and to determine the effect of averaging under the assumption that an averaging could further stabilize the amplitude ratio in a facilitated condition. METHOD: FCR H reflex amplitude ratios of direct and averaged potentials were measured in fifty asymptomatic subjects under three conditions, during rest, during a constant 5 pound isometric contraction under the hand-dynamometer monitoring, and during a moderate constant isometric contraction under the electromyographer's verbal guidance. RESULTS: The lower limits of the amplitude ratios that encompass 97.5% of subjects by the percentile method under three conditions were as follows; (1) during the rest (n=37); 0.47 (direct) and 0.50 (average), (2) during the constant 5 pound isometric contraction under the hand- dynamometer monitoring; 0.47 (direct) and 0.48 (average), and (3) during the moderate constant isometric contraction under the electromyographer's verbal guidance; 0.48 (direct) and 0.46 (average), respectively. CONCLUSION: There seems to be no definite effect of facilitation and averaging on H reflex amplitude ratio. H reflex amplitude ratio measured in facilitated condition without averaging is still useful for the diagnosis of unilateral radiculopathy.

Changes in the excitability of ankle extensor and flexor motoneuones at the onset of voluntary contraction of quadriceps femoris muscle in man / 体力科学

A study was conducted to investigate changes in the excitability of the ankle extensor and flexor motoneurons during voluntary contraction of the quadriceps femoris muscle (Quad) . For this purpose, we used a reaction time task and the H-reflex technique. Subjects lay in the prone position on a bed and performed isometric contraction of the Quad. The strength of the contraction force was about 30% of maximum.<BR>In all subjects we observed strong facilitation of the soleus (Sol) H-reflex, which occurred from the EMG onset of vastus lateralis muscle (VL) . The pretibial muscle (TA) H-reflex was also facilitated at almost the same time as that seen in the Sol H-reflex in nine out of ten subjects. The peak of Sol and TA H-reflex facilitation appeared between 50 and 100 ms after the EMG onset of the VL, and then these facilitations gradually decreased. Weak but constant activities of the Sol and medial gastrocnemius muscle (MG) were observed on the full-wave rectified and averaged EMG record after 50 to 80 ms from the EMG onset of VL. No such EMG activity was observed in TA.<BR>These results suggest that excitatory inputs including those of both descending and peripheral origin induced by voluntary contraction of Quad are responsible for facilitation of the ankle extensor and flexor motoneurons. In addition, removal of presynaptic inhibition of the Ia terminal of the motoneurons by descending motor command might explain the present results.

Muscle fiber conduction velocity in human vastus lateralis during isometric contractions. Relation to muscle fiber composition / 体力科学

Relationship between muscle fiber conduction velocity and muscle fiber composition was studied in vastus lateralis of well-trained athlete students, who differed considerably regarding their fiber type distribution with averaged 69.2% fast twitch (FT) muscle fibers for sprinters (12 male subjects) and 39.7% FT muscle fibers for distance runners (7 male subjects) . Measurement of muscle fiber conduction velocity during brief and maintained isometric contraction was made directly, using the zero-crossing time delay method between two surface myoelectric signals. Muscle fiber conduction velocities increased 4.40 to 4.84 m/sec for sprinters and 3.91 to 4.31 m/sec for distance runners as developing force increased from 25 to 100% maximum voluntary contraction (MVC) . The correlation coefficients between conduction velocity and % FT fibers were 0.59, 0.63, 0.64 and 0.84 for 25, 50, 75 and 100% MVC, respectively. During maintained at 50% of MVC conduction velocities in sprinters decreased linealy from 4.77 to 4.38 m/sec and in distance runners decreased from 4.11 to 3.96 m/sec at only last stage. It was suggested that the individual difference in conduction velocity was caused by different muscle fiber composition and that the changes of conduction velocity depended on the recruitment of muscle fibers.