Integrated EMG Research Articles

The Comparative Analysis of EMG Activities on The Upper and Lower Limb Muscles during Nordic Walking

PURPOSE The purpose of the study was to investigate muscle activity on the upper and lower muscles during Nordic walking (PW) and power walking (NW). METHODS Within the last six months that affect gait, such as a fracture or joint surgery inexperienced college student who is physically healthy (20 students; age: 20.1±1.7 years, height: 161.6±4.5 cm, weight: 53.5±6.5 kg) were enrolled in this study and all subjects agreed to evaluate walking by using Nordic pole. Surface electromyography systems (BTS FREEEMG 300, Italy) were attached to Tibialis anterior (TA), Gastrocnemius medialis (GM), Rectus femoris (RF), Biceps femoris caput longus (BF), Biceps brachii caput longus (BB), Triceps brachii caput longus (TB), Flexor caput radialis (FCR), Extensor digitorum (ED), and integrated electromyography (IEMG) were measured. RESULTS The result showed that the NW did influence the IEMG. The EMG activity the TA (t=3.6, p<.01) during NW was significantly lower and the TB (t=3.8, p<.01), FCR (t=6.4, p<.01), ED (t=2.1, p<.05) significantly higher than the corresponding values in power walking. CONCLUSIONS Lower limb muscles by NW are less used than by PW. Upper limb muscles are by NW are Nhe text should be typed double-spaced on one side of the page. 색인어: ë ¸ë¥´ë”•ì›Œí‚¹, 파워워킹, ê·¼ì „ë„, 근활성도 Keywords: Nordic walking, Power walking, Electromyography (EMG), Muscle activity

Acupuncture combined with rehabilitation training for foot drop after stroke

To compare the clinical efficacy difference between acupuncture combined with rehabilitation and simple rehabilitation for foot drop after stroke. Ninety-eight patients were randomly divided into a combination group and a rehabilitation group, 49 cases in each one. Acupuncture and rehabilitation were used in the combination group. The acupoints were Yanglingquan (GB 34), Zusanli (ST 36), Guangming (GB 37), Xuanzhong (GB 39), Sanyinjiao (SP 6), etc., while rehabilitation included training for musculi hippicus strength and musculi triceps surae. Only the same rehabilitation was applied in the rehabilitation group. The treatment was given six times a week for continuous six weeks. Musculi hippicus force, shank triceps spasticity, toe flexion improvement and the maximum integral EMG (iEMG) of the musculi tibialis anterior and caput laterale musculi gastrocnemii were compared between the two groups,and the effects were evaluated. After treatment, the musculi hippicus force, iEMG of musculi tibialis anterior and caput laterale musculi gastrocnemii, the function scores of the lower limbs by Fugl-Meyer of the two groups were better than those before treatment (all P<0.05), with the better effect in the combination group (all P<0.05). And the scores of shank triceps tension were decreased in the two groups (both P<0.05), more apparently for the combination therapy (P<0.05). The improvement rate of toe flexion of the combination group was 87.76% (43/49), which was obviously higher than 69.39% (34/49) of the rehabilitation group (P<0.05). The cured rate of the combination group was 48.98%(24/49), and it was better than 28.57% (14/49) of the rehabilitation group (P<0.05). Acupuncture combined with rehabilitation achieves better effect than simple rehabilitation for foot drop after stroke.

The role of the supporting lower limb function in the premotor changes in the H-reflex of m. soleus

In studies on healthy humans we examined changes in the H reflex amplitude and the intensity of background EMG of the soleus muscle within the premotor period of voluntary extension of the contralateral ankle joint. The tested persons were in the lying prone position with relaxed legs, or in the standing position with support on both feet or only on one foot with additional hand support. The soleus H reflex was induced using the standard technique by transcutaneous stimulation (1 ms long current pulses) of the tibial nerve afferents in the region of the popliteal dimple. Using superficial electrodes, we recorded the integral EMG reflex discharge from the m. soleus, amplified, and visualized it using a two-channel digital oscillograph, Handiscope HS3 (TiePieEngeneering, Netherlands). In other tests, we also recorded tonic background EMG activity from the soleus muscle. After fullwave rectification and low-frequency filtration we estimated the area under the integral curve enveloping oscillations of the above mentioned EMG. In the lying position the extension of contralateral ankle joint evoked anticipatory facilitation of the testing soleus H-reflex. It manifested in 90–60 ms and reached the maximum 30 ms before the conditioning movement. Considerable changes of the soleus background EMG-activity did not occur during the premotor period. Consequently, it is supposed that the mechanism leading to the H-reflex facilitation is the decrease of presynaptic inhibition at 1a. In the standing position with support on both feet contralateral ankle joint extension caused anticipatory inhibition of the soleus H-reflex and simultaneous suppression of background EMG 90–60 ms before the conditioning movement. These results indicate the anticipatory changes of muscle tone and suggest participation of postsynaptic mechanism in the inhibition of the testing H-reflex. When the moving contralateral extremity had no support, the contralateral ancle joint extension did not cause anticipatory inhibition but facilitation of the soleus H-reflex. Its time course was similar to that observed in the lying position. The considerable changes of the soleus background EMG-activity did not arise. The results of the experiments indicate that the nature of premotor changes in the spinal neuron circuits, associated with the lower limb muscles, depends not only on the type of upcoming voluntary movement. Being caused by the contralateral limb movements, they depend greatly on the fulfillment or nonfulfillment of the support function by the lower limbs.

Real Time Identification of Human Forearm Kinematics from Surface EMG Signal Using Artificial Neural Network Models

This work identifies the human forearm kinematics in real time by utilizing the surface electromyography (SEMG) signal using two different artificial neural network models. Here, the SEMG signals from biceps brachii muscle are captured using Ag-AgCl electrodes. Two time domain features Integrated EMG (IEMG) and number of zero crossing (ZC) are derived from the measured SEMG signals after segmenting the raw SEMG signal into 250 millisecond window. These two time domain features are used as the input signals for identifying the human forearm kinematics. Human forearm kinematics is determined using two neural network models, (1) Multi Layered Perceptron Neural Network (MLPNN) model and (2) Radial Basis Function Neural Network (RBFNN) model. The results obtained from the both models are compared in this work. The results indicate that the RBFNN model is giving better identification results with an average regression coefficient value of 0.756767 and 0.389113 for the identification of angular displacement and angular velocity respectively when compared with MLPNN model.

足関節背屈角制限による歩行安定靴の開発

It is known that a passive dynamic walk for a biped robot is stabilized by limiting its angle of the ankle of the stance leg. Since the passive dynamic walk has a similarity with a relaxed human walking, it is anticipated that the ankle angle limitation also contributes to stabilize a human walk. In previous researches, we realized this ankle angle limitation mechanism into human shoes, and showed the stability effect of this shoes by recording integral EMG signals at the muscles that are known to contribute to posture control of a leg. In this paper, we show that the proposing shoes do not produce unnatural ankle torque and thus lighten load of legs in natural way during a walk. The analysis is done by the gait analysis using 3D motion sensors with force plates.

Effects of custom-made insoles on idiopathic pes cavus foot during walking

From a subject group of pes cavus, the purpose of this study was to evaluate the biomechanical characteristics of lower limbs, based on plantar foot pressure and electromyography (EMG) activities, by the effects on two kind of custom-made insoles. Ten individuals among thirty females with a clinical diagnosis of idiopathic pes cavus (mean age (SD): 22.3 (0.08) years) were selected for the study. The plantar foot pressure data and EMG activities of four lower limb muscles were collected, when subjects walked on a treadmill, under three different experimental conditions. The plantar foot pressure data was analyzed, after the bilateral foot was divided into three areas of masks and into four sections of stance phase, to compare plantar foot pressure. The EMG activities were analyzed for integrated EMG (IEMG) value. The results show that plantar foot pressure concentrated in particular parts is decreased by custom-made insoles. In the case of EMG, all the muscle activities decreased significantly. The custom-made insoles dispersed pressure concentrated by the higher medial longitudinal arch and improved the efficient use of muscles. In particular, the extension structure in the forefoot of custom-made insoles was more efficient for pes cavus. Therefore, it could help patients to walk, by offering support to prevent the disease of pes cavus deformity, and to relieve the burden and fatigue in the lower limbs on gait.

Changes in postural control during a repetitive reaching task

Background: A reaching movement is an important action in daily life. When a reaching movement is directed to a target placed at a distance greater than arm length in standing, a driving or braking force must be created to initiate and to terminate whole body movement (Tyler and Karst, 2004). Therefore, the central nervous system activates postural muscles at an appropriate timing and subsequent initiates joint motion in lower limb. Though it is well known that motor components such as the peak velocity of arm movements improve through reaching training, it remains unclear how postural components improve. Purpose: The repeated reaching training is widely adopted as one of rehabilitation programs on a clinical treatment. However, changes in postural control during reaching training have been rarely reported. Therefore, the purpose of this study is to investigate change in muscle activity and joint angle of lower limbs through repeated reaching training in standing posture. Methods: Fifteen healthy subjects (23± 2 years) participated. All subjects provided written informed consent, as approved by the ethics committee of Hokkaido University Faculty of Health Sciences. Subjects performed reaching to a small target placed in the nearly maximum reach distance as quickly as possible. One hundred trials of reaching with right arm were repeated for three consecutive days and they were examined again after discontinuing training for one day. The surface electromyography (EMG) of tibialis anterior (TA) and gastrocnemius (GAS) was recorded. Kinematic data were collected using a three-dimensional motion analysis system. The integrated EMG (IEMG) were calculated for driving phase (from the reaching onset to the time when hand velocity was maximal) and braking phase (from the time when hand velocity was maximal to termination time of reaching). Hip, knee, and ankle joint angles were calculated. Mean value of the parameters in the first 10 trials on the first training day were compared with those of the other 10 trials on the first training day, and with those of the first 10 trials on the other training day using one-way repeated measure ANOVA and a post-hoc test. The significance level was set at p< 0.05. Results: On the first day, the normalized IEMG of the right TA in driving phase (p< 0.01) and the left GAS in braking phase (p< 0.01) significantly increased through repeated reaching training. Also, the maximum ankle dorsiflexion angle in driving phase (p< 0.05) and the maximum hip flexion angle in braking phase (p< 0.05) significantly increased. Training effects on these parameters were retained after a two-day rest period. Conclusion(s):We found that changes in postural control occurred in both driving and braking phase during a repetitive reaching task. Training effects were retained after subjects discontinued training. These results suggest postural learning not only to initiate thewhole body forwardmovement but also to terminate the movement occur during a repetitive reaching task. Implications:A better understanding of the postural control mechanism during repetitive reaching training is useful for physical therapy practices.

Frequency analysis of electromyogram of the triceps surae muscle taken while the stroke patients walk

Background: Many groups have reported results of frequency analysis of electromyogram (EMG) while the muscle with spasticity contracts in stroke patients.However, very few reports on characteristics of the muscle with spasticity during exercise have been published, and the majority is static evaluation using Fast Fourier Transform (FFT). Purpose: We carried out and examined dynamic frequency characteristics of contraction characteristics of the triceps surae while the stroke patients walk using Wavelet Transform (WT) which analyzes temporal information and frequency information of conventional FFT at same time. Methods: Subject of the present study was nine healthy men (age 28.0± 2.83), healthy group (HG), and nine stroke patients (age 70.17± 9.38), stroke group (SG), who were in the recovery stage and the rehabilitation ward of our hospital. These patients have their hemiplegia after stroke, and can walk by themselves or while being supervised. We measured the dominant feet of the HG and the paralyzed legs of the SG. Surface EMGmonitored muscle activation while the subjects freely walked 10m on a walkway at the optimum speed. Also, a foot switch sensor was attached on the plantar part to identify a single walking cycle. EMGMaster (Ozawa Medical Instruments) was used for surface EMG to monitor medial and lateral heads of gastrocnemius muscle. The data after fourth steps from walking starts were analyzed. Integral EMG analysis and wavelet transform (12.5Hz to 200Hz) were carried out to any given data of three walking cycles. Calculated integrated values of both groups were normalized using the integrated values during a single walking cycle. Also, the frequency range was divided into two categories; a low-frequency band (LFB) of 45Hz and lower and highfrequency band of 75Hz and higher (HFB) to calculate the power density of HFB to LFB, H/L ratio, of each muscle. As a statistical analysis, the Wilcoxon signed-rank test was used to compare the integrated values and H/L ratio between the HG and SG. Results: Each evaluation item of the HG and SG was compared. The HG has a significantly high integrated value (p< 0.05), and the SG has significantly high H/L ratio (p< 0.05). Conclusion(s): Although muscle activity characteristics of the triceps surae of the stroke patients is low as an integrated value, the ratio of HFB is high as dynamic frequency characteristics. This indicates strong activity of fast fibers. By taking the facts of low integrated value and atrophy of the presence of fast-twitch fibers into account, synchronization defect in the motor units possibly caused a frequency rise. Implications: These findings are expected to help treatment to improve quality of muscle activity in rehabilitation for stroke patients to walk.

SEMG Pattern Recognition of Muscle Force of Upper Arm for Intelligent Bionic Limb Control

Two new feature extraction methods, window sample entropy and window kurtosis, were proposed, which mainly aims to complete the surface Electromyography (sEMG)-muscle force pattern recognition for intelligent bionic limb. The inspiration is drawn from physiological process of muscle force generation. Five hand movement tasks were implemented for sEMG-muscle force data record. With two classical features: Integrated Electromyography (IEMG) and Root Mean Square (RMS), two new features were fed into the wavelet neural network to predict the muscle force. To solve the issues that amputates' residual limb couldn't provide full train data for pattern recognition, it is proposed that force was predicted by neural network which is trained by contralateral data in this paper. The feasibility of the proposed features extraction methods was demonstrated by both ipsilateral and contralateral experimental results. The ipsilateral experimental results give very promising pattern classification accuracy with normalized mean square 0.58 ± 0.05. In addition, unilateral transradial amputees will benefit from the proposed method in the contralateral experiment, which probably helps them to train the intelligent bionic limb by their own sEMG.

Neuromuscular efficiency of the vastus lateralis and biceps femoris muscles in individuals with anterior cruciate ligament injuries

ObjectiveTo analyze strength and integrated electromyography (IEMG) data in order to determine the neuromuscular efficiency (NME) of the vastus lateralis (VL) and biceps femoris (BF) muscles in patients with anterior cruciate ligament (ACL) injuries, during the preoperative and postoperative periods; and to compare the injured limb at these two times, using the non-operated limb as a control. MethodsEMG data and BF and VL strength data were collected during three maximum isometric contractions in knee flexion and extension movements. The assessment protocol was applied before the operation and two months after the operation, and the NME of the BF and VL muscles was obtained. ResultsThere was no difference in the NME of the VL muscle from before to after the operation. On the other hand, the NME of the BF in the non-operated limb was found to have increased, two months after the surgery. ConclusionsThe NME provides a good estimate of muscle function because it is directly related to muscle strength and capacity for activation. However, the results indicated that two months after the ACL reconstruction procedure, at the time when loading in the open kinetic chain within rehabilitation protocols is usually started, the neuromuscular efficiency of the VL and BF had still not been reestablished.

Effect of a combined inversion and plantarflexion surface on ankle kinematics and EMG activities in landing

PurposeThe purpose of this study was to examine the effects of landing on a combined inversion and plantarflexion surface on the ankle kinematics and electromyographic (EMG) activities of medial gastrocnemius (MG), peroneus longus (PL), and tibialis anterior (TA) muscles. MethodsTwelve recreational athletes performed five drop landings from an overhead bar of 30 cm height on to three surfaces: a flat surface, a 25° inversion surface, and a combined surface of 25° inversion and 25° plantarflexion. The kinematic variables and integrated EMG (IEMG) of the three muscles were assessed using a one-way repeated measures ANOVA and a 3 × 3 (surface × muscle) ANOVA, respectively (p < 0.05). ResultsThe IEMG results showed a significant muscle by surface interaction. The flat surface induced higher TA activity than the two tilted surfaces. The inverted surface produced significantly higher inversion peak angle and velocity than the flat surface, but similar PL activity across the surfaces. The MG IEMG, ankle plantarflexion angle, and inversion range of motion were significantly higher for the combined surface compared to the inverted surface. ConclusionThese findings suggest that compared to the inversion surface, the combined plantarflexion and inversion surface seems to provide a more unstable surface condition for lateral ankle sprains during landing.

Effects of Acute Static Stretching on Electromyography (EMG) and Peak Force Responses

The purpose of the present study was to investigate the possibility of an interaction between the stretching-induced-force-deficit and bilateral-deficit during maximal voluntary isometric hand flexion under the stretch and non-stretch, bilateral, and unilateral conditions through measurement of EMG and force production. Force output and associated EMG were recorded during either unilateral or bilateral 3-second maximal voluntary isometric hand flexion (MVC) against a force transducer. The effect of the stretch on the right hand in a unilateral MVC was decreased in force with a decrease in integrated EMG (IEMG) activity. The left hand bilateral force in the stretch condition was significantly smaller than the left hand unilateral force in the non-stretched condition. It was concluded that a cumulative deficit might indicate activation of multiple inhibitory mechanisms or pathways or possibly a greater activation of a single inhibitory mechanism or pathway. Trends were observed that may prove to be significant with a stronger experimental design and greater subject numbers with less variability between subjects.

Effects of load on good morning kinematics and EMG activity.

Many strength and conditioning coaches utilize the good morning (GM) to strengthen the hamstrings and spinal erectors. However, little research exists on its electromyography (EMG) activity and kinematics, and how these variables change as a function of load. The purpose of this investigation was to examine how estimated hamstring length, integrated EMG (IEMG) activity of the hamstrings and spinal erectors, and kinematics of the lumbar spine, hip, knee, and ankle are affected by changes in load. Fifteen trained male participants (age = 24.6 ± 5.3 years; body mass = 84.7 ± 11.3 kg; height = 180.9 ± 6.8 cm) were recruited for this study. Participants performed five sets of the GM, utilizing 50, 60, 70, 80, and 90% of one-repetition maximum (1RM) in a randomized fashion. IEMG activity of hamstrings and spinal erectors tended to increase with load. Knee flexion increased with load on all trials. Estimated hamstring length decreased with load. However, lumbar flexion, hip flexion, and plantar flexion experienced no remarkable changes between trials. These data provide insight as to how changing the load of the GM affects EMG activity, kinematic variables, and estimated hamstring length. Implications for hamstring injury prevention are discussed. More research is needed for further insight as to how load affects EMG activity and kinematics of other exercises.

B-14 足関節背屈角制限による歩行安定靴の開発(シューズ)

It is known that a passive dynamic walk for a biped robot is stabilized by limiting its angle ofthe ankle of the stance leg. Since the passive dynamic walk has a similarity with a relaxed human walking, it is anticipated that the ankle angle limitation also contributes to stabilize a human walk. The purpose of this research is to realize this ankle angle limitation mechanism into human shoes, and investigate the effect of this shoes with the stabilization of human walk. In this paper, a simple configuration of the stabilized shoes is shown. In the shows, an angle of the ankle is limited by the attachment on a shin and a heel which are pulled together by a rubber sheet. A series of experiments were conducted to measure the stability of walking by recording integral EMG signals at the muscles that are known to posture control of a leg. The results showed that the muscles were less active during wearing the shoes with ankle angle limitation.

재활환자 모의보행 패턴분석을 이용한 하지 편측 장애자의 정량적 재활상태 모니터링

Abstract: In this paper, to quantitatively evaluate the degree of rehabilitation for the disabled of unilateral lowerextremity, we compared the EMG pattern of normal and simulated abnormal gait. The EMG signal was measuredat a rate of 1 kHz on the quadriceps and biceps femoris, the pressure sensor was attached to the sole in order todistinguish the gait cycle. Integrated EMG (IEMG) was obtained by the gait cycle, and classified four patterns thatwere the normal gait pattern, amplitude decrease pattern, reversed pattern, and irregular pattern. For comparisonof the patterns, a curve fitting was performed using the trigonometric functions. The result of curve fitting, themethod using a variable A that corresponds to the amplitude of the regression curve was able to distinguish thereverse pattern and remaining pattern. The coefficient of determination (R 2 ) representing coincidence of the patternof the regression curve and EMG was confirmed the biggest value at the normal gait. Therefore, the degree of normalgait can be confirmed using the coefficient of determination. This results show that it is possible to quantitativelyconfirm the degree of unilateral lower extremity disabled rehabilitation, and it will be contributed to the study of effi-cient rehabilitation methods by objective analysis.Key words: Gait analysis, IEMG, Curve fitting, Comparison of EMG pattern, Evaluation of rehabilitation

Eficiência neuromuscular dos músculos vasto lateral e bíceps femoral em indivíduos com lesão de ligamento cruzado anterior

ObjectiveTo analyze strength and integrated electromyography (IEMG) data in order to determine the neuromuscular efficiency (NME) of the vastus lateralis (VL) and biceps femoris (BF) muscles in patients with anterior cruciate ligament (ACL) injuries, during the preoperative and postoperative periods; and to compare the injured limb at these two times, using the non‐operated limb as a control. MethodsEMG data and BF and VL strength data were collected during three maximum isometric contractions in knee flexion and extension movements. The assessment protocol was applied before the operation and two months after the operation, and the NME of the BF and VL muscles was obtained. ResultsThere was no difference in the NME of the VL muscle from before to after the operation. On the other hand, the NME of the BF in the non‐operated limb was found to have increased, two months after the surgery. ConclusionsThe NME provides a good estimate of muscle function because it is directly related to muscle strength and capacity for activation. However, the results indicated that two months after the ACL reconstruction procedure, at the time when loading in the open kinetic chain within rehabilitation protocols is usually started, the neuromuscular efficiency of the VL and BF had still not been reestablished.

The effects of seat height and foot placement on lumbar spine load during sit-to-stand tasks

The purpose of this study was to determine the influence of seat height and foot position in the sagittal plane on L5-S1 joint load. Fourteen healthy male adults stood up from a chair with three different seat heights and positions of the feet in the sagittal plane. L5-S1 net joint torque, mechanical work, range of motion and electromyographic activity of the erector spinae muscle were measured. L5-S1 net joint work increased by about 50% from high to low seat position. The mean and peak L5-S1 net joint torques increased about 30% from foot-back to foot-neutral position. These results were reinforced by a greater integrated electromyography signal from the erector spinae from high to low seat position and from foot-back to foot-neutral position. A high chair and placement of the feet behind the knees may be advisable to lessen lumbar load during sit-to-stand movements.

Relationship between weight of rescuer and quality of chest compression during cardiopulmonary resuscitation.

BackgroundAccording to the guidelines for cardiopulmonary resuscitation (CPR), the rotation time for chest compression should be about 2 min. The quality of chest compressions is related to the physical fitness of the rescuer, but this was not considered when determining rotation time. The present study aimed to clarify associations between body weight and the quality of chest compression and physical fatigue during CPR performed by 18 registered nurses (10 male and 8 female) assigned to light and heavy groups according to the average weight for each sex in Japan.MethodsFive-minute chest compressions were then performed on a manikin that was placed on the floor. Measurement parameters were compression depth, heart rate, oxygen uptake, integrated electromyography signals, and rating of perceived exertion. Compression depth was evaluated according to the ratio (%) of adequate compressions (at least 5 cm deep).ResultsThe ratio of adequate compressions decreased significantly over time in the light group. Values for heart rate, oxygen uptake, muscle activity defined as integrated electromyography signals, and rating of perceived exertion were significantly higher for the light group than for the heavy group.ConclusionChest compression caused increased fatigue among the light group, which consequently resulted in a gradual fall in the quality of chest compression. These results suggested that individuals with a lower body weight should rotate at 1-min intervals to maintain high quality CPR and thus improve the survival rates and neurological outcomes of victims of cardiac arrest.

Hip Muscle Activity during Isometric Contraction of Hip Abduction

[Purpose] This study aimed to determine the effect of varying hip flexion angle on hip muscle activity during isometric contraction in abduction. [Subjects] Twenty-seven healthy men (mean age=21.5 years, SD=1.2) participated in this study. [Methods] Surface electromyography (EMG) was recorded of the upper portion of the gluteus maximus (UGM), lower portion of the gluteus maximus (LGM), tensor fasciae latae (TFL), and gluteus medius (GMed) during isometric contraction under two measurement conditions: hip flexion angle (0, 20, 40, 60, and 80 degrees) and abduction of the hip joint at 20, 40, 60, and 80% maximum strength. Integrated EMG (IEMG) were calculated and normalized to the value of maximum voluntary contraction (MVC). [Results] Results indicated that the IEMG of both the UGM and LGM increased significantly with increases in hip flexion angle, whereas the IEMG of the TFL decreased significantly. The maximum activities of the UGM and the LGM were 85.7 ± 80.8%MVC and 38.2 ± 32.9%MVC at 80 degrees of hip flexion, respectively, and that of the TFL was 71.0 ± 39.0%MVC at 40 degrees of hip flexion. [Conclusion] The IEMG of the GMed did not change with increases in hip flexion angle. Hip flexion angle affected the activity of the GM and TFL during isometric contraction in abduction.

Prior history of FDI muscle contraction: different effect on MEP amplitude and muscle activity

Motor evoked potentials (MEPs) in the right first dorsal interosseous (FDI) muscle elicited by transcranial magnetic stimulation of left motor cortex were assessed in ten healthy subjects during maintenance of a fixed FDI contraction level. Subjects maintained an integrated EMG (IEMG) level with visual feedback and reproduced this level by memory afterwards in the following tasks: stationary FDI muscle contraction at the level of 40 ± 5 % of its maximum voluntary contraction (MVC; 40 % task), at the level of 20 ± 5 % MVC (20 % task), and also when 20 % MVC was preceded by either no contraction (0-20 task), by stronger muscle contraction (40-20 task) or by no contraction with a previous strong contraction (40-0-20 task). The results show that the IEMG level was within the prescribed limits when 20 and 40 % stationary tasks were executed with and without visual feedback. In 0-20, 40-20, and 40-0-20 tasks, 20 % IEMG level was precisely controlled in the presence of visual feedback, but without visual feedback the IEMG and force during 20 % IEMG maintenance were significantly higher in the 40-0-20 task than those in 0-20 and 40-20 tasks. That is, without visual feedback, there were significant variations in muscle activity due to different prehistory of contraction. In stationary tasks, MEP amplitudes in 40 % task were higher than in 20 % task. MEPs did not differ significantly during maintenance of the 20 % level in tasks with different prehistory of muscle contraction with and without visual feedback. Thus, in spite of variations in muscle background activity due to different prehistory of contraction MEPs did not vary significantly. This dissociation suggests that the voluntary maintenance of IEMG level is determined not only by cortical mechanisms, as reflected by corticospinal excitability, but also by lower levels of CNS, where afferent signals and influences from other brain structures and spinal cord are convergent.