scholarly journals Electromyographic measures of muscle activation and changes in muscle architecture of human elbow flexors during fatiguing contractions

2008 ◽  
Vol 104 (6) ◽  
pp. 1720-1726 ◽  
Author(s):  
Thorsten Rudroff ◽  
Didier Staudenmann ◽  
Roger M. Enoka
Keyword(s):  
Muscle Activation ◽  
Biceps Brachii ◽  
Surface Emg ◽  
Muscle Architecture ◽  
Surface Measurement ◽  
Emg Activity ◽  
Time To Failure ◽  
Elbow Flexors ◽  
Emg Amplitude ◽  
Rate Of Increase

The study compared changes in intramuscular and surface recordings of EMG amplitude with ultrasound measures of muscle architecture of the elbow flexors during a submaximal isometric contraction. Ten subjects performed a fatiguing contraction to task failure at 20% of maximal voluntary contraction force. EMG activity was recorded in biceps brachii, brachialis, and brachioradialis muscles using intramuscular and surface electrodes. The rates of increase in the amplitude of the surface EMG for the long and short heads of biceps brachii and brachioradialis were greater than those for the intramuscular recordings measured at different depths. The amplitude of the intramuscular recordings from three muscles increased at a similar rate ( P = 0.13), as did the amplitude of the three surface recordings from two muscles ( P = 0.83). The increases in brachialis thickness (27.7 ± 5.7 to 30.9 ± 3.5 mm; P < 0.05) and pennation angle (10.9 ± 3.5 to 16.5 ± 4.8°; P = 0.003) were not associated with the increase in intramuscular EMG amplitude ( P > 0.58). The increase in brachioradialis thickness (22.8 ± 4.8 to 25.5 ± 3.4 mm; P = 0.0075) was associated with the increase in the amplitude for one of two intramuscular EMG signals ( P = 0.007, r = 0.79). The time to failure was more strongly associated with the rate of increase in the amplitude of the surface EMG than that for the intramuscular EMG, which suggests that the surface measurement provides a more appropriate measure of the change in muscle activation during a fatiguing contraction.

scholarly journals Increase in heterogeneity of biceps brachii activation during isometric submaximal fatiguing contractions: a multichannel surface EMG study

2014 ◽  
Vol 111 (5) ◽  
pp. 984-990 ◽  
Author(s):  
Didier Staudenmann ◽  
Jaap H. van Dieën ◽  
Dick F. Stegeman ◽  
Roger M. Enoka
Keyword(s):  
Spatial Distribution ◽  
Muscle Activation ◽  
Biceps Brachii ◽  
Principal Component ◽  
Motor Units ◽  
Surface Emg ◽  
Emg Activity ◽  
Triceps Brachii ◽  
Sustained Contraction ◽  
Emg Amplitude

The effects of fatigue emerge from the beginning of sustained submaximal contractions, as shown by an increase in the amplitude of the surface electromyogram (EMG). The increase in EMG amplitude is attributed to an augmentation of the excitatory drive to the motor neuron pool that, more importantly than increasing discharge rates, recruits additional motor units for the contraction. The aim of this study was to determine whether the spatiotemporal distribution of biceps brachii (BB) activity becomes more or less heterogeneous during a fatiguing isometric contraction sustained at a submaximal target force. Multiple electrodes were attached over the entire BB muscle, and principal component analysis (PCA) was used to extract the representative information from multiple monopolar EMG channels. The development of heterogeneity during the fatiguing contraction was quantified by applying a cluster algorithm on the PCA-processed EMG amplitudes. As shown previously, the overall EMG amplitude increased during the sustained contraction, whereas there was no change in coactivation of triceps brachii. However, EMG amplitude did not increase in all channels and even decreased in some. The change in spatial distribution of muscle activity varied across subjects. As found in other studies, the spatial distribution of EMG activity changed during the sustained contraction, but the grouping and size of the clusters did not change. This study showed for the first time that muscle activation became more heterogeneous during a sustained contraction, presumably due to a decrease in the strength of common inputs with the recruitment of additional motor units.

Spinal Mechanisms Contribute to Differences in the Time to Failure of Submaximal Fatiguing Contractions Performed With Different Loads

2008 ◽  
Vol 99 (3) ◽  
pp. 1096-1104 ◽  
Author(s):  
Malgorzata Klass ◽  
Morgan Lévénez ◽  
Roger M. Enoka ◽  
Jacques Duchateau
Keyword(s):  
Biceps Brachii ◽  
Motor Evoked Potential ◽  
H Reflex ◽  
Time To Failure ◽  
Elbow Flexors ◽  
Task Failure ◽  
Constant Torque ◽  
Rate Of Increase ◽  
Position Task ◽  
Fatiguing Contractions

This study compared the mechanisms that limit the time to failure of a sustained submaximal contraction at 20% of maximum when the elbow flexors either supported an inertial load (position task) or exerted an equivalent constant torque against a rigid restraint (force task). The surface electromyogram (EMG), the motor-evoked potential (MEP) in response to transcranial magnetic stimulation (TMS) of the motor cortex, and the Hoffmann reflex (H-reflex) and maximal M-wave (Mmax) elicited by electrical stimulation of the brachial plexus were recorded in biceps brachii during the two tasks. Although the time to failure for the position task was only 44% of that for the force task, the rate of increase of the average EMG (aEMG; % initial MVC) and MEP area (% Mmax) did not differ significantly during the two tasks. At task failure, however, the increases in normalized aEMG and MEP area were significantly ( P < 0.05) greater for the force task (36.4 and 219.9%) than for the position task (22.4 and 141.7%). Furthermore, the superimposed mechanical twitch (% initial MVC), evoked by TMS during a brief MVC of the elbow flexors immediately after task failure, was increased similarly in both tasks. Although the normalized H-reflex area (% Mmax) decreased during the two fatiguing contractions, the reduction was more rapid and greater during the position task (59.8%) compared with the force task (34.7%). Taken together, the results suggest that spinal mechanisms were a major determinant of the briefer time to failure for the position task.

scholarly journals Reflex Inhibition in Human Biceps Brachii Decreases With Practice of a Fatiguing Contraction

2008 ◽  
Vol 100 (5) ◽  
pp. 2843-2851 ◽  
Author(s):  
Zachary A. Riley ◽  
Stéphane Baudry ◽  
Roger M. Enoka
Keyword(s):  
Motor Neurons ◽  
Radial Nerve ◽  
Biceps Brachii ◽  
Motor Units ◽  
Elbow Flexion ◽  
Emg Activity ◽  
Time To Failure ◽  
Reflex Inhibition ◽  
Single Motor Units ◽  
Rate Of Increase

The purpose of the study was to examine the influence of practice on time to failure of a submaximal contraction with the elbow flexor muscles and on reflex inhibition from brachioradialis afferents onto biceps brachii motor neurons. Fifteen subjects practiced sustaining an isometric contraction (20% of maximum) with the elbow flexors until failure. Spike-triggered stimulation was used to assess the influence of radial nerve stimulation on the discharge of single motor units in biceps brachii before and after three practice sessions. Time to failure increased from 760 ± 333 s in session 1 to 1,103 ± 415 s in session 3 ( P < 0.03) and was accompanied by a slower rate of increase in electromyographic (EMG) activity of the short head of biceps brachii ( P < 0.05). Stimulation of the radial nerve prolonged the interspike interval before practice ( n = 56; 7.2 ± 6.8 ms; P < 0.001), and this effect was reduced after practice ( n = 62; 2.3 ± 3.6 ms; P < 0.01). The reduction was greater for motor units in the short head of biceps brachii than for those in the long head ( P < 0.05) and was associated with a slower rate of increase in EMG ( r = 0.57, P = 0.03). The decrease in reflex inhibition was the main predictor of the increase in time to failure ( r2 = 0.60, P = 0.001). These results demonstrate that practice reduced an antagonistic inhibition and improved the ability of the muscles to perform a synergistic action of elbow flexion.

scholarly journals Magnetic resonance imaging and electromyography as indexes of muscle function

1992 ◽  
Vol 73 (4) ◽  
pp. 1578-1583 ◽  
Author(s):  
G. R. Adams ◽  
M. R. Duvoisin ◽  
G. A. Dudley
Keyword(s):  
Skeletal Muscle ◽  
Magnetic Resonance ◽  
Biceps Brachii ◽  
Surface Emg ◽  
Magnetic Resonance Images ◽  
Emg Activity ◽  
Triceps Brachii ◽  
Relative Resistance ◽  
Rate Of Increase ◽  
Exercise Induced

Electromyography (EMG) is commonly used to determine the electrical activity of skeletal muscle during contraction. To date, independent verification of the relationship between muscle use and EMG has not been provided. It has recently been shown that relaxation- (e.g., T2) weighted magnetic resonance images (MRI) of skeletal muscle demonstrate exercise-induced contrast enhancement that is graded with exercise intensity. This study was conducted to test the hypothesis that exercise-induced magnetic resonance (MR) contrast shifts would relate to EMG amplitude if both measures reflect muscle use during exercise. Both MRI and EMG data were collected for separate eccentric (ECC) and concentric (CON) exercise of increasing intensity to take advantage of the fact that the rate of increase and amplitude of EMG activity are markedly greater for CON muscle actions. Seven subjects 30 +/- 2 (SE) yr old performed five sets of 10 CON or ECC arm curls with each of four resistances representing 40, 60, 80, and 100% of their 10 repetition maximum for CON curls. There was 1.5 min between sets and 30 min between bouts (5 sets of 10 actions at each relative resistance). Multiple echo, transaxial T2-weighted MR images (1.5 T, TR/TE 2,000/30) were collected from a 7-cm region in the middle of the arm before exercise and immediately after each bout. Surface EMG signals were collected from both heads of the biceps brachii and the long head of the triceps brachii muscles. CON and ECC actions resulted in increased integrated EMG (IEMG) and T2 values that were strongly related (r = 0.99, P < 0.05) with relative resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Effects of Sampling Frequency and Sample Window Size on Median Frequency of Surface EMG

2019 ◽  
Vol 63 (1) ◽  
pp. 1369-1372
Author(s):  
Pramiti Sarker ◽  
Gary Mirka
Keyword(s):  
Biceps Brachii ◽  
Window Size ◽  
Elbow Flexion ◽  
Surface Emg ◽  
Sampling Frequency ◽  
Emg Activity ◽  
Median Frequency ◽  
Surface Electrodes ◽  
Emg Signal ◽  
Sample Window

Muscle fatigue can be evaluated through the assessment of the downward shift in the median frequency (MDF) of the electromyographic (EMG) signal collected through surface electromyography. Previous research has shown that the value of MDF may be affected by sampling parameters. The purpose of this study was to quantify the combined effect of different sampling frequencies and window sizes on the calculated MDF. A sample of 24 participants performed a simple static elbow flexion exertion (15% MVC) and the EMG activity of the biceps brachii was periodically sampled using surface electrodes for four seconds at a frequency of 4096 Hz as the biceps brachii became fatigued. These collected data were then down-sampled to create a dataset of four window sizes (1s, 2s, 3s, and 4s) and five sampling frequencies (256 Hz, 512 Hz, 1024 Hz, 2048 Hz, and 4096 Hz). Median frequencies were calculated for each combination of sampling frequency and window size and then compared with the 4096 Hz / 4 s condition (considered gold standard) and the errors were calculated. Results suggest the use of a minimum sampling frequency of 512 Hz and a window size of 4s.

Kinematics, Kinetics, and Muscle Activation during Explosive Upper Body Movements

1996 ◽  
Vol 12 (1) ◽  
pp. 31-43 ◽  
Author(s):  
Robert U. Newton ◽  
William J. Kraemer ◽  
Keijo Häkkinen ◽  
Brendan J. Humphries ◽  
Aron J. Murphy
Keyword(s):  
Muscle Activation ◽  
Biceps Brachii ◽  
Average Power ◽  
Upper Body ◽  
Emg Activity ◽  
Neural Activation ◽  
Loading Conditions ◽  
Force Output ◽  
Triceps Brachii ◽  
Average Force

The aim of this study was to investigate the kinematics, kinetics, and neural activation of the traditional bench press movement performed explosively and the explosive bench throw in which the barbell was projected from the hands. Seventeen male subjects completed three trials with a bar weight of 45% of the subject's previously determined 1RM. Performance was significantly higher during the throw movement compared to the press for average velocity, peak velocity, average force, average power, and peak power. Average muscle activity during the concentric phase for pectoralis major, anterior deltoid, triceps brachii, and biceps brachii was higher for the throw condition. It was concluded that performing traditional press movements rapidly with light loads does not create ideal loading conditions for the neuromuscular system with regard to explosive strength production, especially in the final stages of the movement, because ballistic weight loading conditions where the resistance was accelerated throughout the movement resulted in a greater velocity of movement, force output, and EMG activity.

Influence of fatigue on the simulated relation between the amplitude of the surface electromyogram and muscle force

2010 ◽  
Vol 368 (1920) ◽  
pp. 2765-2781 ◽  
Author(s):  
Jakob L. Dideriksen ◽  
Dario Farina ◽  
Roger M. Enoka
Keyword(s):  
Muscle Fibre ◽  
Linear Relation ◽  
Action Potentials ◽  
Muscle Activation ◽  
Muscle Force ◽  
Surface Emg ◽  
Integrative Model ◽  
Surface Electromyogram ◽  
Maximal Force ◽  
Emg Amplitude

A linear relation between surface electromyogram (EMG) amplitude and muscle force is often assumed and used to estimate the contributions of selected muscles to various tasks. In the presence of muscle fatigue, however, changes in the properties of muscle fibre action potentials and motor unit twitch forces can alter the relation between surface EMG amplitude and force. A novel integrative model of motor neuron control and the generation of muscle fibre action potentials was used to simulate surface EMG signals and muscle force during three fatigue protocols. The change in the simulated relation between surface EMG amplitude and force depended on both the level of fatigue and the details of the fatiguing contraction. In general, surface EMG amplitude overestimated muscle force when fatigue was present. For example, surface EMG amplitudes corresponding to 60 per cent of the amplitude obtained at maximal force without fatigue corresponded to forces in the range 10–40% of the maximal force across three representative fatigue protocols. The results indicate that the surface EMG amplitude cannot be used to predict either the level of muscle activation or the magnitude of muscle force when the muscle exhibits any fatigue.

scholarly journals Muscle Activation and Perceived Loading During Rehabilitation Exercises: Comparison of Dumbbells and Elastic Resistance

2010 ◽  
Vol 90 (4) ◽  
pp. 538-549 ◽  
Author(s):  
Lars L. Andersen ◽  
Christoffer H. Andersen ◽  
Ole S. Mortensen ◽  
Otto M. Poulsen ◽  
Inger Birthe T. Bjørnlund ◽  
...  
Keyword(s):  
Repeated Measures ◽  
Muscle Activation ◽  
Musculoskeletal Diseases ◽  
External Rotation ◽  
Emg Activity ◽  
Absolute Maximum ◽  
Maximal Voluntary Isometric Contraction ◽  
Emg Amplitude ◽  
Elastic Resistance ◽  
Resistance Exercises

BackgroundHigh-intensity resistance training plays an essential role in the prevention and rehabilitation of musculoskeletal injuries and disorders. Although resistance exercises with heavy weights yield high levels of muscle activation, the efficacy of more user-friendly forms of exercise needs to be examined.ObjectiveThe aim of this study was to investigate muscle activation and perceived loading during upper-extremity resistance exercises with dumbbells compared with elastic tubing.DesignA single-group, repeated-measures study design was used.SettingExercise evaluation was conducted in a laboratory setting.ParticipantsSixteen female workers (aged 26–55 years) without serious musculoskeletal diseases and with a mean neck and shoulder pain intensity of 7.8 on a 100-mm visual analog scale participated in the study.MeasurementsElectromyographic (EMG) activity was measured in 5 selected muscles during the exercises of lateral raise, wrist extension, and shoulder external rotation during graded loadings with dumbbells (2–7.5 kg) and elastic tubing (Thera-Band, red to silver resistance). The order of exercises and loadings was randomized for each individual. Electromyographic amplitude was normalized to the absolute maximum EMG amplitude obtained during maximal voluntary isometric contraction and exercise testing. Immediately after each set of exercise, the Borg CR10 scale was used to rate perceived loading during the exercise.ResultsResistance exercise with dumbbells as well as elastic tubing showed increasing EMG amplitude and perceived loading with increasing resistance. At the individually maximal level of resistance for each exercise—defined as the 3 repetitions maximum—normalized EMG activity of the prime muscles was not significantly different between dumbbells (59%–87%) and elastic tubing (64%–86%). Perceived loading was moderately to very strongly related to normalized EMG activity (r=.59–.92).LimitationsThe results of this study apply only for exercises performed in a controlled manner (ie, without sudden jerks or high acceleration).ConclusionsComparably high levels of muscle activation were obtained during resistance exercises with dumbbells and elastic tubing, indicating that therapists can choose either type in clinical practice. The Borg CR10 can be a useful aid in estimating intensity of individual rehabilitation protocols.

Shoulder Muscle Activation Levels During the Push-Up-Plus Exercise on Stable and Unstable Surfaces

2017 ◽  
Vol 26 (4) ◽  
pp. 281-286 ◽  
Author(s):  
Rafaela J.B. Torres ◽  
André L.T. Pirauá ◽  
Vinícius Y.S. Nascimento ◽  
Priscila S. dos Santos ◽  
Natália B. Beltrão ◽  
...  
Keyword(s):  
Muscle Activation ◽  
Biceps Brachii ◽  
Emg Activity ◽  
Activity Levels ◽  
Triceps Brachii ◽  
Serratus Anterior ◽  
Upper Trapezius ◽  
Unstable Surface ◽  
Hands And Feet ◽  
Push Up

The aim of this study was to evaluate the acute effect of the use of stable and unstable surfaces on electromyography (EMG) activity and coactivation of the scapular and upper-limb muscles during the push-up plus (with full protraction of the scapula). Muscle activation of anterior deltoid (AD), posterior deltoid (PD), pectoralis major, biceps brachii (BB), triceps brachii (TB), upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) levels and coactivation index were determined by surface EMG in 20 young men during push-up plus performed on a stable and unstable condition (2 unstable devices applied to hands and feet). The paired t test and Cohen d were used for statistical analysis. The results showed that during the execution of the push-up plus on the unstable surface an increased EMG activity of the scapular stabilizing muscles (SA, MT, and LT) was observed, while AD and PD muscles showed a decrease. During exercise execution on the unstable surface there was a higher index of coactivation of the scapular muscles (SA–MT and UT–LT pairs). No significant differences were observed in TB–BB and AD–PD pairs. These results suggest that the push-up-plus exercise associated with unstable surfaces produced greater EMG activity levels and coactivation index of the scapular stabilizing muscle. On the other hand, the use of an unstable surface does not promote the same effect for the shoulder muscles.

Task failure during fatiguing contractions performed by humans

2005 ◽  
Vol 99 (2) ◽  
pp. 389-396 ◽  
Author(s):  
Katrina S. Maluf ◽  
Roger M. Enoka
Keyword(s):  
Motor Unit ◽  
Pressor Response ◽  
Emg Activity ◽  
Time To Failure ◽  
Postural Activity ◽  
Rate Of Increase ◽  
Position Task ◽  
Rate Coding ◽  
The Difference ◽  
Fatiguing Contractions

By comparing the physiological adjustments that occur when two similar fatiguing contractions are performed to failure, it is possible to identify mechanisms that limit the duration of the more difficult task. This approach has been used to study two fatiguing contractions, referred to as the force and position tasks, which differed in the type of feedback given to the subject and the amount of support provided by the surroundings. Even though the two tasks required a similar net muscle torque during submaximal isometric contractions, the duration that the position task could be sustained was consistently much briefer than that for the force task. The position task involved a greater rate of increase in EMG activity and more marked changes in motor unit recruitment and rate coding compared with the force task. These observations are consistent with the hypothesis that the motor unit pool was recruited more rapidly during the position task. The difference in motor unit behavior appeared to be caused by variation in synaptic input, likely involving heightened sensitivity of the stretch reflex during the position task. Upon repeat performances of the two fatiguing contractions, some subjects were able to increase the time to failure for the force task but not the position task. Furthermore, the time to failure for the position task could be influenced by the postural demands associated with maintaining the position of the limb, and the difference in the two durations was enhanced when the postural activity evoked a pressor response. These observations indicate that the difference in the duration of the two fatiguing contractions was attributable to differences in the control strategy used to sustain the tasks and the magnitude of the associated postural activity.

Sign in / Sign up

Export Citation Format

Share Document