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 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.

Reflex responses in active muscles elicited by stimulation of low-threshold afferents from the human foot

1992 ◽  
Vol 67 (5) ◽  
pp. 1375-1384 ◽  
Author(s):  
A. M. Aniss ◽  
S. C. Gandevia ◽  
D. Burke
Keyword(s):  
Motor Units ◽  
Medial Gastrocnemius ◽  
Emg Activity ◽  
Onset Latency ◽  
Single Motor ◽  
Reflex Responses ◽  
Posterior Tibial ◽  
Single Motor Units ◽  
Low Threshold ◽  
Stimulation Of

1. Reflex responses were elicited in muscles that act at the ankle by electrical stimulation of low-threshold afferents from the foot in human subjects who were reclining supine. During steady voluntary contractions, stimulus trains (5 pulses at 300 Hz) were delivered at two intensities to the sural nerve (1.2-4.0 times sensory threshold) or to the posterior tibial nerve (1.1-3.0 times motor threshold for the intrinsic muscles of the foot). Electromyographic (EMG) recordings were made from tibialis anterior (TA), peroneus longus (PL), soleus (SOL), medial gastrocnemius (MG), and lateral gastrocnemius (LG) muscles by the use of intramuscular wire electrodes. 2. As assessed by averages of rectified EMG, stimulation of the sural or posterior tibial nerves at nonpainful levels evoked a complex oscillation with onset latencies as early as 40 ms and lasting up to 200 ms in each muscle. The most common initial responses in TA were a decrease in EMG activity at an onset latency of 54 ms for sural stimuli, and an increase at an onset latency of 49 ms for posterior tibial stimuli. The response of PL to stimulation of the two nerves began with a strong facilitation of 44 ms (sural) and 49 ms (posterior tibial). With SOL, stimulation of both nerves produced early inhibition beginning at 45 and 50 ms, respectively. With both LG and MG, sural stimuli produced an early facilitation at 52-53 ms. However, posterior tibial stimuli produced different initial responses in these two muscles: facilitation in LG at 50 ms and inhibition in MG at 51 ms. 3. Perstimulus time histograms of the discharge of 61 single motor units revealed generally similar reflex responses as in multiunit EMG. However, different reflex components were not equally apparent in the responses of different single motor units: an individual motor unit could respond slightly differently with a change in stimulus intensity or background contraction level. The multiunit EMG record represents a global average that does not necessarily depict the precise pattern of all motor units contributing to the average. 4. When subjects stood erect without support and with eyes closed, reflex patterns were seen only in active muscles, and the patterns were similar to those in the reclining posture. 5. It is concluded that afferents from mechanoreceptors in the sole of the foot have multisynaptic reflex connections with the motoneuron pools innervating the muscles that act at the ankle. When the muscles are active in standing or walking, cutaneous feedback may play a role in modulating motoneuron output and thereby contribute to stabilization of stance and gait.

Mind-Muscle Connection: Verbal Instructions Alter Electromyographic Activity for Elbow Flexors and Extensors During Co-Contraction Training

2020 ◽  
pp. 003151252094908
Author(s):  
Rafael A. Fujita ◽  
Marina M. Villalba ◽  
Nilson R. S. Silva ◽  
Matheus M. Pacheco ◽  
Matheus M. Gomes
Keyword(s):  
Strength Training ◽  
Elbow Joint ◽  
Biceps Brachii ◽  
Elbow Flexion ◽  
Emg Activity ◽  
Elbow Extension ◽  
Verbal Instruction ◽  
Triceps Brachii ◽  
Verbal Instructions ◽  
Lateral Head

Co-contraction training has demonstrated similar electromyographic (EMG) activity levels compared to conventional strength training. Since verbal instructions can increase EMG activity on target muscles during conventional exercises, the same should occur during co-contraction. In this study we analyzed whether different verbal instructions would alter the EMG activity of target muscles - biceps brachii (BB) and triceps brachii lateral head (TB) - during co-contraction training for the elbow joint. Seventeen males with experience in strength training performed a co-contraction set in two verbal instruction conditions to emphasize either elbow flexion or elbow extension. Surface electrodes were fixed over biceps brachii and triceps brachii lateral head muscles. We measured EMG mean amplitude and analyzed data with 2-way ANOVA. We found a significant interaction between muscle and verbal instruction ( p = 0.002). Post hoc tests indicated that verbal instructions ( p = 0.001) influenced the BB EMG activity (elbow flexion: M = 68.74, SD = 17.96%; elbow extension: M = 53.47, SD = 16.13%); and also showed difference ( p = 0.006) in the EMG activity between BB and TB with verbal instruction emphasizing the elbow extension (BB: M = 53.47, SD = 16.13%; TB: M = 69.18, SD = 21.79%). There was a difference in the EMG ratio of BB/TB ( p = 0.001) when focusing on elbow flexion ( M = 1.09, SD = 0.30) versus elbow extension ( M = 0.81, SD = 0.25). As verbal instruction modified the magnitude of muscle recruitment during co-contractions for elbow joint muscles, there is a clear mind-muscle connection of importance to this method of training. Also, of importance to trainers, verbal instructions seemed to affect individuals differentially.

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.

Effect of Reaction Time Condition on EMG Activities of the Biceps Brachii Muscle in Elbow Flexion and Forearm Supination

1988 ◽  
Vol 67 (3) ◽  
pp. 807-813
Author(s):  
Jose Alvin P. Mojica ◽  
Ryuichi Nakamura ◽  
Yoshiaki Yamada ◽  
Ichiro Tsuji
Keyword(s):  
Biceps Brachii ◽  
Elbow Flexion ◽  
Emg Activity ◽  
Biceps Brachii Muscle ◽  
Response Uncertainty ◽  
Motor Set ◽  
Temporal And Spatial ◽  
Temporal And Spatial Characteristics ◽  
Spatial Specificity ◽  
Simple Rt

Under simple- and choice-RT conditions, the biceps brachii muscle was examined in 8 healthy male subjects to determine how the temporal and spatial characteristics of elbow flexion and forearm supination differed at the initial phase of EMG activity and whether preparation or the presence of response uncertainty influenced the EMG outputs of the two movements. In the simple-RT condition, RT of supination was significantly faster than that of flexion but EMG activity of supination was less than that of flexion. In contrast, in the choice-RT condition, RT of flexion was significantly faster than that of supination but EMG activity of flexion was significantly reduced compared to supination. These findings indicate that advanced preparation or motor set facilitates the differentiation of RTs and EMG activities of the response movements and that response uncertainty causes a significant change in the temporal and spatial specificity of both elbow flexion and forearm supination.

scholarly journals Modulation of Stretch Reflexes of the Finger Flexors by Sensory Feedback From the Proximal Upper Limb Poststroke

2009 ◽  
Vol 102 (3) ◽  
pp. 1420-1429 ◽  
Author(s):  
Gilles Hoffmann ◽  
Derek G. Kamper ◽  
Jennifer H. Kahn ◽  
William Z. Rymer ◽  
Brian D. Schmit
Keyword(s):  
Upper Limb ◽  
Stretch Reflex ◽  
Sensory Input ◽  
Biceps Brachii ◽  
Elbow Flexion ◽  
Spinal Reflex ◽  
Reflex Response ◽  
Emg Activity ◽  
Triceps Brachii ◽  
Flexor Digitorum

Neural coupling of proximal and distal upper limb segments may have functional implications in the recovery of hemiparesis after stroke. The goal of the present study was to investigate whether the stretch reflex response magnitude of spastic finger flexor muscles poststroke is influenced by sensory input from the shoulder and the elbow and whether reflex coupling of muscles throughout the upper limb is altered in spastic stroke survivors. Through imposed extension of the metacarpophalangeal (MCP) joints, stretch of the relaxed finger flexors of the four fingers was imposed in 10 relaxed stroke subjects under different conditions of proximal sensory input, namely static arm posture (3 different shoulder/elbow postures) and electrical stimulation (surface stimulation of biceps brachii or triceps brachii, or none). Fast (300°/s) imposed stretch elicited stretch reflex flexion torque at the MCP joints and reflex electromyographic (EMG) activity in flexor digitorum superficialis. Both measures were greatest in an arm posture of 90° of elbow flexion and neutral shoulder position. Biceps stimulation resulted in greater MCP stretch reflex flexion torque. Fast imposed stretch also elicited reflex EMG activity in nonstretched heteronymous upper limb muscles, both proximal and distal. These results suggest that in the spastic hemiparetic upper limb poststroke, sensorimotor coupling of proximal and distal upper limb segments is involved in both the increased stretch reflex response of the finger flexors and an increased reflex coupling of heteronymous muscles. Both phenomena may be mediated through changes poststroke in the spinal reflex circuits and/or in the descending influence of supraspinal pathways.

Discharge Variability of Motor Units in an Intrinsic Muscle of Transplanted Hand

2008 ◽  
Vol 99 (5) ◽  
pp. 2232-2240 ◽  
Author(s):  
Dario Farina ◽  
Marco Pozzo ◽  
Marco Lanzetta ◽  
Roger M. Enoka
Keyword(s):  
Motor Neurons ◽  
Action Potentials ◽  
Discharge Rate ◽  
Motor Units ◽  
Surface Emg ◽  
Intrinsic Muscle ◽  
Single Motor Units ◽  
Abductor Digiti Minimi ◽  
The Individual ◽  
Ramp Contractions

The study analyzed the discharge characteristics of the motor units in an intrinsic muscle of a transplanted hand. Multichannel electromyographic (EMG) recordings were obtained in 11 experimental sessions over 16 mo starting from day 205 after a hand was transplanted in a 35-yr-old man who had lost his right hand 22 yr earlier. The action potentials discharged by single motor units were identified from the surface EMG signals of the abductor digiti minimi muscle in the transplanted hand as the individual performed 60-s maximal and linearly increasing (ramp) contractions. Discharge rate decreased from 27.1 ± 8.4 pulses per second (pps) at the start of the maximal contractions to 17.2 ± 2.9 pps at the end ( P < 0.001) and increased from 17.4 ± 4.3 to 22.1 ± 5.0 pps during the ramp contractions ( P < 0.05). The SD of the interspike interval (ISI) nearly related to the mean ISI with a similar regression slope for the maximal (0.49 ± 0.09) and ramp contractions (0.43 ± 0.10). The coefficient of variation for ISI was higher than values in able-bodied persons and did not change during either the maximal (36.8 ± 10.8%) or the ramp contractions (35.9 ± 7.4%). High-frequency bursts of activity with <20 ms between two and six action potentials occurred during both maximal and ramp contractions. In conclusion, motor neurons that reinnervated a muscle in a transplanted hand discharged action potentials with a high degree of variability that suggested greater synaptic noise during the voluntary contractions.

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.

Functional Activity of Superior Head of Human Lateral Pterygoid Muscle during Isometric Force

2005 ◽  
Vol 84 (6) ◽  
pp. 548-553 ◽  
Author(s):  
S. Ruangsri ◽  
T. Whittle ◽  
K. Wanigaratne ◽  
G.M. Murray
Keyword(s):  
Computer Tomography ◽  
Functional Activity ◽  
Isometric Force ◽  
Motor Units ◽  
Emg Activity ◽  
Single Muscle ◽  
Lateral Pterygoid Muscle ◽  
Functional Activities ◽  
Single Motor ◽  
Single Motor Units

There is controversy as to the jaw tasks for which the superior head of the human lateral pterygoid muscle (SHLP) becomes active. The aim was to describe the functional activities of SHLP single motor units (SMUs) during horizontal isometric force tasks. In 11 subjects, 48 SMUs were recorded from computer-tomography-verified SHLP sites during generation of horizontal isometric force in the contralateral (CL), protrusive (P), and ipsilateral (IL) directions and intermediate directions (CL-P, IL-P). In eight subjects, SHLP SMUs were active in CL, CL-P, and P. Qualitatively, SHLP EMG activity increased with increased isometric force. Forty-two SMUs were active in directions other than IL; 6 exhibited activity at IL and other directions. The similarity of these data to previous human lateral pterygoid (IHLP) data supports the notion that SHLP and IHLP should be regarded as a single muscle, with activities shaded according to the biomechanical demands of the task.

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