Muscle electrical activity during force modulation exercise

During muscle fatigue, acute changes in the interaction between the sensorimotor cortex and peripheral neurons have been widely studied. However, it is still unclear about the effect of antagonist muscle prefatigue on corticomuscular coupling and central modulation. The purpose of this study was to investigate the changes in the magnitude of electroencephalogram-electromyography (EEG-EMG) coherence and phase synchronization index (PSI) induced by antagonistic muscle prefatigue. Twelve young male volunteers conducted a 30-s long, nonfatiguing isometric elbow extension with a target force level of 20% maximum voluntary contraction (MVC) before and after a fatiguing sustained elbow flexion contraction at 20% MVC until task failure. Coherence and PSI between the EEG recorded over the sensorimotor cortex and the surface EMG of the triceps brachii (TB) muscle were quantified for the pre- and post-fatigue elbow extension contractions. Coherence and PSI in the gamma frequency band (35-60 Hz) were found significantly decreased in the postfatigue elbow extension contraction than the prefatigue contraction. The power of the EEG in the beta and gamma band were significantly increased, while the EMG power showed no significant changes when the antagonistic muscle was prefatigued. PSI in the gamma frequency band between the EMG of the TB muscle and the EEG were found significantly decreased during postfatigue elbow extension contraction compared with prefatigue contraction. Antagonistic muscle prefatigue led to significantly lower gamma band corticomuscular coherence and phase coupling during an isometric elbow extension position task. The lower corticomuscular coupling may indicate a central modulation mechanism of antagonist muscle prefatigue that related to decreased descending common drive or joint instability compensation modulation mechanism.

The purpose of this study was to investigate the influence of force tremor (FT) on the mechanomyogram (MMG) recorded by a condenser microphone (MIC) and an accelerometer (ACC) for the measurement of agonist and antagonist muscles during submaximal isometric contractions. Following determination of the isometric maximum voluntary contraction (MVC), 10 male subjects were asked to perform elbow flexion and extension at 20%, 40%, 60%, and 80% MVC. Surface electromyogram (EMG) and MMG of the biceps brachii (BB) and triceps brachii (TB) were recorded simultaneously using a MIC (MMG-(MIC)) and an ACC (MMG-(ACC)). We analyzed the root mean square (RMS) for all signals and compared the sum of the power spectrum amplitude (SPA) at 3-6 Hz and 8-12 Hz between the MMG-(MIC) and the MMG-(ACC). During elbow flexion and extension, the RMS of the EMG and the MMG-(MIC) of the agonist were significantly (p<0.05) higher than those of the antagonist in each contraction level. The RMS of the MMG-(ACC) of the antagonist showed no significant (p>0.05) difference from that of the agonist, or tended to be higher than the agonist. The SPA of the MMG-(MIC) of the agonist at 3-6 Hz and 8-12 Hz tended to be higher than the antagonist in elbow flexion and extension at each contraction level. The SPA of the MMG-(ACC) of the agonist and that of the antagonist showed no significant (p>0.05) difference, or the antagonist MMG-(ACC) tended to be higher than that of the agonist. These results suggest the MMG detected by a MIC appears to be less affected by FT than is the ACC because of its inherent characteristic to reduce FT in simultaneously evaluated agonist and antagonist muscles by means of MMG during submaximal isometric contraction.

The aim of this randomized controlled crossover study was to investigate the effect of a bout of unaccustomed eccentric exercise (ECC) followed by a consecutive bout of the same intensity on local muscle blood flow, amplitude, and frequency of the electromyographic (EMG) signal from the exercised tibialis anterior muscle. Sixteen healthy male participants (age, 25.7 (0.6) years; body mass index 24.8 (1) kg·m(-2) participated in this study. Two identical bouts of high-intensity ECC were performed on the tibialis anterior muscle 7 days apart. Control sessions involving no exercise were performed 4 weeks either before or after the exercise sessions. Changes in local total blood flow [ΔtHb], EMG root mean square, and median power frequency were recorded during isometric maximum voluntary contraction of ankle dorsiflexion. Measurements were performed before, immediately after, and the day after both ECCs (ECC1 and ECC2). The participants rested quietly in a chair in the control session. Eccentric exercise 1 led to a significant decrease in [ΔtHb] on the day after (p ≤ 0.05), whereas ECC2 did not. Median power frequency decreased significantly in ECC2 compared with ECC1 (p < 0.01). Root mean square was unchanged in all the instants. The present study showed that adaptation is depicted in the local muscle blood flow and the frequency contents of the EMG after an unaccustomed ECC inducing muscle soreness. These alterations provide a potential mechanism for a rapid adaptation, which decreases susceptibility of the muscle to develop further soreness in the subsequent ECC bout.

Push-up is considered as an excellent exercise for both assessment and training in athletes. However, the influence of its mode of application on activation of shoulder girdle musculature has been scantily studied by previous research in young overhead athletes. To investigate the activity of pectoralis major (PM) and triceps brachii (TB) muscle during push-up exercise performed on the push-up bar and perfect push-up using shoulder width (SW), narrow shoulder width (NSW) and wide shoulder width (WSW) hand positions in young overhead athletes. 24 young overhead athletes were recruited for the present study. Surface electromyography (EMG) was recorded for the PM and the TB muscles during the performance of push-up exercise on the push-up bar and perfect push-up using different hand positions (SW, NSW, and WSW). Root mean square (RMS) of the EMG signal was analyzed during each variation of push-up exercise for both muscles. Muscle activity was calculated as percentage maximum voluntary isometric contraction (% MVIC). EMG activity of PM muscle was significantly greater in WSW hand position as compared to SW (p < 0.01) and NSW (p < 0.01) hand position; whereas, the activity of TB was significantly greater in NSW hand position as compared to SW (p < 0.01) and WSW (p < 0.01) hand position. There were no significant differences in the EMG activity of PM (p = 0.54) and TB (p = 0.68) muscles between the push-up bar versus the perfect push-up. WSW hand position may be used during a push-up when the goal is to strengthen PM; whereas, an NSW hand position may be utilized for the selective strengthening of TB muscle. Both perfect push-up and push-up bar may be utilized by overhead athletes for performing push-ups based on the availability of equipment.

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PURPOSE: Effective arm swing and core muscle activation are involved in acceleration and maximal sprinting, yet muscle activity in these areas have not been measured via electromyography (EMG) during over ground sprinting trials. The purpose of this study was to explore the relationship between muscle activation of the upper body and measures of performance during sprint acceleration and maximal sprinting. METHODS: Sixteen participants (20.93 ± 0.96 yrs.; 1.71 ± 0.07 m; 67.69 ± 11.81 kg) completed six 40-m sprint trials on an outdoor track, with three from a block start and three from a split start. Muscle activation was measured via EMG in the triceps brachii, biceps brachii, upper trapezius, anterior deltoid, latissimus dorsi, erector spinae, rectus abdominis, and oblique muscles, recorded as a percentage of maximal voluntary isometric contraction. Split times recorded during each sprint were used to calculate acceleration, net horizontal force (Fh), and the ratio of Fh and resultant ground reaction force (%RF) using previously validated methods. Repeated measures multilevel modeling was used to evaluate the relationship between mean upper body muscle activation and average acceleration, Fh, and %RF during each 10-m window of the sprint. RESULTS: During the 0-10 m window, mean activation of the upper trapezius showed a significant positive relationship with acceleration (t = 2.66, p = 0.01), Fh (t = 2.20, p = 0.03), and %RF (t = 2.57, p = 0.01), erector spinae activation was positively associated with %RF (t = 2.42, p = 0.02), and biceps activation was negatively associated with Fh (t = -2.23, p = 0.03). In the 30-40 m window, there was a significant negative relationship between mean latissimus dorsi activation and %RF (t = -2.16, p = 0.04). There were no significant relationships between upper body muscle activation and indicators of sprint performance detected during the 10-20 m or 20-30 m windows. CONCLUSIONS: These results indicate that upper trapezius muscle activity is important during initial sprint acceleration, which agrees with past research on scapular restriction limiting maximal acceleration while sprinting. After the initial period of sprint acceleration, there was no evidence that greater activation of certain upper body muscles was related to improving maximal sprinting performance.

Five men performed submaximal isometric, concentric or eccentric contractions until exhaustion with the left arm elbow flexors at respectively 50%, 40% and 40% of the prefatigued maximal voluntary contraction force (MVC). Subsequently, and at regular intervals, the surface electromyogram (EMG) during 30-s isometric test contractions at 40% of the prefatigued MVC and the muscle performance parameters (MVC and the endurance time of an isometric endurance test at 40% prefatigued MVC) were recorded. Large differences in the surface EMG response were found after isometric or concentric exercise on the one hand and eccentric exercise on the other. Eccentric exercise evoked in two of the three EMG parameters [the EMG amplitude (root mean square) and the rate of shift of the EMG mean power frequency (MPF)] the greatest (P less than 0.001) and longest lasting (up to 7 days) response. The EMG response after isometric or concentric exercise was smaller and of shorter duration (1-2 days). The third EMG parameter, the initial MPF, had already returned to its prefatigued value at the time of the first measurement, 0.75 h after exercise. The responses of EMG amplitude and of rate of MPF shift were similar to the responses observed in the muscle performance parameters (MVC and the endurance time). Complaints of muscle soreness were most frequent and severe after the eccentric contractions. Thus, eccentric exercise evoked the greatest and longest lasting response both in the surface EMG signal and in the muscle performance parameters.

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Aims To investigate the relationship between mechanomyogram (MMG), electromyogram (EMG) and bite force during isometric contraction of the human masseter muscle. Methods Data were obtained from 16 healthy Japanese males (Mean age: 25.6 ± 2.3 years). The measuring device for MMG consisted of an amorphous sensor and a small magnet. The bite force, MMG and EMG signals were recorded simultaneously during isometric contraction of the masseter muscle. The subjects were instructed to perform 0, 5, 10, 20, 30, 40, 50, and 60% maximal voluntary contractions (MVC) for 20 seconds. The average rectified value (ARV) for MMG and EMG were calculated from 1 to 5 second samples. The median frequency of the power spectrum (MFPS) for MMG and EMG were determined with the use of a fast Fourier transformation algorithm. Results The mean ARV for MMG increased up to 20% MVC and then gradually decreased at the higher force levels. The mean ARV for EMG increased with bite force in a monotonic fashion. The mean MFPS for MMG clearly increased up to 10% MVC and then gradually increased. On the other hand, the mean MFPS for EMG clearly increased up to 10% MVC, but then gradually decreased with bite force. Conclusion These findings suggest that the MMG analysis combined with the EMG may be a more useful method for evaluating the status of the masseter muscle.

The relationship between relative force, electromyogram (EMG) and time to fatigue was examined in seven male and seven female subjects [mean (SD) age, 21.7 (3.2) years] during isometric handgrip exercise. Subjects performed sustained submaximal contractions of the right handgrip at three different intensities: 30%, 50%, and 75% of the pretrial maximum voluntary contraction (MVC). EMG was sampled in 1-s epochs every 15 s during the contractions, and the integrated EMG (IEMG) values were then normalized to that of the pretrial MVC. As expected, time to fatigue was longest at 30% MVC and shortest at 75% MVC, but women performed consistently longer than men at each of the three intensities [woman vs men; 400.7 (35.8) vs 364.3 (34.4) s, 205.1 (15.6) vs 139.4 (13) s, and 89.9 (11.4) vs 66.4 (6.4) s, for 30%, 50%, and 75% MVC, respectively; P < 0.05)]. IEMG increased in a non-linear fashion over time during each trial, with the magnitude of IEMG being proportional to the intensity of the contraction. At the endurance limit, IEMG was greatest in the 75% MVC trial, however, no IEMG values reached those obtained in the related MVC [30%, 57.2 (6.9)%, 50%, 84.6 (5.7)%; 75%, 92.8 (7.4)%]. In conclusion, endurance time during sustained submaximal isometric handgrip exercise is dependent up on the intensity of the effort, with women having significantly larger endurance times than men. The related increase in IEMG is also proportional to the intensity of effort, however, the factors causing force to fail prior to the final IEMG reaching its predicted maximum remain to be elucidated.

Nowadays, telemonitoring is a new trend with huge potential of providing patients with innovative medical solutions to improve the quality of their treatment. In this paper, a new elbow flexion and extension rehabilitation telemonitoring wearable device using inertial and Electromyography (EMG) sensors is presented. The proposed system not only allows remote monitoring of the elbow joint angle but also provides information on the muscle activity of the main muscles involved in elbow flexion and extension, biceps brachii and triceps brachii. This new approach can help to monitor the musculoskeletal conditions that affect the elbow joint movement in order to obtain a wider frame of reference to improve the diagnosis and treatment of elbow rehabilitation. The hardware system relies on signal processing, data collection and wireless transmission through Wi-Fi communication of the measured inertial and EMG signals from a patient to a Personal Computer (PC) where a physician can monitor remotely through a graphical user interface. All stages from design, implementation and preliminary testing of the wearable device are presented. The measured flexion-extension angles and electrical muscle activity demonstrate that our device is reliable.

Spectral parameters such as the mean and median frequencies have been documented to be reliable outcome variables for the assessment of muscle fatigue. The objective of this paper is to examine young subjects' surface electromyography (EMG) signals at different levels of maximum voluntary contractions (MVC) and to analyze spectral shifts in mean and median frequencies (MNF, MDF). In this study, continuous stream of EMG data sets from lower extremity muscles are used to characterize muscular fatigue from minimum to maximum MVC level. EMG data were recorded from the biceps brachii muscles during isometric contraction at constant torque levels using automated dynamometer. EMG metrics such as MNF, MDF, root mean square (RMS), and rectified root mean square (RRMS) were computed to assess muscle fatigue patterns.

Background/AimsExternal anal sphincter (EAS) plays an important role in fecal and gas voluntary continence. Like every muscle, it can be affected by repeated efforts due to fatigability (physiological response) and/or fatigue (pathological response). No standardized fatiguing protocol and measure method to assess EAS fatigability has existed. The aim is to test a simple, standardized protocol for fatiguing and measuring EAS fatigability and fatigue to understand better the part of EAS fatigability in the pathophysiology of fecal incontinence.MethodsPatients with anorectal disorders evaluated with anorectal manometry were included. They had to perform 10 repetitions of maximum voluntary contraction (MVC) of 20 seconds. Measurement was made with an anorectal manometry catheter and a surface recording electromyography (EMG). The primary outcome was the difference in EMG root mean square between the first and the last MVC. Secondary outcomes were differences in other EMG and manometry parameters between the first and the last MVC. Difficulties and adverse effects were recorded.ResultsNineteen patients underwent the fatiguing protocol. All patients completed the entire protocol and no complications were found. No difficulty was declared by the examiner. A significant decrease in root mean square was found between the first and last MVC (0.01020 ± 0.00834 mV vs 0.00661 ± 0.00587 mV; P = 0.002), in maximum anal pressure area under the curve of continuous recordings of anal pressure and mean and total EMG power (P < 0.05).ConclusionsThis protocol is simple and minimally invasive to measure EAS fatigue and fatigability. We highlighted a fatigue of EAS in many patients with anorectal disorders.

In this study, a comparison of EMG power spectrum statistics (MF and MPF) was made between men and women. Thirteen men and sixteen women produced ramp elbow flexions and extensions. . Surface EMG signals from triceps brachii (TB), anconeus (AN) and biceps brachii (BB) were recorded. The MPF and MF of the power spectrum were computed for each muscle at 10, 20, 40, 60 and 80% MVC. Significant differences in both the MPF and MF values at high force levels were found between men and women for the TB and the BB. These could be explain by differences in skinfold thickness and possibly fiber type carateristics between the two groups.

We analyzed the time course of changes in muscle activity of the prime mover and synergist muscles during a sustained brake-pulling action and investigated the relationship between muscle activity and braking force fluctuation (FF). Thirty-two participants performed a continuous fatiguing protocol (CFP) at 30% of maximal voluntary contraction (MVC) until failure. Surface electromyography was used to analyze root mean square (RMS) values in the flexor digitorum superficialis (FD), flexor carpi radialis (FC), extensor digitorum communis (ED), extensor carpi radialis (EC), brachioradialis (BR), biceps brachii (BB), and triceps brachii (TB). The FF and RMS in all muscles increased progressively (P<0.01) during the CFP, with sharp increments at time limit particularly in FD and FC (P<0.001). The RMS of the FD and FC were comparable to the baseline MVC values at time limit, in comparison to the other muscles that did not reach such levels of activity (P<0.003). The three flexor/extensor ratios used to measure coactivation levels decreased significantly (P<0.001). In contrast to RMS, MVC was still depressed at the minute 10 of recovery. The results suggest that the time limit was mainly constrained by fatigue-related mechanisms of the FD and FC but not by those of other synergist and antagonist muscles.