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Soundmyogram analysis during sustained maximal voluntary contraction in sprinters and long distance runners
No full textThe aim of this study was to describe the influence of the different fiber type composition of the vastus lateralis muscle on the soundmyogram (SMG) time and frequency domain characteristics. The SMG was recorded from the vastus lateralis belly during exhausting maximal voluntary contraction (MVC) of the leg extensors in 7 sprinters (SPR) and 7 long distance runners (LDR). Seven sedentary males (SED) were investigated in the same experimental conditions. In the SPR the effort time was shorter and the MVC was greater while the SMG root mean square and the SMG frequency. content, at the onset of contraction, were higher than in the SED and LDR, respectively. Throughout exertion the SMG RMS showed clear reduction for SPR and SED only and the SMG power spectra presented a compression towards the lower frequencies. The reported phenomena were less pronounced in the LDR than in SPR and SED. These results can be explained when the differences in the % of fast twitch fibers area, belonging to stronger and more fatiguing F motor units, in the three groups of subjects are considered and suggest that SMG characteristics reflect the muscle fiber typing
Changes of muscular sound during sustained isometric contraction up to exhaustion
No full textThe sound (SMG) generated by the biceps muscle during isometric exercise at 20, 40, 60, and 80% of maximum voluntary contraction (MVC) up to exhaustion has been recorded by a contact transducer and integrated (iSMG), together with the surface electromyogram (EMG) in eight young untrained men. At the onset of exercise, iSMG and integrated surface EMG (iEMG) amplitude increased linearly with exercise. iSMG remained constant for 253 +/- 73 (SD), 45 +/- 16, 21 +/- 5, and 0 s at the four levels of contraction. Then iSMG increased linearly at 20% MVC, fluctuated at 40% MVC, and decreased exponentially at 60 and 80% MVC. iSMG exhaustion-to-onset ratio was 5.0 at 20%, 1.0 at 40%, and 0.2 at 60 and 80% MVC. On the contrary, independently of exercise intensity, iEMG increased with time, being 1.4 higher at exhaustion than at the onset. The nonunivocal iSMG changes with time and effort of exercise suggest that the sound may be a useful tool to acquire different information to EMG and output force during muscle contraction up to fatigue
Electromyogram and mechanomyogram changes in fresh and fatigued muscle during sustained contraction in men
No full textIn surface electromyogram (EMG) and mechanomyogram (MMG) the electrical and mechanical activities of recruited motor units (MU) are summated. Muscle fatigue influences the electrical and mechanical properties of the active MU. The aim of this study was to evaluate fatigue-induced changes in the electrical and mechanical properties of MU after a short recovery period, using an analysis of force, surface EMG and MMG. In seven subjects the EMG and MMG were recorded from the biceps brachii muscle during sustained isometric effort at 80% of the maximal voluntary contraction (MVC), before (test 1) and 10 min after (test 2) a fatiguing exercise. From the time and frequency domain analysis of the signals, the root mean square (rms) and the mean frequency (f) of the power spectrum were calculated. The results were that the mean MVC was 412 (SEM 90) N and 304 (SEM 85) N in fresh and fatigued muscle, respectively; during tests 1 and 2 the mean EMG rms increased from 0.403 (SEM 0.07) mV to 0.566 (SEM 0.09) mV and from 0.476 (SEM 0.07) mV to 0.63 (SEM 0.09) mV, respectively; during test 1 the mean MMG rms decreased from 9.4 (SEM 0.8) mV to 5.7 (SEM 0.9) mV; in contrast, during test 2 constantly lower values were observed throughout contraction; during tests 1 and 2 the EMG f declined from 122 (SEM 7) Hz to 74 (SEM 7) Hz and from 106 (SEM 8) Hz to 60 (SEM 7) Hz, respectively; during test 1 the MMG f increased in the first 6 s from 19.3 (SEM 1.4) Hz to 23.9 (SEM 2.9) Hz, falling to 13.9 (SEM 1.3) Hz at the end of contraction; in contrast, during test 2 the MMG f declined continuously from 18.7 (SEM 1) Hz to 12.4 (SEM 0.8) Hz. The lower MVC after the fatiguing exercise and the changes in the EMG parameters confirmed that 10 min after the fatiguing exercise, the mechanical and electrical activities of MU were altered. In addition, the MMG results suggested that after a 10-min recovery, some highly fatigable MU might not be recruitable
Muscular sound and force relationship during isometric contraction in man
No full textThe contracting muscle generates a low frequency sound detectable at the belly surface, ranging from 11 to 40 Hz. To study the relationship between the muscular sound and the intensity of the contraction a sound myogram (SMG) was recorded by a contact sensor from the biceps brachii of seven young healthy males performing 4-s isometric contractions from 10% to 100% of the maximal voluntary contraction (MVC), in 10% steps. Simultaneously, the electromyogram (EMG) was recorded as an index of muscle activity. SMG and EMG were integrated by conventional methods (iSMG and iEMG). The relationship between iSMG and iEMG vs MVC% is described by parabolic functions up to 80% and 100% MVC respectively. Beyond 80% MVC the iSMG decreases, being about half of its maximal value at 100% MVC. Our results indicate that the motor unit recruitment and firing rate affect the iSMG and iEMG in the same way up to 80% MVC. From 80% to 100% MVC the high motor units' discharge rate and the muscular stiffness together limit the pressure waves generated by the dimensional changes of the active fibres. The muscular sound seems to reflect the intramuscular visco-elastic characteristics and the motor unit activation pattern of a contracting muscle
EMG and mechanomyogram changes in fresh and fatigued muscle during sustained contraction in humans
No full textAim of this study was to evaluate the persistence of the fatigue-induced changes in motor unit (MU) electrical and mechanical properties after a short period of recovery. In 7 subjects the force, EMG and mechanomyogram (MMG) were recorded from m. biceps brachii during a 20 s isometric effort at 80% of the maximal voluntary contraction (MVC), before (test 1) and 10 min after (test 2) an intermittent fatiguing exercise (6 s on - 4 s off cycles at 50% MVC). It resulted that: a) the MVC was 412±90 N (mean±SEM) and 304±85 N in fresh and fatigued muscle, resp. (P<0.05); b) during test 1 and 2 the EMG root mean square (RMS) increased linearly from 0.40±0.01 mV to 0.57±0.01 mV (P<0.05) and from 0.48±0.01 mV to 0.63±0.01 mV (P<0.05), resp.; c) during test 1 the MMG RMS dropped from 9.4±0.8 mV to 5.7±0.9 mV (P<0.05); during test 2 constant lower values were observed throughout contraction; d) during test 1 and 2 the EMG mean frequency (MF) declined from 122±7 Hz to 74±7 Hz (P<0.05) and from 106±8 Hz to 60±7 Hz (P<0.05), respectively; e) during test 1 the MMG MF increased in the first 6 s from 19.3±1.4 Hz to 23.9±2.9 Hz (P<0.05), falling to 13.9±1.3 Hz at the end of contraction; during test 2 the MMG MF declined continuously from 18.7±1 Hz to 12.4±0.8 Hz (P<0.05). The lower MVC after the fatiguing exercise and the changes in the EMG and MMG parameters, in particular, the lower initial values of the MMG RMS and the lack of the increase in the MMG MF during the first part of test 2, suggest that even 10 min after the fatiguing exercise some highly fatigable MUs, probably the fast twitch MUs, may not be fully recruitable at their maximal firing rate
The surface mechanomyogram as a tool to describe the influence of fatigue on biceps brachii motor unit activation strategy : historical basis and novel evidence
No full textThe surface mechanomyogram (MMG) (detectable at the muscle surface as MMG by accelerometers, piezoelectric contact sensors or other transducers) is the summation of the activity of single motor units (MUs). Each MU contribution is related to the pressure waves generated by the active muscle fibres. The first part of this article will review briefly the results obtained by our group studying the possible role of motor unit recruitment and firing rate in determining the characteristics of the MMG during stimulated and voluntary contractions. The second part of this article will study the MMG and EMG during a short isometric force ramp from 0 to 90% of the maximal voluntary contraction (MVC) in fresh and fatigued biceps brachii. The aim is to verify whether changes in motor unit activation strategy in voluntarily fatigued muscle could be specifically reflected in the time and frequency domain parameters of the MMG. MMG-RMS vs. %MVC: at fatigue the MMG-RMS did not present the well known increment, when effort level increases, followed by a clear decrement at near-maximal contraction levels. MMG-MF vs. %MVC: compared to fresh muscle the fatigued biceps brachii showed an MF trend significantly shifted towards lower values and the steeper MF increment, from 65 to 85% MVC, was not present. The alteration in the MMG and EMG parameters vs. %MVC relationships at fatigue seems to be related to the impossibility of recruiting fast, but more fatigable MUs, and to the lowering of the global MUs firing during the short isometric force ramp investigated
Muscle sound and electromyogram spectrum analysis during exhausting contractions in man
No full textThe changes in the soundmyogram (SMG) and electromyogram (EMG) frequency content during exhausting contractions at 20%, 40%, 60% and 80% of the maximal voluntary contraction (MVC) were investigated by the spectral analysis of the SMG and EMG detected from the biceps brachii muscles of 13 healthy men. The root mean squares (rms) of the two signals were also calculated. Throughout contraction the EMG rms always increased while this was true only at 20% MVC for the SMG. A marked decrease was detected at 60% and 80% MVC. With fatigue the EMG spectra presented a compression towards the lower frequencies at all exercise intensities. The SMG showed a more complex behaviour with a transient increase in its frequency content, followed by a continuous compression of the spectra, at 60% and 80% MVC, and a nearly stable frequency content at lower contraction intensities. This study suggested that different aspects of the changes in the motor unit's activation strategy at different levels of exhausting contractions can be monitored by SMG and EMG signals
Influence of motor units recruitment and firing rate on the soundmyogram and EMG characteristics in cat gastrocnemius
No full textThe separate contributions of the recruitment level and of the firing rate of the motor units on the soundmyogram and electromyogram time domain parameters were investigated during stimulation of the motor nerve of the cat gastrocnemius muscle. Upon orderly increase in the number of active motor units at a fixed firing rate, both the peak to peak amplitude (P-P(max)) and the root mean square (RMS) of the sound myogram increased. At full recruitment the increase in firing rate from 2.5 to 50 Hz induced an exponential decline in the P-P(max). The RMS, however, followed this trend only from 15 to 50 Hz while showing an increase from 2.5 to 10 Hz. During simultaneous changes of recruitment and firing rate, the effect of increasing the number of motor units on the P-P(max) and RMS is dampened by the increasing firing rate. The peak to peak amplitude of the EMG compound action potential increased with the number of active motor units. Moreover, its amplitude was not influenced by the firing rate. The EMG RMS, however, increases as a function of the firing rate. The results indicate that both the number and the firing rate of the active motor units contribute to the determination of the soundmyogram characteristics. Moreover, the peculiar changes of the soundmyogram time domain properties, compared to the ones of the EMG, allow one to differentiate the influence of the motor units number and firing rate on the electrical and mechanical performance of the muscle when stimulated
Torque and surface mechanomyogram parallel reduction during fatiguing stimulation in human muscles
No full textThe purpose of the study was to verify, by means of torque and mechanomyogram (MMG) compared analysis, the validity of MMG as a tool to investigate the contractile changes due to localized muscular fatigue induced by stimulation protocols usually employed for sport training and rehabilitation programs. Ten healthy sedentary subjects participated in the study. Torque produced by the dominant biceps brachii (BB) and vastus lateralis (VL) during transcutaneous stimulated contractions has been recorded by a load cell strapped to the subjects' wrist and distal one-third of the tibia, respectively. MMG was detected over the muscle bellies during a monopolar supramaximal stimulation of the main motor point. After potentiation, the fatiguing stimulation was administered. It consisted of 50 cycles, with 2 s of 50 Hz and 25 s of 2 Hz. Averaged normalized values of peak torque (pT) and MMG peak-to-peak (MMG-pp) of the subjects group decreased from their initial 100% values to 55% (pT) and 60% (MMG-pp) for BB and to 43% (pT) and 47% (MMG-pp) for VL. The pT% and MMG-pp% changes throughout the stimulation protocol presented high correlation (BB: R=0.95, P < 0.001; VL: R=0.94, P < 0.001). This correlation suggests that MMG could be used to follow muscle mechanical fatigue development when torque output is not or hardly detectable such as during electrical stimulation programs employed for sport training or rehabilitation protocols
Surface EMG and mechanomyogram disclose isokinetic training effects on quadriceps muscle in elderly people
No full textMaximum voluntary contraction (MVC) and cross-sectional area (CSA) of fast and slow twitch fibers are reduced in the lower limb muscles of elderly subjects. Isokinetic training at medium and high velocities has been widely used to improve muscle performance and force in young as well as elderly subjects. EMG and mechanomyogram (MMG) are compound signals in which the electrical and mechanical activities of recruited motor units (MUs) are summated. The aim of the present study was to verify the hypothesis that isokinetic training in the elderly induces changes in EMG and MMG parameters, compatible with a functional retrieval of fast twitch fiber MUs. In ten sedentary males (62-78 years), the surface EMG and MMG were recorded from the vastus lateralis muscle during isometric contractions at 20, 40, 60, 80 and 100% of the MVC, before and after 12 weeks of isokinetic training (six series of ten repetitions, each at an angular velocity of 2.09 rad s-1 and 4.19 rad s-1, two times a week). With training: (a) MVC and CSA increased by about 35(plus or minus)5% and 8(plus or minus)1%, respectively (P<0.05); (b) the ratio MVC/CSA increased significantly in all subjects by 25(plus or minus)5%; (c) the EMG root mean square and MMG spectral mean frequency increased significantly at the highest workloads. In conclusion, our data indicate that isokinetic training in the elderly improved muscle size and performance significantly. The EMG and MMG changes suggest that these results may be due to a retrieval of the fast twitch fiber MUs, contributing to muscle action. (copyright) Springer-Verlag 2005
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