MMG Responses Research Articles

Mechanomyography and tissue oxygen saturation during electrically-evoked wrist extensor fatigue in people with tetraplegia.

Repetitive electrically-evoked muscle contractions lead to the early onset of muscle fatigue. This study assessed the relationship between muscle mechanomyography (%RMS-MMG) and tissue oxygen saturation (%TSI) in extensor carpi radialis (ECR) during electrically-evoked fatiguing exercise in individuals with tetraplegia. Skin-surface mechanomyography (MMG) and near-infrared spectroscopy (NIRS) sensors were placed on the ECR of seven individuals with tetraplegia. All participants performed repetitive electrically-evoked wrist extension to fatigue while their muscle MMG and NIRS responses were monitored against their power output (PO). One out of seven participants showed no changes in %TSI throughout the repeated wrist FES-evoked contraction. The other six participants' %TSI was positively correlated with %PO before fatigue onset. At 50%POpeak , %TSI was negatively correlated (0.489) significantly with declining %PO as the ability of the muscle to take up oxygen became limited. The %RMS-MMG behaved analogously during pre and post-fatigue against declining %PO, whereby both displayed positive correlations of 0.443 and 0.214, respectively, (%RMS-MMG decreased) throughout the exercise session. Regression analysis revealed that %TSI was proportional to pre-fatigue and inversely proportional to %RMS-MMG during post-fatigue. The significant changes in muscle mechanomyography and tissue oxygenation correlations after 50%POpeak implied that the muscle contraction mechanical-and-physiological behavior association had been altered following FES-evoked fatigue.

Low-load blood flow restriction elicits greater concentric strength than non-blood flow restriction resistance training but similar isometric strength and muscle size.

Low-load venous blood flow restriction resistance training (RT + BFR) has been demonstrated to increase muscle strength to a greater degree than low-load non-BFR resistance training (RT) during isotonic training, but no previous investigations have examined RT + BFR versus RT during isokinetic training. The purpose of the present study was to examine the effects of 4 weeks of isokinetic low-load RT + BFR versus low-load RT on indices of muscle strength, muscle size, and neural adaptations. Thirty women (mean ± SD; 22 ± 2years) participated in this investigation and were randomly assigned to 4 weeks of either RT + BFR (n = 10), RT (n = 10), or control (n = 10) group. Resistance training consisted of 75 reciprocal forearm flexion-extension isokinetic muscle actions of the forearm flexors performed at a velocity of 120°s-1. Concentric peak torque increased to a greater extent for RT + BFR after 4 weeks (36.9%) compared to RT (25.8%), but there were similar increases in isometric torque (23.3-42.1%). For both RT + BFR and RT, there were similar increases in muscle cross-sectional area and muscle thickness of the biceps brachii after 2 weeks (11.3-14.3% and 12.4-12.9%, respectively) and 4 weeks (18.7-21.9% and 19.0-20.0%, respectively). There were similar increases in mechanomyographic amplitude, mechanomyographic mean power frequency, and electromyographic mean power frequency, but no changes in electromyographic amplitude for all conditions (including control). These findings indicated that low-load RT + BFR elicited greater increases in concentric strength than low-load RT, but elicited comparable increases in isometric strength and muscle size. There were also no differences in any of the EMG and MMG responses among conditions.

Intelligent Multi-Microgrid Energy Management Based on Deep Neural Network and Model-Free Reinforcement Learning

In this paper, an intelligent multi-microgrid (MMG) energy management method is proposed based on deep neural network (DNN) and model-free reinforcement learning (RL) techniques. In the studied problem, multiple microgrids are connected to a main distribution system and they purchase power from the distribution system to maintain local consumption. From the perspective of the distribution system operator (DSO), the target is to decrease the demand-side peak-to-average ratio (PAR), and to maximize the profit from selling energy. To protect user privacy, DSO learns the MMG response by implementing a DNN without direct access to user’s information. Further, the DSO selects its retail pricing strategy via a Monte Carlo method from RL, which optimizes the decision based on prediction. The simulation results from the proposed data-driven deep learning method, as well as comparisons with conventional model-based methods, substantiate the effectiveness of the proposed approach in solving power system problems with partial or uncertain information.

IMPACT OF SKINFOLD THICKNESS ON WAVELET-BASED MECHANOMYOGRAPHIC SIGNAL

Surface mechanography (MMG) is a non-invasive technique that captures signs of low-frequency vibrations of skeletal muscles through the skin. However, subcutaneous structures may interfere with the acquisition of MMG signals. The objective of this study was to verify the influence of skinfold thickness (ST) on the MMG wavelet-based signal in the rectus femoris muscle during maximal voluntary contraction in two groups of individuals: group I (n = 10, ST <10 mm ) and group II (n = 10, ST equal to or> 20 mm). Negative correlation was observed between the 19 Hz, 28 Hz and 39 Hz frequency bands with ST. There was a statistical difference in almost all frequency bands, especially in the X and Y axes. All MMG axes in group II presented higher magnitudes in frequency bands 2 and 6 Hz (like low-pass filter). Thus, these results can be applied to calibrate MMG responses as biofeedback systems.

Mechanomyography for Intraoperative Assessment of Cortical Breach During Instrumented Spine Surgery

We sought to determine the utility of mechanomyography (MMG) in detecting and preventing pedicle breach in instrumented lumbar spine surgery. In a prospective nonrandomized trial without controls, we selected consecutive patients to undergo intraoperative MMG during instrumented lumbar spine surgery. MMG testing was performed at the original pilot hole, after tapping, and after screw placement, with the minimum current to elicit a recorded MMG response. All patients underwent a postoperative computed tomography scan, and a single radiologist interpreted each pedicle to identify breach. Chi-square test was used to compare patients with and without breaches. Two sample Student's t-tests were used to compare changes in functional outcomes. Sensitivity and specificity of MMG were computed using receiver operating characteristic curve analysis. There were 122 consecutive instrumented lumbar surgery patients enrolled, with a total of 890 lumbar pedicle screws tested with MMG. The medial or inferior breach rate was 2.25%, with no statistically significant difference in Oswestry Disability Index or visual analog scale between patients who breached and who did not. For the MMG measurement from the original pilot hole, the area under the receiver operating characteristic was 0.835; the maximum combination of sensitivity (80.42%) and specificity (80.6%) was found using MMG current ≤12 mA. We found that an MMG cutoff of >12 mA resulted in a 99.5% likelihood of no medial or inferior breach. MMG can be safely used during instrumented lumbar spine surgery. A cutoff value of >12 mA for MMG can accurately predict and prevent medial and inferior pedicle screw breach.

Mechanomyographic responses for the biceps brachii are associated with failure times during isometric force tasks.

In order to characterize the physiological adjustments within the neuromuscular system that contribute to task failure, this study examined the surface mechanomyographic (MMG) response during maximal and submaximal isometric force tasks of the elbow flexors sustained to failure. The time and frequency components of the MMG signal have shown to be influenced by motor unit activation patterns as well as tetanus. Therefore, it was hypothesized that the rate of change for the MMG response would associate with failure times and would be reduced to a similar degree between the two tasks. The isometric force tasks were performed by the dominant elbow flexors of twenty healthy males (age: 25 ± 4 years) and MMG was collected from the biceps brachii. Regression analyses were used to model the relationships between the rates of change for MMG versus failure times. There were high levels of interindividual variability in the response patterns, yet the models demonstrated significant negative associations between the rate of change for the MMG responses and failure times during both tasks (R 2 = 0.41–0.72, P < 0.05). Similarly, the mean MMG amplitude and frequency values were reduced to comparable levels at the failure point of the two tasks. The results of this study demonstrated that force failure is associated with the rate of diminution in the properties of the muscle force twitch.

Mechanomyographic responses during recruitment curves in the soleus muscle.

In this study we examined relationships among mechanomyographic (MMG), electromyographic (EMG), and peak twitch torque (PTT) responses as well as test-retest reliability when recorded during recruitment curves in the soleus muscle. PTT, EMG (M-wave, H-reflex), and MMG responses were recorded during recruitment curves in 16 subjects (age 24 ± 2 years) on 2 separate days. The sum of the M-wave and H-reflex (M+H) was calculated. Correlations among variables and test-retest reliability were determined. MMG was correlated with PTT (mean r = 0.93, range r = 0.59-0.99), the M-wave (0.95, 0.04-0.98), and M+H (0.91, 0.42-0.97), but was unrelated to the H-reflex (-0.06, -0.56 to 0.47). Reliability was consistently high among most variables, but normalizing to the maximum value improved MMG reliability and the minimum detectable change. MMG responses predicted 86%-90% of the variability in PTT, M-wave, and M+H; thus, MMG may be a useful alternative for estimating twitch torque and maximal activation. Muscle Nerve 56: 107-116, 2017.

Muscle- and Mode-Specific Responses of the Forearm Flexors to Fatiguing, Concentric Muscle Actions.

Background: Electromyographic (EMG) and mechanomyographic (MMG) studies of fatigue have generally utilized maximal isometric or dynamic muscle actions, but sport- and work-related activities involve predominately submaximal movements. Therefore, the purpose of the present investigation was to examine the torque, EMG, and MMG responses as a result of submaximal, concentric, isokinetic, forearm flexion muscle actions. Methods: Twelve men performed concentric peak torque (PT) and isometric PT trials before (pretest) and after (posttest) performing 50 submaximal (65% of concentric PT), concentric, isokinetic (60°·s−1), forearm flexion muscle actions. Surface EMG and MMG signals were simultaneously recorded from the biceps brachii and brachioradialis muscles. Results: The results of the present study indicated similar decreases during both the concentric PT and isometric PT measurements for torque, EMG mean power frequency (MPF), and MMG MPF following the fatiguing workbout, but no changes in EMG amplitude (AMP) or MMG AMP. Conclusions: These findings suggest that decreases in torque as a result of fatiguing, dynamic muscle actions may have been due to the effects of metabolic byproducts on excitation–contraction coupling as indicated by the decreases in EMG MPF and MMG MPF, but lack of changes in EMG AMP and MMG AMP from both the biceps brachii and brachioradialis muscles.

Mechanomyographic and metabolic responses during continuous cycle ergometry at critical power from the 3-min all-out test

There are limited data regarding metabolic responses during continuous exhaustive rides at critical power (CP) from the 3-min all-out test. In addition, no previous studies have examined the mechanomyographic (MMG) responses at CP from the 3-min all-out test. Therefore, this study examined the metabolic and MMG responses during continuous exercise at CP determined from the 3-min all-out test. Nine college-aged females (mean±SD: age 23.0±3.6yrs) performed an incremental test to exhaustion on a cycle ergometer to identify the gas exchange threshold, peak oxygen consumption rate (V˙O2 peak) and heart rate peak (HR peak). The V˙O2, HR, MMG amplitude and mean power frequency (MPF) responses were examined during continuous rides to exhaustion at CP (81±6% peak power). There were significant increases in V˙O2 and HR over time and there was no significant difference between V˙O2 peak and V˙O2 at exhaustion or HR peak and HR at exhaustion. There were, however, no significant changes for MMG amplitude or MPF over time. Therefore, the current findings suggested that the 3-min all-out test overestimated CP and the demarcation between the heavy and severe intensity domains. Specifically, the V˙O2 and HR responses did not reach a steady state and were driven to peak values. Furthermore, the non-significant change in MMG amplitude and MPF were consistent with the responses observed at fatiguing power outputs (i.e., >80% peak power).

A wavelet‐based analysis of surface mechanomyographic signals from the quadriceps femoris

The purpose of this study was to use a wavelet analysis designed specifically for surface mechanomyographic (MMG) signals to examine the MMG responses of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles. Fifteen healthy men [age (mean +/- SD): 26.4 +/- 6.1 years] volunteered to perform isometric muscle actions of the dominant leg extensors at 20%, 40%, 60%, 80%, and 100% of the maximum voluntary contraction (MVC). During each muscle action, surface MMG signals were detected from the VL, RF, and VM and processed with the MMG wavelet analysis. The results show that, for the VL and VM muscles, there was compression of the total MMG intensity spectra toward low frequencies for most force levels above 20% MVC. For the RF, however, the peak of the total MMG intensity spectrum occurred at approximately 30-40 HZ for all force levels. Because the VL, RF, and VM are all innervated by the femoral nerve, the discrepancies among the three muscles for total MMG intensity in each wavelet band may have been due to differences in architecture, muscle stiffness, and/or intramuscular pressure.

Control Entropy of mechanomyogram (MMG) and electromyogram (EMG) during fatiguing isometric muscle actions

The purpose of this study was to determine if Control Entropy (CE) of MMG and EMG would decline during fatiguing isometric muscle actions. Procedures were approved by the Hope HSRB. Subjects performed one isometric leg extension (30° flexion) at the 1‐RM of the non‐dominant leg to volitional fatigue. MMG and EMG signals were recorded from the vastus medialis (VM) and rectus femoris muscles (RF) using commercial software (Biopac Systems, CA). The effort was divided into epochs (10% of time‐to‐fatigue) and mean and peak‐to‐peak (P‐P) amplitude MMG and EMG data were analyzed using repeated measures ANOVA (α=0.05). CE was calculated in Matlab (Mathworks, MA) using 2 and 8 bit partitions, and varying window lengths according to the following equation: CEKS[x(t)] =hKS[sign(dx/dt(t))]. P‐P amplitude of VM‐MMG and RF‐EMG declined (p&lt;0.05), while RF‐MMG (p=0.58) trended lower over time. Mean amplitude of VM‐EMG declined (p&lt;0.05). CE of the MMG declined over the course of the effort for males, but not for females. When accounting for gender, a significant effect was observed for P‐P of VM .MMG, RF‐EMG and mean VM‐EMG. In addition, CE of EMG exhibited an unexpected response whereby it increased at the onset of the muscle action. These results support previous reports of a differential MMG response in males vs females. The attenuated CE response of MMG in females vs. males may shed light on the nature of this difference between genders.

Effects of Vascular Restriction on Muscular Function during Intermittent Submaximal Isometric Exercise

It is generally accepted that a threshold intensity of 65% 1-RM is needed to induce muscle hypertrophy; however, recent studies using low-intensity resistance exercise (20% 1-RM) combined with vascular restriction (KAATSU) have also been able to demonstrate increases in muscle size and strength. PURPOSE: To investigate EMG and MMG responses of the vastus lateralis (VL) before, during, and after low intensity intermittent isometric exercise in combination with moderate vascular restriction and to examine the percent voluntary activation (PVA) of the VL. METHODS: Twelve healthy males volunteered to participate in this study (mean + SD age = 23.7±4.1 years). Each participant visited the laboratory 3 times: one familiarization trial and two experimental trials, separated by at least 48 h. The two experimental trials consisted of the same testing and isometric exercise protocol; however, the participants experienced either the KAATSU or no-KAATSU conditions in random order. For the experimental trials, the following procedures were performed in order: a) Resting blood pressure assessment after 5 min rest (for the KAATSU trial only), b) five-minute warm-up on a stationary cycle ergometer with a power output of 50 W and a pedaling cadence of 50–70 rpm, c) two pre-exercise 5-s isometric MVCs with 1 min rest between trials, d) five sets of 20 intermittent isometric contractions (2-s on and 1 -s off) at 20% of MVC with a 30-s interset rest period, and e) two post-exercise isometric 5-s MVCs with 1 min rest between trials. RESULTS: For MVC torque, PVA, EMG amplitude, EMG mean power frequency (MPF), MMG amplitude, and MMG MPF, there was no interaction and no main effects for time or session for the pre- and post-exercise isometric MVCs with and without KAATSU. The average normalized EMG amplitude (%MVC) increased from repetitions 1–4 to 5–8 to 9–12 and MMG amplitude increased significantly from set 1 to 2 for both the KAATSU and no-KAATSU sessions. CONCLUSIONS: The present study demonstrated no significant change in post-exercise torque values and % activation, suggesting that the exercise task was not intense enough to cause muscular fatigue in either treatment condition.

Sex Differences in Mechanomyographic Responses to Voluntary Isometric Contractions

This study was designed to compare mechanomyography (MMG) and the force relationship during isometric ramp contractions of biceps brachii muscles in females and males to identify sex differences in the MMG responses. Subjects (10 females and 9 males; age range, 20-26 yr) were asked to exert an isometric elbow flexion torque from 5 to 80% maximal voluntary contraction (MVC) at a constant rate of 10% MVC per second. The MMG signal was normalized to muscle cross-sectional area (CSA) as measured by ultrasound imaging. MVC and CSA were significantly different between the two sex groups (males>females); however, there was no sex difference in the MVC relative to muscle CSA (MVC/CSA). The root mean squared amplitude of the MMG (RMSMMG) was significantly greater in the male group than the female group. The RMSMMG relative to muscle CSA was also different between the two sex groups (males>females). The sex difference in the RMSMMG/CSA was more pronounced with increasing torque. The torque levels at which the inflection points in the MMG amplitude were located were different between the two sex groups. The mean power frequency (MPF) of the MMG in the female group increased monotonously, which was different from that in the male group. Our results suggest that the sex differences in MMG responses and motor unit (MU) activation strategy result from the predominant activity of the MU with slow-twitch fibers and an effective fused tetanus in females. In addition, the sex-related differences in muscle morphology, subcutaneous adipose tissue, and muscle stiffness appear to be insufficiently reflected in the present MMG responses, particularly relative to muscle CSA.

MMG and EMG Responses to Repeated, Concentric Muscle Actions

MMG and EMG Responses to Repeated, Concentric Muscle Actions

Mechanomyographic and electromyographic responses to repeated concentric muscle actions of the quadriceps femoris

In comparison to isometric muscle action models, little is known about the electromyographic (EMG) and mechanomyographic (MMG) amplitude and mean power frequency (MPF) responses to fatiguing dynamic muscle actions. Simultaneous examination of the EMG and MMG amplitude and MPF may provide additional insight with regard to the motor control strategies utilized by the superficial muscles of the quadriceps femoris during a concentric fatiguing task. Thus, the purpose of this study was to examine the EMG and MMG amplitude and MPF responses of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) during repeated, concentric muscle actions of the dominant leg. Seventeen adults (21.8 ± 1.7 yr) performed 50 consecutive, maximal concentric muscle actions of the dominant leg extensors on a Biodex System 3 Dynamometer at velocities of 60° s −1 and 300° s −1. Bipolar surface electrode arrangements were placed over the mid portion of the VL, RF, and VM muscles with a MMG contact sensor placed adjacent to the superior EMG electrode on each muscle. Torque, MMG and EMG amplitude and MPF values were calculated for each of the 50 repetitions. All values were normalized to the value recorded during the first repetition and then averaged across all subjects. The cubic decreases in torque at 60° s −1 ( R 2 = 0.972) and 300° s −1 ( R 2 = 0.931) was associated with a decline in torque of 59 ± 24% and 53 ± 11%, respectively. The muscle and velocity specific responses for the MMG amplitude and MPF demonstrated that each of the superficial muscles of the quadriceps femoris uniquely contributed to the control of force output across the 50 repetitions. These results suggested that the MMG responses for the VL, RF, VM during a fatiguing task may be influenced by a number of factors such as fiber type differences, alterations in activation strategy including motor unit recruitment and firing rate and possibly muscle wisdom.

EMG and MMG of agonist and antagonist muscles as a function of age and joint angle

The aim of this study was to determine the effect of elbow joint position on electromyographic (EMG) and mechanomyographic (MMG) activities of agonist and antagonist muscles in young and old women. Surface EMG and MMG were recorded from the triceps and biceps brachii, and brachioradialis muscles during isometric elbow extensions in young and old women. The measurements were carried out at an optimal joint angle ( A o), as well as at smaller ( A s = A o − 30°) and larger ( A l = A o + 30°) angles. The normalized to force EMG amplitude (RMS-EMG/ F) was smaller in old women compared to young in all muscles. The RMS-EMG/ F of the triceps brachii muscle was not affected by muscle length while that of the biceps brachii and brachioradialis muscles increased at shortest muscle length in both groups. The normalized to force MMG amplitude (RMS-MMG/ F) was smaller in old than in young in the triceps brachii muscle only. There was an increase in RMS-MMG/ F with triceps brachii and biceps brachii muscle shortening in both groups, and in the brachioradialis muscle – in young only. Compared to young, older women exhibited a bigger force fluctuation during maximum voluntary contraction, but these did not contribute significantly to the RMS-MMG. Skinfold thickness accounted for the RMS-EMG/ F and RMS-MMG/ F differences seen between old and young women in the biceps brachii muscle only. It is concluded that, the EMG and MMG response to muscles length change in agonist and antagonist muscles is generally similar in old and young women but the optimal angle shifts toward a bigger value in older women.

Comparison of the fast Fourier transform and continuous wavelet transform for examining mechanomyographic frequency versus eccentric torque relationships

The purpose of this study was to compare the eccentric torque-related patterns for mechanomyographic (MMG) center frequencies (mean power frequency (MPF), median frequency (MDF), and average instantaneous mean power frequency (AIMPF)) determined by the fast Fourier transform (FFT) and continuous wavelet transform (CWT). Eight adults (mean ± S.D. age = 22.5 ± 2.4 years) performed submaximal to maximal, eccentric isokinetic muscle actions of the biceps brachii on a Cybex 6000 dynamometer. The mean MMG MPF, MDF, and AIMPF values for both the absolute and normalized data from 10 to 100% eccentric peak torque (PT) were highly intercorrelated at r = 0.908–0.985. Linear models provided the best fit for the absolute MMG MPF ( r = 0.873), MDF ( r = 0.831), and AIMPF ( r = 0.924), as well as normalized MMG MPF ( r = 0.869), MDF ( r = 0.816), and AIMPF ( r = 0.920) versus percentage eccentric PT relationships. There were no significant differences ( p > 0.05) among the linear slope coefficients for the MMG MPF, MDF, and AIMPF versus percentage eccentric PT relationships for either the absolute or normalized data. These results suggested that Fourier or wavelet transform procedures can be used to examine the patterns of MMG responses during eccentric muscle actions of the biceps brachii.

Mechanomyographic response to transcranial magnetic stimulation from biceps brachii and during transcutaneous electrical nerve stimulation on extensor carpi radialis

Transcranial magnetic stimulation (TMS) elicits short latency excitatory responses in the target muscles, termed motor evoked potential (MEP). When TMS is delivered during a voluntary contraction, the MEP is followed by a period of silence called silent period (SP). These MEP parameters are in general recordable by electromyography (EMG). Mechanomyography (MMG) on the other hand is the mechanical counterpart of EMG. Thus, this study has been conducted to observe whether the MEP parameters from MMG signals showed similar trait of EMG recordings. Five normal healthy male subjects were included in this study. The subjects were required to perform right biceps brachii muscles contraction at diverse graded of load level at 5, 10, 20, 30, 40, 60, and 100% maximum voluntary contraction (MVC). MEPs by single pulse TMS on left hemisphere were obtained from both EMG electrode and MMG accelerometer at rest and at different levels of predetermined load level. MEP amplitude and area obtained both from EMG and MMG record were increased with the increase of muscle contraction with a maximum of 60% MVC. With increasing the level of contraction there was a shortening of onset latency and decreasing in the length of silent period in both EMG and MMG signals. We also recorded the EMG- and MMG-MEP from the right extensor carpi radialis muscle during transcutaneous electric nerve stimulation in order to observe neural changes in sensory stimulation from both EMG and MMG responses. The EMG-MEP was not visible in electrical artifact whereas it was obvious in MMG responses. In accordance with other study, this study showed that the voluntary contraction of biceps brachii muscle influenced the MEP parameter which are moreover obtainable by MMG even in electrical noise may provide insight for future study.

Muscle tissue oxygenation, pressure, electrical, and mechanical responses during dynamic and static voluntary contractions.

Dynamic muscle contractions have been shown to cause greater energy turnover and fatigue than static contractions performed at a corresponding force level. Therefore, we hypothesized that: (1) electro- (EMG) and mechanomyography (MMG), intramuscular pressure (IMP), and reduction in muscle oxygen tension (rTO(2)) would be larger during dynamic (DYN) than intermittent static (IST) low force contractions; and that (2) oxygen tension would remain lower in the resting periods subsequent to DYN as compared to those following IST. Eight subjects performed elbow flexions with identical time-tension products: (1) DYN as a 20 degrees elbow movement of 2 s concentric and 2 s eccentric followed by a 4 s rest; and (2) IST with a 4 s contraction followed by a 4 s rest. Each session was performed for 1 min at 10 and 20% of the maximal voluntary contraction (MVC). The force, bipolar surface EMG, MMG, IMP, rTO(2) were measured simultaneously from the biceps brachii, and the data presented as the mean values together with the standard error of the means. Comparison of the corresponding time periods showed the EMG(rms) and MMG(rms) values to be larger during DYN than IST (concentric phase: DYN vs IST were 14.2 vs 9.4, and 22.0 vs 15.9%(max)-EMG(rms); eccentric phase: in DYN, the MMG was approximately 1.5 and approximately 2.0-fold IST at 10 and 20%MVC, respectively). In contrast, the IMP of the concentric phase in DYN was lower than in IST (2.3 vs 29.5 and 10.9 vs 42.0 mmHg at 10 and 20%MVC, respectively), and a similar picture was seen for the eccentric phase. However, no differences were seen in rTO(2) in either the contraction or the rest periods. In a prolonged rest period (8 s) after the sessions, DYN but not IST showed rTO(2) above baseline level. In conclusion, rTO(2) in DYN and IST were similar in spite of major differences in the MMG and EMG responses of the muscle during contraction periods. This may relate to the surprisingly lower IMP in DYN than IST.

The Effect of Glycerol on Torque, Electromyography, and Mechanomyography

The purpose of this investigation was to determine the effect of hyperhydration on the electromyographic (EMG) and mechanomyographic (MMG) responses during isometric and isokinetic muscle actions of the biceps brachii. Eight (22.1 +/- 1.8 years, 79.5 +/- 22.8 kg) subjects were tested for maximal isometric, submaximal isometric, and maximal concentric isokinetic muscle strength in either a control (C) or hyperhydrated (H) state induced by glycerol ingestion while the EMG and MMG signals were recorded. Although fluid retention was significantly greater during the H protocol, the analyses indicated no change in torque, EMG amplitude, EMG mean power frequency (MPF), MMG amplitude, or MMG MPF with hyperhydration. These results indicated that glycerol-induced fluid retention does not affect the torque-producing capabilities of a muscle, the impulses (EMG) going to a muscle, or muscular vibrations (MMG). It has been suggested that EMG and MMG can be used as direct electrical/mechanical monitoring, which could be presented to trainers and athletes; however, before determining the utility of these signals, the MMG and EMG responses should be examined under a variety of conditions such as in the present study.