Foam property tests to evaluate the potential for longwall shield dust control.

Tests were conducted to determine properties of four foam agents for their potential use in longwall mining dust control. Foam has been tried in underground mining in the past for dust control and is currently being reconsidered for use in underground coal longwall operations in order to help those operations comply with the Mine Safety and Health Administration's lower coal mine respirable dust standard of 1.5 mg/m3. Foams were generated using two different methods. One method used compressed air and water pressure to generate foam, while the other method used low-pressure air generated by a blower and water pressure using a foam generator developed by the U.S. National Institute for Occupational Safety and Health. Foam property tests, consisting of a foam expansion ratio test and a water drainage test, were conducted to classify foams. Compressed-air-generated foams tended to have low expansion ratios, from 10 to 19, with high water drainage. Blower-air-generated foams had higher foam expansion ratios, from 30 to 60, with lower water drainage. Foams produced within these ranges of expansion ratios are stable and potentially suitable for dust control. The test results eliminated two foam agents for future testing because they had poor expansion ratios. The remaining two foam agents seem to have properties adequate for dust control. These material property tests can be used to classify foams for their potential use in longwall mining dust control.

Open-air sprays for capturing and controlling airborne float coal dust on longwall faces.

Float dust deposits in coal mine return airways pose a risk in the event of a methane ignition. Controlling airborne dust prior to deposition in the return would make current rock dusting practices more effective and reduce the risk of coal-dust-fueled explosions. The goal of this U.S. National Institute for Occupational Safety and Health study is to determine the potential of open-air water sprays to reduce concentrations of airborne float coal dust, smaller than 75 µm in diameter, in longwall face airstreams. This study evaluated unconfined water sprays in a featureless tunnel ventilated at a typical longwall face velocity of 3.6 m/s (700 fpm). Experiments were conducted for two nozzle orientations and two water pressures for hollow cone, full cone, flat fan, air atomizing and hydraulic atomizing spray nozzles. Gravimetric samples show that airborne float dust removal efficiencies averaged 19.6 percent for all sprays under all conditions. The results indicate that the preferred spray nozzle should be operated at high fluid pressures to produce smaller droplets and move more air. These findings agree with past respirable dust control research, providing guidance on spray selection and spray array design in ongoing efforts to control airborne float dust over the entire longwall ventilated opening.

Characterization of airborne float coal dust emitted during continuous mining, longwall mining and belt transport.

Float coal dust is produced by various mining methods, carried by ventilating air and deposited on the floor, roof and ribs of mine airways. If deposited, float dust is re-entrained during a methane explosion. Without sufficient inert rock dust quantities, this float coal dust can propagate an explosion throughout mining entries. Consequently, controlling float coal dust is of critical interest to mining operations. Rock dusting, which is the adding of inert material to airway surfaces, is the main control technique currently used by the coal mining industry to reduce the float coal dust explosion hazard. To assist the industry in reducing this hazard, the Pittsburgh Mining Research Division of the U.S. National Institute for Occupational Safety and Health initiated a project to investigate methods and technologies to reduce float coal dust in underground coal mines through prevention, capture and suppression prior to deposition. Field characterization studies were performed to determine quantitatively the sources, types and amounts of dust produced during various coal mining processes. The operations chosen for study were a continuous miner section, a longwall section and a coal-handling facility. For each of these operations, the primary dust sources were confirmed to be the continuous mining machine, longwall shearer and conveyor belt transfer points, respectively. Respirable and total airborne float dust samples were collected and analyzed for each operation, and the ratio of total airborne float coal dust to respirable dust was calculated. During the continuous mining process, the ratio of total airborne float coal dust to respirable dust ranged from 10.3 to 13.8. The ratios measured on the longwall face were between 18.5 and 21.5. The total airborne float coal dust to respirable dust ratio observed during belt transport ranged between 7.5 and 21.8.

Experimental study on foam coverage on simulated longwall roof.

Testing was conducted to determine the ability of foam to maintain roof coverage in a simulated longwall mining environment. Approximately 27 percent of respirable coal mine dust can be attributed to longwall shield movement, and developing controls for this dust source has been difficult. The application of foam is a possible dust control method for this source. Laboratory testing of two foam agents was conducted to determine the ability of the foam to adhere to a simulated longwall face roof surface. Two different foam generation methods were used: compressed air and blower air. Using a new imaging technology, image processing and analysis utilizing ImageJ software produced quantifiable results of foam roof coverage. For compressed air foam in 3.3 m/s (650 fpm) ventilation, 98 percent of agent A was intact while 95 percent of agent B was intact on the roof at three minutes after application. At 30 minutes after application, 94 percent of agent A was intact while only 20 percent of agent B remained. For blower air in 3.3 m/s (650 fpm) ventilation, the results were dependent upon nozzle type. Three different nozzles were tested. At 30 min after application, 74 to 92 percent of foam agent A remained, while 3 to 50 percent of foam agent B remained. Compressed air foam seems to remain intact for longer durations and is easier to apply than blower air foam. However, more water drained from the foam when using compressed air foam, which demonstrates that blower air foam retains more water at the roof surface. Agent A seemed to be the better performer as far as roof application is concerned. This testing demonstrates that roof application of foam is feasible and is able to withstand a typical face ventilation velocity, establishing this technique's potential for longwall shield dust control.

CFD gas distribution analysis for different continuous-miner scrubber redirection configurations.

The U.S. National Institute for Occupational Safety and Health (NIOSH)'s Pittsburgh Mining Research Division (PMRD) recently developed a series of models using computational fluid dynamics (CFD) to study gas distribution around a continuous mining machine with various fan-powered flooded bed scrubber discharge configurations in an exhaust curtain working face. CFD models utilizing species transport model without reactions in FLUENT were constructed to evaluate the redirection of scrubber discharge toward the mining face rather than behind the return curtain. The study illustrates the gas distribution in the slab (second) cut. The following scenarios are considered in this study: 100 percent of the discharge redirected back toward the face on the off-curtain side; 100 percent of the discharge redirected back toward the face, but divided equally to both sides; and 15 percent of the discharge redirected toward the face on the off-curtain side, with 85 percent directed toward the return curtain. These models are compared against a model with a conventional scrubber discharge where air is directed away from the face into the return. The models were validated against experimental data, proving to accurately predict sulfur hexafluoride (SF6) gas levels at four gas monitoring locations. This study includes a predictive simulation examining a 45° scrubber angle compared with the 23° angle for the 100 percent redirected, equally divided case. This paper describes the validation of the CFD models based on experimental data of the gas distribution results.

Sampling and analysis method for measuring airborne coal dust mass in mixtures with limestone (rock) dust.

Airborne coal dust mass measurements in underground bituminous coal mines can be challenged by the presence of airborne limestone dust, which is an incombustible dust applied to prevent the propagation of dust explosions. To accurately measure the coal portion of this mixed airborne dust, the National Institute for Occupational Safety and Health (NIOSH) developed a sampling and analysis protocol that used a stainless steel cassette adapted with an isokinetic inlet and the low temperature ashing (LTA) analytical method. The Mine Safety and Health Administration (MSHA) routinely utilizes this LTA method to quantify the incombustible content of bulk dust samples collected from the roof, floor, and ribs of mining entries. The use of the stainless steel cassette with isokinetic inlet allowed NIOSH to adopt the LTA method for the analysis of airborne dust samples. Mixtures of known coal and limestone dust masses were prepared in the laboratory, loaded into the stainless steel cassettes, and analyzed to assess the accuracy of this method. Coal dust mass measurements differed from predicted values by an average of 0.5%, 0.2%, and 0.1% for samples containing 20%, 91%, and 95% limestone dust, respectively. The ability of this method to accurately quantify the laboratory samples confirmed the validity of this method and allowed NIOSH to successfully measure the coal fraction of airborne dust samples collected in an underground coal mine.

Influence of continuous mining arrangements on respirable dust exposures.

In underground continuous mining operations, ventilation, water sprays and machine-mounted flooded-bed scrubbers are the primary means of controlling respirable dust exposures at the working face. Changes in mining arrangements - such as face ventilation configuration, orientation of crosscuts mined in relation to the section ventilation and equipment operator positioning - can have impacts on the ability of dust controls to reduce occupational respirable dust exposures. This study reports and analyzes dust concentrations measured by the Pittsburgh Mining Research Division for remote-controlled continuous mining machine operators as well as haulage operators at 10 U.S. underground mines. The results of these respirable dust surveys show that continuous miner exposures varied little with depth of cut but are significantly higher with exhaust ventilation. Haulage operators experienced elevated concentrations with blowing face ventilation. Elevated dust concentrations were observed for both continuous miner operators and haulage operators when working in crosscuts driven into or counter to the section airflow. Individual cuts are highlighted to demonstrate instances of minimal and excessive dust exposures attributable to particular mining configurations. These findings form the basis for recommendations for lowering face worker respirable dust exposures.

Reduced susceptibility to eccentric exercise-induced muscle damage in resistance-trained men is not linked to resistance training-related neural adaptations.

The purpose of this study was to examine the acute effects of maximal concentric vs. eccentric exercise on the isometric strength of the elbow flexor, as well as the biceps brachii muscle electromyographic (EMG) responses in resistance-trained (RT) vs. untrained (UT) men. Thirteen RT men (age: 24 ± 4 years; height: 180.2 ± 7.7 cm; body weight: 92.2 ± 16.9 kg) and twelve UT men (age: 23 ± 4 years; height: 179.2 ± 5.0 cm; body weight: 81.5 ± 8.6 kg) performed six sets of ten maximal concentric isokinetic (CON) or eccentric isokinetic (ECC) elbow flexion exercise in two separate visits. Before and after the exercise interventions, maximal voluntary contractions (MVCs) were performed for testing isometric strength. In addition, bipolar surface EMG signals were detected from the biceps brachii muscle during the strength testing. Both CON and ECC caused isometric strength to decrease, regardless of the training status. However, ECC caused greater isometric strength decline than CON did for the UT group (p = 0.006), but not for the RT group. Both EMG amplitude and mean frequency significantly decreased and increased, respectively, regardless of the training status and exercise intervention. Resistance-trained men are less susceptible to eccentric exercise-induced muscle damage, but this advantage is not likely linked to the chronic resistance training-induced neural adaptations.

Evaluations of bit sleeve and twisted-body bit designs for controlling roof bolter dust.

Drilling into coal mine roof strata to install roof bolts has the potential to release substantial quantities of respirable dust. Due to the proximity of drill holes to the breathing zone of roof bolting personnel, dust escaping the holes and avoiding capture by the dust collection system pose a potential respiratory health risk. Controls are available to complement the typical dry vacuum collection system and minimize harmful exposures during the initial phase of drilling. This paper examines the use of a bit sleeve in combination with a dust-hog-type bit to improve dust extraction during the critical initial phase of drilling. A twisted-body drill bit is also evaluated to determine the quantity of dust liberated in comparison with the dust-hog-type bit. Based on the results of our laboratory tests, the bit sleeve may reduce dust emissions by one-half during the initial phase of drilling before the drill bit is fully enclosed by the drill hole. Because collaring is responsible for the largest dust liberations, overall dust emission can also be substantially reduced. The use of a twisted-body bit has minimal improvement on dust capture compared with the commonly used dust-hog-type bit.

Relationship between innervation zone width and mean muscle fiber conduction velocity during a sustained isometric contraction.

OBJECTIVES: To examine the relationship between the biceps brachii muscle innervation zone (IZ) width and the mean muscle fiber conduction velocity (MFCV) during a sustained isometric contraction. METHODS: Fifteen healthy men performed a sustained isometric elbow flexion exercise at their 60% maximal voluntary contraction (MVC) until they could not maintain the target force. Mean MFCV was estimated through multichannel surface electromyographic recordings from a linear electrode array. Before exercise, IZ width was quantified. Separate non-parametric one-way analyses of variance (ANOVAs) were used to examine whether there was a difference in each mean MFCV variable among groups with different IZ width. In addition, separate bivariate correlations were also performed to examine the relationships between the IZ width and the mean MFCV variables during the fatiguing exercise. RESULTS: There was a significant difference in the percent decline of mean MFCV (%ΔMFCV) among groups with different IZ width (χ(2) (3)=11.571, p=0.009). In addition, there was also a significant positive relationship between the IZ width and the %ΔMFCV (Kendall's tau= 0.807; p<0.001). CONCLUSIONS: We believe that such relationship is likely influenced by both muscle fiber size and the muscle fiber type composition.

CFD analysis on gas distribution for different scrubber redirection configurations in sump cut.

The National Institute for Occupational Safety and Health's Office of Mine Safety and Health Research recently developed a series of models using computational fluid dynamics (CFD) to study the gas distribution around a continuous mining machine with various fan-powered flooded bed scrubber discharge configurations. CFD models using Species Transport Model without reactions in FLUENT were constructed to evaluate the redirection of scrubber discharge toward the mining face rather than behind the return curtain. The following scenarios are considered in this study: 100 percent of the discharge redirected back toward the face on the off-curtain side of the continuous miner; 100 percent of the discharge redirected back toward the face, but divided equally to both sides of the machine; and 15 percent of the discharge redirected toward the face on the off-curtain side of the machine, with 85 percent directed into the return. These models were compared against a model with a conventional scrubber discharge, where air is directed away from the face into the return. The CFD models were calibrated and validated based on experimental data and accurately predicted sulfur hexafluoride (SF6) gas levels at four gas monitoring locations. One additional prediction model was simulated to consider a different scrubber discharge angle for the 100 percent redirected, equally divided case. These models identified relatively high gassy areas around the continuous miner, which may not warrant their use in coal mines with medium to high methane liberation rates. This paper describes the methodology used to develop the CFD models, and the validation of the models based on experimental data.

Influences of dynamic exercise on force steadiness and common drive.

OBJECTIVES: To investigate the influences of dynamic exercise on force steadiness and common drive to motor units. METHODS: Seventeen men (age 24±4 years; height 181.7±5.7 cm; mass 89.6±14.9 kg) performed 6 sets of 10 repetitions of maximal isokinetic concentric (CON) or eccentric exercise (ECC) with their dominant elbow flexors on separate experimental visits. Before and after the interventions, maximal strength testing and submaximal trapezoid isometric contractions were performed. To quantify force steadiness, we calculated the amplitude of force fluctuations in the flat area of the submaximal trapezoid contractions. In addition, surface electromyographic (EMG) signals from the same portion where we calculated the force steadiness were decomposed into individual motor unit action potential trains. The mean firing rate curves of the detected motor units were then cross-correlated with one another to quantify the common drive. RESULTS: Although both interventions induced similar strength losses, the ECC caused greater force fluctuations (p=0.002). In addition, unlike the CON, which did not cause any changes in the common drive, the ECC induced an increased common drive to motor units. CONCLUSIONS: We believe that the increased common drive is an important factor causing greater force fluctuations following the ECC.

Examination of redirected continuous miner scrubber discharge configurations for exhaust face ventilation systems.

The U.S. National Institute for Occupational Safety and Health (NIOSH) Office of Mine Safety and Health Research (OMSHR) has recently studied several redirected scrubber discharge configurations in its full-scale continuous miner gallery for both dust and gas control when using an exhaust face ventilation system. Dust and gas measurements around the continuous mining machine in the laboratory showed that the conventional scrubber discharge directed outby the face with a 12.2-m (40-ft) exhaust curtain setback appeared to be one of the better configurations for controlling dust and gas. Redirecting all the air toward the face equally up both sides of the machine increased the dust and gas concentrations around the machine. When all of the air was redirected toward the face on the off-curtain side of the machine, gas accumulations tended to be reduced at the face, at the expense of increased dust levels in the return and on the curtain side of the mining machine. A 6.1-m (20-ft) exhaust curtain setback without the scrubber operating resulted in the lowest dust levels around the continuous mining machine, but this configuration resulted in some of the highest levels of dust in the return and gas on the off-curtain side of the mining face. Two field studies showed some similarities to the laboratory findings, with elevated dust levels at the rear corners of the continuous miner when all of the scrubber exhaust was redirected toward the face either up the off-tubing side or equally up both sides of the mining machine.

Best practice in the conduct of key nonclinical cardiovascular assessments in drug development: current recommendations from the Safety Pharmacology Society.

A cardiovascular safety pharmacology assessment is routinely conducted prior to first administration of a new chemical entity or biopharmaceutical to man. These assessments are used to inform clinicians of potential effects in those initial clinical studies. They may also indicate more subtle effects having more relevance for longer term patient treatment studies such as a potential effect in a Thorough QT (TQT) study or a small persistent increase in blood pressure. Many pharmaceutical companies use the nonclinical studies for early decision making to avoid the clinical development of any compound likely to have a positive signal in a TQT study. These latter purposes generally require more sensitive assay systems and a confidence in their translation to man. At present it is often unclear whether any given study meets the standard required to convincingly detect these subtle effects. The Safety Pharmacology Society (SPS) brought together a group of over 50 experts to discuss best practices for dog and monkey cardiovascular assessments in safety pharmacology and toxicology studies in order to build overall confidence in the ability of a study to test a given hypothesis. It is clearly impossible to dictate a very specific standard practice for assays which are conducted globally in very different facilities using different equipment. However it was clear that a framework could be described to improve comparison and interpretation. Recommendations can be summarized on the basis of three key criteria: 1) know your study population quantitatively and qualitatively, 2) know how well your current study matches the historical data and 3) support your conclusions on the basis of the specific study's determined ability to detect change.

Linearity and reliability of the mechanomyographic amplitude versus dynamic constant external resistance relationships for the biceps brachii.

The purpose of this study was to examine the linearity and reliability of the mechanomyographic (MMG) amplitude versus concentric and eccentric dynamic constant external resistance (DCER) relationships for the biceps brachii. Nineteen healthy men (mean ± SD age = 22.9 ± 2.5 years) performed submaximal to maximal unilateral DCER muscle actions of the dominant forearm flexors on two occasions separated by at least 48 h. During each muscle action, the surface MMG signal was detected from the biceps brachii with an accelerometer. The coefficients of determination ranged from 0.01 to 0.90 for the concentric muscle actions and 0.14 to 0.88 for the eccentric muscle actions, thus demonstrating a wide range of linearity. The intra-class correlation coefficients and standard errors of measurement for the linear MMG amplitude versus DCER slope coefficients were 0.361 (48.0%) for the concentric muscle actions and 0.512 (35.5%) for the eccentric muscle actions, indicating poor reliability. These findings demonstrated that the MMG amplitude versus concentric and eccentric DCER relationships were not consistently linear or reliable.

Cross-talk among monopolar surface electromyographic signals from the superficial quadriceps femoris muscles.

This study used a within-subjects design. The purpose of this study was to examine cross-talk among monopolar surface electromyographic (EMG) signals from the superficial quadriceps femoris muscles. The "efficiency of electrical activity" technique for assessing muscle function uses monopolar EMG. Thus, knowledge of the potential for cross-talk among the superficial quadriceps femoris muscles when using monopolar recording will be valuable in rehabilitative settings. Fourteen healthy men (mean +/- SD age = 22.0 +/- 3.9 years) volunteered to perform submaximal to maximal isometric muscle actions of the dominant leg extensors in 10% increments from 10% to 100% of the maximum voluntary contraction (MVC). During each muscle action, monopolar surface EMG signals were detected from the superficial quadriceps femoris muscles. Three separate cross-correlations were performed to examine cross-talk among the vastus lateralis and rectus femoris, vastus medialis and rectus femoris, and vastus lateralis and vastus medialis. The peak cross-correlation coefficients ranged from R(x,y) = 0.182-0.944, with the greatest cross-talk occurring between the vastus lateralis and vastus medialis. In addition, the cross-correlation coefficients generally increased with force. These findings showed moderate to large degrees of crosstalk among monopolar surface EMG signals from the superficial quadriceps femoris muscles. Thus, the monopolar EMG signals from these muscles should be interpreted carefully and with the understanding that at least a portion of the signal from each muscle is due to cross-talk.

Linearity and reliability of the EMG amplitude versus dynamic torque relationships for the superficial quadriceps femoris muscles.

PURPOSE: The purpose of the present investigation was to determine the linearity and reliability of the electromyographic (EMG) amplitude versus dynamic torque relationships for the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM). METHODS: Nine healthy men (mean +/- SD age = 25.3 +/- 4.7 years) and eleven healthy women (mean +/- SD age = 22.0 +/- 1.3 years) performed a series of randomly ordered, submaximal to maximal, concentric isokinetic muscle actions of the leg extensors at 30 degrees x s(1) on two occasions separated by at least 48 hours. During each muscle action, surface EMG signals were detected from the VL, RF and VM of the dominant thigh with bipolar surface electrode arrangements. RESULTS: The coefficients of determination for the EMG amplitude versus dynamic torque relationships ranged from r2 = 0.75-0.98 and 0.64-0.99 for the VL, r2 = 0.79-0.99 and 0.60-0.98 for the RFE and r2 = 0.44-0.98 and 0.51-0.98 for the VM for trials 1 and2, respectively. In some cases, the linear EMG amplitude versus torque slope coefficient for trial 1 was significantly different from that for trial 2 for the VL and RF, but not for the VM. The intraclass correlation coefficients for the linear EMG amplitude versus torque coefficients were 0.730 (VL), 0.709 (RF), and 0.888 (VM). CONCLUSION: These results indicated that the EMG amplitude versus dynamic torque relationships for the superficial quadriceps femoris muscles did not demonstrate enough linearity and reliability to be used for examining the contributions of neural versus hypertrophic factors to training-induced strength gains.

Wavelet-based analysis of surface mechanomyographic signals from subjects with differences in myosin heavy chain isoform content.

The purpose of this study was to use a wavelet analysis designed specifically for surface mechanomyographic (MMG) signals to determine if the % myosin heavy chain (MHC) isoform content affected the shape of the MMG frequency spectrum during isometric muscle actions. Five resistance-trained (mean +/- SD age = 23.2 +/-3.7 yrs), five aerobically-trained (mean +/- SD age = 32.6 +/- 5.2 yrs), and five sedentary (mean +/- SD age = 23.4 +/- 4.1 yrs) men performed isometric muscle actions of the dominant leg extensors at 20%, 40%, 60%, 80%, and 100% of the maximum voluntary contraction (MVC). Surface MMG signals were detected from the vastus lateralis during each muscle action and processed with the MMG wavelet analysis. In addition, muscle biopsies were taken from the vastus lateralis and analyzed for % MHC isoform content. The results showed that there were distinct differences among the three groups of subjects for % MHC isoform content. These differences were not manifested, however, in the isometric force-related changes in the total intensity of the MMG signal in each wavelet band. It is possible that factors such as the thicknesses of the subcutaneous adipose tissue and/or iliotibial band reduced the potential influence of differences in % MHC isoform content on the MMG signal.

MMG-EMG cross spectrum and muscle fiber type.

The purpose of this study was to investigate fiber type-related differences in the patterns of responses for mechanomyographic-electromyographic (MMG-EMG) cross spectrum mean power frequency (MPF) in resistance-trained and aerobically-trained subjects during a fatiguing muscle action. Five resistance-trained and five aerobically-trained men performed a 45-s isometric muscle action of the dominant leg extensors at 50% MVC while MMG and EMG signals were recorded simultaneously from the vastus lateralis muscle. In addition, a biopsy was taken to determine the myosin heavy chain (MHC) isoform content of the vastus lateralis. The resistance-trained and aerobically-trained subjects demonstrated similar patterns of responses for MMG-EMG cross spectrum MPF during the sustained muscle action. The vastus lateralis of the resistance-trained subjects demonstrated primarily Type II MHC isoform expression, indicative of fast-twitch muscle fibers, while that of the aerobically-trained subjects was composed mostly of Type I MHC isoform expression, indicative of slow-twitch fibers. Thus, the differences in fiber type characteristics were not manifested in the patterns of responses for MMG-EMG cross spectrum MPF.

An examination of the frequency-specific behavior of the mechanomyographic amplitude versus isometric torque relationship.

The purpose of this study was to examine the patterns of responses for mechanomyographic (MMG) amplitude versus isometric torque in different frequency bands for the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles. Eleven men (mean +/- SD age = 20.1 +/- 1.1 yrs) performed submaximal to maximal isometric step muscle actions of the dominant leg extensors from 10% to 100% of the maximum voluntary contraction (MVC). During each muscle action, three separate surface mechanomyographic (MMG) signals were detected from the VL, RF and VM. Each MMG signal was decomposed into 9 different frequency bands (5-15, 15-25, 25-35, 35-45, 45-55, 55-65, 65-75, 75-85, and 85-95 Hz), and the root-mean-square amplitude of the signal in each frequency band was calculated. The results showed that for the VL and RF muscles, MMG amplitude plateaued from 80-100% MVC in the 15-25 and 25-35 Hz frequency bands. For the VM, however, the plateau in MMG amplitude from 80-100% MVC occurred in the 5-15 and 15-25 Hz bands. These findings indicated that there were both muscle- and frequency-specific discrepancies in the MMG amplitude versus isometric torque relationship that could be due to differences in muscle architecture and/or fiber type composition.