Sharon R. Perry

MMG and EMG responses of the superficial quadriceps femoris muscles.

Eighteen adults performed isometric muscle actions of the leg extensors at 25, 50, 75, and 100% maximal voluntary contraction (%MVC) at leg flexion angles of 25, 50, and 75 degrees. The results indicated that isometric torque production increased as leg flexion angle increased (75 degrees > 50 degrees > 25 degrees). For each muscle tested (rectus femoris, vastus lateralis, and vastus medialis), the EMG amplitude increased up to 100%MVC at each leg flexion angle (25, 50, and 75 degrees). The MMG amplitude for each muscle, however, increased up to 100%MVC at 25 and 50 degrees of leg flexion, but plateaued from 75 to 100%MVC at 75 degrees of leg flexion. We hypothesize that the varied patterns for the MMG amplitude-isometric torque relationships were due to leg flexion angle differences in: (1) muscle stiffness, (2) intramuscular fluid pressure, or (3) motor unit firing frequency.

Mechanomyographic and electromyographic responses during submaximal cycle ergometry.

Abstract The purpose of this study was to examine the mechanomyographic (MMG) and electromyographic (EMG) responses during continuous, cycle ergometer workbouts performed at constant power outputs. Eight adults [mean (SD) age, 21.5 (1.6) years] volunteered to perform an incremental test to exhaustion for the determination of peak power (W˙peak) and four, 15-min (or to exhaustion) rides at constant power outputs of 50%, 65%, 80%, and 95% W˙peak. Piezoelectric crystal contact sensors were placed on the vastus lateralis (VL) and vastus medialis (VM) muscles to record the MMG signals. Bipolar surface electrode arrangements were placed on the VL and VM to record the EMG signals. Five-second samples of the MMG and EMG signals were recorded every 30 s at power outputs of 50%, 65%, and 80% W˙peak, and every 15 s at 95% W˙peak. The amplitudes of the selected portions of the signals were normalized to the first values recorded during the continuous rides, and regression analyses were used to determine whether the slope coefficients for the MMG and EMG versus time relationships were significantly (P < 0.05) different from zero. The results indicate that EMG amplitude increased (range of slope coefficients: 0.03–0.56) during the continuous rides for both muscles at all four power outputs (except the VM at 50% W˙peak), while MMG amplitude increased (slope coefficient at 95% W˙peak for VM=0.19), decreased (range of slope coefficients for VL and VM at 50% and 65% W˙peak=−0.14 to −0.24), or remained unchanged (range of slope coefficients for VL and VM at 80% W˙peak and VL at 95% W˙peak=−0.06 to 0.12) depending on the power output. The patterns of the MMG responses, however, were similar for the VL and VM muscles, except at 95% W˙peak. Fatigue-induced changes in motor-unit recruitment and discharge rates, or muscular compliance may explain the differences between power outputs in the patterns of the MMG amplitude responses.

Effect of mathematical modeling on the estimation of critical power.

PURPOSE The purposes of this study were to re-examine the findings of previous studies by comparing the critical power (CP) estimates from five mathematical models and to determine the time to exhaustion during cycle ergometry at the lowest CP estimate from the five models. METHODS Nine adult males performed a maximal incremental test to determine peak power and five or six randomly ordered trials on a cycle ergometer for the estimation of CP. Two linear, two nonlinear, and one exponential mathematical model were used to estimate CP. The subjects then completed two trials to exhaustion, or 60 min, at their lowest estimate of CP from the five models. RESULTS The nonlinear three-parameter model (Nonlinear-3) produced a mean CP that was significantly (P < 0.05) less than the mean CP values derived from the other four models and was the lowest CP estimate for each subject. Two and three subjects, however, did not complete 60 min of cycling during the first and second trials at CP, respectively. At the end of the trials the subjects who completed 60 min of cycling had a mean heart rate of 92% of their maximum and a mean rating of perceived exertion of 17. CONCLUSION These findings support previous studies that have indicated that in many cases CP overestimates the power output that can be maintained for at least 60 min.

Mean power frequency and amplitude of the mechanomyographic and electromyographic signals during incremental cycle ergometry

The purpose of this investigation was to determine the relationships for mechanomyographic (MMG) amplitude, MMG mean power frequency (MPF), electromyographic (EMG) amplitude, and EMG MPF versus power output during incremental cycle ergometry. Seventeen adults volunteered to perform an incremental test to exhaustion on a cycle ergometer. The test began at 50 W and the power output was increased by 30 W every 2 min until the subject could no longer maintain 70 rev min(-1). The MMG and EMG signals were recorded simultaneously from the vastus lateralis during the final 10 s of each power output and analyzed. MMG amplitude, MMG MPF, EMG amplitude, EMG MPF, and power output were normalized as a percentage of the maximal value from the cycle ergometer test. Polynomial regression analyses indicated that MMG amplitude increased (P<0.05) linearly across power output, but there was no change (P>0.05) in MMG MPF. EMG amplitude and MPF were fit best (P<0.05) with quadratic models. These results demonstrated dissociations among the time and frequency domains of MMG and EMG signals, which may provide information about motor control strategies during incremental cycle ergometry. The patterns for amplitude and frequency of the MMG signal may be useful for examining the relationship between motor-unit recruitment and firing rate during dynamic tasks.

Mechanomyographic and electromyographic responses to eccentric and concentric isokinetic muscle actions of the biceps brachii

The purpose of the present investigation was to examine the effects of forearm angular velocity on the mechanomyographic (MMG) and electromyographic (EMG) responses to eccentric and concentric isokinetic muscle actions. Ten adult male volunteers (mean ± SD age = 23 ± 2 years) performed maximal eccentric and concentric muscle actions of the forearm flexors at 30°, 90°, and 150° s−1. There was no significant (P > 0.05) velocity‐related change in peak torque (PT) for the eccentric muscle actions, but there was a significant (P < 0.05) decrease in PT for the concentric muscle actions. For the eccentric and concentric muscle actions, there was a significant (P < 0.05) velocity‐related increase in MMG amplitude. There was no significant (P < 0.05) change in EMG amplitude across velocity for the eccentric or concentric muscle actions. The results indicated velocity‐related dissociations among the PT, MMG, and EMG responses to maximal eccentric and concentric isokinetic muscle actions.

Gender comparisons of the mechanomyographic responses to maximal concentric and eccentric isokinetic muscle actions.

PURPOSE The purpose of this study was to determine whether there is a gender difference in the velocity-related patterns of mechanomyographic (MMG) responses to maximal isokinetic concentric (CON) and eccentric (ECC) muscle actions. METHODS Adult males (N = 15) and females (N = 16) performed maximal CON and ECC muscle actions of the leg extensors on a calibrated Cybex 6000 dynamometer at velocities of 30, 90, and 150 degrees.s-1. MMG was detected by a piezoelectric crystal contact sensor placed over the vastus lateralis muscle. RESULTS The results indicated that there were decreases in CON peak torque (PT) across velocities, while ECC PT remained constant with increasing velocity for both genders. MMG amplitude increased significantly (P < 0.05) with velocity in both the males and females for CON and ECC muscle actions. There was a gender difference in the velocity-related patterns of MMG responses to maximal isokinetic CON muscle actions; however, there was no gender difference in the pattern of ECC MMG responses. CONCLUSIONS The gender difference in CON MMG responses may be attributed to the greater percent decline in CON PT across velocity for the females than the males. In addition, the males displayed greater CON and ECC MMG amplitudes at all muscle action velocities than the females, possibly because of gender differences in muscle mass and/or thickness of the adipose tissue layer.

Gender, muscle, and velocity comparisons of mechanomyographic and electromyographic responses during isokinetic muscle actions

The purpose of this study was to examine the responses of peak torque (PT), mean power output (MP), mechanomyographic (MMG) and electromyographic (EMG) amplitude and mean power frequency (MPF) of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) in males and females during maximal, concentric isokinetic muscle actions. Subjects performed maximal leg extensions at 60° s−1, 120° s−1, 180° s−1, 240° s−1, 300° s−1, 360° s−1, 420° s−1, and 480° s−1. No gender differences were obser‐ved, but there were muscle‐specific differences for the patterns of MMG MPF, EMG amplitude, and EMG MPF. The MP and MMG amplitude increased to 180–240° s−1, plateaued, and then decreased to 480° s−1. MMG MPF for the VL and VM remained unchanged to 300° s−1, but then increased to 480° s−1. The EMG amplitude for the RF and EMG MPF for the VL decreased across velocity. Overall, these findings indicated that there were muscle‐specific, velocity‐related differences in the associations among motor control strategies (EMG amplitude and MPF) and the mechanical aspects of isokinetic muscular activity (MMG amplitude and MPF).

Mechanomyographic amplitude and mean power output during maximal, concentric, isokinetic muscle actions.

The purpose of this study was to determine the velocity‐related patterns for mechanomyographic (MMG) amplitude, electromyographic (EMG) amplitude, mean power output (MP), and peak torque (PT) of the superficial muscles of the quadriceps femoris (vastus lateralis [VL], rectus femoris [RF], and vastus medialis [VM]) during maximal, concentric, isokinetic leg extensions. Twelve adult women (mean ± SD: 22 ± 3 years of age) performed such leg extensions at velocities of 60°, 120°, 180°, 240°, and 300°/s on a Cybex 6000 dynamometer. PT decreased (P < 0.05) across velocity to 240°/s. MP and MMG amplitude for each muscle (VL, RF, and VM) increased (P < 0.05) with velocity to 240°/s and then plateaued. EMG amplitude increased (P < 0.05) to 240°/s for the VL, remained unchanged across velocity (P > 0.05) for the RF, and increased (P < 0.05) to 300°/s for the VM. The results indicated close similarities between the velocity‐related patterns for MMG amplitude and MP, but dissociations among EMG amplitude, MMG amplitude, and PT. These findings support the recent hypothesis that MMG amplitude is more closely related to MP than PT during maximal, concentric, isokinetic muscle actions and, therefore, may be useful for monitoring training‐induced changes in muscle power.

The effect of leg flexion angle on the mechanomyographic responses to isometric muscle actions

Abstract The purpose of this investigation was to examine the effect of leg flexion angle on the relationship between mechanomyographic (MMG) amplitude and isometric torque production. Adult males (n = 9) performed isometric muscle actions of the leg extensors at 25, 50, 75, and 100 percent maximal voluntary contraction (%MVC) on a calibrated CYBEX 6000 dynamometer at 25, 50, and 75° below full extension. A piezoelectric MMG recording device was placed over the mid-portion of the rectus femoris. At 25° of leg flexion, the MMG amplitude increased to 100%MVC. At 50 and 75° of leg flexion, however, MMG amplitude increased to 75%MVC, and then did not change significantly (P > 0.05) between 75 and 100%MVC. These findings indicate that the MMG amplitude-isometric torque relationship is joint angle specific and may be the result of leg flexion angle differences in: (1) muscle stiffness, or (2) motor unit activation strategies.

MMG AND EMG RESPONSES DURING FATIGUING ISOKINETIC MUSCLE ACTIONS AT DIFFERENT VELOCITIES

The purpose of this study was to determine mechanomyographic (MMG) and electromyographic (EMG) responses of the superficial quadriceps muscles during repeated isokinetic contractions in order to provide information about motor control strategies during such activity, and to assess uniformity in mechanical activity (MMG) between the investigated muscles. Ten adults performed 50 maximal concentric muscle contractions at three randomly selected contraction velocities (60, 180, and 300 degrees.s(-1)) on different days. Surface electrodes and an MMG sensor were placed on the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM). EMG and MMG amplitude and peak torque (PT) were calculated for each contraction, normalized, and averaged across all subjects. The results demonstrated that MMG amplitude more closely tracked the fatigue-induced decline in torque production at each velocity than did EMG amplitude. This indicates that MMG amplitude may be useful for estimating force production during fatiguing dynamic contractions when a direct measure is not available, such as during certain rehabilitative exercises. MMG amplitude responses of the VL, RF, and VM were not uniform for each velocity or across velocities, indicating that it may be possible to detect the individual contribution of each muscle to force production during repeated dynamic contractions. Therefore, MMG amplitude may be clinically useful for detecting abnormal force contributions of individual muscles during dynamic contractions, and determining whether various treatments are successful at correcting such abnormalities.