Superficial Quadriceps Muscles Research Articles

MMG AND EMG RESPONSES DURING 25 MAXIMAL, ECCENTRIC, ISOKINETIC MUSCLE ACTIONS

PURPOSE The purpose of this investigation was to examine mechanomyographic (MMG) and electromyographic (EMG) amplitude responses of the superficial quadriceps femoris muscles during 25 maximal, eccentric, isokinetic muscle actions of the dominant leg. METHODS Seven healthy, adult females (age 22.1 ± 2.4 y) volunteered to perform 25 eccentric muscle actions at 120°s−1, using a calibrated Cybex 6000 dynamometer. Bipolar surface electrode arrangements were placed on the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM). An MMG sensor was placed between the EMG electrodes on each muscle. The EMG and MMG amplitude values (root mean square), as well as peak torque (PT) were calculated for the 25 muscle actions, normalized to each respective maximal value, then averaged across all subjects. RESULTS Polynomial regression analyses indicated that PT demonstrated a cubic relationship (p < 0.05) across the 25 repetitions. Normalized EMG amplitude demonstrated a linear (p < 0.05) increase for the VL, a quadratic (p < 0.05) relationship for the RF, and no change (p > 0.05) for the VM across the 25 repetitions. Normalized MMG amplitude demonstrated a linear (p < 0.05) decrease for the VL and VM, and a cubic (p < 0.05) relationship for the RF across repetitions. There was no difference (p > 0.05) in slope values between the VL and VM for the normalized MMG amplitude versus repetition number relationship. CONCLUSION The differences found between the EMG amplitude and MMG amplitude of the VL, RF, and VM indicate dissociation between the two signals during repetitive, dynamic activity. The findings may also indicate that analysis of the EMG and MMG signals is useful for detecting the unique contribution of each muscle to torque production during such activity, since the responses differed between the VL, VM, and RF. For example, the MMG amplitude of the RF may have more influence on torque production in the present study, as evidenced by the similar pattern of its MMG amplitude response and PT over the 25 repetitions.

MMG and EMG responses during fatiguing isokinetic muscle contractions 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.

MECHANOMYOGRAPHIC AND ELECTROMYOGRAPHIC RESPONSES OF THE SUPERFICIAL QUADRICEP FEMORIS MUSCLES DURING FATIGUING, CONCENTRIC, ISOKINETIC MUSCLE ACTIONS

The purpose of this investigation was to examine mechanomyographic (MMG) and electromyographic (EMG) responses of the superficial quadricep muscles during fatiguing isokinetic muscle actions of the dominant leg extensors. Ten adults (age 21 ± 3 years) volunteered to perform 50 consecutive, maximal concentric muscle actions using a calibrated Cybex 6000 dynamometer at a contraction velocity of 180°s−1. Bipolar surface electrode arrangements were placed over the longitudinal axes of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM). An MMG sensor was placed between the EMG electrodes on each muscle. The EMG and MMG amplitude values (root mean square, rms) were calculated for the muscle action producing the highest torque and every five muscle actions beginning with the fifth and ending with the fiftieth. The MMG and EMG amplitude values, and torque were normalized to each respective maximal value then averaged across all subjects. Polynomial regression analyses indicated that torque decreased (p < 0.05) quadratically across the 50 muscle actions, while MMG amplitude decreased linearly for the VL and RF, but quadratically for the VM. EMG amplitude decreased linearly for the VL and VM, and remained unchanged for the RF. These findings indicated that there were differences between the superficial quadriceps muscles in MMG and EMG responses to fatiguing, dynamic muscle actions.

Activation linearity and parallelism of the superficial quadriceps across the isometric intensity spectrum.

The purpose of this study was to assess neuromuscular activation of the three superficial portions of the quadriceps femoris muscles during linearly increasing isometric contraction intensities. Thirty healthy volunteers were assessed for isometric electromyographic (EMG) activity of the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) muscles with the knee at 60 degrees of flexion. For 5 s, subjects performed isometric contractions equivalent to 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90% of the average of three maximal voluntary contractions (MVC), in random order. Full-wave rectified and integrated EMG signals over the middle 3 s of each contraction were expressed as a percentage of the activity recorded during the three averaged MVCs. One sample t-tests and 95% confidence intervals were calculated at each relative torque level. A two-factor analysis of variance (muscle by intensity) with repeated measures was performed to evaluate parallel activation across the intensity levels. Activation linearity was assessed via regression analysis for each muscle. VM activation was shown to be significantly lower than expected at 20-70% MVC. VL and RF activations were significantly higher than expected at 10% MVC, and RF EMG was less than expected at 40-70% MVC. EMG of VM was shown to increase significantly more than VL and RF from 80% to 90% MVC. Significant linear and quadratic relations were also demonstrated for all three muscles. Parallel activation of the superficial quadriceps muscles occurred from low to moderate intensities, whereas convergence was noted at near maximal intensities.

Quadriceps EMG/force relationship in knee extension and leg press.

This study compared the relationship between surface electromyographic (EMG) activity and isometric force of m. quadriceps femoris (QF) in the single-joint knee extension (KE) and the multi-joint leg press (LP) exercises. Nine healthy men performed unilateral actions at a knee angle of 90 degrees at 20, 40, 60, 80, and 100% of maximal voluntary contraction (MVC). EMG was measured from m. vastus lateralis (VL), m. vastus medialis (VM), m. rectus femoris (RF), and m. biceps femoris (BF). There were no differences in maximum EMG activity of individual muscles between KE and LP. The QF EMG/force relationship was nonlinear in each exercise modality. VL showed no deviation from linearity in neither exercise, whereas VM and RF did. BF activity increased linearly with increased loads. The EMG/force relationship of all quadricep muscles studied appears to be similar in isometric multi-joint LP and single-joint KE actions at a knee angle of 90 degrees. This would indicate the strategy of reciprocal force increment among muscles involved is comparable in the two models. Furthermore, these data suggest a nonuniform recruitment pattern among the three superficial QF muscles and surface EMG recordings from VL to be most reliable in predicting force output.

PARALLEL QUADRICEPS ACTIVATION AND LINEARITY ACROSS THE ISOMETRIC INTENSITY SPECTRUM.

1036 The purpose of this study was to assess linear and parallel activation of the 3 superficial heads of the quadriceps femoris muscles during sub-maximal isometric contractions. 30 healthy, volunteers were assessed for isometric EMG activity of the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) muscles with the knee at 60 deg of flexion. Subjects performed 5 s isometric contractions equivalent to 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90% of the average of three maximal voluntary contractions (MVC), in a random order. Full-wave rectified and integrated EMG signals over the middle 3 s of each contraction were expressed as a percentage of the activity recorded during the averaged MVC's. One sample t-tests and 95% confidence intervals were calculated at each relative torque level. A 2 factor ANOVA (muscle by intensity) with repeated measures was performed to evaluate parallel activation across the intensity levels. Activation linearity was assessed via regression analysis for each muscle. VM activation was shown to be significantly lower than the expected %MVC at 20% to 70%. VL and RF activation were significantly higher than expected at 10% MVC, and RF EMG was less than expected at 40% to 70% MVC. VM EMG was shown to increase significantly more than the VL and RF from 80% MVC to 90% MVC. Significant linear and quadratic relations were also demonstrated for all 3 muscles. Parallel activation of the superficial quadriceps muscles was observed from low to moderate intensities, while convergence was noted at near maximal intensities.

The Effects of Training History and Muscle Fatigue on Load Sharing in a Multiple Muscle System

The effects of exercise training history and localized muscle fatigue on the load sharing patterns in a multiple muscle system were investigated. Six male and six female subjects of various training backgrounds performed fatiguing isokinetic knee extension exercises of quick onset and slow onset fatigue. Electromyographic data collected from the 4 superficial quadriceps muscles as well as the hamstring muscles was fed into an EMG-based model of the knee joint. The relative torque contribution of each muscle as predicted by the model was uniquely different for each of the 5 quadricep muscles modeled. The load sharing patterns were effected by the training group among other factors but they were not significantly effected by the interaction of training group and the onset of fatigue.

Effect of Foot Position on the Electromyographical Activity of the Superficial Quadriceps Muscles During the Parallel Squat and Knee Extension

Effect of Foot Position on the Electromyographical Activity of the Superficial Quadriceps Muscles During the Parallel Squat and Knee Extension

Effect of Foot Position on the Electromyographical Activity of the Superficial Quadriceps Muscles During the Parallel Squat and Knee Extension

Effect of Foot Position on the Electromyographical Activity of the Superficial Quadriceps Muscles During the Parallel Squat and Knee Extension

Effect of electrical stimulation current frequencies on isometric knee extension torque.

The purpose of this study was to compare the isometric knee extension torques of male and female subjects during maximal voluntary contractions (MVCs), electrical stimulation only, and electrical stimulation superimposed onto MVCs at electrical stimulation current frequencies of 20, 50, and 100 Hz. An asymmetrical, bidirectional, nonionizing waveform of 1-msec pulse duration was delivered through the femoral nerve and the superficial quadriceps femoris muscles at maximally tolerated intensity for each subject. The male subjects (n = 20) demonstrated significantly greater absolute torques under all contraction conditions than did the female subjects (n = 20) (p less than .01); when the torques were expressed as a percentage of each subject's MVC torque, however, no significant differences were observed between the sexes. Overall, the superimposed contractions at 50 and 100 Hz and the MVCs had similar torque values, all being significantly greater than the torque values produced by electrical stimulation only at frequencies of 20, 50, and 100 Hz and by the superimposed contractions at 20 Hz. Superimposing electrical stimulation onto MVCs did not result in greater torques than those produced by the MVCs alone. The three most effective contraction conditions, in terms of subject comfort (minimal discomfort) and increased torque, were the superimposed contractions at 50 and 100 Hz and MVCs alone, all of which involved a voluntary component.

Electromyographic assessment of quadriceps muscle group during knee extension with weighted boot

An electromyographic study was conducted using three superficial quadriceps muscles in a knee extension progressive resistance exercise from 90 degrees to 180 degrees with a weighted boot. Continuous recordings were taken on five females and five males in the preexercise position with the knee at 90 degrees, during the exercise, and in the post-exercise position. It was found that the greatest muscle action potentials were produced by the rectus femoris and that the vastus lateralis and vastus medialis exhibited similar action potentials throughout the exercise. All subjects demonstrated increased muscle action potentials within the exercise bout as the gravitational torque increased and between exercise bouts with additional weight increments. No amplitude in muscle action potentials were recorded from the muscles during the pre-exercise and post-exercise positions in which the leg was hanging freely with suspension weights up to 24.13 kilograms attached. This finding suggested viscoclastic connective tissues were supporting the downward gravitational force with the knee at 90 degrees.