Raw EMG Signals Research Articles

NEUROMUSCULAR ACTIVATION AND RPE OF THE QUADRICEPS AT 10% AND 80% MVC

964 The purpose of this study was to examine neuromuscular activation and ratings of perceived exertion (RPE) at 10% and 80% quadriceps MVC in healthy males. 17 college-aged volunteers (mean age = 22.6 years, mean height = 178.9 cms, mean weight = 78.8 kg) were assessed for isometric EMG activity of the vastus medialis (VM) and vastus lateralis (VL) at 10% and 80% MVC, and RPE at 80% MVC. Perceived exertion was measured with a modified category ratio scale(CR-10). 10% and 80% MVC's were performed with the knee at 60 deg of flexion for 5 s. Raw EMG signals were sampled via telemetry (rate = 1000 Hz) and integrated (IEMG, 3 s) for each contraction and muscle (bandpass = 16-500 Hz, CMRR = 130 dB). A one-sample t-test was performed for each variable and 95% confidence intervals (CI) were calculated. The mean and CI for each variable are as follows: 10% MVC VM IEMG (t16 = 5.05, p<0.001,.95 CI = 3.11± 1.3), 80% MVC VM IEMG (t16 = 22.51, p<0.001,.95 CI = 73.2± 6.89), 10% MVC VL IEMG (t16 = 8.10, p<0.001,.95 CI = 9.41± 2.47), 80% MVC VL IEMG (t16 = 39.56, p<0.001,.95 CI = 87.32± 4.68), and 80% MVC RPE (t16 = 11.85, p<0.001,.95 CI = 5.24± 0.93). The results demonstrated that at 10% and 80% MVC, VM activation is lower than torque output. VL activation appears to correspond with torque output at 10% MVC but is higher at 80% MVC. RPE appeared to be underestimated in the quadriceps at 80% MVC. Alterations in vastii muscle recruitment at various intensities may have a significant impact on RPE during isolated muscle contractions.

Effect of work station design on sitting posture in young children.

The purpose of the study was to compare muscular activity levels and sitting posture displayed by 10 children (mean age = 4.7 years) when performing tracing tasks while seated at a traditional work station (level desk top, 5 degrees backward sloping seat) and at an ergonomically designed work station (15 degrees sloping desk top, 15 degrees forward sloping seat). EMG profiles of latissimus dorsi (LD), erector spine (ES), and superior trapezius (ST) were sampled using Medi-trace disposable surface electrodes for 10 min on the non-dominant side. Muscle activity was sampled (1000 Hz) every 2 min for 5000 ms while the subjects performed the tracing tasks at each station. Raw EMG signals of the five trials for each muscle were processed by removing signal offset, full-wave rectification, and integration. The subjects' posture was monitored from a lateral view using a Panasonic VHS video camera while the children were seated at each work station. Neck flexion angle and the angle between the torso and thigh (hip angle) were manually sampled from the video images each 1 min as an indication of the posture adopted by the subjects during the tracing tasks. Use of t-tests for dependent means indicated that there was no significant difference in either mean ES or ST muscle activity as a function of work station design. However, subjects demonstrated significantly less LD activity when seated at the ergonomic work station (mean = 20.9 V ms) compared with the traditional work station (mean = 24.4 V ms, t = -2.88, p = 0.018).(ABSTRACT TRUNCATED AT 250 WORDS)

Net shoulder joint moment and muscular activity during light weight-handling at different displacements and frequencies.

The purpose of this study was to calculate net shoulder (gleno-humeral) joint moments from inverse dynamics and to measure muscular activity from six shoulder muscles (supraspinatus, infraspinatus, middle deltoid, anterior deltoid, trapezius, and pectoralis major) during light weight-handling at two different displacements (horizontal and vertical) and frequencies (40 and 60 cycles/min), to simulate an occupational cervicobrachial working task (light weight displacement). Ten normal adult male subjects were asked to move a known weight, representing 15% of the maximal lifted weight, in both horizontal and vertical conditions at frequencies of 40 cycles/min and 60 cycles/min. Raw EMG signals from six shoulder muscles were recorded and synchronized with the cinematographic data during three trials of 6 s each. The raw EMG signals of each muscle were full wave rectified and filtered at 3 Hz. The linear envelope (LE EMG) signals were normalized by time (% cycle) and by amplitude (% MVC), and for the analysis of variance, the normalized LE EMG signals were integrated (IN LE EMG). The average shoulder angular velocities, joint moments, and moment powers were computed from cinematographical data. No significant differences were observed between both tasks for the supraspinatus, infraspinatus, and pectoralis major IN LE EMG data as well as for integrated normalized shoulder joint moment for the whole cycle of movement. IN LE EMG data from middle deltoid, anterior deltoid, and trapezius muscles were significantly higher (p less than 0.05) when performing the vertical displacement task for the whole cycle of movement. This muscular activity difference between vertical and horizontal tasks indicated that the vertical displacement conditions induced higher muscular loads on the shoulder than the horizontal weight displacement conditions, although the vertical displacements were approximately 15% longer than the horizontal displacements. The non-significant difference of IN LE EMG between frequencies obtained for all muscles indicated that neither frequencies induced more muscular activity.

Dynamic Muscle Modeling via Spectral Electromyography

The current method of using processed EMG has certain limitations when one attempts to study the muscle behavior during continuous motions. In addition, since it ignores several useful information in the raw EMG signal, it was felt that these lost information may be the key to better understanding of the muscle behavior. Studies have shown that spectral Electromyography retains such useful information and have speculated that spectral EMG might provide better knowledge of the muscle activity. This study shows that the spectral EMG is sensitive to the changes in external torque and the joint velocity but not to the changes in the sampling area. The effect of performing submaximal tasks during dynamic conditions on the muscle effort is also explained by using an agonistic-antagonistic muscle model based on spectral EMG.

A computer-based system for measuring the masseteric silent period.

Measurement of the masseter muscle's silent period may become an important tool in the diagnosis and prognosis of dysfunction of the stomatognathic system. It is therefore important that a standardized method be used to measure this phenomenon. This article describes a system in which a two-channel visual biofeedback electromyograph is used so that the subject can exert the same force each time the silent period is elicited by the clinician's tapping on the subject's chin with a reflex hammer. Raw EMG signals are recorded from both masseter muscles. The signals are then rectified and fed into a computer that is programmed to detect periods in which the EMG activity is lower than the activity due to clenching. The signals are sampled every 0.4 msec, and they are then expressed graphically and in numerical values.