Surface Electromyography Electrodes Research Articles

Power Output, Mechanomyographic, and Electromyographic Responses to Maximal, Concentric, Isokinetic Muscle Actions in Men and Women

The purpose of this study was to examine the responses of peak torque (PT), mean power output (MP), mechanomyographic (MMG) and electromyographic (EMG) amplitudes, and mean power frequencies (MPFs) of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) in men and women during dynamic muscle actions. Twelve women (mean ± SD age = 22 ± 3 years) and 11 men (22 ± 3 years) performed maximal, concentric, isokinetic leg extensions at velocities of 60, 120, 180, 240, and 300°·1 on a Cybex 6000 dynamometer. Piezoelectric MMG-recording sensors and bipolar surface EMG electrodes were placed over the VL, RF, and VM muscles. No sex-related differences were found among the velocity-related patterns for PT, MP, MMG amplitude, MMG MPF, or EMG MPF. There were, however, sex-related differences in the patterns of EMG amplitude across velocity. The results indicated similar velocity-related patterns of increase of MP and MMG amplitude for all 3 muscles and of EMG amplitude for the VL and VM in the women. Velocity-related decreases (p < 0.05) were found for PT and EMG MPF for the VL. EMG amplitude for all muscles in the men and for the RF in the women as well as EMG MPF for the RF and VM remained unchanged (p > 0.05) across velocity. MMG MPF increased (p ≤ 0.05) only between 240 and 300°·s-1. Overall, these findings suggested that there were sex- and muscle-specific, velocity-related differences in the associations among motor unit activation strategies (EMG amplitude and MPF) and the mechanical aspects of muscular activity (MMG amplitude and MPF). With additional examination and validation, however, MMG may prove useful to practitioners for monitoring training-induced changes in muscle power output.

Development of a Closed Kinetic Chain Power Training Device for the Hip Rotators

Introduction: Golfers with optimal transverse plane rotational capability, particularly through the hip joints are better able to generate effective golf swing power. Unfortunately, a device that enables controlled, progressively increased training resistance to the hip rotator muscles in a manner that functionally simulates the golf swing does not presently exist. The purpose of this single subject, crossover design study was to compare hip rotator muscle electromyographic (EMG) amplitudes and activation sequences during a golf swing, and during a simulated golf swing on a pneumatic resistance closed kinetic chain exercise device designed specifically to train the muscular rotators of the hips. Methods: A 52-year-old nonimpaired, right handed male (180 cm, 81.9 kg) who had trained on the device for six months served as the test subject. Following static stretching of the low back and extremities, the subject performed a standard warm-up of 10–12 progressively more intense practice golf swings with a standard driver. Following this bilateral hip external rotator/abductor (gluteus maximus) and hip adductor/internal rotator muscle groups were instrumented with surface EMG electrodes and in-shoe plantar pressure sensors (for event timing purposes). Norquest (Noraxon, Scottsdale, AZ) EMG and Pedar (Novel, Minneapolis, MN) pressure sensor systems triggered from side-by-side laptop computers were used for both data collection and analysis. Each trial consisted of three complete movements for the given condition with alternating order to control for potential order effects. Although the device can also provide eccentric resistance, only minimal (35–40 psi) and moderate (75–80 psi) concentric resistances were evaluated. Results: Both minimal (MIN) and moderate (MOD) device resistances displayed similar muscle activation duration, timing of peak EMG amplitudes, and muscle activation sequencing (relative to peak left foot plantar force onset) compared to the golf swing for the right and left gluteus ▭ maximus (GM) and hip adductor (HA) muscles (Fig. 1). As the device was set with increasing concentric resistance, progressive and predictable increases in right (17%, 37%) and left (9%, 28%) peak GM (Fig. 2) and right (5%, 33%) and left (25%, 30%) HA (Fig. 3) muscle activation amplitudes were observed.Fig. 1Fig. 2Fig. 3Discussion: The pneumatic resistance closed kinetic chain exercise device provided an effective and safe method of progressively increasing concentric resistance to increase hip rotator power during transverse plane movement. By applying resistance in functionally similar movement patterns and velocities, the hip rotators can be trained to facilitate greater crossover to golf performance. Comparative training effect studies on specific golf performance parameters and with other sport movements that require hip rotator muscle power are being planned.

EFFECTS OF INCREMENTAL LOAD ON THE MECHANICS AND MUSCULAR ACTIVITY OF RISING TO ERECT STANCE

Movement efficiency during activities of daily living is essential for functional success. The current study examined the effects of incremental load on rising to an erect stance from a full kneeling position. PURPOSE: To examine the effects of incremental load on the location of the center of mass of the body, trunk slope, knee angle, and kneel width at foot-down during rising to an erect stance from a full kneeling position. To examine the effects of incremental load on the latency of onse and temporal ratio of the erector spinae (ES) and rectus femoris (RF) during the same rising movement. METHODS: Nine right leg dominant females (mean ± SD, age: 21.89 ± 1.83 y; height: 165.18 ± 5.10 cm; body mass: 62.96 ± 7.82 kg) with a body fat weight of 25% or less (21.62 ± 1.71%) were videotaped rising to an erect stance from a full kneeling position under four incremental load (IL) conditions. The selection of each IL followed a randomized single-blind format. Each IL was based on a selected percentage of lean body weight (LBW) (35%, 40%, 45%, and 50%) and included the body fat weight of each subject. Surface electromyography electrodes were used to examine the muscular activity of the ES (L-3 level), and RF prior to and during the completion of the rising movement. RESULTS: No statistically significant (P < .05) difference existed in the mechanical variables across IL. The latency of onset of the ES was the only electromyographic variable to be significantly (P < .05) different across IL. Post-hoc analysis revealed a statistically significant (P < .05) difference between the 35% LBW IL and the 50% LBW IL. CONCLUSION: These data suggest that the application of an external load does not significantly alter the mechanical or electromyographic patterns presented during rising to an erect stance from a full kneeling position.

THE EFFECTS OF ORAL CONTRACEPTIVES ON ELECTROMYOGRAPHY AND MECHANOMYOGRAPHY DURING ISOTONIC MUSCLE ACTIONS

The purpose of this investigation was to determine whether there are changes in electromyography (EMG) and mechanomyography (MMG) between non-oral contraceptive (NOC) and oral contraceptive (OC) subjects during concentric (CON) and eccentric (ECC) muscle actions. Eighteen healthy, physically active women (Mean ± SEM, 24 ± 1 yrs, 1.64 ± 0.69 m, 60.5 ± 1.6 kg) were recruited and tested six times throughout one complete menstrual cycle. The NOC group (n = 9) were not taking any form of hormonal treatment and all had normal menstrual cycles lasting between 26 and 32 days. The OC group (n = 9) had been taking OC for at least 6 months. Each participant performed one maximal isotonic strength (1-RM) test of the leg extensors. For each of the six testing sessions, each participant performed randomly assigned 3-s submaximal isotonic muscle actions at 20, 40, 60, and 80% of 1-RM. Bipolar surface EMG electrodes were placed mid-thigh over the rectus femoris with a piezoelectric MMG recording device placed between the two electrodes. Four separate three-way (group by day by percent of 1-RM) mixed factorial repeated measures ANOVAs were used to determine differences in normalized isotonic CON EMG, ECC EMG, CON MMG, AND ECC MMG across the menstrual cycle for both the NOC and OC groups. There were no significant three-way or two-way interactions involving group for CON EMG, ECC EMG, CON MMG or ECC MMG across the menstrual cycle. Therefore, there are no differences in electrical or mechanical properties of the rectus femoris between NOC and OC subjects during isotonic muscle actions.

Power Output, Mechanomyographic, and Electromyographic Responses to Maximal, Concentric, Isokinetic Muscle Actions in Men and Women

The purpose of this study was to examine the responses of peak torque (PT), mean power output (MP), mechanomyographic (MMG) and electromyographic (EMG) amplitudes, and mean power frequencies (MPFs) of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) in men and women during dynamic muscle actions. Twelve women (mean +/- SD age = 22 +/- 3 years) and 11 men (22 +/- 3 years) performed maximal, concentric, isokinetic leg extensions at velocities of 60, 120, 180, 240, and 300 degrees x s(-1) on a Cybex 6000 dynamometer. Piezoelectric MMG-recording sensors and bipolar surface EMG electrodes were placed over the VL, RF, and VM muscles. No sex-related differences were found among the velocity-related patterns for PT, MP, MMG amplitude, MMG MPF, or EMG MPF. There were, however, sex-related differences in the patterns of EMG amplitude across velocity. The results indicated similar velocity-related patterns of increase of MP and MMG amplitude for all 3 muscles and of EMG amplitude for the VL and VM in the women. Velocity-related decreases (p <or = 0.05) were found for PT and EMG MPF for the VL. EMG amplitude for all muscles in the men and for the RF in the women as well as EMG MPF for the RF and VM remained unchanged (p > 0.05) across velocity. MMG MPF increased (p < or = 0.05) only between 240 and 300 degrees x s(-1). Overall, these findings suggested that there were sex- and muscle-specific, velocity-related differences in the associations among motor unit activation strategies (EMG amplitude and MPF) and the mechanical aspects of muscular activity (MMG amplitude and MPF). With additional examination and validation, however, MMG may prove useful to practitioners for monitoring training-induced changes in muscle power output.

Back muscle contraction patterns of patients with low back pain before and after rehabilitation treatment: an electromyographic evaluation.

The aims of this study were to conduct a comparative investigation of muscle function between patients with low back pain (LBP) and healthy persons, and to determine whether intensive rehabilitation can change back muscle contraction synergy. Twenty healthy persons and 20 patients with chronic LBP were asked to perform symmetrical and asymmetric tasks. The patients with LBP were tested in the weeks immediately before and after 12 weeks of LBP rehabilitation. Tasks include "carrying" weights up and down and with a 45 degrees left rotation. Eight-channel surface electromyographic electrodes were placed on the surface of paraspinal muscles over the lumbar region. Correlations between the right and left corresponding muscles and between values before and after treatment were determined. Lifting capacity for patients with LBP were also measured before and after treatment. Results from electromyographic profiles showed that the muscle activity strategies varied between healthy persons and patients with LBP. The correlation coefficients for spinal muscles have shown very reproducible intrasubject muscle contraction synergies. Unbalanced electromyographic patterns found in patients with LBP given symmetrical tasks were not affected by rehabilitation treatment.

A PILOT STUDY ON THE EFFECT OF MENSTRUAL CYCLE ON TORQUE, ELECTROMYOGRAPHY, AND MECHANOMYOGRAPHY

The purpose of this pilot investigation was to determine the effect of the menstrual cycle on torque production and amplitudes of electromyography (EMG) and mechanomyography (MMG) during isometric muscle actions of the rectus femoris. Two groups of healthy, active women (24.4 ± 4.6 yrs, 71.45 ± 19.31 kg, 1.67 ± .07 m) were recruited and tested five times through one complete menstrual cycle. The first group (n = 6) were not taking any form of hormonal treatment (NOC) and all had normal menstrual cycles lasting between 26 and 32 days. The second group (n = 5) had been taking oral contraceptive (OC) for at least 6 months. Each participant performed maximal isometric muscle actions (MVC) of the leg extensors on a Cybex II isokinetic dynamometer at 45o of leg flexion followed by randomly assigned sub-maximal isometric muscle actions at 25, 50 and 75% of MVC. The OC group tested on days 1, 5, 10, 15, and 20 of their menstrual cycle. The NOC group tested on days 1, 5, 10, ovulation, and 5 days post ovulation. Ovulation was predicted using basal body temperature and ovulation kits. Bipolar surface EMG electrodes were placed mid-thigh over the rectus femoris with a piezoelectric MMG recording device placed between the two electrodes. Three separate three-way (group × day × % MVC) mixed factorial repeated measures ANOVAs were used to determine differences in EMG amplitude (μV), MMG amplitude (mV), and torque (Nm) across the menstrual cycle for both the NOC and OC groups. There were no significant three-way or two-way interactions involving “group” for EMG amplitude, MMG amplitude, or torque. Therefore, the subjects exhibited the same pattern of responses across the menstrual cycle and at the various levels of MVC.

Clinical utility of surface EMG: report of the therapeutics and technology assessment subcommittee of the American Academy of Neurology.

This report reviews the clinical uses of surface electromyography (SEMG) as a diagnostic tool for neurologic disorders. SEMG is assessed with regard to the evaluation of patients with neuromuscular diseases, low back pain, and disorders of motor control. This broadens the scope of a previous assessment of SEMG in neurologic practice by the American Association of Electrodiagnostic Medicine1 in which its utility was examined with regard to neuromuscular diseases only. Needle electromyographic evaluation (NEMG), in combination with nerve conduction studies, is the gold standard methodology for assessing the neurophysiologic characteristics of neuromuscular diseases. Moreover, fine-wire EMG (FWEMG) often has been used in the evaluation of gait disorders, kinesiologic studies, and research and is also considered a standard. Nevertheless, NEMG and FWEMG are both invasive and painful, and this limits their use when activity from several muscles needs to be monitored simultaneously. SEMG is a technique to measure muscle activity noninvasively using surface electrodes placed on the skin overlying the muscle. SEMG differs from NEMG and FWEMG with respect to technical requirements and electrical properties. Unlike NEMG, SEMG electrodes record from a wide area of muscle territory, have a relatively narrow frequency band (range, 20 to 500 Hz), have low-signal resolution, and are highly susceptible to movement artifact. SEMG electrodes typically are approximately 10 mm in diameter and usually are passive (i.e., they are simple conductive surfaces requiring low skin resistance). They can, however, be active, incorporating preamplifier electronics that lessen the need for low skin resistance and improve the signal-to-noise ratio. SEMG can record both voluntary and involuntary muscle activity in addition to externally stimulated muscle action potentials such as motor evoked potentials after central or peripheral nerve stimulation.2 SEMG has also been used in several non-neurologic settings such as obstetric monitoring and animal research, but these potential …

Short-latency changes in voice F0 and neck surface EMG induced by mechanical perturbations of the larynx during sustained vowel phonation.

Nineteen healthy young adult males with normal voice and speech attempted to sustain the vowel /u/ at a constant pitch (target: 180 Hz) and a constant and comfortable loudness level while receiving a sudden mechanical perturbation to the larynx (thyroid prominence) via a servo-controlled probe. The probe moved toward or away from the larynx in a ramp-and-hold fashion (3.3-mm displacement, 0.7 N force, 20-ms rise time, 250-ms duration) as the subjects attempted to maintain a constant probe-larynx pressure. Eighty stimuli were applied in each direction, one stimulus per phonation. Pairs of surface electromyography (EMG) electrodes were attached to the skin of the anterior neck over laryngeal, infralaryngeal, and supralaryngeal areas. The rectified EMG signals, the voltage analog of the voice fundamental frequency (VAF0), and the voltage analog of the probe displacement were digitized and signal-averaged relative to the onset of the stimulus. Sudden perturbation of the larynx induced an instantaneous decrease or increase in VAF0, depending on the direction of the probe's movement, and a short-latency increase in the EMG (30-35 ms) and VAF0 (55-65 ms). We argue that the instantaneous VAF0 change was related to a mechanical effect, and the short-latency VAF0 and EMG changes to reflexogenic effects-the latter most likely associated with both intrinsic and extrinsic laryngeal sensorimotor mechanisms. Further physiological studies are needed to elucidate the sources of the VAF0 and EMG responses. Once elucidated, the present method may provide a powerful noninvasive tool for studying laryngeal neurophysiology. The theoretical and clinical implications of the present findings are addressed.

Vagal stimulation for reciprocal coupling between glottic and upper esophageal sphincter activities in the canine.

Glottic adduction couples with relaxation of the tonically contracted upper esophageal sphincter (UES) to constitute the end point of pharyngeal swallowing. Together with deglutitive laryngeal elevation, this reciprocal relationship contributes to protecting the lungs from aspiration. Degrees of uncoordination between glottic and upper esophageal sphincters can be seen under diverse circumstances of neurologic damage such as stroke, gastroesophageal reflux, and in the growing elderly population presenting with weaker musculature. We hypothesized that reciprocal coupling between glottic closure and UES relaxation may be artificially reestablished through vagal stimulation if the appropriate neural centers and their leading pathways remain capable of exciting a critical number of motor units. Orderly recruitment of the vagus nerve was produced in three dogs with a circuit superimposing 600-Hz, 3800-0-microA blocking over 10-70-Hz, 0-2300-microA stimulating currents. Amplitudes of motor unit or compound muscle action potentials were recorded from the thyroarytenoideus and cricopharyngeus via surface electromyographic electrodes. Stimulation was accompanied by a drop in UES intraluminal pressure. The reciprocal relationship between the two muscles could be time locked within certain stimulus parameters. We submit that electronic coupling between the glottic and UESs may show promise in preventing aspiration under selected circumstances.

Electromyographic timing analysis of forward and backward cycling

Backward walking to running progressions are becoming a popular, nontraditional component of functional knee rehabilitation programs. The purpose of this electromyographic (EMG) and motion analysis study was to compare the activation duration of the vastus medialis, vastus lateralis, rectus femoris, medial hamstrings, lateral hamstring, tibialis anterior, and gastrocnemius muscles during forward and backward cycling. We hypothesized that the hamstrings would demonstrate greater activation duration during backward cycling. The right lower extremity of 12 healthy subjects (6 male and 6 female) was instrumented with surface EMG electrodes and retroreflective markers to confirm lower extremity kinematic consistency between conditions. Statistical analysis of hip, knee, and ankle kinematics (200 Hz sampling rate) and gender failed to reveal significant differences between conditions (P > 0.05). Quadrant analysis of muscle activation duration with Bonferroni corrections for multiple comparisons revealed that medial and lateral hamstring activation duration was greater during the early recovery phase (quadrant III) of backward cycling than forward cycling (P < 0.00156). Rectus femoris activation duration was greater in the early propulsive phase of backward cycling (quadrant 1) (P < 0.00156) and in the early recovery phase of forward cycling (quadrant III) (P < 0.00156). These findings lend support for the use of backward cycling during the early recovery phase (quadrant III) to achieve a selective hamstring muscle response of relatively decreased patellofemoral stress and anterior cruciate ligament strain.

Intersubject variability and intrasubject reproducibility of the bereitschaftspotential.

We assessed the intersubject variability and intrasubject reproducibility of the bereitschaftspotential (BP). Twenty healthy volunteers performed extensions of their wrist in a self-paced manner every 5-10 seconds. A surface electromyography (EMG) electrode was attached to the wrist extensor group of the dominant hand to record at least 100 wrist movements, and electroencephalography electrodes were placed over the scalp. Trials were performed at baseline, 15 minutes, 4 hours, and 4 weeks. Measures derived from the BP included area 1 (-2000 to -650 msec), area 2 (-650-0 msec), total area (area 1 + area 2), amplitude at -650 msec, amplitude at peak negativity prior to EMG onset, and amplitude at 0 msec (trigger). Our findings revealed different variability/reproducibility depending on the particular BP measure being analyzed. Using intraclass correlation coefficient (ICC) and concordance correlation coefficient (CCC) as measures of intrasubject reproducibility, area 2, amplitude at peak negativity prior to EMG onset, and amplitude at 0 msec produced the best values. We conclude that in studies that attempt to quantify BP changes before and after an intervention in the same group of subjects, the most reproducible BP measures are those pertaining to the late BP component.

Effect of Upper Extremity Strength Training on Puck Speed in Collegiate Ice Hockey Players

203 We demonstrate in collegiate level ice hockey players that a specialized upper extremity strength training program can increase the puck speed of the slap shot and the wrist shot by 10.43±0.35 miles per hour (MPH) and 9.66±0.37 MPH, respectively. This increase is statistically significant when compared to pre-training puck speeds (p≤0.01). Ten collegiate ice hockey players volunteered to participate in this study. The initial phase of the study characterized which muscle groups are involved in the execution of the slap shot and the wrist shot. This was determined using a 16-channel, non-invasive telemetric surface electromyography (EMG) system. Surface EMG electrodes were placed on the wrist extensors (WE) and flexors (WF), biceps (BC), triceps (TC), anterior (AD) and posterior deltoid(PD), trapezius (TP), and lattisimus dorsi (LD), bilaterally. EMG collection was synchronized to a motion analysis system utilizing six high-speed digital video cameras collecting at 240 Hz. Reflective markers were placed on the trunk and both upper extremities of each volunteer, as well as on the hockey stick and puck. Players performed six trials of a slap shot and six trials of a wrist shot from a distance of six meters from a standard hockey goal. All trials took place indoors on a smooth concrete floor from a standing position on roller blades. Only those trials in which the puck entered the goal were counted. Puck speed and point of contact/release were determined from the motion analysis. Following the initial phase, all players participated in a six week upper extremity strength training program designed to enhance the performance of those muscles which are specifically involved in the slap shot and the wrist shot. At the end of the six week period, the players were then retested using the same non-invasive surface EMG and digital motion analysis system. Changes in puck speed for the slap shot and the wrist shot were analyzed for significance (p ≤ 0.05) using a two-way paired Students' t-test. The muscle groups involved in the slap shot at the point of puck contact are on the dominant arm: LD, AD, TC, WE and WF; and on the non-dominant arm: TP, BC, TC, WF. The muscle groups involved in the wrist shot at the point of puck release are on the dominant arm: WE, WF, and TC; and on the non-dominant arm: LD, WE and WF. Given all other player parameters being equal, a 10 MPH increase in puck speed during the execution of the two basic hockey shots should translate into a significant increase in the percentage of successful shots on goal. Our study demonstrates that sport-specific strength training when guided by surface EMG analysis in combination with digital motion analysis can enhance sports performance.

THE RELATIONSHIPS AMONG ELECTROMYOGRAPHY, MECHANOMYOGRAPHY, AND PEAK TORQUE DURING REPEATED MAXIMAL CONCENTRIC ISOKINETIC MUSCLE ACTIONS

365 The purpose of this study was to describe and compare the relationships among electromyography (EMG), mechanomyography (MMG), and peak torque (PT) during repeated maximal concentric isokinetic muscle actions. Nine adult males(age 22-26 years) volunteered to perform 50 maximal isokinetic concentric muscle actions of the leg extensors on a Cybex II. Bipolar surface EMG electrodes were placed over the vastus lateralis muscle with the piezoelectric MMG recording device placed between the EMG electrodes. Coefficient of determination (r2) was used to assess variance shared for EMG and MMG versus PT. One-way ANVOVA was used to examine the differences in percent (%) decline values between EMG, MMG and PT observed during the 50 repetitions. The r2 values for the EMG and MMG amplitudes versus PT values were 0.03 and 0.79, respectively. In addition, one-way ANOVA with Tukey Post Hoc tests indicated significant (p<0.05) differences in% decline values for EMG(-1.9±30.43%) and PT (65.5±6.03%), however% decline values for PT were not significantly (p>0.05) different from MMG (65.3±22.0). The results of this study demonstrated that MMG more accurately reflects torque output during fatiguing isokinetic contractions when compared to EMG.

Electromyographic amplitude and frequency changes in the iliocostalis lumborum and multifidus muscles during a trunk holding test.

Muscle endurance is an important variable to measure in the assessment of back muscle function. This study investigated the electromyographic (EMG) activity and fatigue patterns of iliocostalis lumborum and multifidus muscles during a trunk holding test. Sixteen male subjects (mean age = 24.2 years, SD = 4.2, range = 20.6-31.9) without low back pain or known pathology were recruited in the study. Surface EMG electrodes were used to record the activity of iliocostalis lumborum and mutifidus muscles during a 60-second isometric contraction. To reflect the activity level and fatigue rate of the muscles. EMG amplitude (root mean square [RMS] values) and a frequency variable (median frequency [MF]) were measured. The multifidus muscle displayed a higher level of activity, initial MF, and normalized MF slope than did the iliocostalis lumborum muscle. There was no difference, however, in the normalized RMS slope between the two muscles. The correlations between the normalized MF slope and the RMS slope of the two muscles were nonsignificant. This study shows that monitoring frequency changes of the EMG signals may enable therapists to quantify the fatigue changes of individual muscles during the trunk holding test. The higher fatigue rate shown in the multifidus muscle compared with the iliocostalis lumborum muscle may be due to the higher activity level of the multifidus muscle during te trunk holding contraction. This greater activity of the multifidus muscle during the contraction might be explained by the functional differences between these two muscles.

MECHANOMYOGRAPHIC, ELECTROMYOGRAPHIC, AND PEAK TORQUE RESPONSES TO CONCENTRIC ISOKINETIC MUSCLE ACTIONS OF THE BICEPS BRACHII 1413

The purpose of this investigation was to examine the effects of velocity of muscle action on the electromyographic (EMG) and mechanomyographic (MMG) responses to concentric isokinetic exercise of the biceps brachii. Ten adult males (age=20-27 yrs) performed maximal concentric muscle actions of the forearm flexors at velocities of 30, 90, and 150°·s-1 on a Cybex 6000 isokinetic dynamometer. Bipolar surface EMG electrodes were placed over the biceps brachii muscle of the dominate arm with a piezoelectric MMG recording device placed between the EMG electrodes. One way repeated measures ANOVA's with Tukey post-hoc procedures were used to determine differences across the velocities for peak torque, EMG, and MMG.Table The results of the present study indicated a velocity-related dissociation between the peak torque and MMG responses to concentric isokinetic muscle actions during forearm flexion. This is in agreement with previous findings for the leg extensors (vastus lateralis). The present findings in conjunction with previous findings for the vastus lateralis suggest that the velocity-related increase in MMG during concentric isokinetic muscle actions is independent of muscle architecture (pennate vs. fusiform).

MECHANOMYOGRAPHIC, ELECTROMYOGRAPHIC, AND PEAK TORQUE RESPONSES TO ECCENTRIC ISOKINETIC MUSCLE ACTIONS OF THE BICEPS BRACHII 136

The purpose of this investigation was to examine the effects of velocity of muscle action on the mechanomyographic (MMG) and electromyographic (EMG) responses to eccentric isokinetic exercise. Ten adult males (age=20-27 yrs) performed maximal eccentric muscle actions of the forearm flexors at velocities of 30,90, and 150°·s-1 on a Cybex 6000 isokinetic dynamometer. Bipolar surface EMG electrodes were placed over the biceps brachii muscle with a piezoelectric MMG recording device placed between the EMG electrodes. One-way repeated measures ANOVAs with Tukey post-hoc procedures were used to determine differences across the velocities for peak torque, EMG, and MMG. Table The results of the present investigation indicated velocity-related dissociations among the peak torque, MMG, and EMG responses to eccentric isokinetic muscle actions during forearm flexion. The present investigation in conjunction with previous findings for the vastus lateralis suggest that the velocity-related increase in MMG is independent of muscle architecture(fusiform vs. pennate).

Input-output properties and gain changes in the human corticospinal pathway.

Experiments were done to determine the form of the input-output relation (i.e. stimulus intensity vs response amplitude) of the corticospinal pathway of the first dorsal interosseous and the tibialis anterior, respectively. Our purpose was to determine from these quantitative relations which input-output parameters would be useful measures in studies dealing with motor cortical task dependence. The motor cortex was excited by focal transcranial magnetic stimuli and the evoked motor response were recorded with surface electromyographic electrodes. In some experiments the discharge probability of single motor units in response to magnetic stimuli of increasing intensity was determined from intramuscular recordings. For both muscles the form of the input-output relation was sigmoidal. The steepness of the relation increased, up to 4-7 times the value at rest, with increasing tonic background activity. The threshold decreased, but only slightly, with increasing tonic background activity. The minimum value of the threshold was reached at activation levels of about 10-20% of the maximum tonic effort, whereas the steepness of the relation reached its maximum at higher activation levels, typically about 30-40% of the maximum tonic effort. These observations imply that these two input-output parameters of the corticospinal pathway - one reflecting the bias level (threshold) and the other the gain (slope) - are determined by different neural mechanisms. The plateau level of the sigmoidal input-output relation was not influenced by the background activation level, except that in some subjects (4/9) it could not be reached when no background motor activity was present. This was probably due, for the most part, to limitation of the maximum stimulator output. Additionally, this finding may reflect a change in the intrinsic excitability of the motor cortex in going from rest to activity, or that convergent inputs from different descending and afferent systems are required for maximal activation of motoneuron pools. Thus, the threshold, steepness and plateau level characterize the input-output parameters of the human corticospinal pathway for a given level of motor activity. In contrast to the nonlinear input-output relation of the corticospinal pathway as whole, which includes the motoneuron pool and any spinal interneuronal relays, the discharge probability of all single motor units was a linearly increasing function of the stimulus strength (r> or =0.9, P<0.01). Thus, the sigmoidal input-output relation of the corticospinal pathway, as a whole, is not due to the input-output properties of single motoneurons. The possible neural mechanisms which underlie the shape and parameters of the input-output relation as well as the methodological implications of the results are considered.

Reflex muscle contraction in anterior shoulder instability

Reduced proprioception may contribute to recurrent anterior shoulder instability. Twelve patients with unilateral shoulder instability were investigated for evidence of deficient proprioception with an activated pneumatic cylinder and surface electromyography electrodes; the contralateral normal shoulder was used as a control. The latency between onset of movement and the detection of muscle contraction was used as an index of proprioception. No significant difference in muscle contraction latency was detected between the stable and unstable shoulders, suggesting that there was no significant defect in muscular reflex activity. This study does not support the use of proprioception-enhancing physiotherapy in the treatment of posttraumatic anterior shoulder instability.

Contraction of the abdominal muscles associated with movement of the lower limb.

Activity of the trunk muscles is essential for maintaining stability of the lumbar spine because of the unstable structure of that portion of the spine. A model involving evaluation of the response of the lumbar multifidus and abdominal muscles to leg movement was developed to evaluate this function. To examine this function in healthy persons, 9 male and 6 female subjects (mean age = 20.6 years, SD = 2.3) with no history of low back pain were studied. Fine-wire and surface electromyography electrodes were used to record the activity of selected trunk muscles and the prime movers for hip flexion, abduction, and extension during hip movements in each of those directions. Trunk muscle activity occurring prior to activity of the prime mover of the limb was associated with hip movement in each direction. The transversus abdominis (TrA) muscle was invariably the first muscle that was active. Although reaction time for the TrA and oblique abdominal muscles was consistent across movement directions, reaction time for the rectus abdominis and multifidus muscles varied with the direction of limb movement. Results suggest that the central nervous system deals with stabilization of the spine by contraction of the abdominal and multifidus muscles in anticipation of reactive forces produced by limb movement. The TrA and oblique abdominal muscles appear to contribute to a function not related to the direction of these forces.