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PubMed1985

Effects of applied vibration on triphasic electromyographic patterns in neurologically ballistic head movements.

Vibration of agonist or antagonist muscle tendon produced changes in the triphasic electromyographic pattern of neck muscles; EMG signals were rectified, averaged, and also integrated by planimetry. The triphasic EMG envelopes obtained during fast horizontal head rotation showed unmodified early agonist pulse, the action pulse (PA), under all conditions; increased antagonist pulse, the braking pulse (PB), only with antagonist muscle vibration; and increase of late agonist pulse, the clamping pulse (PC), only with agonist muscle vibration. Vibration experiments can be considered as a model for studying interactions between central and peripheral effects on control of normal movements.

Electromyography↗
PubMed1992

Application and validation of a three-dimensional mathematical model of the human masticatory system in vivo.

A previously described three-dimensional mathematical model of the human masticatory system, predicting maximum possible bite forces in all directions and the recruitment patterns of the masticatory muscles necessary to generate these forces, was validated in in vivo experiments. The morphological input parameters to the model for individual subjects were collected using MRI scanning of the jaw system. Experimental measurements included recording of maximum voluntary bite force (magnitude and direction) and surface EMG from the temporalis and masseter muscles. For bite forces with an angle of 0, 10 and 20 degrees relative to the normal to the occlusal plane the predicted maximum possible bite forces were between 0.9 and 1.2 times the measured ones and the average ratio of measured to predicted maximum bite force was close to unity. The average measured and predicted muscle recruitment patterns showed no striking differences. Nevertheless, some systematic differences, dependent on the bite force direction, were found between the predicted and the measured maximum possible bite forces. In a second series of simulations the influence of the direction of the joint reaction forces on these errors was studied. The results suggest that they were caused primarily by an improper determination of the joint force directions.

Adult↗
PubMed1993

Self-generated rapid taps directed to the opposite forearm in man: anticipatory reduction in the muscle activity of the target arm.

A brief hammer tap applied passively (by the experimenter) to the forearm elicits a short-latency reflex response in the forearm flexors and extensors. When the same tap is performed actively (by the subject) using the opposite forearm, the reflex response is preceded by a short-lasting anticipatory reduction in the muscle activity appearing around the impact. This anticipatory reduction is interpreted as an alternative mode of feedforward motor control associated with damping of kinetic impulses generated within the bimanual system.

Electromyography↗
PubMed1995

Kinesthetic reference for human orthograde posture.

Humans with occluded vision were subjected to superslow tilts of the supporting platform, producing the inclination of the subject's body in the sagittal plane, but subthreshold for the most vestibular and proprioceptive phasic reactions. Two types of perturbation were used: sinusoidal tilts (frequency 0.007 Hz, amplitude 1.5 degrees) and ramps (amplitude 1.0 and 0.25 degrees, angular velocity 0.04 degrees/s). During slow sinusoidal tilts of the platform, the ankle angle and body position undergo periodical changes, but these changes have significant phase lead relative to the platform movement: 119 +/- 26 for ankle angle and 55 +/- 19 degrees for body sway. Gains were about 0.9 for both parameters. Large phase shift (tens of seconds) indicated a long delay in compensation of body inclination by ankle joint. The ramp tilt produced an initial body deviation followed by a slow (seconds or tens of seconds) approach of body position to a new steady level after the termination of ramp. Large slow body movements were superimposed with small irregular oscillations (about 10% of the amplitude of large displacements) of higher frequency. These oscillations resembled normal stabilograms on a stationary support. Thus, the usual process of stabilization of body gravity center was continued, though not around a fixed set-point but relative to a slowly changing position. Data obtained support the hypothesis that, besides operative control assigned to compensate deviations from a reference position, the system of postural control includes at least one additional level, which elaborates this reference using information about mutual position of body links, muscular torques and interaction with the support on the basis of criteria taking into account the energy cost of standing and demands for stability and security.

Adult↗
PubMed2006

Effects of lumbar stabilization using a pressure biofeedback unit on muscle activity and lateral pelvic tilt during hip abduction in sidelying.

OBJECTIVE: To assess the effects of lumbar spine stabilization using a pressure biofeedback unit on the electromyographic activity and angle of lateral pelvic tilt during hip abduction in a sidelying position. DESIGN: Comparative, repeated-measures study. SETTING: University research laboratory. PARTICIPANTS: Eighteen able-bodied volunteers (9 men, 9 women) with no history of pathology. INTERVENTION: Subjects were instructed to perform hip abduction in a sidelying position in both the preferred hip abduction (PHA) and hip abduction with lumbar stabilization (HALS). A pressure biofeedback unit was used for lumbar stabilization. MAIN OUTCOME MEASURES: Surface electromyography was recorded from the quadratus lumborum, gluteus medius, internal oblique, external oblique, rectus abdominis, and multifidus muscles. Kinematic data for lateral pelvic tilt angle were measured using a motion analysis system. Dependent variables were examined with 2 (PHA vs HALS) x 2 (men vs women) analysis of variance. RESULTS: Significantly decreased electromyographic activity in the quadratus lumborum (PHA, 60.39% +/- 15.62% of maximum voluntary isometric contraction [MVIC]; HALS, 27.90% +/- 13.03% of MVIC) and significantly increased electromyographic activity in the gluteus medius (PHA, 25.03% +/- 10.25% of MVIC; HALS, 46.06% +/- 21.20% of MVIC) and internal oblique (PHA, 24.25% +/- 18.10% of MVIC; HALS, 44.22% +/- 20.89% of MVIC) were found when the lumbar spine was stabilized. Lateral pelvic tilt angle (PHA, 13.86 degrees +/- 4.66 degrees; HALS, 5.55 degrees +/- 4.16 degrees) was decreased significantly when the lumbar spine was stabilized. In women the electromyographic activity (percentage of MVIC) in gluteus medius, external oblique, and rectus abdominis was significantly higher than that observed in men. CONCLUSIONS: With lumbar stabilization, the gluteus medius and internal oblique activity was increased significantly, and the quadratus lumborum activity was decreased significantly, causing reduced lateral pelvic tilt in a sidelying position. These results suggest that hip abduction with lumbar stabilization is useful in excluding substitution by the quadratus lumborum.

Adult↗
PubMed2005

Activity of inferior head of human lateral pterygoid muscle during standardized lateral jaw movements.

OBJECTIVE: (a) To describe the changes in electromyographic (EMG) activity from selected jaw muscles during a standardized lateral jaw movement with the teeth together, and (b) to investigate the effects on jaw muscle activity of changes in both the rate of lateral jaw movement and the relative magnitude of jaw-closing force. DESIGN: In 16 healthy volunteers, recordings were made using a jaw-tracking system, of mid-incisor point (MIPT) movements, as well as EMG activity from the contralateral inferior head of the lateral pterygoid muscle (IHLP), and bilateral anterior and posterior temporalis, masseter and submandibular muscles, during lateral jaw movement tasks at two speeds and two closing force levels with the teeth together. RESULTS: The IHLP was the only muscle to show a consistent increase in activity in association with the outgoing phase of the task and a decrease during the return phase. Under high closing force at slow speed, the EMG activities of the IHLP and bilateral anterior temporalis and masseter muscles were significantly (p < 0.05) higher than those under a low closing force, while there was no significant change (p > 0.05) in bilateral posterior temporalis and submandibular muscles. The change from slow to fast lateral movement at low force did not significantly (p > 0.05) alter the mean activity except for the IHLP (increase in activity) and the contralateral anterior temporalis (decrease in activity). CONCLUSIONS: The data suggest that the IHLP is one of the principal jaw muscles involved in a lateral jaw movement with the teeth together while the other jaw muscles may play a contributory or facilitatory role.

Adolescent↗
PubMed2006

Heterogeneous activation of the medial pterygoid muscle during simulated clenching.

The aim of this study was to investigate whether the medial pterygoid muscle shows differential activation under experimental conditions simulating force generation during jaw clenching. To answer this question, the electromyographic activity of the right medial pterygoid was recorded with two intramuscular electrodes placed in an anterior and posterior muscle region, respectively. Intraoral force transfer and force measurement were achieved by a central bearing pin device equipped with strain gauges. The activity distribution in the muscle was recorded in a central mandibular position during generation of eight different force vectors at a constant amount of force (F=150 N). The investigated muscle regions showed different amounts of EMG activity. The relative intensity of the activation in the two regions changed depending on the task. In other words, the muscle regions demonstrated heterogeneous changes of the EMG pattern for various motor tasks. The results indicate a heterogeneous activation of the medial pterygoid muscle under test conditions simulating force generation during clenching. This muscle behaviour might offer an explanatory model for the therapeutic effects of oral splints.

Adult↗
PubMed2005

Postural uncertainty leads to dynamic control of cutaneous reflexes from the foot during human walking.

Cutaneous reflexes evoked by stimulation of nerves innervating the foot are modulated in a phase-dependent manner during locomotion. The pattern of modulation of these reflexes has been suggested to indicate a functional role of cutaneous reflexes in assisting to maintain stability during walking. We hypothesized that if cutaneous reflexes assist in maintaining stability during gait, then these reflexes should be modulated in a context-dependent manner when subjects are asked to walk in an environment in which stability is challenged. To do this, we asked subjects to walk on a treadmill under five conditions: (1) normally, (2) with the arms crossed, (3) while receiving unpredictable anterior-posterior (AP) perturbations, (4) with the arms crossed while receiving unpredictable AP perturbations, and (5) with the hands holding onto fixed handles. Cutaneous reflexes arising from electrical stimulation of the superficial peroneal (SP; relevant to stumbling) or distal tibial (TIB; relevant to ground contact sensation) nerves were recorded bilaterally, at four points in the step cycle. Reflexes evoked with SP nerve stimulation showed marked facilitation during the most unstable walking condition in 4 of the 7 muscles tested. SP nerve-evoked reflexes in the muscles of the contralateral leg also showed suppression during the most stable walking condition. Reflexes evoked with TIB nerve stimulation were less affected by changes in the walking task. We argue that the specific adaptation of cutaneous reflexes observed with SP nerve stimulation supports the hypothesis that cutaneous reflexes from the foot contribute to the maintenance of stability during walking.

Adult↗
PubMed2005

Maintenance of upright standing posture during trunk rotation elicited by rapid and asymmetrical movements of the arms.

Nine healthy subjects standing upright, initiated small, medium and large (S, M and L conditions, respectively) forward movements of their right (Rt) arm together with backward movements of their left (Lt) arm. They also performed medium-size movements while holding a 3 kg dumbbell in each hand (D condition). Movements started with the arm hanging alongside the body and ended when the shoulder reached a desired orientation. The arm and trunk movements were videotaped and recorded by accelerometers taped to the wrists, shoulders, and hips bilaterally. The torque around the vertical axis was measured using a force-plate on which the subjects stood. EMGs were recorded with surface electrodes bilaterally from the shoulder, trunk, and thigh muscles. Trajectories of the center of foot pressure were measured in additional experiments. In association with arm movements, there was a small counterclockwise (ccw: the Rt shoulder forward and the Lt backward) rotation of the trunk, followed by large alternate rotations of the trunk, first clockwise (cw) and subsequently ccw. The intervals from the hand acceleration to the shoulder and hip accelerations were, respectively, 0+/-15 ms (mean and S.D. for all subjects) and -17+/-15 ms. The force-plate showed initial cw and later ccw torques 63+/-41 ms after hand acceleration. The EMGs of the Rt hamstrings (Ham) and Lt rectus femoris (RFem) were followed by those of the Lt Ham and Rt RFem which, respectively preceded the alternate trunk rotations. The integrated EMGs and torques increased with increasing amplitude of arm movement and load. The integrated torques increased in the order of S, M, L, and D conditions. The integrated EMGs of the thigh muscles correlated with the integrated torques (medians: r=0.880, 0.696, 0.785, and 0.688, respectively, in the Rt Ham, Lt Ham, Rt RFem, and Lt RFem). The trajectories of the center of foot pressure showed variations, initially toward the Rt side and then the Lt side which, respectively coincided with the initial and later phases of the trunk rotations and the muscle activation. The trunk muscles were generally coactivated between the Rt and Lt muscles, and the integrated EMGs increased with increasing the integrated torques. Our results showed that alternate rotations of the upper trunk, produced by rapid arm movements, were transmitted to the hip in part due to cocontraction of trunk muscles, and each pair of hip joint muscles contributed to the maintenance of the standing posture by stabilizing the hip joints against alternating trunk rotations.

Adaptation, Physiological↗
PubMed2004

Mechanics and control of the flat versus normal foot during the stance phase of walking.

OBJECTIVE: To compare walking stance phase rearfoot and forefoot motion, ankle joint moments and extrinsic foot muscle EMG profiles between normal and pes planus feet. DESIGN: A cross-sectional comparative study. BACKGROUND: Musculoskeletal conditions are often attributed to pes planus, in which motion is assumed to be excessive and the muscle control inadequate. However, many of the speculated differences in mechanics and control between the normal and the pes planus foot have not been quantified. METHODS: Kinematic and kinetic data were obtained from video recordings of skin surface markers and a force plate, and EMG was recorded with surface electrodes. Analysis of variance was carried out to compare the group profiles. RESULTS: In the pes planus group: the forefoot was less adducted (P < .05) at toe-off, and total transverse plane range of motion, at 8 degrees versus 10 degrees, was less (P < .01); the peak plantarflexor ankle moment at push-off was greater (P < .05); the invertor moment was greater at foot flat (P < .05); for the EMG profiles, activity early in stance, relative to the mean stance phase activity was higher (P < .01) in tibialis anterior and lower (P < .05) in the peronei, soleus and medial and lateral gastrocnemius. CONCLUSIONS: Despite reaching statistical significance, the group differences were small for the task of laboratory walking at a natural pace. The main implications of the differences were for restraint of motion. The expectations of excessive motion and muscle effort in the pes planus group were therefore not substantiated. RELEVANCE: Symptomatic pes planus subjects did not reveal the expected biomechanical differences from normal subjects. The underlying causes of symptoms were not identifiable.

Adaptation, Physiological↗
PubMed2005

Proprioceptive coordination of movement sequences in humans.

OBJECTIVE: To estimate the processing time and neuromuscular delay required to extract and process sensory information from the ankle in order to coordinate an upper extremity movement sequence. METHODS: Nineteen able-bodied subjects were tested on their ability to perform a motor task that involved extension of their left index finger when their left ankle was passively plantar flexed at random velocities through a predetermined target angle. RESULTS: We found that the able-bodied subjects were able to adjust their finger responses up to ankle velocities of 70 degrees /s (300 ms). Reaction time, defined as the delay between onset of ankle rotation and how quickly the index finger could be extended, was 215 ms. The processing time and conduction delay was estimated to be approximately 85 ms. CONCLUSIONS: These results indicate that the nervous system processes kinesthetic input related to joint rotation of the ankle with the central mechanisms to execute a planned coordinated task with the upper extremity. SIGNIFICANCE: The time required to process proprioceptive information from the leg to perform a coordinated task with the upper extremity may vary throughout the lifespan. Understanding the effects of age, exercise, or injury on proprioceptive processing time may have important clinical implications.

Adult↗
PubMed2006

Postural responses to multidirectional stance perturbations in cerebellar ataxia.

Previous studies of patients with focal cerebellar damage underscored the importance of the cerebellum for balance control. These studies were restricted to postural control in the pitch plane, and focused mainly on leg muscle responses. Here, we examined the effect of degenerative cerebellar lesions on postural control in multiple directions, and studied how such lesions affect intersegmental coordination of the legs, trunk and arms. We formulated two main questions. (a) Do patients with cerebellar ataxia predominantly have balance problems in the sagittal or frontal planes? (b) Is instability in cerebellar ataxia associated with increased joint motion or with reduced joint motion? We selected nine patients with autosomal dominant spinocerebellar ataxia (SCA)--three with pure ataxia and six with mild extra-cerebellar features--and 12 matched controls. Upright standing subjects received support surface rotations (7.5 degrees at 60 degrees /s) that were randomly delivered in eight different directions of pitch or roll. We used full body kinematics to determine displacements of the center of mass (COM) and of individual body segments. We also collected surface EMG from 10 leg, trunk and arm muscles. Primary variables of interest were COM displacement and trunk control (angles and muscle responses). Secondary analyses focused on angles and muscle responses of the legs and arms. COM analysis demonstrated that SCA patients had greatest instability following backward and laterally directed perturbations. Major factors in causing this instability were, first, a marked reduction of stimulus-induced knee flexion and, second, excessive "hypermetric" motion of the pelvis (in roll) and trunk (in pitch). Muscle responses of SCA patients were characterized by increased late balance correcting activity. Responses of patients with pure ataxia were comparable to those of patients with mild extra-cerebellar features. A main underlying cause of postural instability in SCA patients appears to be "locking" of the knees, which may reflect compensation (by reducing interaction between body links) or reduced vestibulocerebellar control over leg muscles. The observed pathophysiology is very different from that seen in other patient populations.

Adult↗