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PubMed1976

EMG feedback therapy: review of treatment of 114 patients.

Advances in the understanding of the relationship of proprioceptive (kinesthetic) feedback to motor physiology have prompted the study of therapeutic effects of audiovisual displays of EMG activity. Patients with various manifestations of disturbed neuromotor control were studied prospectively for three years. This group included 114 patients with hemiparesis, torticollis, dystonia, and spinal cord or peripheral nerve injury. Initially, all but one of these patients had some residual volitional motor activity, which was insufficient for adequate function, and all patients had had conventional therapy with little or no functional recovery. Prior to EMG feedback therapy, the duration of illness was from three months to 35 years. The shaping of a patient's motor responses usually occurred gradually, often over an 8 to 12 week period. This modification was accomplished by feeding processed audio-visual signals back to the patient. These signals were proportional to the degree of activity of the muscles responsible for the defective function. The concept of microvolt-second, as a unit of muscle activity, is introduced and defined. Patterned movements, which were previously defective were observed to improve to varying degrees. Following the initial course of treatment, reinforcement was required by some patients. The mechanisms of improvement after EMG feeback therapy are not well understood; however, some hypotheses are presented. The results of this study indicate that EMG feedback therapy may induce significant functional recovery in patients with disturbed neuromotor control.

Activities of Daily Living↗

PubMed1975

Motor responses to sudden limb displacements in primates with specific CNS lesions and in human patients with motor system disorders.

Central feedback pathways for motor control were studied by recording EMG responses to sudden upper limb displacements in humans and monkeys using a precision torque motor to generate step load changes. Normal human subjects showed three short-latency EMG responses (M1, M2 and M3) which appear to correspond to those recorded from trained monkeys. The M2 and M3 components, thought to represent feedback in supraspinal pathways, were significantly increased when the subjects were instructed to actively compensate for the load changes. Parkinsonian patients with rigidity showed evidence of markedly increased feedback over the interval for the M2 and M3 responses and appeared to have lost the ability to modulate feedback according to the motor task being performed. The results are discussed with reference to recent research on motor control mechanisms in primates and a tentative model for the basis of Parkinsonian rigidity is proposed.

Animals↗

PubMed2004

A model of cerebellum stabilized and scheduled hybrid long-loop control of upright balance.

A recurrent integrator proportional integral derivative (PID) model that has been used to account for cerebrocerebellar stabilization and scaling of transcortical proprioceptive feedback in the control of horizontal planar arm movements has been augmented with long-loop force feedback and gainscheduling to describe the control of human upright balance. The cerebellar component of the controller is represented by two sets of gains that each provide linear scaling of same-joint and interjoint long-loop stretch responses between ankle, knee, and hip. The cerebral component of the model includes a single set of same-joint linear force feedback gains. Responses to platform translations of a three-segment body model operating under this hybrid proprioception and force-based long-loop control were simulated. With low-velocity platform disturbances, "ankle-strategy"-type postural recovery kinematics and electromyogram (EMG) patterns were generated using the first set of cerebeller control gains. With faster disturbances, balance was maintained by including the second set of gains cerebellar control gains that yielded "mixed ankle-hip strategy"-type kinematics and EMG patterns. The addition of small amounts of simulated muscular coactivation improved the fit to certain human datasets. It is proposed that the cerebellum switches control gainsets as a function of sensed body kinematic state. Reduction of cerebellar gains with a compensatory increase in muscular stiffness yielded posture recovery with abnormal motions consistent with those found in cerebellar disease. The model demonstrates that stabilized hybrid long-loop feedback with scheduling of linear gains may afford realistic balance control in the absence of explicit internal dynamics models and suggests that the cerebellum and cerebral cortex may contribute to balance control by such a mechanism.

Biomechanical Phenomena↗

PubMed1993

An electromyographic study of whether the digastric muscles are controlled by jaw-closing proprioceptors in man.

Whether in the oral system the digastric muscles (which lack muscle spindles) are under the control of proprioceptive information from the masseter muscles (which contain muscle spindles) was investigated by analysing whether and how the masseters and digastrics showed coordinated behaviour during a static, forceful bite. Subjects were asked to maintain a 100-N force for 15 s with and without visual guidance; bite force exerted, and masseter and digastric electromyograms (EMGs) were recorded. Under visual guidance all subjects co-contracted their digastric muscles during the isometric bite. They held the force for a short time, followed by periods with fluctuations (peak-to-peak force amplitude about 15-20 N). Fluctuations in bite force correlated with the masseter EMGs, the maximum in the correlogram occurring at about -50 ms with the force lagging the masseter. In 75% of the subjects a significant periodic component in the masseter and in the force spectra was found at about 4 Hz. This was also seen in the amplitude spectra of the forces, which showed in 80% of the subjects a significant elevation between 7-10 Hz as well. No correlation between the digastric EMGs and the bite forces, and between the EMGs of masseter and digastric could be detected. Spectra of digastric EMGs showed no prominent maxima. When subjects were deprived of visual feedback, maxima at -50 ms in the cross-correlation functions of the masseters and the forces were reduced considerably; periodicities of +/- 250 ms disappeared.(ABSTRACT TRUNCATED AT 250 WORDS)

Bite Force↗

PubMed1976

Electromyographic feedback to improve ankle dorsiflexion, wrist extension, and hand grasp.

Electromyographic feedback was used to train a patient with hemiplegia in the functional use of the muscles of his right upper and lower limbs. The patient trained with the therapist over a period of two and one-half months, engaging in exercises for ankle dorsiflexion, wrist extension, and hand grasp twice a week for one to one and one-half hours. Feedback was recorded with surface electrodes placed over the extensor surface of the forearm and the tibialis anterior; the electromyographic activity was displayed on a meter. After training, muscle control proved functional for walking, handwriting, and daily self-care activities.

Ankle↗

PubMed2004

A device for investigating neuromuscular control in the human masticatory system.

A new apparatus has been developed to study the control of mastication in humans. The subject places his/her teeth on fixed upper and mobile lower bite plates; the device then enables opening and closing movements of the lower jaw against a controlled resistance. It is also possible to vary the number of teeth in contact with the device during an experiment from the entire dental arcade to a single tooth. The specially designed lower bite plate is dynamic and allows for both rotation and translation of the lower jaw during movement, thus, permitting the natural curvilinear trajectory of the jaw. The lower bite plate can follow chewing initiated by the subject without resisting the movement ('no force' mode) via a dedicated microprocessor controlled compensation mechanism. Another function of the device is to inject a constant predetermined load onto the lower bite plate so that the subject 'chews' against a fixed resistance simulating rapidly yielding food bolus ('fixed force' mode). The device can be programmed to increase or decrease the force during the closing or opening phase of chewing by feeding the position information into the force compensation system so both position and force change in parallel, hence, simulating a bite onto a non-yielding, or sticky, food bolus ('normal chewing' mode). By use of a jaw position compensation mechanism, the device can actively move the lower jaw, following any imposed position pattern ('position controlled' mode). The chewing simulator also has a mode that holds the position at a fixed level and allows the force to change ('position hold' mode). Furthermore, the device can inject additional rapid or slow forces or displacements onto the lower bite plate in order to elicit reflexes so that the response of jaw muscles to such stimuli can be examined at various jaw positions, force levels, phases of motion and velocities. The different modes of the apparatus can be used to study the operation and feedback control of human mastication; in particular whether modulations in jaw muscle activity and reflexes are due to changes in force, velocity, position, chewing cycle phase or a combination of these factors.

Afferent Pathways↗

PubMed1985

Stimulation by central command of locomotion, respiration and circulation during exercise.

We studied the relationships between exercise (locomotion) and respiratory and circulatory responses in 19 cats that walked or ran normally on a treadmill, and in 16 paralyzed animals during fictive locomotion, i.e., locomotory activity in motor nerves to the legs. Preparations included anesthetized cats with intact brains and unanesthetized decorticate (hypothalamic) and decerebrate (mesencephalic) animals. Spontaneous actual locomotion and fictive locomotion occurred in all preparations except the mesencephalic cats. Electrical stimulation or injection of a GABA antagonist (picrotoxin) into the hypothalamic locomotor region caused locomotion to develop. In all cases when locomotion occurred, respiration and arterial pressure increased in proportion to the level of locomotor activity despite control or ablation of respiratory feedback mechanisms. Respiration and arterial pressure increased similarly during fictive locomotion despite the absence of muscular contraction or limb movement and the lack of change of metabolic rate. We conclude that the study provides experimental support for the feed-forward, or command signal, hypothesis for the genesis of proportional changes of respiration and circulation that occur during exercise. Feedback mechanisms are not required for its operation. We suggest that command signals emanating from the hypothalamus provide the primary drive for changes of respiration and circulation during exercise.

Animals↗

PubMed2006

Time to task failure varies with the gain of the feedback signal for women, but not for men.

Varying the gain of the feedback signal during a target-matching task alters the synaptic input onto the motor neuron pool. The purpose was to determine the influence of the gain of the feedback signal on the time to failure for men and women when maintaining arm position while supporting a submaximal inertial load with the elbow flexor muscles. While seated with the upper arm vertical, 15 women and 14 men maintained a constant elbow angle (1.57 rad) and supported a load equal to 15% of maximal voluntary contraction (MVC) force until failure. The task was performed on separate days with either a low gain or a high gain for the joint-angle signal. The percent decline in MVC force after the fatiguing contraction was similar for the low- and high-gain conditions (P = 0.24), and did not differ for men and women (P = 0.11). The discharge of motor units in biceps brachii declined at a greater rate during the high-gain condition for men and women, but only the women experienced a briefer time to failure for the high-gain session (8.7 +/- 2.3 min) compared with the low-gain session (11.9 +/- 4.8; P = 0.003). The men had similar times to failure for the low- (6.0 +/- 2.2 min) and high-gain conditions (5.9 +/- 2.1 min; P = 0.35). Linear and stepwise, multiple-regression analyses revealed that the time to failure for the men was associated with the absolute target force, the standard deviation (SD) for the resultant wrist acceleration, and the brachialis aEMG (P <or= 0.02), whereas the time to failure for the women was associated with the rate of decline in motor unit discharge, the SD for the resultant wrist acceleration, and the changes in mean arterial pressure and heart rate (P <or= 0.001). Despite each subject exerting the same net muscle torque during the two gain conditions and a similar effect of feedback gain on the discharge rate of motor units for all subjects, the time to failure for the fatiguing contractions was limited by different mechanisms for the men and women.

Adolescent↗

PubMed2004

Augmented visual feedback increases finger tremor during postural pointing.

Physiological tremor in the upper limb of eight adults was examined during the performance of a unilateral pointing task under conditions where the visual feedback, limb used and target size were altered. All subjects were required to aim a hand-held laser pointer at a circular target 5.5 m away with the goal of keeping the laser emission within the centre of the target. Visual feedback was defined as either normal vision (NV) of their limb tremor, where the laser was switched off, or augmented vision (AV) where the laser was switched on. Postural tremor from the segments of the upper limb, forearm muscle EMG activity, and target accuracy measures were recorded and analysed in the time and frequency domains. Accuracy-tremor relations were assessed using cross correlation and linear regression. Results revealed a high degree of similarity in the general pattern of the tremor output seen for each limb segment across conditions with only scalar (amplitude) changes being seen as a function of the different constraints imposed. For any single condition the tremor amplitude increased from proximal to distal segments. The frequency profile for the tremor in any segment displayed two prominent frequency peaks (at 2-4 Hz and 8-12 Hz). A third, higher frequency peak (18-22 Hz) was observed in the index fingers only. Across all conditions significant coupling relations were observed only between the hand-finger and forearm-upper arm segment pairs. Altering the visual feedback was shown to have the greatest effect on limb tremor with increased tremor and EMG activity and decreased coupling being seen under AV conditions. In trying to reduce tremor output when the augmented feedback was provided novice subjects instead increased muscle activity which resulted in increased tremor. Overall these results indicate that the physiological tremor output observed in neurologically normal subjects is not simply the product of intrinsic oscillations but is influenced by the nature of the task being performed.

Adult↗

PubMed1997

Task-involvement and ego-involvement goals during actual and imagined movements: their effects on cognitions and vegetative responses.

It has been experimentally proven many times that the mental rehearsal of an activity not only improves motor performance but also has vegetative effects whose magnitude is correlated with the amount of imagined effort. These beneficial effects of mental imagery have been explained in terms of central programming structures capable of anticipating the metabolic demands of the task. Twenty-four subjects were asked to actually perform and also imagine an isometric contraction of the forearm under various goal conditions: a task-involving goal (8 subjects), an ego-involving goal (8 subjects), and no goal (8 subjects). During the contractions, electromyographic potential and heart rate were measured. Afterwards, the subjects were asked to indicate the amount of effort expended under different feedback conditions. The results showed no trace of electromyographic activity during the imagined contractions when the lack of movement was controlled using a force sensor. On the other hand, a significantly faster in heart rate was observed with a task- or ego-involving goal than with no goal, during both actual and imagined contraction. Similarly, as predicted, subjects said they applied less effort in the positive feedback condition, and more effort in the negative feedback condition with an ego-involving goal. The results are discussed in the light of goal theories, while regarding goals not only as serving to anticipate metabolic expenditures but also as promoting a self-image of competence, particularly in threatening, ego-involving situations.

Adult↗

PubMed1987

Specific and nonspecific effects of EMG biofeedback.

This study investigated the effects of performance feedback and EMG biofeedback on perceptions of the "self" (i.e., self-esteem, self-control, self-efficacy, and locus of control) as well as on a self-control behavior (study skills) the subjects performed outside the laboratory. Forty-seven college students were randomly assigned to one of four groups in a 2(high and low success feedback) x 2(true and false EMG biofeedback) factorial experiment with repeated measures. All of the participants received four sessions of EMG biofeedback, and later they were asked to self-monitor their study habits for 2 weeks. Results showed that the self-esteem measure and perceptions of study skills improvement were differentially affected by success feedback but unrelated to the true or false EMG manipulation. Shifts toward an internal locus of control and perceptions of improved self-control were also noted, but they were independent of the subjects' group membership. Implication of the results are briefly discussed.

Adult↗

PubMed1998

Feedback control during mastication of solid food textures--a clinical-experimental study.

STATEMENT OF PROBLEM: On the basis of animal experiments, it has been hypothesized that the dynamics of food reduction are controlled by peripheral receptors. Studies on this subject in human beings are rare. PURPOSE: This study investigated the influence of periodontal and joint proprioceptors on mastication in human beings. MATERIAL AND METHODS: Both jaw joints and the chewing-side teeth were consecutively anesthetized in a 6-person panel by chewing wine gum. The effects on the kinematics, chewing force, and electromyographic activity were measured. RESULTS: The results substantiate a positive feedback of periodontal receptors for chewing force control. A substantial influence of joint receptors on movement control could not be found. CONCLUSION: Despite the absence of proprioception in both jaw joints and the periodontal receptors in the chewing side, the characteristics of the measured kinematic and dynamic values remained essentially unchanged.

Adult↗

PubMed1993

Jaw-jerk reflex activity in relation to various clenching tasks in man.

In order to investigate whether the mandibular stretch (jaw-jerk) reflex is modulated in a task-dependent manner, jaw-jerk reflexes were elicited in eight subjects during clenching with unilateral and bilateral tooth support, respectively. The reflexes were examined in the electromyographic (EMG) activity recorded by means of surface electrodes and were elicited by means of small transient jaw displacements at a constant value of 80 microns. Low levels of background EMG were applied ranging from 1 to 30% maximal voluntary contraction (MVC) as controlled by means of visual feedback. Linear relationships were observed between reflex amplitude and level of background EMG. The slope in these relationships served as a measure of reflex gain. For the masseter as well as the anterior temporal muscles, the reflex gain, averaged over both sides, was larger during clenching with unilateral tooth support than with bilateral tooth support (P < 0.05). Furthermore, the gain was larger on the side without tooth support during unilateral clenching and larger on the side without visual feedback of elevator muscle activity during bilateral clenching. It can be concluded that the jaw-jerk reflex is modulated to subserve the stabilization of the mandible, with the reflex sensitivity being larger the more that alternative stabilizing factors such as mechanical tooth contact, visual feedback and feedback from periodontal pressure receptors around the teeth are lacking. The reflex modulation may be of functional importance in stabilizing the mandible during its movement in the chewing process, as the food is predominantly placed unilaterally between the antagonistic teeth during individual chewing cycles.

Adolescent↗

PubMed2005

Modulation of beta oscillations in the subthalamic area during motor imagery in Parkinson's disease.

Activation of the basal ganglia has been shown during the preparation and execution of movement. However, the extent to which the activation during movement is related to efferent processes or feedback-related motor control remains unclear. We used motor imagery (MI), which eliminates peripheral feedback, to further investigate the role of the subthalamic area in the feedforward organization of movement. We recorded local field potential (LPF) activity from the region of the subthalamic nucleus (STN) in eight patients with Parkinson's disease off dopaminergic medication during performance of a warned reaction time task. Patients were instructed to either extend the wrist [motor execution (ME)], to imagine performing the same task without any overt movement (MI), or, in a subgroup, to perform a non-motor visual imagery (VI) task. MI led to event-related desynchronization (ERD) of oscillatory beta activity in the region of the STN in all patients that was similar in frequency, time course and degree to the ERD occurring during ME. The degree of ERD during MI correlated with the ERD in trials of ME and, like ME, was accompanied by a decrease in cortico-STN coherence, so that STN LFP activity during MI was similar to that in ME. The ERD in ME and MI were both significantly larger than the ERD in VI. In contrast, event-related synchronization (ERS) was significantly smaller in trials of MI, and even smaller in trials of VI, than during ME. The data suggest that the activity in the region of the human STN indexed by the ERD during movement is related to the feedforward organization of movement and is relatively independent of peripheral feedback. In contrast, sensorimotor feedback is an important factor in the ERS occurring in the STN area after completion of movement, consistent with a role for this region in trial-to-trial motor learning or the re-establishment of postural set following movements.

Cortical Synchronization↗

PubMed2003

Low-threshold motor unit membrane properties vary with contraction intensity during sustained activation with surface EMG visual feedback.

Single-motor unit (MU) activities were detected from the abductor pollicis and abductor digiti minimi muscles providing the subjects with visual feedback of multichannel surface electromyogram (EMG) signals. The subjects could modulate the force to observe on the surface recordings a single dominant MU and modulate its firing rate for contractions of 300 s with a noninvasive EMG feedback. The firing rate was maintained at approximately 8 pulses per second [low-frequency (LF) contraction] and at approximately 12 pulses per second [high-frequency (HF) contraction]. Single-MU conduction velocity (CV) decreased slightly but significantly over time, and it was possible to identify a significantly larger rate of decrease of CV during the HF with respect to the LF contractions. CV initial value significantly increased with the average firing rate, and CV values were significantly correlated to the instantaneous firing rate (R ranging from 0.21 to 0.39). Both additional MU recruitment and substitution were observed during the contractions. The study provides evidence that 1). it is possible to follow the same MU in a hand muscle at two different intensities (HF and LF) for 300-s durations by using visual feedback of surface EMG, 2). low-threshold single-MU CV changes over time since the beginning of the contraction, and 3). it is possible to distinguish between CV changes of the same MU at slightly different firing rates. The technique provides a practical method for the noninvasive assessment of both control and membrane properties of single MUs.

Adult↗

PubMed1999

Electromyogram-controlled functional electrical stimulation for treatment of the paralyzed upper extremity.

Spinal cord lesions at level C5 to C6 lead to loss of hand functions and lesions at C4 to additional deficits of arm functionality. The presented dual channel surface stimulator with dual channel electromyogram (EMG) measurement was developed to investigate control strategies for an EMG-controlled implantable stimulation system and serves in addition as a therapy device for patients with partial innervation but weak muscle force. Four different control strategies for stimulation amplitude are available. The amplitude can be preset manually or can follow the preprocessed EMG signals proportionally. The shoulder control program allows proportional control of both stimulation channels with one EMG channel while the second EMG channel serves as the channel selector. Finally, a special feedback training program triggers a stimulation burst when EMG activity is detected. During a 2 year patient study, 18 patients from 2 hospitals and 1 rehabilitation center performed the feedback training. Almost all patients obtained an improvement of functionality. Apart from muscle strengthening, the feedback effect led to an improvement of proprioception and supported relearning of motions. For the documentation of the training status, functional muscle test (British Medical Research Council) and measurements of power, angle, torque, muscle fatigue, and EMG were performed. Obviously, EMG triggered stimulation provides several advantages compared to conventional passive electrical stimulation.

Arm↗

PubMed2006

Controlling balance during quiet standing: proportional and derivative controller generates preceding motor command to body sway position observed in experiments.

To compensate for significant time delays in the control of human bipedal stance, it was suggested that a feed-forward control mechanism is needed to generate a preceding motor command to the body sway position observed in quiet standing. In this article, we present evidence that a feedback proportional-derivative (PD) controller can effectively generate a desired preceding motor command. We also discuss the following characteristics of the proposed PD controller: (1) the level of robustness of the controller with respect to neurological time delays and (2) how well the controller replicates the system's dynamics observed in experiments with able bodied subjects, i.e. how well the controller generates the observed preceding motor command. Human quiet stance was simulated using an inverted pendulum model regulated by a PD controller. The simulations were used to calculate the center of mass (COM) position and velocity data, and the motor command (ankle joint torque) data as a function of time. These data and the data obtained in the experiments were compared using cross-correlation functions (CCFs). The results presented herein imply that a PD feedback controller is capable of ensuring balance during human bipedal quiet stance, even if the neurological time delays are considerable. The proposed feedback controller can generate the preceding motor command that was observed in the experiments. Therefore, we conclude that a feed-forward mechanism is not necessary to compensate for the long closed-loop time delay in human bipedal stance as suggested in recent literature, and that the PD controller is a good approximation of the control strategy applied by able bodied subjects during quiet stance.

Adult↗

PubMed2004

Assessing respiratory drive and central motor pathway in humans: clinical implications.

Feedback from sensory elements as well as projection from higher Central Nervous System structures modify the level and pattern of motor outflow to the respiratory muscles and hence ventilation. In this review we describe the different methods to evaluate the degree to which higher centers determine the level and pattern of ventilation and coordinate use of the respiratory muscles in healthy humans and in patients with a number of respiratory disorders.

Diaphragm↗