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C J De Luca

Publications and source records attributed to C J De Luca.

At least 19 recordsLinked to original sources
PubMed2001

Time-frequency parameters of the surface myoelectric signal for assessing muscle fatigue during cyclic dynamic contractions.

The time-dependent shift in the spectral content of the surface myoelectric signal to lower frequencies has proven to be a useful tool for assessing localized muscle fatigue. Unfortunately, the technique has been restricted to constant-force, isometric contractions because of limitations in the processing methods used to obtain spectral estimates. A novel approach is proposed for calculating spectral parameters from the surface myoelectric signal during cyclic dynamic contractions. The procedure was developed using Cohen class time-frequency transforms to define the instantaneous median and mean frequency during cyclic dynamic contractions. Changes in muscle length, force, and electrode position contribute to the nonstationarity of the surface myoelectric signal. These factors, unrelated to localized fatigue, can be constrained and isolated for cyclic dynamic contractions, where they are assumed to be constant for identical phases of each cycle. Estimation errors for the instantaneous median and mean frequency are calculated from synthesized signals. It is shown that the instantaneous median frequency is affected by an error slightly lower than that related to the instantaneous mean frequency. In addition, we present a sample application to surface myoelectric signals recorded from the first dorsal interosseous muscle during repetitive abduction/adduction of the index finger against resistance. Results indicate that the variability of the instantaneous median frequency is related to the repeatability of the biomechanics of the exercise.

Electromyography↗
PubMed2001

Motor control of low-threshold motor units in the human trapezius muscle.

The firing pattern of low-threshold motor units was examined in the human trapezius and first dorsal interosseous (FDI) muscles during slowly augmenting, low-amplitude contractions that were intended to mimic contractile activity in postural muscles. The motor unit activity was detected with a special needle electrode and was analyzed with the assistance of computer algorithms. The surface electromyographic (EMG) signal was recorded. Its root-mean-square (RMS) value was calculated and presented to the subject who used it to regulate the muscle force level. In the trapezius, there was minimal, if any, firing rate modulation of early recruited motor units during slow contractions (< or =1% EMG(max)/s), and later recruited motor units consistently presented higher peak firing rates. As the force rate of the contraction increased (3% EMG(max)/s), the firing rates of the motor units in the trapezius approached an orderly hierarchical pattern with the earliest recruited motor units having the greatest firing rate. In contrast, and as reported previously, the firing rates of all motor units in the FDI always presented the previously reported hierarchical "onion-skin" pattern. We conclude that the low-threshold motor units in the postural trapezius muscle, that is the motor units that are most often called on to activate the muscle in postural activities, have different control features in slow and fast contractions. More detailed analysis revealed that, in the low force-rate contractions of the trapezius, recruitment of new motor units inhibited the firing rate of active motor units, providing an explanation for the depressed firing rate of the low-threshold motor units. We speculate that Renshaw cell inhibition contributes to the observed deviation of the low-threshold motor units from the hierarchical onion-skin pattern.

Adult↗
PubMed1998

Electromyographic analysis of grand-plié in ballet and modern dancers.

PURPOSE: The purpose of this report is to describe lower extremity muscle activity in grand-plié, as determined by EMG analysis; to compare and contrast muscle function in grand-plié and demi-plié to support the hypothesis that grand-plié is not simply a deeper demi-plié, but rather a fundamentally different movement in terms of muscle use; and to present further evidence in support of the hypothesis that ballet dancers use muscles differently than modern dancers in dance movement. METHODS: Surface electromyography was used to analyze lower extremity muscle activity during grand-plié in first position with lower extremities turned out in five ballet and seven modern female professional dancers. RESULTS: Electromyographic (EMG) activity of tibialis anterior included continuous activity from heel-off during the lowering phase, through midcycle, and ending at heel-on during the rising phase in all grand-pliés; the majority of tibialis anterior EMG tracings in ballet dancers had additional activity at the end of the rising phase. All EMG tracings for vastus lateralis and medialis included a peak of activity during the lowering phase, a decrease (valley) at midcycle, followed by another peak during the rising phase; increased activity at the end of the rising phase was observed in most grand-plié in ballet, and not modern, dancers. Adductor EMG activity was also observed in all tracings with a peak during the lowering phase from heel-off to midcycle, a valley at midcycle, followed by a peak of activity in early rising phase; the midcycle valley was of lower, and the rising phase peak of higher, activity in ballet compared with modern dancers. Variation of EMG patterns was observed for lateral and medial gastrocnemius, gluteus maximus, and hamstrings. CONCLUSIONS: The data support the concept that lower extremity muscle activity in dance movement is comprised of three major types: (a) unique, characteristic activity required for the execution of the movement; (b) varied activity which is characteristic of dancers of different dance idioms; and (c) varied activity which may depend on factors such as balance, personal habit, and individual training background. Furthermore, EMG activity of vastus lateralis and medialis at the midcycle valley in grand-plié was significantly less in ballet dancers than in modern dancers despite similar degree of knee flexion, suggesting that ballet dancers may have lower patellofemoral joint reaction force at midcycle than modern dancers.

Analysis of Variance↗
PubMed1998

Hand dominance and motor unit firing behavior.

Daily preferential use was shown to alter physiological and mechanical properties of skeletal muscle. This study was aimed at revealing differences in the control strategy of muscle pairs in humans who show a clear preference for one hand. We compared the motor unit (MU) recruitment and firing behavior in the first dorsal interosseous (FDI) muscle of both hands in eight male volunteers whose hand preference was evaluated with the use of a standard questionnaire. Myoelectric signals were recorded while subjects isometrically abducted the index finger at 30% of the maximal voluntary contraction (MVC) force. A myoelectric signal decomposition technique was used to accurately identify MU firing times from the myoelectric signal. In MUs of the dominant hand, mean values for recruitment threshold, initial firing rate, average firing rate at target force, and discharge variability were lower when compared with the nondominant hand. Analysis of the cross-correlation between mean firing rate and muscle force revealed cross-correlation peaks of longer latency in the dominant hand than in the nondominant side. This lag of the force output with respect to fluctuations in the firing behavior of MUs is indicative of a greater mechanical delay in the dominant FDI muscle. MVC force was not significantly different across muscle pairs, but the variability of force at the submaximal target level was higher in the nondominant side. The presence of lower average firing rates, lower recruitment thresholds, and greater firing rate/force delay in the dominant hand is consistent with the notion of an increased percentage of slow twitch fibers in the preferentially used muscle, allowing twitch fusion and force buildup to occur at lower firing rates. It is suggested that a lifetime of preferred use may cause adaptations in the fiber composition of the dominant muscle such that the mechanical effectiveness of its MUs increased.

Action Potentials↗
PubMed1997

Classification of back muscle impairment based on the surface electromyographic signal.

A surface electromyographic (EMG) procedure for classifying muscle impairments in persons with low back pain (LBP) is described. The procedure was studied using a device, the Back Analysis System (BAS), to acquire and process EMG signals from six bilateral muscle sites during sustained isometric contractions designed to progressively fatigue the lower back. Back muscle impairment was determined on the basis of the different ways in which the EMG median frequency parameters change as a function of contraction duration and muscle site. The article describes a series of studies that have been useful in developing an automated procedure for identifying back muscle impairment by comparing individual test results to a normative database. To date, the research results have produced multivariate discriminant functions that have identified two muscle impairment categories associated with deconditioning and imbalances secondary to LBP. We have found that the functions can distinguish individuals with and without LBP with an accuracy of approximately 90%. Other studies are described in which the technique is applied to monitoring changes in muscle performance capability that occur following rehabilitation for LBP. Many of our findings here are also compared to the results of independent studies by others using similar procedures. The need for further research and development of the technique to improve its clinical applicability is also described.

Diagnosis, Computer-Assisted↗
PubMed1997

Development of new protocols and analysis procedures for the assessment of LBP by surface EMG techniques.

Spectral parameters of the surface electromyographic (EMG) signal from lumbar back muscles assessed during a fatiguing isometric contraction can be used to classify different categories of low back pain (LBP) subjects and control subjects without LBP. In the test protocol currently used at the NeuroMuscular Research Center at Boston University, subjects contract their back muscles at 80% of their maximal voluntary contraction (MVC) force. This fatigue-based protocol has been successfully applied to persons with subacute or chronic LBP; those in acute pain, however, have not been included because of their inability to perform a maximal exertion. In this paper we will examine the force sensitivity of the currently used EMG parameters and also give an overview of some of our efforts to develop new test procedures. Our goal is to develop force-insensitive surface EMG parameters that can be used for classification purposes in populations of subjects who develop low trunk extension forces. In addition, the development of a model to predict MVC from anthropometrical measurements will be presented.

Adult↗
PubMed1996

Rank-ordered regulation of motor units.

Myoelectric signals were detected from the tibialis anterior muscle of 5 subjects with a quadrifilar needle electrode while the subjects generated isometric forces that increased linearly with time (10% of maximal voluntary contraction/s) up to maximal voluntary level. Motor unit firing rates were studied as a function of force throughout the full range of muscle force output. The relationship between force and firing rate was found to contain three distinct regions. At recruitment and near maximal force levels, firing rates increased more rapidly with force than in the intermediate region. Furthermore, in the regions with rapid increases, the rate of change of firing rate was correlated to the recruitment threshold, with higher recruitment threshold motor units displaying greater rates of change. In the intermediate region, all motor units had similar rates of change of firing rate. A weak positive correlation was found between initial firing rate and recruitment threshold. Firing rates of motor units at any instant were found to be ordered according to the recruitment order: at any given time in the contraction motor units with lower recruitment thresholds had higher firing rates than units with higher recruitment thresholds. Firing rates of all motor units were observed to converge to the same value at maximal forces. Mechanisms underlying motor unit recruitment and firing rate modulation are discussed in the context of a conceptual model.

Action Potentials↗
PubMed1995

Open-loop and closed-loop postural control mechanisms in Parkinson's disease: increased mediolateral activity during quiet standing.

Stabilogram-diffusion analysis was used to gain insights into how idiopathic Parkinson's disease (IPD) affects the postural control mechanisms involved in maintaining erect stance. Twenty-two subjects with IPD and twenty-four healthy elderly subjects were studied under eyes-open, quiet-standing conditions. The postural control mechanisms in the parkinsonian subjects, compared to the healthy elderly, were characterized by an increase in the effective stochastic activity in the mediolateral direction. Mediolateral posturographic measures were also associated with a history of falls and poor performance on clinical measures of balance. It is hypothesized that the increase in mediolateral activity in subjects with IPD may reflect an attempt to maintain potentially stabilizing movements during quiet standing in the face of impaired movement in the anteroposterior direction. This study supports the notion that mediolateral instability is an important posturographic marker of functional balance impairment in the elderly.

Aged↗
PubMed1995

Spectral electromyographic assessment of back muscles in patients with low back pain undergoing rehabilitation.

STUDY DESIGN: A surface electromyographic procedure for evaluating back muscle impairment was studied in patients undergoing rehabilitation for low back pain. OBJECTIVES: The results were analyzed to determine whether the electromyographic procedure was able to: 1) distinguish muscle impairment between patients with low back pain and normal subjects, and 2) monitor changes in muscle function after low back pain rehabilitation. METHODS: Patients with chronic low back pain (n = 85) were tested to measure the median frequency of the electromyographic signals from six lumbar electrode sites during sustained trunk extensions. A subset (n = 28) of these patients was re-tested after low back pain rehabilitation. A discriminant function for classifying subjects into "low back pain" and "normal" groups was formulated using the electromyographic data from a subset of the patients with low back pain (n = 28) and a normative sample (n = 42). Results for this "learning" sample were compared with results using the same function on the remaining "holdout" sample of patients (n = 57) and an additional normative sample (n = 6). Differences in electromyographic parameters before and after rehabilitation also were analyzed. RESULTS: The discriminant function classified subjects into low back pain and normal groups, with 86% and 89% correct classification for the "learning" and "holdout" samples, respectively. These classification results were independent of trunk extensor strength. Changes in median frequency after the rehabilitation program were consistent with improvements in back muscle fatigability. CONCLUSION: These findings demonstrate how electromyographic spectral measurements may be used to identify and monitor back muscle impairment in patients undergoing rehabilitation for low back pain.

Adult↗
PubMed1995

The effects of spaceflight on open-loop and closed-loop postural control mechanisms: human neurovestibular studies on SLS-2.

Stabilogram-diffusion analysis was used to examine how prolonged periods in microgravity affect the open-loop and closed-loop postural control mechanisms. It was hypothesized that following spaceflight: (1) the effective stochastic activity of the open-loop postural control schemes in astronauts is increased; (2) the effective stochastic activity and uncorrelated behavior, respectively, of the closed-loop postural control mechanisms in astronauts are increased; and (3) astronauts utilized open-loop postural controls schemes for shorter time intervals and smaller displacements. Four crew members and two alternates from the 14-day Spacelab Life Sciences 2 Mission were included in the study. Each subject was tested under eyes-open, quiet-standing conditions on multiple preflight and postflight days. The subjects' center-of-pressure trajectories were measured with a force platform and analyzed according to stabilogram-diffusion analysis. It was found that the effective stochastic activity of the open-loop postural control schemes in three of the four crew members was increased following spaceflight. This result is interpreted as an indication that there may be in-flight adaptations to higher-level descending postural control pathways, e.g., a postflight increase in the tonic activation of postural muscles. This change may also be the consequence of a compensatory (e.g., "stiffening") postural control strategy that is adopted by astronauts to account for general feeling of postflight unsteadiness. The crew members, as a group, did not exhibit any consistent preflight/postflight differences in the steady-state behavior of their closed-loop postural control mechanisms or in the functional interaction of their open-loop and closed-loop postural control mechanisms. These results are interpreted as indications that although there may be in-flight adaptations to the vestibular system and/or proprioceptive system, input from the visual system can compensate for such changes during undisturbed stance.

Humans↗
PubMed1995

Age-related changes in open-loop and closed-loop postural control mechanisms.

In an earlier posturographic investigation (Collins and De Luca 1993) it was proposed that open-loop and closed-loop control mechanisms are involved in the regulation of undisturbed, upright stance. In this study, stabilogram-diffusion analysis was used to examine how the natural aging process affects the operational characteristics of these control mechanisms. Stabilogram-diffusion analysis leads to the extraction of repeatable center-of-pressure (COP) parameters that can be directly related to the steady-state behavior and functional interaction of the neuromuscular mechanisms underlying the maintenance of erect posture. Twenty-five healthy young males (aged 19-30 years) and twenty-five elderly males (aged 71-80 years) who were free of major gait and postural disorders were included in the study. An instrumented force platform was used to measure the time-varying displacements of the COP under each subject's feet during quiet standing. The COP trajectories were analyzed as one-dimensional and two-dimensional random walks, according to stabilogram-diffusion analysis. Using this technique, it was demonstrated cross-sectionally that healthy aging is associated with significant changes in the 'quasi-static' dynamics of the postural control system. (It was also shown that more traditional posturographic analyses, i.e., summary statistics, were not sensitive enough to detect these age-related differences.) It was found that the steady-state behavior of the open-loop postural control mechanisms in the elderly is more positively correlated and therefore perhaps more unstable, i.e., the output of the overall system has a greater tendency to move or drift away from a relative equilibrium point over the short term. In contrast with this result, it was also found that the steady-state behavior of the closed-loop postural control mechanisms in the elderly is more negatively correlated and therefore perhaps more stable, i.e., over the longer term, there is an increased probability that movements away from a relative equilibrium point will be offset by corrective adjustments back towards the equilibrium position. In addition, it was demonstrated that the elderly utilize open-loop control schemes for longer time intervals and correspondingly larger COP displacements during periods of undisturbed stance. This result suggests that in the elderly there is a greater delay, on average, before closed-loop feedback mechanisms are called into play. Finally, it was shown that there is an increased heterogeneity of postural control abilities in healthy older adults.

Adult↗
PubMed1995

The effects of visual input on open-loop and closed-loop postural control mechanisms.

In an earlier posturographic investigation (Collins and De Luca 1993) it was proposed that open-loop and closed-loop control mechanisms are involved in the regulation of undisturbed, upright stance. In this study, stabilogram-diffusion analysis was used to examine how visual input affects the operational characteristics of these control mechanisms. Stabilogram-diffusion analysis leads to the extraction of repeatable center-of-pressure (COP) parameters that can be directly related to the resultant steady-state behavior and functional interaction of the neuromuscular mechanisms underlying the maintenance of erect posture. Twenty-five healthy male subjects (aged 19-30 years) were included in the study. An instrumented force platform was used to measure the time-varying displacements of the COP under each subject's feet during quiet standing. The subjects were tested under eyes-open and eyes-closed conditions. The COP trajectories were analyzed as one-dimensional and two-dimensional random walks, according to stabilogram-diffusion analysis. Using this technique, it was found that visual input affects the performance of the postural control system in one of two different ways--either it significantly modifies the steady-state behavior of the open-loop postural control mechanisms, or it significantly alters the characteristics of the other closed-loop feedback mechanisms that are involved in balance control. This result is interpreted as an indication that the visual system is integrated into the postural control system in one of two different ways. The experimental population was roughly evenly divided between these two schemes. For the first group (13 of 25 subjects), visual input principally caused a decrease in the "effective" stochastic activity of the open-loop control mechanisms in both the mediolateral and anteroposterior directions. For the second group (12 of 25 subjects), visual input caused an increase in the effective stochastic activity and uncorrelated behavior of the closed-loop control mechanisms in the anteroposterior direction only. On the basis of these results, it is hypothesized that visual input, in both schemes, serves to decrease the stiffness of the musculoskeletal system. In the former case, this may be accomplished by decreasing the level of muscular activity across the joints of the lower limb, whereas, in the latter case, reduced stiffness may be achieved by reducing the gain(s) of the other postural feedback mechanisms, i.e., the proprioceptive and/or vestibular systems. Using stabilogram-diffusion analysis, it was also found that the two groups of subjects behaved similarly under eyes-closed conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1995

Effects of muscle fiber type and size on EMG median frequency and conduction velocity.

This paper describes an in vitro method for comparing surface-detected electromyographic median frequency (MF) and conduction velocity (CV) parameters with histochemical measurements of muscle fiber type composition and cross-sectional area (CSA). Electromyographic signals were recorded during electrically elicited tetanic contractions from rat soleus, extensor digitorum longus, and diaphragm muscles placed in an oxygenated Krebs bath. Fibers were typed as slow oxidative, fast oxidative glycolytic, and fast glycolytic based on histochemical enzyme stains. Muscles with a greater percentage of fast glycolytic and fast oxidative glycolytic fibers exhibited greater initial values of MF and CV as well as a greater reduction in these variables over the course of the contraction. Regression indicated that fiber type composition could be predicted based on two MF parameters. A weighted measure of muscle fiber CSA was found to be linearly related to both initial MF and CV. The results of this study suggest that MF and CV parameters recorded during a muscular contraction are related to muscle fiber type composition and muscle fiber CSA.

Animals↗
PubMed1994

Common drive of motor units in regulation of muscle force.

The neuromuscular system is responsible for all our interactions with our environment. Although recent decades have witnessed numerous discoveries that have shed light into various properties of this system, the basic principles underlying its overall operation still remain poorly understood. In this article, Carlo J. De Luca and Zeynep Erim discuss the concept of common drive of motor units that provides a possible scheme for the control of motor units, unifying various seemingly isolated findings that have been reported. According to this concept, a pool of motor units that makes up a muscle is controlled collectively during a contraction of that muscle. The unique firing patterns of individual motor units are effected, not by separate command signals sent to these units, but by one common drive to which motor units respond differently. The specific architecture of the system and the orderly gradation in the inherent properties of individual elements enable a single source to control the activities of all the motor units in a given pool. Such an arrangement relieves the CNS from the burden of monitoring and regulating each motor unit separately.

Animals↗
PubMed1994

AR modeling of myoelectric interference signals during a ramp contraction.

We investigated the time-varying behaviour of the autoregressive (AR) parameters in a myoelectric (ME) signal detected during a linear force increasing contraction. The AR parameters of interest were the reflection coefficients, the AR model spectrum, and the prediction errors. We used well-conditioned ME signals for which the complete time record of the motor units firings was available. In addition, the influence of the recruitment of a new motor unit, the conduction velocity of action potentials, and additive broad-band noise were investigated using simulated ME signals. The simulated ME signals were constructed from a selected group of the available motor unit action potential trains. The results revealed that, as the contraction progressed, the AR parameters displayed a time-varying behavior which coincided with the recruitment of newly recruited motor units whose spectrum of the waveform differed from that of the rest of the ME signal. This property of the AR parameters was obscured by the presence of broad-band noise and low-amplitude motor unit action potentials, both of which are more pronounced during low-level force contractions.

Action Potentials↗
PubMed1994

Electrically evoked myoelectric signals in back muscles: effect of side dominance.

This work had two goals, to study the effect of hand dominance on myoelectric signal variables and fatigue indexes in back muscles and to assess the repeatability of the estimates of such variables. Myoelectric manifestations of muscle fatigue were studied in the right and left longissimus dorsi muscles of five right-handed and five left-handed normal male subjects. Myoelectric signals (M waves), evoked by stimulation applied to a muscle's motor point, were detected with surface electrodes. Each test consisted of eliciting a tetanic contraction of 30 s duration with supramaximal stimulation at 25 Hz and was repeated five times on 5 different days for each subject. The mean and median frequencies of the resulting power spectra of the M waves were plotted vs. time, and fatigue indexes were obtained from the time course of these variables. Only two-thirds of the elicited contractions provided signals of sufficiently good quality to obtain reliable estimates of the mean and median frequencies. Criteria for acceptability are described. Analysis of variance and paired comparisons showed a statistically significant effect of side dominance on fatigue indexes in the right-handed subjects but not in the left-handed subjects. Normalized initial slope and other fatigue indexes based on spectral variables demonstrated myoelectric manifestations of fatigue that were greater on the dominant side. We surmise that the differences are related to the fiber type modifications associated with the unilateral usage of the upper limbs and the consequent activation of the nondominant side of the back.

Adult↗