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[161] AUTOMATIC DECOMPOSITION OF THE ELECTROMYOGRAM
Kevin C. McGill, PhD
Rehabilitation R&D Center, VA Palo Alto Health Care
System, Palo Alto, CA 94304; email:
mcgill@roses.stanford.edu
PURPOSE--The electromyogram (EMG) is the electrical signal recorded by needle or surface electrodes during a muscular contraction. Interpretation of the EMG is an important part of the diagnostic evaluation of patients with suspected neuromuscular disorders. EMG signals are made up of discharges of groups of muscle fibers known as motor-unit action potentials (MUAPs). The purpose of this project is to develop methods for estimating physiological characteristics of muscle and nerve from EMG signals and MUAP waveforms. Such methods are expected to make EMG examinations more objective, reproducible, and diagnostically sensitive.
METHODOLOGY--EMG signals were recorded using needle electrodes from brachial biceps, anterior tibial, and first dorsal interosseous during moderate voluntary contractions in control subjects. The signals were decomposed into their constituent MUAPs using computer-aided decomposition as described below. In addition, MUAPs and compound muscle action potentials (CMAPs) were recorded using surface electrodes from intrinsic hand muscles in response to electrical stimulation at the wrist. Computer simulations were used to analyze the MUAP and CMAP waveforms in terms of the following parameters: the dispersion of the arriving nerve volley, the shape and duration of the intracellular action potential, the muscle-fiber conduction velocity, the distribution of muscle-fiber semi-lengths, and the location of the recording electrodes.
PROGRESS--We have developed three methods for estimating MUAP properties from EMG signals. Spike analysis uses statistical techniques to estimate the number of active motor units and their mean discharge rate. Automatic decomposition, intended for routine clinical use, uses pattern recognition techniques to estimate MUAP waveforms and discharge rates, but not complete discharge patterns. Computer-aided decomposition, intended for research use, allows interactive identification of complete motor-unit discharge patterns.
RESULTS--Our results show that CMAP and MUAP shapes are determined by anatomical as well as physiological factors. CMAPs and MUAPs (both surface- and needle-recorded) can be divided into four parts corresponding to four stages of electrical activity in the muscle: 1) the rising edge corresponds to the initiation of the action potential at the endplate; 2) the spike corresponds to the propagation of the action potential along the fibers; 3) the terminal phase corresponds to the termination of the action potential at the muscle/tendon junction; and 4) the slow afterwave corresponds to the negative afterpotential of the action potential. Based on these findings, we have developed new, noninvasive techniques for measuring the dispersion of motor-nerve conduction velocities and the muscle velocity recovery function.
FUTURE PLANS--The next phase of this project will investigate motor-unit discharge patterns in patients with post-stroke hemiplegia. We hypothesize that weakness associated with hemiplegia is due in part to an inability to recruit motor units and drive them at normal discharge rates.
[162] PHYSIOLOGICAL BASIS OF STRENGTH FOLLOWING SURGICAL TENDON TRANSFER
Richard L. Lieber, PhD; J. Fridén, MD,
PhD
Departments of Orthopaedics and Bioengineering,
Biomedical Sciences Graduate Group, University of California
and VA Medical Center San Diego, CA 92161; email:
rlieber@ucsd.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A745-2RA)
PURPOSE--The purpose of this project is to understand the biomechanical design of the human wrist. We are using intraoperative sarcomere length measurements to not only validate and refine the experimental model, but to provide concrete guidelines for surgeons performing such procedures.
METHODOLOGY--Sarcomere length was measured intraoperatively in five patients undergoing tendon transfer of the flexor carpi ulnaris (FCU) to the extensor carpi radialis longus (ECRL) for radial nerve palsy. All measurements were made with the elbow in 20° of flexion.
RESULTS--Prior to tendon transfer, FCU sarcomere length ranged from 2.84±0.12 µm (mean±SEM) with the wrist flexed to 4.16±0.15 µm with the wrist extended. After transfer into the ECRL tendon, sarcomere length ranged from 4.82±0.11 µm with the wrist flexed (the new longest position of the FCU) to 3.20±0.09 µm with the wrist extended, resulting in a shift in the sarcomere length operating range to significantly longer sarcomere lengths (p<0.001). At these longer sarcomere lengths, the FCU muscle was predicted to develop high active tension only when the wrist was highly extended. A biomechanical model of this tendon transfer was generated using normative values obtained from previous studies of muscle architectural properties, tendon compliance and joint moment arms. Predicted sarcomere lengths pre- and post-tendon transfer agreed well with intraoperative experimental measurements. Variation in FCU muscle length over the range 200 mm to 260 mm resulted in large changes in absolute peak moment produced as well as the angular dependence of peak moment. This was due to the change in the region of FCU operation on its sarcomere length-tension curve relative to the magnitude of the ECRL moment arm. These data demonstrate the sensitivity of a short-fibered muscle such as the FCU to affect the functional outcome of surgery. In addition, we demonstrated that intraoperative sarcomere length measurements, combined with biomechanical modeling provide the surgeon with a powerful method for predicting the functional effect of tendon transfer surgery.
[163] REPEATABILITY OF ESTIMATES OF MYOELECTRIC SIGNAL VARIABLES AND PARAMETERS
Michelangelo Buonocore, MD; Roberto Casale, MD; Fabrizio
Castellani, MS; Carlo Cisari, MD; Ugo Dimanico, MD; G.
Galardi, MD; Roberto Merletti, PhD; Alberto Rainoldi,
MS
Fondazione S. Maugeri IRCCS, Area Cravino, Pavia, Italy;
Centro di Bioingegneria, Lab. for Neurom. Syst. Eng., Osp.
V. Valletta, Torino 10135, Italy; Az. Osp. di Novara,
Novara, Italy; Az. Osp. Santa Croce e Carle, Cuneo, Italy;
Osp. San Raffaele IRCSS, Milano, Italy; email:
merletti@polito.it
Sponsor: Camera di Commercio di Torino; Fondazione Cassa di Risparmio and Compagnia di San Paolo di Torino; Fondazione S. Maugeri, Regione Piemonte; Italian Ministry for University and Scientific Research; European Concerted Action on Surface EMG for Non-Invasive Assessment of Muscles (SENIAM)
PURPOSE--The variance of repeated measurements in control subjects is a factor conditioning clinical applications of surface EMG techniques and myoelectric manifestations of muscle fatigue. It is the purpose of this study to assess this variance and find the contributions due to repeated trials (same day), different days, and different subjects for either voluntary or electrically elicited muscle contractions.
METHODOLOGY--Repeated measurements of surface EMG variables have been performed on controls (3-5 times/day, 4-5 days for each of 10 subjects and for each protocol) in isometric conditions on the vastus medialis and the biceps brachii muscles. Mean and median spectral frequencies (MDF and MNF), average rectified and root mean square values (ARV and RMS), muscle fiber conduction velocity (CV), and the crosscorrelation coefficient (CC) between the two double differential signals used for the estimation of CV were computed every second during electrically elicited contractions either tetanic (stimulation frequency of 20 Hz) or single twitch (stimulation frequency of 2 Hz) lasting 30 s. The initial values of these variables and their rate of change (initial slope) versus time were computed for each of the 15-20 contractions produced by each subject. The Intraclass Correlation Coefficient and ANOVA were used to evaluate variability over trials, days, and subjects.
PROGRESS--The protocols based on electrically elicited contractions have been completed and involved the vastus medialis and the biceps. Those focused on voluntary contractions are underway.
PRELIMINARY RESULTS--During fatiguing stimulated muscle contractions (f=20 Hz), initial values were defined as the intercept at t=0 of a regression line or exponential curve and initial slope was the derivative of such line or curve at t=0. During single-twitch nonfatiguing contractions (f=2 Hz) the average value of each variable was computed over the 30 s of contraction. During fatiguing contractions the initial value of spectral variables appeared to be the most repeatable with ICC near 85 percent, while it was below 50 percent for all the other variables. The ICC of initial slope was 52 percent for spectral variables and below 30 percent for the others.
The ICC obtained from single-twitch contractions were near 60 percent, but the ICC of CV was found to increase to 82 percent if the electrode location was carefully chosen in order to obtain a CC value above 95 percent. In addition, results obtained with interelectrode distances of 10 mm were more repeatable than those obtained with 5 mm. Although the values of ICC may appear low in some cases, it should be kept in mind that tests were performed on controls, and the values of EMG variables were within a narrow range. It is concluded that estimates of muscle fiber CV obtained using single-twitch stimulation are comparable with those obtained from more painful and complex needle procedures and that a 10 mm interelectrode distance is preferable to 5 mm for muscles that are long enough. Fatigue indices are not very repeatable, and their reliable estimates require methodological improvements.
FUTURE PLANS AND IMPLICATIONS--This work is being extended to voluntary contractions performed at 10, 30, 50, and 70 percent of the maximal voluntary contraction level. The biceps, as well as other muscles, are being investigated. We believe that the technique is very promising, but further work on normal and pathological cases is required to assess reliability and normal ranges before generalized clinical applications may be considered.
[164] MODEL-BASED UNDERSTANDING AND TEACHING OF SURFACE EMG
Elena Avignone, MS; Michelangelo Buonocore, MD; Roberto
Casale, MD; Ugo Dimanico, MD; Davide Emanville, MS; G.
Galardi, MD; Francesco Laterza, MS; Michele Matacchione MS;
Roberto Merletti, PhD; Alberto Rainoldi, MS
Fondazione S. Maugeri IRCCS, Area Cravino, Pavia, Italy;
Centro di Bioingegneria, Lab. for Neurom. Syst. Eng., Osp.
V. Valletta, Torino 10135, Italy; Az. Osp. di Novara,
Novara, Italy; Az. Osp. Santa Croce e Carle, Cuneo, Italy;
Osp. San Raffaele IRCSS, Milano, Italy; email:
merletti@polito.it
Sponsor: Camera di Commercio di Torino; Fondazione Cassa di Risparmio and Compagnia di San Paolo di Torino; Fondazione S. Maugeri, Regione Piemonte; Italian Ministry for University and Scientific Research; European Concerted Action on Surface EMG for Non-Invasive Assessment of Muscles (SENIAM)
PURPOSE--Clinical applications based on surface EMG techniques and myoelectric manifestations of muscle fatigue are conditioned by the availability of the knowledge necessary for the interpretation of these signals. Such knowledge is scarce and scattered. As a consequence these new techniques are often applied empirically, without proper background and training, and without awareness of their possibilities and limitations. It is the purpose of this work to develop and make available to the clinical community proper educational tools based on multimedia approach and suitable for self training and continued education.
METHODOLOGY--Two tools have been developed and provide the first half of the total educational package. The first tool is a mathematical model, operating with an easy graphycal interface under Windows (3.11 or 95), that allows the user to construct and activate the muscle the signals of which are to be studied. For each of the up to 100 motor units that may be simulated, the user specifies the number of fibers, their length, innervation and termination zones, the depth and size of the (circular) territory, the fiber orientation, and the conduction velocity (CV). The user then specifies the conductivities of the medium, the location and spacing of the surface electrodes, the modalities for estimating muscle fibers CV, other computational details and whether the simulated contraction is voluntary or stimulated (random or synchronized firing of the motor units). One of the following modes of operation is then selected: a) computation of signal variables, b) display of signals detected by the electrodes, c) display of one signal versus one model parameter, or d) display of a signal variable versus one model parameter. At this stage, the computational part of the model is initiated and the required output is generated, displayed graphically, and saved as an ASCII file for export. The model simulates each of the two depolarized zones of a muscle fiber as a current tripole and adds the contributions of all the tripoles for each discrete time value during the simulation.
The second tool is a traditional multimedia course organized in five sections on a) signal analysis, b) EMG signals, c) biophysics and detection, d) single motor unit signal, e) interference signal and compound action potential. After each section, questions and exercises are provided for self evaluation.
PRELIMINARY RESULTS--The model has been used for research and teaching. Among the many options is the investigation of the relationship between estimated and real variables (for example, CV), of effects not so easy to predict, such as the effect of tissue anisotropy, of eletrode-fiber misalignement. Other didactically interesting simulations concern the estimate of CV along the muscle length, crosstalk, and so forth.
FUTURE PLANS--The second half of the total educational package concerns more clinical and practical aspects, such as how and where to place the electrodes, how to measure force, single twitch response, and the like, how to associate these findings to pathologies, and how to use the model for clinical signal interpretation. The entire package will be made available on compact disk.
[165] EFFECTS OF INTRAMUSCULAR APONEUROTOMY AND RECOVERY ON PENNATE SKELETAL MUSCLE
Reinald Brunner; Peter A. Huijing, PhD; Richard Jaspers;
Johan Pel
Department of Pediatric Orthopaedics, Children's
Hospital Basel, University of Basel, Basel, Switzerland;
Institute of Fundamental and Clinical Movement Sciences,
Faculty of Human Movements Sciences, Vrije Universiteit,
1081 BT Amsterdam, The Netherlands; Integrated Biomedical
Engineering for Restoration of Human Function, Institute of
Biomedical Technology, Faculty of Mechanical Engineering,
University of Twente, Enschede, The Netherlands; email:
P_A_J_B_M_Huijing@FBW.VU.NL
Sponsor: Ciba-Geigy Jubileum Stiftung, Basel
PURPOSE--Intramuscular aponeurotomy is used clinically both to lengthen muscle and to weaken overactive muscle. Little is known about effects on muscle physiology and mechanisms of muscle recovery after such a intervention. The purpose of this project is to evaluate acute and long-term effects and the mechanisms by which these effects are reached.
METHODOLOGY--The medial gastrocnemius muscle of three groups of Wistar rats (age 15 wks) was studied: length-force characteristics and muscle geometry were determined 6 wks after proximal aponeurotomy at 50 percent length and immobilization in maximal dorsiflexion (3 days); 6 wks after sham operation and identical immobilization and 6 wks of no special treatment (controls).
After determining length-force characteristics in the second and third groups, proximal aponeurotomy was performed to asses its acute effects.
PRELIMIMARY RESULTS--Acutely, proximal aponeurotomy (groups 2 and 3) caused tearing of the muscle endomysial network. This tear along muscle fibers increased progressively in length if the muscle was exposed to high active lengths, but remained incomplete. The distal part of the muscle is not connected anymore by its proximal aponeurosis to the origion, but neurovascular supply remained intact.
This caused a scaled length-force curve at approximately 55 percent (i.e., force decreased but length force curves normalized for force showed only minor changes). This is compatible with the observation that the distal part of the muscle, despite being active, contributes only little to the muscle force. After recovery, the length force curve of the first group shifted to higher muscle lengths (i.e., became longer), but optimum force recovered to values similar to controls. The severed ends of the aponeurosis were reconnected by new aponeurotic tissue. Some muscle fibers of the distal muscle part showed degenerative changes near their proximal end. Muscle geometry showed extensive alterations compared to controls.
IMPLICATIONS--Despite acute effect of decreased muscle force, aponeurotomy is an appropriate method for lengthening short muscles. Full recovery of maximal muscle force can be expected, but on the ascending limb force may be decreased because of shifts of the length force curve to higher lengths. This fact needs to be taken into account when muscle weakening is a major indication for surgery.
[166] MUSCLE CO-CONTRACTION: EFFECT ON INTRA-ARTICULAR CONTACT PRESSURE
Richard V. Baratta, PhD, Carlos A. Guanche, MD
Bioengineering Laboratory, Department of Orthopaedic
Surgery, Louisiana State University Medical Center, New
Orleans, LA 70112
Sponsor: Irvin Cahen Chair in Orthopaedic Research
PURPOSE--Muscle co-contraction can change the anatomic relationsip between articulating surfaces, particularly in the knee joint. The purpose of this study is to study the effect of knee flexor and extensor co-contraction on the contact stress distribution of the tibio-femoral joint.
METHODOLOGY--Thin film pressure sensors are placed in both compartments of cadaveric knees with minimal soft tissue stripping. Tension in quadriceps and hamstrings are applied by a servo-hydraulic actuator, and changes in peak pressure, contact area, and mean pressure are computed and examined as fuctions of joint angle and muscle co-contraction
PROGRESS--To date, we have performed six experiments. Pending statistical analysis of the results, posterior shifts in the center of pressure with the addition of quadriceps tension can be found; these are partially offset with the addition of hamstrings tension. It also appears that the relative increase of peak pressure and mean pressure per unit of hamstrings tension is less than the increase in pressure due to tension of the extensor muscles.
[167] MUSCLE FIBER DAMAGE DUE TO ECCENTRIC CONTRACTIONS
Richard L. Lieber; D.K. Mishra, MD; Robert Benz, MD;
Tina Patel; J. Fridén, MD, PhD
Departments of Orthopaedics and Bioengineering,
Biomedical Sciences Graduate Group, University of
California; VA Medical Center, San Diego, CA 92161; email:
rlieber@ucsd.edu
Sponsor: National Institute of Arthritis and Musculoskeletal Disorders, Skin Diseases Muscle Biology Program
PURPOSE--The purpose of these studies was to determine the timing of the loss in cytoskeletal desmin that was previously observed. Since cytoskeletal loss can result in myofibrillar disruption, we felt that understanding its timing would provide insights into the damage mechanism.
METHODOLOGY--Rabbit extensor digitorum longus (EDL) and tibialis anterior (TA) muscles were examined 5 min or 15 min after eccentric exercise and 1 hour or 1 day after 30 min of an eccentric exercise protocol (n=16 rabbits). Muscles were cyclically activated at 40 Hz for 400 ms (approximately 50 percent Po) and allowed to relax for 600 ms over the treatment period. This stimulation frequency (40 Hz) was chosen based on motor unit studies, which demonstrated that at this frequency force decline was due to fatigue of the muscle fibers themselves and not the neuromuscular junction or motor nerve. The frequency was also chosen to produce the force level observed during moderate intensity exercise. We also eccentrically exercised the slow soleus muscle and measured contractile and structural parameters.
RESULTS--The earliest change noted was a significant loss of desmin labeling in 2.5±0.63 percent of the rabbit extensor digitorum longus muscle (EDL) muscle fibers (p<0.005) 5 min after initiation of eccentric exercise. Some loss of tibialis anterior (TA) fiber desmin was also apparent at this time period (0.24±0.19 percent), but the magnitude was not significantly different from zero (p>0.2). Fifteen min after initiation of exercise, desmin loss was more pronounced, increasing to 7.4±1.4 percent and 4.6±1.0 percent in the EDL and TA, respectively (p<0.005). Finally, 1 day after 30 min of eccentric exercise the percentage of fibers without desmin staining rose to 23.4±3.7 percent and 7.7±2.4 percent in the EDL and TA, respectively (p<0.001). Loss of desmin staining occurred in the absence of contractile or metabolic protein disruption. Increased staining intensity of the intrasarcomeric cytoskeletal protein titin and an inability to exclude plasma fibronectin was also observed in most but not all fibers which had lost desmin staining. Desmin disruption thus represents a very early structural manifestation of muscle injury during eccentric contraction. Soleus muscles showed no such abnormalities. Soleus muscle stiffness decreased by only 30 percent over the 30 min treatment period while isometric force decreased by 85 percent. These data indicate that, while soleus muscles decreased their force generating capability significantly, there were a number of cross-bridges still attached that were not generating force.
[168] SURFACE AND WIRE EMG CROSSTALK IN NEIGHBORING MUSCLES
Moshe Solomonow, PhD; Richard V. Baratta, PhD; Bing-He
Zhou, EE; Robert D. D'Ambrosia, MD
Department of Orthopaedics, School of Medicine in New
Orleans, Louisiana State University Medical Center, New
Orleans, LA 70112
Sponsor: National Science Foundation, Arlington, VA 22330
PURPOSE--EMG crosstalk between neighboring muscles presents a long-standing controversy without final conclusion as to its existence and, if so, to the mechanism underlying the process. We set an experimental protocol to clearly delineate whether crosstalk exists and under what circumstances.
METHODOLOGY--We undertook an investigation in animal model in which the muscle nerves of the soleus, medial, and lateral gastrocnemius, and tibialis anterior muscles were supramaximally stimulated while surface and wire EMG from all the muscles were recorded. Later, the muscle nerves were all cut, except for the nerve to the medial gastrocnemius, which was supramaximally stimulated while surface and wire EMG from all the muscles were recorded. Any EMG in the muscles in which their nerves were cut was considered pure and true crosstalk.
RESULTS--It was shown in a cat model that the extent of the crosstalk in the soleus, tibialis anterior, and the lateral gastrocnemius was less than 4-5 percent during maximal stimulation of the medial gastrocnemius when recording with surface electrodes. When recording with wire electrodes, the crosstalk was limited to 1-2 percent of maximal EMG activity in the corresponding muscles.
In several animals with a confirmed fat layer over the muscles, the crosstalk values in the inactive muscles ranged between 16-32 percent, suggesting that adipose tissue is responsible for inducing significant crosstalk in surface recordings of the EMG. There was no impact on the wire recordings.
It was concluded that when using electrodes appropriately sized to the muscle dimensions and correctly placed, the amount of crosstalk in surface and wire recordings is negligible. However, when recording surface EMG from muscles covered with adipose tissue, the EMG will be contaminated with significant crosstalk and may lead to false conclusions.
[169] CONTROL OF JOINT MOTION WITH SYNERGISTIC STIMULATION OF ITS AGONIST/ANTAGONIST MUSCLES
Moshe Solomonow, PhD; Richard V. Baratta, PhD; Bing-He
Zhou, EE
Department of Orthopaedics, School of Medicine in New
Orleans, Louisiana State University Medical Center, New
Orleans, LA 70112
Sponsor: National Science Foundation, Arlington, VA 22330
PURPOSE--Joint motion requires complex and simultaneous activation levels from the agonist and antagonist muscles in order to accomplish the intended task, while subject to various internal and external disturbances. This project initiated trials using antagonistic stimulation of the muscle groups crossing the joint with various levels of weighted motor unit recruitment in the agonist and antagonist to reaffirm our data collected from the elbow joint of humans. The objective was to improve the external control of a joint with regard to various loading conditions.
METHODOLOGY--Agonist/Antagonist muscle coactivation strategies were implemented through electrical stimulation. These strategies were based on the compromise between the physiological need for joint stabilization by the antagonist at high force levels and the need to prevent joint laxity at low force levels. These two conflicting requirements resulted in two coactivation parameters. The first, antagonist gain, was the linear gain of the antagonist muscle with respect to the input command. This parameter came into play when high net joint torques were called for. The second parameter, overlap, was a range of crossover of the antagonist unto the agonist domain. Strategies combining antagonist gain and overlap were tested as to their ability to track linear, step, sinusoidal, and pseudo-random input signals.
RESULTS--It was found that moderate amounts of antagonist gain (5 percent) and overlap (25 percent) would provide optimal tracking and minimal distortion during isometric and various types of load-moving contractions. When controlled by these strategies, the dynamic frequency response of the cat ankle joint showed small yet statistically significant differences on the dynamic response of the agonist/antagonist muscle-joint system.
[170] THREE-DIMENSIONAL DESCRIPTION OF MUSCLE PROPERTIES
Moshe Solomonow, PhD; Richard V. Baratta, PhD
Department of Orthopaedics, School of Medicine in New
Orleans, Louisiana State University Medical Center, New
Orleans, LA 70112
Sponsor: National Science Foundation, Arlington, VA 22330
PURPOSE--Traditional descriptive models of muscle properties are limited to the length-tension relationship obtained from isometric contractions, and from force-velocity curves obtained from isotonic contraction. Unfortunately, combining both curves to yield the force-length-velocity relationships is invalid, as data obtained in isometric contractions could differ by as much as 50 percent from those of shortening contraction. This problem was solved by describing length-force and velocity in a load-moving contraction.
METHODOLOGY--We have set up a protocol by which a muscle was stimulated electrically through its nerve, allowing shortening while applying displacing loads of different size. The initial length of the muscle when loaded and the final length after supramaximal stimulation provided a set of points with which the passive and total length-load (force) ratios were plotted as a function of load values. The shortening curve of the muscle during stimulation was recorded and differentiated mathematically to yield its velocity at any given length and for any given load, thereby allowing the construction of a load-length-velocity curve.
RESULTS--The initial results provide the first valid description of load-length-velocity of an isolated muscle, which could be used in large-scale modeling of human movement, neuroprosthesis design, and general understanding of muscle functions.
[171] LATERAL OR MYO-FASCIAL FORCE TRANSMISSION IN SKELETAL MUSCLE
Peter A. Huijing, PhD; Guus Baan; Richard Jaspers; Guido
Rebel
Institute of Fundamental and Clinical Movement Sciences,
Faculty of Human Movements Sciences, Vrije Universiteit,
1081 BT Amsterdam, The Netherlands; Integrated Biomedical
Engineering for Restoration of Human Function, Institute of
Biomedical Technology, Faculty of Mechanical Engineering,
University of Twente, Enschede, The Netherlands; email:
P_A_J_B_M_Huijing@FBW.VU.NL
Sponsor: Ciba-Geigy Jubileum Stiftung, Basel
PURPOSE--Experiments on single myofibers and small bundles of myofibers indicate that lateral force transmission can take place. On the basis of morphological studies of 'in-series fibered muscle' and biomechanical modeling, it has been argued that force could also be transmitted laterally from the tapered ends of myofibers onto paired myofibers via the intramuscular connective tissue component. Shearing of the interfaces between myofibers is hypothesized to be the mechanisms of transmission. The interfaces are made up of basal membranes of both myofibers and their common endomysium.
The purpose of this project is to study the functional importance of such effects in fully activated whole muscle.
METHODOLOGY--Gastrocnemius medialis and EDL muscle of Wistar rats were studied: length force characteristics and muscle geometry were determined. The morphology of EDL muscle allows interference with myotendinous force transmission for selected parts of the muscle by performing distal tenotomy. Aponeurotomy allows interference with the inter fiber interfaces.
PRELIMIMARY RESULTS--It is estimated that by tenotomy of head II, III, and IV, up to 55 percent of the physiological cross-sectional area is prevented from using myotendinous force transfer.
The decrease in force is always considerably less than 55 percent. For example, optimum force decreased to 84 percent of whole muscle optimum force, as optimum length shifted by 1.6 mm to higher muscle length. The shift of optimum length is compatible with changes of estimates of active fiber length. Interference with interfiber interfaces decreased lateral force transmission in proportion to the magnitude of interference, but did not fully eliminate it.
IMPLICATIONS--These results show the importance of lateral force transfer from myofibers in whole muscle to the intramuscular connective tissue. So, in fact, two parallel paths for force transfer are available: myo-tendinous and myo-fascial transfer. Regarding myo-fascial force transfer, the possibility has to be considered that force will be transmitted from the muscle by other than myotendinous paths.
[172] ISOMETRIC LENGTH-FORCE CHARACTERISTICS OF PENNATE MUSCLES DURING AND AFTER SHORTENING: EXPERIMENTAL AND MODELLING RESULTS
Peter A. Huijing, PhD; Henk J. Grootenboer; Bart
Koopman; Kenneth Meijer; Bart van der Linden
Institute of Fundamental and Clinical Movement Sciences,
Faculty of Human Movements Sciences, Vrije Universiteit,
1081 BT Amsterdam; Integrated Biomedical Engineering for
Restoration of Human Function, Institute of Biomedical
Technology, Faculty of Mechanical Engineering, University of
Twente, Enschede, The Netherlands;
email: P_A_J_B_M_Huijing@FBW.VU.NL
Sponsor: Ciba-Geigy Jubileum Stiftung, Basel
PURPOSE--The purpose of this project was twofold: to study effects of shortening history on isometric length-force curves of pennate muscle by experimental and modelling approaches, and to study muscle geometry and its functional effects by planimetric and finite element modelling (FEM).
METHODOLOGY--Variables of muscle geometry (i.e., fiber length, aponeurosis length, and fiber and aponeurosis angles), were determined during maximal activation. Isometric length-force curves were determined without previous shortening and after shortening over different length ranges at a number of shortening speeds. A descriptive model was designed to account for these effects.
An FEM was constructed that takes into account muscle fiber properties as well as aponeurosis and tendon properties and the mechanical interaction of these variables.
RESULTS--After previous shortening, length-force characteristics of maximally active rat medial gastrocnemius muscle differ very substantially from that determined in fully isometric contractions. Particularly at lengths at or over optimum length attained after low-speed shortening, muscle force is decreased compared to the fully isometric case. Actual isometric length-force properties can be constructed by connecting points of different curves according to shortening history. Negative length-force slopes found in the fully isometric condition are not present at lengths well over optimum.
FEM shows that a secondary distribution of mean fiber mean sarcomere length develops on activation through mechanical interaction of fibers and elastic components. FEM could not predict well either fully isometric or shortening history influenced length force curves, due to a primary distribution of fiber mean sarcomere length. However, FEM showed mechanisms of interaction between adjacent bundles of fibers within a muscle leading to secondary distributions of fiber mean sarcomere lengths. Indications for lateral force transfer from myofibers were also found.
IMPLICATIONS--Due to alterations of length-force curves, it is not appropriate to consider actual force delivered by a muscle as a result of combination of a fully isometric length force-curve and a force-velocity curve.
[173] SKELETAL MUSCLE LENGTH-FORCE CHARACTERISTICS DURING MAXIMAL AND SUBMAXIMAL ACTIVATION
Peter A. Huijing, PhD; Guus C. Baan; Boris Roszek; Peter
Bosch
Institute of Fundamental and Clinical Movement Sciences,
Faculty of Human Movements Sciences, Vrije Universiteit,
1081 BT Amsterdam, The Netherlands; Integrated Biomedical
Engineering for Restoration of Human Function, Institute of
Biomedical Technology, Faculty of Mechanical Engineering,
University of Twente, Enschede, The Netherlands;
email: P_A_J_B_M_Huijing@FBW.VU.NL
Sponsor: Ciba-Geigy Jubileum Stiftung, Basel
PURPOSE--The purpose of this project was to make a link between the results of experiments studying muscle properties under maximal activation and the in vivo properties of muscle that are rarely characterized by maximal activation. For that purpose several conditions of submaximal activation were imposed on in situ muscles for a systematic analysis.
METHODOLOGY--In addition to variables of muscle geometry (i.e., fiber length, aponeurosis length, and fiber and aponeurosis angles), the number of sarcomeres in series within fibers and filament-length parameters were determined. Submaximal activity of was induced in two ways: 1) in fully recruited muscle: stimulation frequencies between 100 and 15 Hz were imposed. This was performed for constant frequency (CSF) or decreasing frequency (DSF) protocols. A Hill-type model was constructed based on 100 Hz length force characteristics and force-frequency characteristics to describe length-frequency-force results for DSF protocols.
RESULTS--Length-force characteristics of submaximally active rat medial gastrocnemius and EDL muscle differ very substantially from that of the maximally active muscle. With all motor units active, force decreased at lower stimulation frequencies and muscle optimum length shifted to higher muscle lengths. If the low stimulation frequencies followed higher ones (history effects), the decrease in force was smaller (i.e., potentiation occurred). The shift of optimum length was also smaller in this case. Comparison of the model and experimental results show that these effects of stimulation history are quite specific for different DSF protocols.
IMPLICATIONS--Length-force and force velocity properties of submaximally active muscle are likely to be very much dependent on the degree of activation and its short time history. In effect, it creates the need for a control which may referred to as intramuscular coordination. For functional electrostimulation, these findings will have important implications, as well as for modelling of muscle and movement.
[174]MODELING TENDON DEVELOPMENT, ADAPTATION, AND REGENERATION: A PILOT STUDY
Dennis R. Carter, PhD; Gary S. Beaupre, PhD; Tishya A.L.
Wren, PhD; Eric E. Sabelman, PhD; R. Lane Smith, PhD
Rehabilitation Research and Development Center, VA Palo
Alto Health Care System, Palo Alto, CA 94304; Biomechanical
Engineering Division, Stanford University, Stanford, CA
94305; email: wren@bones.stanford.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Pilot Project #A2058-AP)
PURPOSE--Tendon healing typically occurs through a process involving scar tissue, producing a structure with inferior mechanical properties compared to normal tendon. The long-term objective of this project is to develop a biomechanical framework for understanding how to promote better repair, resulting in a repaired or regenerated tendon having improved mechanical properties.
The specific objective of this pilot study is to answer three key questions:
METHODOLOGY--In this study we used a microstructural model to characterize soft tissues, such as tendon and ligament. This model uses mixture theory to represent collagen fibers embedded in a ground substance. We also used a phenomenological model to predict tendon mechanical properties and strength, based upon tendon age and mechanical loading history.
PROGRESS--We have successfully developed a microstructural model for uniaxial tensile and fatigue behavior of a wide range of soft skeletal connective tissues including tendon, ligament, meniscus, and articular cartilage. In addition, we have developed an analytical framework for describing changes in uniaxial tendon properties in response to the mechanical loading history as represented by a daily strain stimulus.
RESULTS--Our microstructural model produces stress-strain curves that closely resemble the curves obtained from mechanical testing, including the nonlinear toe region, linear elastic, and failure regions. The results of our phenomenological model focusing on growth, development, and adaptation of tendons to mechanical loading histories shows how tendons and ligaments achieve a desired stiffness by adjusting both their size and material properties during normal growth and under conditions of increased and decreased loading. These two models are providing new insights into previous experimental studies, and we plan on using these models to suggest new and improved clinical techniques for tendon repair and regeneration.
[175] LIGAMENTO-MUSCULAR PROTECTIVE REFLEX IN THE KNEE, SHOULDER, ANKLE, AND ELBOW
Moshe Solomonow, PhD; Robert D. D'Ambrosia, MD; Carlos
A. Guanche, MD
Department of Orthopaedics, School of Medicine in New
Orleans, Louisiana State University Medical Center, New
Orleans, LA 70112
Sponsor: National Science Foundation, Arlington, VA 22330
PURPOSE--The ligaments are considered to be the primary restraints of a joint, keeping the bones aligned in their natural kinematic state throughout the range of motion. A growing pool of evidence shows that the musculature significantly contributes toward joint stability as well as protection of the ligaments. Our early work with the anterior cruciate ligament (ACL) shows the variety of mechanoreceptors present in this ligament, and also that a reflex arc exists from these mechanoreceptors to the muscles crossing the knee. Strain applied directly to the ACL resulted in reflex contraction of the hamstrings in animal models and in humans. We investigate whether such a protective reflex exists in other joints.
METHODOLOGY--We undertook several new studies to determine if such a ligamento-muscular reflex arc exists in other joints while stimulating articular nerve branches emerging from the ligaments. To date we have found that the protective reflex exists in the shoulder, elbow, and ankle, in addition to the knee.
RESULTS--Therefore, a synergistic relationship probably exists between the ligaments and muscles of every joint to ensure preservation of the tissue, prevention of damage, and proper kinematic alignment of the bones when various internal and external disturbing loads are applied. During surgery, the neural integrity of the ligament-joint should be preserved as much a possible in order to avoid joint arthropathy, and then utilized to design the appropriate postsurgical therapy.
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Last revised Fri 04/30/1999