[139] SURFACE EMG DURING DYNAMIC CONTRACTIONS OF LIMB MUSCLES
D. Farina; S. Gaudenti; Roberto Merletti, PhD; M.
Nazzaro; Alberto Rainoldi, MS
Centro di Bioingegneria, U.SA.S.-Politecnico di Torino,
ASL1-Regione Piemonte, Torino, Italy; Isituto Superiore di
Educazione Fisica, Torino, Italy; Facoltà di Medicina,
Università di Tor Vergata, Roma; email:
merletti@polito.it
Sponsor: Camera di Commercio di Torino, Compagnia San Paolo di Torino, Fondazione CRT di Torino, Regione Piemonte
PURPOSE--Surface EMG is often used to estimate muscle activity levels during dynamic contractions. A poorly investigated issue concerns the changes that affect EMG amplitude due to electrode location along the muscle and relative muscle-electrode shifts during movement. This work provides some preliminary data on the importance of these two factors in the evaluation of activity level of thigh and leg muscles in control subjects.
METHODOLOGY--The EMG from 10 biceps brachii muscles and 59 muscles of the thighs of 10 control subjects were investigated using a linear array of 16 electrodes spaced by 10 mm (silver bars of 1 mm diameter and 10 mm length) spanning the entire length of the muscles under examination. Isometric voluntary flexions of the elbow and extensions of the knee were performed at three different joint angles and at levels of 30, 50, and 70 percent of the maximal voluntary contraction (MVC) level measured at that angle. The EMG was detected differentially from adjacent electrode pairs, amplified and displayed on the screen of a PC. The average rectified value (ARV) of each channel was computed over one-second intervals during a 10-s contraction.
RESULTS--Signals showing propagation of MUAPs from the innervation zone to the tendons were always obtained from the biceps brachii, occasionally from the vastus medialis, vastus lateralis, knee flexors, gastrocnemius medialis and lateralis, and tibialis anterior but almost never from the rectus femoris. The following events were observed in the leg muscles: a) in most instances large non-propagating potentials were evident, particularly on the rectus femoris, b) the EMG amplitude (average rectified value) changed considerably along the array, sometimes by 100 percent with minimal values above the innervation zones, c) changing the knee angle from 105 to 135° and to 165° (for the same MVC fraction) caused relative changes of ARV among the channels of the array and shifts of the innervation zone under the array, d) the shifts of the innervation zone ranged from less than 1 cm (vastus lateralis and medialis, gastrocnemius lateralis and medialis, tibialis anterior) to 3.5-4 cm in the flexors of the knee.
IMPLICATIONS--We concluded that the muscles of the thigh and leg do not show the predictable behaviour of the often investigated biceps brachii. The large nonpropagating components may be attributed to fiber-end effects or to sources distant from the electrodes (possibly crosstalk) and deserve further investigation. Their amplitude variations do not necessarily reflect variations of the level of activation of the muscles. The pattern of activity along the array changes when the knee angle is changing, even if the contraction level remains the same. This fact indicates that the amplitude of surface EMG does not necessarily reflect the level of muscle activation and that relative muscle-electrode movement plays an important role in determining EMG level. As a consequence, great caution must be adopted in the interpretation of EMG in dynamic conditions and proper methods for the compensation and correction of these artifacts must be developed.
[140] A MULTIMEDIA TOOL FOR TEACHING/LEARNING SURFACE EMG
Roberto Merletti, PhD; M. Gazzoni
Centro di Bioingegneria, U.SA.S. - Politecnico di
Torino, ASL1-Regione Piemonte, Torino, Italy; email:
merletti@polito.it
Sponsor: Camera di Commercio di Torino, Compagnia San Paolo di Torino, Fondazione CRT di Torino, Institute for Scientific Interchange, Regione Piemonte
PURPOSE--Teaching of surface EMG techniques is still uncommon in European as well as American academic institutions. A few continuing education initiatives and professional courses address the issue, but in general they are expensive and require interruption of routine activities of busy rehabilitation doctors and physical therapists. We have developed the first of a two-volume multimedia tool that can be installed on a PC. Vol 1, now available, addresses the issues of signal processing, EMG biophysics, signal propagation, detection modalities, and the myoelectric manifestations of muscle fatigue. Vol. 2 is expected to be available in 1999 and will address the issues of electrode location, EMG interpretation during isometric as well as dynamic contractions, applications in ergonomics, rehabilitation, and sport and occupational medicine.
METHODOLOGY--The teaching tool was developed using Toolbook and many interactive animations, examples, and self-evaluation tests totalling more than 200 "pages." Mathematical approaches and equations are avoided and replaced by animations. In particular, animations are used to introduce the concepts of Fourier expansion and power spectrum of a signal, to describe the relation between spatial potential distribution on the skin and time-varying voltage under the electrodes, and to interpret the signals obtained under a linear electrode array. The differences between monopolar, bipolar (or single differential), and double differential detection are described with details about advantages and disadvantages. The generation, propagation and extinction of motor unit action potentials (MUAPs) is simulated to show how surface signals reflect motor unit properties.
RESULTS--Vol 1 is presently available on three floppy discs and will be available on a CD together with Vol 2. Preliminary experience in EMG lectures and courses has been very positive. This tool is not an expert system and does not directly help in clinical decision making. It provides a basic understanding of the biophysics and physiology that underline the genration, detection, and interpretation of surface EMG. It plays an important role in clarifying that EMG is very rich in physiological information, but the extraction of such information requires competence and deep understanding that cannot be provided to the incompetent user by a computer running canned programs. The tool has been evaluated within the European Concerted Action on Surface EMG for NonInvasive Assessment of Muscles (SENIAM).
IMPLICATIONS--Busy rehabilitation professional, undergraduate and graduate students and researchers may benefit from this tool and use it in their spare time, at home as well as in the office. Teachers may find it to be a a useful integration for their lectures and courses. Their feedback would be very much appreciated. Further information is available from merletti@polito.it.
[141] EFFECTS OF INTRAMUSCULAR APONEUROTOMY AND RECOVERY ON PENNATE SKELETAL MUSCLE
Reinald Brunner; Peter A. Huijing, PhD; Richard Jaspers;
Johan Pel; Henk J. Grootenboer; Bart Koopman; Bart van der
Linden
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, Switzerland
PURPOSE--Intramuscular aponeurotomy is used clinically to obtain the lengthening of 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 longer-term effects to explore the mechanisms by which these effects are reached.
METHODOLOGY--The medial gastrocnemius muscle of three groups of Wistar rats (age 15 wk) was studied: length force characteristics and muscle geometry were determined 6 wk after proximal aponeurotomy at 50 percent length and 3-day immobilization in maximal dorsiflexion, 6 wks after sham operation and identical immobilization, and 6 weeks after no special treatment (controls).
After determining length force characteristics in the experimental groups, proximal aponeurotomy was performed to asses its acute effects.
Recently, finite element modeling of acute effects of aponeurotomy was undertaken.
PRELIMIMARY RESULTS--Acutely, proximal aponeurotomy 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; that is, 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 in the first group, the length-force curve 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.
[142] PATTERNS OF MUSCLE SUBSTITUTION USED TO COMPENSATE FOR FOCAL WEAKNESS IN SURVIVORS OF POLIO AND INDIVIDUALS WITH RECENT MUSCULOSKELETAL SURGERY
Alberto Esquenazi, MD; Mukul Talaty, MS BME; Barbara
Hirai; John Whyte, MD, PhD; Mary Ann Keenan, MD
Gait & Motion Analysis Laboratory, MossRehab Hospital,
Philadelphia, PA 19141; Neuro-Orthopaedic Program, Albert
Einstein Medical Center, Philadelphia, PA 19141; email:
aesquena@aehn2.einstein.edu;
mtalaty@aehn2.einstein.edu
Sponsor: Department of the Army, The Pentagon, VA 20310; Post Polio Clinic of the Albert Einstein Healthcare Network
PURPOSE--This ongoing study aims to understand how localized muscle weakness leads to patterns of compensation. The immediate goals are to determine the compensatory substitution patterns for hip and knee weakness while getting out of a chair and to determine the biomechanical characteristics that will predict overuse sites.
METHODOLOGY--Subjects from two groups, Post Polio Syndrome (PPS) and post-surgery (SURG), with clinically documented hip and/or knee extensor weakness have completed the protocol. Subjects performed the sit-to-stand motion with and without assist from arm rests in two different chair heights, while kinetic, kinematic, and dynamic electromyographic data are gathered. The order of performance of the different conditions were randomly assigned, and each task condition was repeated a minimum of six times. Kinetic data consisted of forces under the feet recorded by two force plates. Kinematic data consisted of 3-D motion analysis using infrared markers and a computer-based motion analysis system (Selspot II) recorded on videotape. Dynamic polyelectromyographic data were recorded from a standard set of 11 muscles of the upper and lower limbs and trunk on each side of the body, using surface electrodes and standardized amplification and filtering techniques.
PROGRESS--Data were gathered from 13 subjects with predominant unilateral weakness of the hip extensors, 10 with predominant unilateral weakness of the knee extensors, and 6 SURG subjects with recent unilateral hip or knee surgery. Comparison of groups with weakness in the same muscles from different etiologies are being made. Currently, data analysis on kinetic data has begun in order to determine where subjects shift the lower limb demands while getting out of the chair when weakness is present and how that shifting is affected by chair height.
PRELIMINARY RESULTS--Chair height, weakness, dominance, and use of arms definitely influence the effort expended by the current population in getting out from the chair. Gender may also contribute to different patterns of performance.
FUTURE PLANS--Kinematic and EMG data will be analyzed to further elucidate shifting of muscle demands due to biomechanical changes imposed by the different test conditions. Trends in how performance parameters are affected in the PPS (chronic weakness), as compared to the SURG (acute weakness), population will also be analyzed. In general, trends in muscle use shifting (compensation) will be monitored as part of an ongoing effort to document and model compensation mechanisms.
[143] REPEATABILITY OF SURFACE EMG VARIABLES DURING VOLUNTARY ISOMETRIC CONTRACTIONS OF THE BICEPS BRACHII MUSCLE
Alberto Rainoldi, MS; G. Galardi, MD; L. Maderna; G.
Comi; L. Lo Conte; Roberto Merletti, PhD
Centro di Bioingegneria, U.SA.S.-Politecnico di Torino,
ASL1-Regione Piemonte, Torino, Italy; Dipartimento di
Neuroscienze, Unità Operativa Disturbi del Movimento, Osp.
S. Raffaele, IRCCS, Milano, Italy; email:
merletti@polito.it
Sponsor: European Concerted Action SENIAM, Camera di Commercio di Torino, Compagnia di San Paolo, Fondazione CRT di Torino, and Regione Piemonte
PURPOSE--The value of surface electromyography techniques for noninvasive muscle characterization has been demonstrated by many authors. Either voluntary or electrically elicited isometric contractions have been adopted for the purpose of associating EMG variables to muscle conditions. Spectral features, such as the mean and the median frequency (MNF and MDF), amplitude features, such as the average rectified value and the root mean square value (ARV and RMS), and muscle fiber conduction velocity (CV) have been the variables chosen by most investigators to quantify myoelectric manifestations of muscle fatigue which consist in a "slowing" of the signal reflected by a compression of its power spectrum, a decrease of MDF and MNF, and an increase of ARV and RMS. These changes have been demonstrated to reflect muscle properties and fiber constituency, and have been applied in ergonomics, back analysis, and dentistry. The potential clinical usefulness of this technique is unquestionable but conditioned by an acceptable level of repeatability of the estimates of the variables of interest. Literature data on repeatability are neither complete nor satisfactory, and only a few reports provide results or conclusions with the proper statistical support.
It is the purpose of this work to contribute additional knowledge to the issue of repeatability of estimates of spectral and amplitude variables and muscle fiber CV and estimates of the rate of change of these variables in the biceps brachii muscle of control subjects during voluntary contractions sustained at different torque levels. This work is meant to provide a statistical basis for the investigation of functional muscle structure in control and pathological subjects by means of surface EMG.
METHODOLOGY--Ten nonimpaired male controls, ranging in age from 23 to 43, participated in this evaluation. Each lay on his back with the right dominant arm horizontal and abducted at 90°. The forearm was at 120° with respect to the arm. The arm and forearm were placed in an isometric brace equipped with two torque transducers (one on each side of the arm) and connected to a display that provided the subject with visual feedback about the torque level he produced. The protocol consisted in three experimental sessions repeated on three different days. Three maximal voluntary contractions (MVC) of the elbow flexors were performed at the beginning of each session. Each MVC lasted 3-5 s. Targets were then set on a visual feedback display at 10, 30, 50 and 70 percent of the MVC value. Voluntary contractions of the biceps brachii were then performed in random order with a 5 min rest interval between subsequent contractions. Each contraction was repeated three times at the same fraction of the MVC level.
RESULTS--In order to evaluate the intra- and inter-subject repeatability, the Interclass Correlation Coefficient (ICC) and the Standard Error of the Mean (SEM) were used. Contrary to observations in other muscles, CV estimates appeared to be very repeatable both within and between subjects. CV showed a small but significant increase when contraction force increased from 10 to 50 percent MVC but no change for further increase of force. As force increased, MNF showed a slight decrease possibly related to a wider spreading of the CV values. The rate of time decrement of MNF and CV increased with the level of contraction. MNF initial values are the most "reliable" parameters in the sense that they a) are the most repeatable across experimental sessions and trials performed on the same subject and b) are sensitive to individual differences between subjects. We found a coefficient of variation of the mean in the range of 4 percent and 2 percent for MNF and CV. A small, but statistically significant, increment of the initial value of CV is evident when the contraction level increases from 10 to 30 percent MVC, while a small, but statistically significant, decrement of initial value of MNF is evident as the contraction level increases from 10 to 70 percent MVC. As expected, ARV increases markedly with the level of contraction. The regression lines of MNF and CV versus time become steeper as the contraction level increases, while the slope of ARV increases slightly when the contraction level increases and is mostly affected by individual variability.
IMPLICATIONS--On the basis of our observations, CV would be a better indicator of motor unit recruitment than MNF (or MDF). We find that, in the normal biceps, the effect of contraction level on the initial values of CV and MNF is small and may be detectable only in specific individual cases by repeated contractions. During contractions sustained at high MVC fractions, the normalized rate of decrease of MNF is higher than that of CV, confirming previous observations that factors other than CV affect MNF or MDF. Among these factors, the width of the depolarization zone and the dispersion of the CV values are good candidates for further investigation. These results provide additional evidence in support of the surface EMG technique and of its capability to outline differences between muscles and between subjects.
[144] 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; email: rbarat@lsumc.edu
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 its underlying mechanism. 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 led to false conclusions.
[145] 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; email: rbarat@lsumc.edu
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.
[146] 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; email: rbarat@lsumc.edu
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.
[147] 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: None listed
PURPOSE--The purpose of this project was 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 (FE) modelling.
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.
A FE model 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 length 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 length.
FE modelling shows that a secondary distribution of mean fiber mean sarcomere length develops on activation through mechanical interaction of fibres and elastic components. FE modelling 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, it 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.
[148] SKELETAL MUSCLE LENGTH FORCE CHARACTERISTICS DURING MAXIMAL AND SUBMAXIMAL ACTIVATION.
Peter A. Huijing, PhD; Guus C. Baan; Petra Mela; Peter
H. Veltink
Institute of Fundamental and Clinical Movement Sciences,
Faculty of Human Movements Sciences, Vrije Universiteit,
1081 BT Amsterdam, The Netherlands; 2) 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: None listed
PURPOSE--The purpose of this project was to make a link between results of experiments studying muscle properties under maximal activation and the in vivo properties of muscle rarely characterized by maximal activation.
For that purpose several conditions of submaximal activation were imposed on in situ muscles for a systematic analysis in experimental animals as well as human subjects.
METHODOLOGY--In addition to variables of muscle geometry (i.e., fiber length, aponeurosis length, and fiber and aponeurosis angles), number of sarcomeres in series within fibers, the filament length parameters were determined in the animal model. Submaximal activity was induced in fully recruited muscle by imposing stimulation frequencies between 100 and 15 Hz, both for constant frequency (CSF) or decreasing frequencies (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 decreasing frequency protocols.
RESULTS--Length-force characteristics or joint angle moment characteristics of submaximally active rat medial gastrocnemius and EDL muscle as well as human gastrocnemius and quadriceps 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 animal 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 (FES), these findings will have important implications as well for modelling of muscle and movement.
[149] 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: None listed
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 mechanism 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 was 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 interfiber interfaces.
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.
[150] LIGAMENTO-MUSCULAR PROTECTIVE REFLEX IN THE KNEE, SHOULDER, ANKLE, ELBOW, AND SPINE
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; email: rbarat@lsumc.edu
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 to 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 as possible in order to avoid joint arthropathy, and then utilized to design the appropriate postsurgical therapy.
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