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Biomedical subjects

M Solomonow

Publications and source records attributed to M Solomonow.

At least 55 records · Page 3Linked to original sources
PubMed1997

Reciprocating gait orthosis powered with electrical muscle stimulation (RGO II). Part I: Performance evaluation of 70 paraplegic patients.

Seventy paraplegics were fitted with an improved Reciprocating Gait Orthosis powered with or without (low-level injury) electrical stimulation of the thigh muscles (RGO II) as a secondary rehabilitation phase after the acute period. The patients comprised a broad cross-section of the paraplegic population applying for medical services and varied in age from 16 to 55 years, time since injury ranging from less than 1 to 15 years, injury levels ranging from C-6/7 to T-11/12, and varying levels of spasticity, contractures, scoliosis and other related medical and physiologic problems. The success/failure ratio was dependent on the injury level, which was 1:1 for paraplegics with injury level at C-6/7; 1.67:1 for those with injury of T-1/3; and about 4:1 for paraplegics with injury level from T-3 to T-12. Lack of motivation and medical problems unrelated to the RGO II treatment were the primary reasons for failure. The duration of treatment (outpatient service three times per week) ranged from 2 to 48 weeks (mean: 16). Forty-one patients who completed the RGO II rehabilitation and were sent home with the orthosis for independent use (for at least 6 months and up to 3 years) were surveyed by a staff member for analysis of the meaning and impact of the RGO II on the patient's life and health, and potential problems. It was shown that 80.5% of the 41 patients were regular users and 19.5% were non-users. Thirty-eight of the 41 patients declined an offer to return the RGO II equipment for a full refund, while three patients were willing to return the orthosis. It was concluded that the RGO II is viable orthosis for restoring standing and limited walking in paraplegics while providing sufficient function, safety, and reliability. The most appropriate patients for the use of such an orthosis consist primarily of those with T-3 to T-12 injury level and good motivation, although highly selected patients with higher injury levels also can benefit from its use. Regular use of the RGO II, even for exercise only, had a general positive impact on the patients' health and outlook.

Adolescent↗
PubMed1997

Reciprocating gait orthosis powered with electrical muscle stimulation (RGO II). Part II: Medical evaluation of 70 paraplegic patients.

Medical evaluation was performed on a group of paraplegics who were trained to walk with the Reciprocating Gait Orthosis powered with electrical muscle stimulation (RGO II). The evaluation included changes in spasticity, cholesterol level, bone metabolism, cardiac output and stroke volume, vital capacity, knee extensors torque, and heart rate at the end of a 30-meter walk. After an average of 14 weeks of training during which patients walked for 3 hours per week, significant reductions in spasticity, total cholesterol and low-density lipids, hydroxyproline/creatinine ratio, and increased knee extensor torque were evident. The data also showed that improvements occurred in the calcium/creatinine ratio, serum calcium and alkaline phosphatase levels, cardiac output and stroke volume, and vital capacity, yet these improvements were not statistically significant. The final heart rate at the end of a 30-meter walk showed that the RGO II required only a moderate level of exertion, which was found to be the lowest among the other mechanical or muscle stimulation orthoses available to paraplegics. It was concluded that the limited but reasonable level of functional regain provided by the RGO II is associated with a general improvement in the paraplegic's physiological condition if used for a minimum of 3 to 4 hours per week.

Bone Resorption↗
PubMed1997

Accuracy of formula-derived creatinine clearance in paraplegic subjects.

The usefulness of formula-derived creatinine clearance (CC) is not well established among the paraplegic population. We prospectively collected 24-hour-urines from paraplegic subjects, obtaining 81 collections from 42 patients over 27 months. After validation, 57 collections were used to obtain measured CC. CCs were also estimated using several formulae. Measured CC and estimated CC were then compared. In the case of the Cockroft-Gault formula, the overall correlation was excellent, with an r value of 0.88 and p = 0.0001. In our study 40, 70, and 93% of the estimated CCs were within 10, 20, and 33% of the measured CCs. These numbers are similar to the ones reported by Cockroft and Gault. Also, the data on measured creatinine clearance in paraplegics compared favorably with parallel data obtained from nonparaplegics (91 24-hour-urine collections, 65 validated). We conclude that the Cockroft-Gault formula (and other formulae) estimate creatinine clearance as accurately in the paraplegic population as they do in the nonparaplegic population.

Adult↗
PubMed1996

Motor unit recruitment strategy changes with skill acquisition.

The modifications of motor unit recruitment strategy due to skill acquisition was determined in the elbow flexor-extensor muscles of normal human subjects. The median frequency of the power density spectra of the electromyograms recorded from the biceps and triceps muscles during a 3-s linear increase in flexion force in the range of 0-100% maximal voluntary contraction (MVC) was calculated for each subject, every 2 weeks over a total 6-week period during which subjects practiced linear flexion force increase three times a week. Electromyograms were recorded with two pairs of electrodes of different size and electrode spacing. It was shown that skill acquisition due to the 360 practice trials over the 6-week period caused an increase in the initial motor unit recruitment phase of the agonist's force generation cycle from about 0-65% MVC to about 0-85% MVC. The increase in the recruitment range was gradual and statistically significant for the measurements made every 2 weeks. The recruitment range of the antagonist triceps demonstrated a minor, but statistically insignificant, decrease over the same training period. There was a minor, but statistically insignificant, advantage of using small electrodes and inter-electrode spacing. It was concluded that skill acquisition, due to repeated functional use of a muscle in the same contraction mode, results in a slower, prolonged recruitment of motor units in the initial segment of the force generation cycle, thereby allowing a more precise and accurate control of the increments of force increase. Such conclusions reinforce the concept advocating the plasticity of motor unit control according to the functional demands imposed on the muscle. The results have significant implications in the design of various athletic, occupational and rehabilitation training modalities for optimal performance of various movement functions.

Adult↗
PubMed1996

Evaluation of isometric antagonist coactivation strategies of electrically stimulated muscles.

The performance of various coactivation strategies to control agonist-antagonist muscles in functional electrical stimulation (FES) applications was examined in a cat model using the tibialis anterior and soleus muscles to produce ankle isometric dorsiflexion and plantarflexion torques, respectively. Three types of coactivation strategies were implemented and tested. The first strategy was based on coactivation maps described in the literature as consisting of decreasing antagonistic activity as the input command to the agonist was increased. The second type of strategy was based on the physiologic coactivation data collected from normal subjects exhibiting joint stabilization during the full range of contractions. These strategies included scaled increasing antagonist activity and therefore joint stiffness with increasing agonist input command. A third strategy was devised which at low force levels mimicked the strategies described in the literature and at high force levels resembled strategies exhibited by normal subjects. The three strategies were evaluated based on their ability to track a linear or sinusoidal input command and their efficiency of torque transmission across the joint. Coactivation strategies using increasing antagonist activity resulted in decreased maximal joint torque and efficiency, decreased signal tracking capability for linear inputs, and increased harmonic distortion for sinusoidal inputs. Peak efficiency and tracking ability appeared when a moderate degree of antagonist activity was engaged near the neutral joint position. Signal tracking quality improved with earlier engagement of the antagonist muscles. Our results suggest that strategies combining low-level coactivation as described in the physiological literature and previous FES studies could satisfactorily address the issues of controllability, efficiency, and long-term joint integrity.

Animals↗
PubMed1996

Load, length, and velocity of load-moving tibialis anterior muscle of the cat.

Three-dimensional relationships of load, length, and velocity of shortening of the tibialis anterior muscle in the cat were derived experimentally and fitted with an analytic model. Gravitational loads were applied to the isolated muscle, which arrived at an equilibrium with the passive forces before supramaximal tetanic stimulation was delivered to its nerve. Recordings of initial passive muscle length at equilibrium and length changes throughout the shortening phase up to the final length at active equilibrium were taken and numerically differentiated to obtain each load's instantaneous velocity. A three-dimensional surface was constructed by using instantaneous length and the corresponding velocity for each of several loads. Maximal velocity of shortening was shown to gradually decrease, occurring earlier in the shortening phase (at larger muscle lengths) as loads increased. Whereas load-velocity curves were hyperbolic for middle and short muscle lengths, they were nonmonotonic during shortening above the optimal length. The model was found to correlate well with the experimental data (R = 0.98) and allowed for prediction of both muscle performance boundaries and instantaneous shortening velocity for a given length across the physiological load spectrum, thus offering a realistic estimation of the contractile properties exhibited by the tibialis anterior muscle in functions similar to naturally occurring movements against gravitational loads, which are accelerated and decelerated during the movement.

Animals↗
PubMed1996

Energy expenditure and fatiguability in paraplegic ambulation using reciprocating gait orthosis and electric stimulation.

To clarify the relationship between metabolic energy expenditure and fatiguability in paraplegic persons fitted with orthoses, we measured energy consumption in six thoracic paraplegic patients ambulating by means of reciprocating gait orthosis (RGO) used with and without functional electrical stimulation (FES). The data obtained from persons using both RGO and FES were adjusted to allow for the effects of fatiguability so as to obtain an approximate value for upper-body consumption. The data obtained from persons using RGO only were not adjusted, because no energy consumption occurred in the lower portion of the body. The data, expressed in kcal/kg-min and kcal/kg-m, were plotted against walking speed attained using RGO, and RGO with FES. The results were compared with those from persons fitted with long leg braces (LLB), hip guidance orthoses (HGO) and an FES walking aid (data obtained from available literature). We found that the lowest energy expenditure in kcal/kg-m across the full range of walking speeds occurred when both RGO and FES were used together, followed by RGO only, HGO, LLB, and FES only, respectively. The lowest energy expenditure in kcal/kg-min, for walking speeds, below 0-28 m/s, also occurred when both RGO and FES were used together, followed by RGO only, HGO, LLB, and FES only. The results suggest that, although the use of FES with RGO may increase oxygen uptake, it decreases energy expenditure in the upper extremities, thereby reducing patient fatigue. They also suggest that mechanical orthosis giving passive support to the hip, knee and ankle in combination with FES may provide the most efficient walking aid for paraplegic persons.

Adult↗
PubMed1995

Motor unit recruitment strategy of knee antagonist muscles in a step-wise, increasing isometric contraction.

The purpose of this study was to determine if differences exist between the control strategies of two antagonist thigh muscles during knee flexion and extension muscular coactivation. Surface myoelectric signal (MES) of the quadriceps (rectus femoris) and the hamstrings (semitendinosus) were obtained from both muscles while performing step-wise increasing contractions during flexion and extension with the knee at 1.57 rad of flexion (90 degrees). The median frequency of the power density spectrum, which is related to the average muscle fiber action potential conduction velocity and therefore to motor unit recruitment, was calculated from each MES. The results suggest that, in all the subjects tested, when the muscle acts as antagonist most motor units are recruited up to 50% of the maximal voluntary force, whereas when the muscle acts as antagonist motor units are recruited up to 40% of the maximal voluntary force. The force range past 40-50% of the maximal force is also characterized by differences between the agonist/antagonist.

Adult↗
PubMed1995

Force-velocity relations of nine load-moving skeletal muscles.

The relationship between maximal velocity and load was studied in nine muscles of the cat's hind limb using a technique in which the initial and final muscle lengths are determined by equilibrium of a suspended mass and the muscle's passive and active forces elicited by tetanic stimulation. The maximal velocities of shortening during contraction under each of various loads was used to fit a Hill model using the least-squares method. It was shown that different muscles varied significantly in their ability to generate maximal velocity over a range of loads. The tibialis anterior muscle generate the highest velocity (28.4 cms-1), whereas the tibialis posterior generated the lowest maximal velocity (4.2 cms-1). In general, muscles with predominantly fast twitch fibres and with the largest elongation/shortening range displaced the load at the highest velocities, as compared with muscles with predominantly slow twitch and short excursion range which respond with low velocities. The a/P0 ratio of Hill's equation, which defines the curvature of the force velocity, also varied widely, being most monotonic (0.927) for the soleus and the steepest (0.067) for the extensor digitorum longus, further suggesting that fibre composition is also highly influential on the force-velocity relations of the muscle.

Animals↗
PubMed1995

The effect of tendon on muscle force in dynamic isometric contractions: a simulation study.

Recently, Baratta and Solomonow J. Biomechanics 24, 109-116 (1991) studied the effect of tendon on muscle-tendon complex behavior in cat tibialis anterior (TA) muscle. This was done by determining the relation between neural stimulation and muscle force in a dynamic isometric experiment, both before and after the removal of the distal tendon. From their results, Baratta and Solomonow concluded that in isometric and concentric contractions at mid-range force levels, tendon behaves as a rigid force conductor. This conclusion is in conflict with literature in which several functions are attributed to the elastic behavior of the series elastic element (SEE), of which tendon is the major part. The present study investigates the expected generalizability of their findings, by simulating the experiments using a straightforward Hill-type muscle model. First, model predictions are shown to be in line with the experimental results on cat TA: in dynamic isometric experiments at mid-range force levels, the effect of SEE removal is indeed negligible. Second, the effect of SEE removal is predicted to vary largely among muscles. Third, the most important determinants of the effect of SEE removal in dynamic isometric contractions are shown to be maximum fiber shortening velocity and the ratio of SEE slack length to fibre optimum length.

Animals↗
PubMed1995

Architecture-based force-velocity models of load-moving skeletal muscles.

A predictive model of muscle force-velocity relationships is presented based on functional architectural variables. The parameters of Hill's equation describing muscle force-velocity relationship of nine muscles were estimated by their relationships with variables extracted from the whole-muscle length-force relationship and the percentage of slow-twitch fibres. Specifically, the maximal unloaded velocity (Vo) was estimated through multiple linear regression, from each muscle's fibre composition and the shortening range through which each muscle could produce active force. The maximal isometric force (Po) was also extracted from each muscle's length-force relationship. The ratio of Hill's dynamic constanta to Po and b to Vo, which determines the degree of curvature of the relation, was determined solely by the percent of slow-twitch fibres. This model was verified by fitting it to experimental force-velocity curves of nine different muscles in the cat's hindlimb. It was found that reasonable fits of force-velocity curves would be obtained with correlation coefficient in the range of 0.61 to 0.92, with an average of 0.82. The model predicted that muscles with relatively long shortening ranges would achieve higher maximal velocity, and that muscles with higher percentage of slow-twitch fibres had less pronounced curvature and lower maximal velocity in their force-velocity relationships. RELEVANCE: The results have direct implications in the design of neuroprosthetic limb control systems, which use electrical stimulation to restore function to muscles paralysed from spinal cord injury. The designer is enabled to optimally calibrate the controller according to the predicted individual force-velocity curves of different muscles by using the length-tension curves and fibre composition data available in the literature.

Journal Article↗
PubMed1995

Dynamic performance model of an isometric muscle-joint unit.

The dynamic performance model of the medial gastrocnemius muscle of the cat was determined when generating isometric force at its tendon and when transmitting that force across the joint. The frequency response model of the muscle and of the muscle-joint was developed by fitting the experimentally obtained gain and phase Bode plots with a best fit linear second order system determined by recursive least squares. It was shown that the muscle could be represented with double poles at 2.3 Hz and a time delay of 16 ms whereas the muscle-joint was represented with an additional pole at 1.8 Hz, a zero at 3.8 Hz and 16 ms time delay. The harmonic distortion was less than 5% for sinusoidal force output in the frequency range of 0.4-4 Hz, and a force range of 20-80% of the maximal justifying a linear system model. The model is useful in the design of a neuromuscular prosthesis, using electrical stimulation of the muscle nerves, as a rehabilitation procedure for paralysed patients due to spinal cord injury.

Animals↗
PubMed1995

The dynamic response of the cat ankle joint during load-moving contractions.

The dynamic response of the cat's ankle joint during load-moving activation of the medial gastrocnemius was determined. Sinusoidal-input oscillations of ankle plantar flexion were performed by the muscle at frequencies ranging from 0.4 to 5 Hz against a 10-N load acting via a cable through a pulley with a 2 cm radius. This was followed by sinusoidal muscle length changes against the same load while excluding the joint. The frequency responses of the two conditions were compared and decomposed in terms of their relative phase and gain, and best-fit pole-zero models to yield the dynamic model of the joint isolated from the muscle properties. The muscle displacement transfer function M(j omega) was characterized as two sets of double poles at 2.1 and 3.2 Hz, with a pair of zeros at 0.92 and 20 Hz, and pure time delay of 8 mS. The joint model J(j omega) was obtained by adding a pole at 5 Hz and a zero at 13 Hz. It was concluded that the ankle joint acts as a lag system, introducing significant increase in the phase lag between stimulus input and mechanical output without affecting the frequency-dependent attenuation of gain. Average harmonic distortion was less than 5% in all cases. This particular finding reveals that, despite its inherently nonlinear mechanical characteristics, the joint introduces no degradation in the simplified linear behavior of the muscle-joint system. This model is useful in the design of systems employing electrical stimulation to restore movement to limbs paralyzed by spinal cord injury or stroke.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Electromyography and biomechanics of a dynamic knee brace for anterior cruciate ligament deficiency.

Twelve anterior cruciate ligament (ACL)-deficient subjects performed concentric isokinetic knee extensions at maximum effort both with and without the Bledsoe Pro Shifter knee brace. Electromyogram signals from the quadriceps, hamstrings, knee angle, and the extension force were recorded and evaluated to determine the effects of such dynamic bracing on muscle activity and joint stability. High activity, or asymptomatic, subjects (n = 5) experienced no change in muscle activity, but displayed a decrease in extension force throughout the active range of the brace. Low activity, or symptomatic, subjects (n = 7) exhibited increased quadriceps activity and decreased hamstrings activity, and displayed a minor increase in force in the mid-range (80 degrees to 40 degrees flexion). These results indicate that dynamic bracing prevents quadriceps inhibition in symptomatic subjects by exerting a posteriorly directed force to the superior tibia; thus, the brace compensates externally for the absence of the ACL.

Adult↗
PubMed1995

The glenohumeral-biceps reflex in the feline.

The existence of a reflex arc from the anterior aspects of the glenohumeral capsule to the long head of the biceps was determined in a feline. A single articular branch of the musculocutaneous nerve terminating in the capsule was identified and stimulated with 100 microseconds supramaximal pulse train at 10 pulses per second. It was shown tht stimulation of the musculocutaneous articular nerve elicited myoelectric discharge in the biceps muscle. Transection of the articular nerve just distal to its emergence from the main trunk of the musculocutaneous nerve abolished the myoelectric discharge in the biceps, confirming the afferent nature of this articular nerve. The mean (+/- standard deviation) time delay from the application of the stimulus to the articular nerve to the recording of the corresponding myoelectric discharge in the biceps was 2.7 (+/- 0.3) milliseconds. The existence of a reflex arc from the capsule to the biceps confirms and extends the concept of passive (ligaments) and active (muscles) restraints of a joint and the synergy between them toward maintaining shoulder stability. If demonstrated in the human, such a reflex may have significant implications in modification of surgical procedures and the design of new rehabilitation modalities for treatment of shoulder defects.

Action Potentials↗
PubMed1994

Comparison of isometric and load moving length-tension models of two bicompartmental muscles.

The length-tension relations of two bicompartmental muscles, including parallel and pennated fibers, were experimentally determined for isometric and load moving contractions. Comparison of the isometric and constant mass load length-tension curves obtained from the same preparations demonstrated significant reductions in force, a shift of the optimal length and increased elongation range for shortening contractions under constant mass load. Pennated muscle demonstrated a larger reduction in force and greater shift in the optimal length relative to the changes in a muscle with parallel fibers. A bicompartmental model was fitted to the experimental data to provide quantitative insight to the changes described above, and for use in mathematical models of other bicompartmental muscles, and for design of optimal electrical stimulation system for restoration of function in spinal cord injury patients.

Animals↗