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Biomedical subjects

M Solomonow

Publications and source records attributed to M Solomonow.

108 records · Page 6Linked to original sources
PubMed1983

Fatigue considerations of muscle contractile force during high-frequency stimulation.

In a model for control of muscle force, wherein an induced background tetanus is attenuated by concurrent indirect stimulation at frequencies in the 0.6- to 10-kHz range, evaluation was made for effects on muscle fatigue of differing rates of the tetanic and high-frequency stimuli. Relatively little fatigue, and yet nearly the complete range of attenuation, were favored by lower frequencies of both these stimuli, e.g., tetanic stimulation at 50 Hz and a blocking frequency of 600 Hz.

Animals↗
PubMedDate not supplied

Role of the tendon in the dynamic performance of three different load-moving muscles.

The effect of the tendon's viscoelastic properties on the dynamic performance of three different load-moving muscles was determined. The frequency response models of the cat's medial gastrocnemius (MG), extensor digitorum longus (EDL), and tibialis anterior (TA) with and without their tendons were derived under sinusoidal shortening-lengthening, manipulated by orderly recruitment and derecruitment of motor units together with firing rate increase and decrease. The passive load sizes applied to the muscles were approximately 30%-40% of each muscle's maximal isometric force. It was shown that the tendon has a moderate effect on the dynamic response of muscles while moving loads of fixed mass. The MG and EDL without their tendons show a decrease in high frequency gain (2-5 dB) and increasing phase lag angles (7 degrees-9 degrees). In contrast, the TA without its tendon shows an increase in high frequency gain (2 dB) and decreasing phase lag angles (20 degrees) compared with the same muscle with the tendon. It was concluded that tendon's viscoelastic properties have a moderate effect during load-moving contractions, influencing the dynamic performance of different muscles in a different manner.

Animals↗
PubMedDate not supplied

Mechanoreceptors and reflex arc in the feline shoulder.

A reflex arc from the glenohumeral capsule to the biceps, infraspinatus, supraspinatus, and subscapular muscles was shown in a feline preparation. Branches of the suprascapular and subscapular nerves terminating in the capsule were identified and then stimulated with a 100 microseconds supramaximal pulse at 10 pulses per second. Stimulation of the suprascapular articular nerve elicited electromyographic discharge in the biceps and infraspinatus muscles, whereas stimulation of the subscapular articular nerve elicited electromyographic discharge in the biceps, subscapularis, infraspinatus, and supraspinatus muscles. When the articular nerves were transected between their emergence from the main nerve trunk and the stimulation electrodes, the electromyographic discharge was abolished confirming the afferent nature of the nerves. The mean time delay ( +/- SD) from application of the stimulus to the peak of the recorded electromyographic activity was 3.2 +/- 0.27 msec. Anatomic dissection and staining of the capsule segments where the articular nerves terminated revealed mechanoreceptors consisting primarily of free nerve endings and Golgi tendon organs, Ruffini's endings, and pacinian corpuscles. The existence of a ligamento-muscular reflex arc in the glenohumeral joint extends the concept of passive and active restraints of a joint by virtue of the synergy between ligaments and muscles. That such a reflex exists may advocate modification of surgical repairs of the capsule, leading to preservation of as many neurologic structures as possible; it may also form the foundation for new postsurgical therapeutic modalities.

Animals↗
PubMedDate not supplied

The synergistic action of the anterior cruciate ligament and thigh muscles in maintaining joint stability.

The synergistic action of the ACL and the thigh muscles in maintaining joint stability was studied experimentally. The EMG from the quadriceps and hamstring muscle groups was recorded and analyzed in three separate experimental procedures in which the knee was stressed. The test revealed that direct stress of the ACL has a moderate inhibitory effect on the quadriceps, but simultaneously it directly excites the hamstrings. Similar responses were also obtained in patients with ACL damage during loaded knee extension with tibia subluxation, indicating that an alternative reflex arc unrelated to ACL receptors was available to maintain joint integrity. The antagonist muscles (hamstrings) were clearly demonstrated to assume the role of joint stabilizers in the patient who has a deficient ACL. The importance of an appropriate muscle-conditioning rehabilitation program in such a patient is substantiated.

Adolescent↗
PubMedDate not supplied

Muscular coactivation. The role of the antagonist musculature in maintaining knee stability.

The objective of this study was to quantify the coactivation patterns of the knee flexor and extensor muscles as part of continued efforts to identify the role of the antagonist muscles in maintaining joint stability. The simultaneous EMG from the flexor and extensor muscles of the knee were recorded during maximal effort, slow isokinetic contractions (15 deg/sec) on the plane parallel to the ground to eliminate the effect of gravity. The processed EMG from the antagonist muscle was normalized with respect to its EMG as agonist at maximal effort for each joint angle. The plots of normalized antagonist EMG versus joint angle for each muscle group were shown to relate inversely to their moment arm variations over the joint range of motion. Additional calculations demonstrated that the antagonist exerts nearly constant opposing torque throughout joint range of motion. Comparison of data recorded from normal healthy subjects with that of high performance athletes with hypertrophied quadriceps demonstrated strong inhibitory effects on the hamstrings coactivations. Athletes who routinely exercise their hamstrings, however, had a coactivation response similar to that of normal subjects. We concluded that coactivation of the antagonist is necessary to aid the ligaments in maintaining joint stability, equalizing the articular surface pressure distribution, and regulating the joint's mechanical impedance. The reduced coactivation pattern of the unexercised antagonist to a hypertrophied muscle increases the risk of ligamentous damage, as well as demonstrates the adaptive properties of the antagonist muscle in response to exercise. It was also concluded that reduced risk of knee injuries in high performance athletes with muscular imbalance could result from complementary resistive exercise of the antagonist muscle.

Adolescent↗
PubMedDate not supplied

The effect of joint velocity on the contribution of the antagonist musculature to knee stiffness and laxity.

The electromyographic (EMG) coactivation patterns of the knee flexors and extensors when acting as antagonists were studied as a function of limb velocity to assess their contribution to joint stiffness and laxity. Normalized antagonist coactivation patterns developed from surface EMG recordings from the hamstrings and quadriceps during maximal effort isokinetic extension and flexion, respectively, demonstrated characteristic variations as the joint velocity increased from 15 deg/sec up to 240 deg/sec. The two-tailed t-test (P less than 0.01) was performed on the data obtained from eight normal knees. The results indicate that both hamstrings and quadriceps demonstrate a significant increase (greater than 100%) in their antagonist coactivation pattern during the final 40 degrees of fast extension and flexion movements, respectively, as limb velocity increases. A minor decrease in antagonist activity of the hamstrings (24%) and quadriceps (8%) was evident during the initial phase of the extension and flexion movements, respectively, as joint velocity increased. We concluded that as limb velocity is increased, there is a substantial reflexive (unintentional) increase in the contribution of the antagonist musculature to joint stiffness and reduction of laxity. The results also suggest that strength training of the hamstrings (rather than quadriceps) should be considered as a modality for conservative treatment of ACL deficiencies, as well as an adjunct to surgical reconstruction. Such training can also reduce the risk of high performance athletes in a reflexive manner by increasing joint stiffness.

Adult↗
PubMedDate not supplied

Anterior-posterior and rotational displacement of the tibia elicited by quadriceps contraction.

The anterior-posterior displacement and rotation of the tibia elicited by isolated loading of the quadriceps muscle was determined as a function of joint angle and muscle load using a computerized radiographic technique. Data collected from 12 fresh-frozen cadaveric knees demonstrated that quadriceps contraction can result in significant (less than 7 mm) anterior displacement of the tibia in the range of 0 degrees to 80 degrees of flexion, and a mild (less than 2 mm) posterior displacement in the range of 80 degrees to 120 degrees of flexion. Peak anterior displacement of 6.3 mm was observed at 30 degrees of flexion under a 12 kg load in the quadriceps, while a constant 1.5 mm posterior displacement was observed throughout flexion angles exceeding 80 degrees. It was further shown that the magnitude of the anterior displacement increased nonlinearly as the quadriceps force increased. Loading of the quadriceps also resulted in internal rotation of the tibia in the range of 0 degrees to 90 degrees of flexion, and in external rotation of the tibia in the range of 90 degrees to 120 degrees. Peak internal rotation of 7 degrees was observed at 15 degrees of flexion and a peak external rotation of 1 degrees was detected at 120 degrees of flexion. Larger quadriceps load resulted in larger rotation. We concluded that quadriceps contraction during knee extension has direct impact on anterior displacement and rotation of the tibia and therefore on anterior cruciate ligament stress, increasing it as the muscle's force is increased during knee extension.(ABSTRACT TRUNCATED AT 250 WORDS)

Anterior Cruciate Ligament↗
PubMedDate not supplied

The synergistic action of the capsule and the shoulder muscles.

The existence of a reflex arc from the glenohumeral capsule to several muscles crossing the shoulder joint was determined in the feline model. Three branches of the axillary nerve terminating in the glenohumeral capsule were identified and electrically stimulated with supramaximal, 100-microseconds pulses using bipolar hook electrodes. Stimulation of the anterior and the inferior axillary articular nerves elicited electromyographic activity in the biceps, subscapularis, supraspinatus, and infraspinatus muscles. Stimulation of the posterior axillary articular nerve elicited electromyographic activity in the acromiodeltoid muscle. Transection of the three articular nerves just distal to their emergence from the main axillary nerve resulted in the absence of any electromyographic activity in the muscles on stimulation, confirming the afferent nature of the articular branches. The time from application of the stimulus to the appearance of a response in the muscles varied from 2.7 msec in the biceps to 3.1 msec in the supraspinatus. The existence of a reflex arc from mechanoreceptors within the glenohumeral capsule to muscles crossing the joint confirms and extends the concept of synergism between the passive (ligaments) and active (muscles) restraints of the glenohumeral joint. This provides new information in orthopaedic sciences that has direct application in modification of surgical repairs and therapeutic modalities of shoulder injuries.

Animals↗
PubMedDate not supplied

The EMG-force relationships of skeletal muscle; dependence on contraction rate, and motor units control strategy.

The dependence of the EMG vs force relationships on skeletal muscles contraction rate, and its motor units recruitment control strategy were studied. An electrical nerve stimulation technique capable of orderly excitation of motor units according to their size with simultaneous increase in their discharge rate was applied to isometric preparations of the M. gastrocnemius muscle of the cat. Muscle force and intramuscularly recorded EMG were normalized and plotted against each other. The method of least squares (p less than .05) was used to yield the best fit linear regression polynominials to the pooled data from several preparations. Strong dependency on the motor unit recruitment strategy was exhibited by the results. Linear EMG vs force relationships was evident when all the motor units were recruited to generate the initial 50% of the maximal force while discharge rate continued to increase up to the maximal force. Progressive increase in non-linearity was evident as recruitment of motor units generated 60% and up to 100% of the initial force concurrently with firing rate increase. Contraction rate (force generation rate) increase from 36% sec up to 360% sec resulted in nearly identical normalized EMG vs force relationships, although the maximal force increased by up to 22.5% as the contraction rate increased to 360% sec. The results of this study issue a clear warning against the direct use of EMG to predict muscle force in biomechanical and kinesiological research without correcting for the variables discussed in this paper.

Animals↗
PubMedDate not supplied

Motor unit recruitment strategy of antagonist muscle pair during linearly increasing contraction.

The motor unit recruitment control strategy of the antagonist thigh muscles was determined during linearly increasing isometric flexion and extension of the knees. The median frequency (MF) of the power density spectrum of surface electromyograms recorded from eighteen subjects was used as an indicator of motor units recruitment. The results showed that different recruitment strategies were used by the muscles that are antagonist to each other. When quadriceps and hamstrings acted as agonist most of the motor units were recruited in a linear manner up to 60% of maximal voluntary contraction (MVC). When the muscles acted as antagonist, quadriceps motor units were recruited up to 40% MVC during flexion while during extension the antagonist hamstrings recruited motor units up to 60% MVC. In both muscles, when acting as antagonist, the MF decreased after the recruitment phase, whereas when functioning as agonists, the MF remained relatively constant past the recruitment phase. The results suggested that a single muscle can employ different motor units recruitment strategies in accord with the type of contraction it performs and while acting as an agonist muscle as well as an antagonist.

Adult↗