PubMed Health⌕ Search

Biomedical subjects

R Baratta

Publications and source records attributed to R Baratta.

34 records · Page 2Linked to original sources
PubMed1989

Method for studying muscle properties under orderly stimulated motor units with tripolar nerve cuff electrode.

An electrical nerve stimulation technique, using single tripolar electrode, was shown to be capable of recruiting motor units according to their size, while allowing simultaneous but independent control of firing rate in the active units. Test paradigms consisting of established fundamental physiological concepts of soleus-gastrocnemius architecture, firing rate behaviour of motor units of different sizes, and their susceptibility to fatigue were employed to validate the technique and demonstrate its utility as a basic and applied research tool.

Animals↗
PubMed1989

Orderly stimulation of skeletal muscle motor units with tripolar nerve cuff electrode.

An electrical nerve stimulation technique, using single tripolar electrode, was shown to be capable of recruiting motor units according to their size, while allowing simultaneous but independent control of firing rate in the active units. Test paradigms consisting of established fundamental physiological concepts of soleus-gastrocnemius architecture, motor units conduction velocity, firing rate behavior of motor units of different sizes, and their susceptibility to fatigue were employed to validate the technique and demonstrate its utility as a basic and applied research tool.

Action Potentials↗
PubMed1989

The role of the hamstrings in the rehabilitation of the anterior cruciate ligament-deficient knee in athletes.

There is ample evidence for the synergy between the knee musculature and ligaments, and the overall maintenance of joint integrity. In fact it could be reasonably concluded that the joint's antagonist muscle acts as a 'regulator' compensating for various internal and external disturbances of the intended movement. Undoubtedly, well conditioned muscles provide substantial improvements in joint stiffness and laxity, and reduce the risk of ligamentous injuries in the elite athlete. More research is needed to delineate the details of the questions which this new approach raises.

Athletic Injuries↗
PubMed1989

The RGO Generation II: muscle stimulation powered orthosis as a practical walking system for thoracic paraplegics.

The RGO Generation II reciprocating gait orthosis was jointly developed by Louisiana State University Medical Center and Durr-Fillauer Medical, Inc, to overcome four problems encountered with the existing model: 1) The high energy cost of locomotion; 2) the great arm strength required for patients to stand up from the seated position without assistance; 3) difficulty (especially for patients with hamstring contracture) in remaining standing owing to failure of the knee latch to lock except in full extension; and 4) problems in balancing when ambulating on an incline. The RGO Generation II employs concurrent electrostimulation of the rectus femoris and hamstrings to assist in rising and balancing and a ratchet-type latching device to improve safety and stability in standing. Alternating stimulation of the rectus femoris and contralateral hamstrings are used for locomotion. Testing in six patients with thoracic paraplegia demonstrated an average 30+% reduction in energy expenditure at a walking speed of .05 m/s and a 15+% reduction at .37 m/s; improved mobility and better balance on inclines; and unassisted rising in all patients. Walking range was increased from an average of 100 m to an average of 800 m. More research is needed to provide stair-climbing ability and to further reduce energy expenditure.

Adult↗
PubMed1988

Electromyogram coactivation patterns of the elbow antagonist muscles during slow isokinetic movement.

Electromyograms from the flexor and extensor muscles of normal human elbows were simultaneously recorded during maximal-effort isokinetic movement at 15 degrees/s over the joint's full range of motion. The antagonist electromyogram was normalized with respect to its electromyogram when acting as agonist at maximal effort and plotted as a function of joint angle. The coactivation patterns were nearly inversely related to each muscle's moment arm variations with joint angle, suggesting that the antagonist may have generated constant opposing torque throughout the movement. Female subjects had a statistically significant higher coactivation level of the flexors and extensors compared with that of males, reflecting the increase in joint efficiency associated with daily muscular activity which is manifested by reduction in antagonist activity. The functional role of antagonist coactivation in augmenting ligament stabilizing functions, equalizing the pressure distribution over the articular surface, and regulating the joint's mechanical impedance are discussed. The source of such coactivation appears to be due to proprioceptive and joint kinesthetic afferent input in addition to possible direct common drive.

Adult↗
PubMed1986

Historical update and new developments on the EMG-force relationships of skeletal muscles.

The EMG-force relationships of skeletal muscles are of significant interest to the orthopedic-biomechanics researcher and have been a topic of interest and controversy for the last three decades. We present the developments reported in the literature, from the early 1950s, relevant to this topic, outlining the details of the controversy and providing additional new information resulting from recent studies. New data clearly illustrate that the EMG-force relationships are dependent on the firing rate and recruitment control strategy used by a muscle. Muscles that use motor unit recruitment to obtain the initial 50% of their maximal force, and use firing rate increase to complement the remaining 50%, have a nearly linear EMG-force relationship. Muscles that use recruitment to obtain 60% and up to 100% of their maximal force demonstrate progressive increase in non-linearity of their EMG-force curves. A clear warning is issued against the indiscriminate use of EMG as a representative of muscle force. The recruitment pattern of the muscle under consideration should first be obtained in such a way that the appropriate EMG-force curve is selected.

Animals↗
PubMed1986

EMG-force model of the elbows antagonistic muscle pair. The effect of joint position, gravity and recruitment.

A piecewise linear model of the elbow antagonistic muscle pair under isometric conditions was developed. The model consists of a linear myoelectric signal-joint force relationship with a mild slope for the force range of 0-30%, and a second, linear segment of steeper slope for the range of 30%-100%. The slope of the agonist, whether biceps or triceps, is fixed for most of the force range at about 1.16 regardless of elbow angle, whereas the slope of the antagonist varies with elbow angle. The antagonist muscle varies its response in such a way that it regulates the net torque about the joint, compensating for the effect of the gravity vector on the joint geometry and limb mass to stabilize the joint. The myoelectric profile of the medial gastrocnemius muscle of the cat during recruitment at synchronous firing rate of 51 pps (maximal tetanic rate) was obtained and compared with the above model. The force-EMG relationship for recruitment was fitted with a second-order polynomial similar but not equivalent to that of the EMG-joint force model. The minor differences were attributed to the effect of the antagonist, proprioception, ligament status and joint geometry.

Animals↗
PubMed1985

A technique for recording the EMG of electrically stimulated skeletal muscle.

A technique for recording the myoelectric activity of electrically stimulated muscle through its motor nerve without the interference of stimuli artifacts has been developed and tested. The technique consists of a wide band differential amplifier with fine intramuscular wire electrodes. The amplified signal is passed through a Chebyshev low pass filter with eight poles at a frequency of 550 Hz. A stimulus calibration study shows that low frequency stimuli had negligible effect on the EMG when set below three times suprathreshold. A test procedure shows artifact-free EMG during action potential rate stimulation as well as during superimposed high frequency recruitment stimulation.

Action Potentials↗
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

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↗