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At least 379 records · Page 21Linked to original sources
PubMed2001

Improvement of thigh muscles by neuromuscular electrical stimulation in patients with refractory heart failure: a single-blind, randomized, controlled trial.

OBJECTIVE: To determine the impact of an 8-wk neuromuscular stimulation program of thigh muscles on strength and cross-sectional area in patients with refractory heart failure listed for transplantation. DESIGN: Forty-two patients with a stable disease course were assigned randomly to a stimulation group (SG) or a control group (CG). The stimulation protocol consisted of biphasic symmetric impulses with a frequency of 50 Hz and an on/off regime of 2/6 sec. RESULTS: Primary outcome measures were isometric and isokinetic thigh muscle strength and muscle cross-sectional area. Our results showed an increase of muscle strength by mean 22.7 for knee extensor and by 35.4 for knee flexor muscles. The CG remained unchanged or decreased by -8.4 in extensor strength. Cross-sectional area increased in the SG by 15.5 and in the CG by 1.7. CONCLUSIONS: Activities of daily living as well as quality of life increased in the SG but not in the CG. Subscales of the SF-36 increased significantly in the SG, especially concerning physical functioning by +7.5 (1.3-30.0), emotional role by +33.3 (0-66.6), and social functioning by +18.8 (0-46.9), all P < 0.05. Neither a change nor a decrease was observed in the CG. Neuromuscular electrical stimulation of thigh muscles in patients with refractory heart failure is effective in increasing muscle strength and bulk and positively affects the perception of quality of life and activities of daily living.

Activities of Daily Living↗
PubMedDate not supplied

Acute energetic effects of daunomycin on rabbit heart muscle.

The acute effects of daunomycin on the mechanical and energetic outputs of rabbit papillary muscles have been examined at 27 degrees C using a myothermic technique. Contrary to expectations, daunomycin, in concentrations ranging from 10 to 160 micrograms/ml, acted as a positive inotropic agent in terms of peak stress development and work output. The rate of stress development was, however, slightly depressed, and the major mechanical effect of the drug was to prolong the relaxation phase so that there were large drug-dependent increments in the stress-time integral. Daunomycin at a concentration of 80 micrograms/ml produced a 22% increment in peak stress development and a 74% increment in stress-time integral. The linear relationship between total (active + passive) stress and heat production was altered such that there was a 73% increment in the activation heat component (intercept) and a 37% increase in the energy cost per unit stress development (slope). In afterloaded isotonic contractions, daunomycin increased the mean work output (W; averaged over all load levels) by 49%, but there was an even greater increment in the associated energy expenditure, ET, which rose by 66%. Consequently, the overall mechanical efficiency (W/ET X 100%) fell slightly. It is concluded that, in the rabbit, daunomycin in the acute situation increases total calcium delivery to the myofilaments and decreases the "apparent" transduction efficiency. These acute effects are the opposite of those reported in papillary muscles taken from rabbits in cardiac failure induced by chronic daunomycin administration. The short-term effects of daunomycin in the rabbit differ substantially from those seen in the rat and guinea pig.

Animals↗
PubMedDate not supplied

Effects of CM7857, a derivative of disopyramide, on electrophysiologic properties of canine Purkinje fibers and inotropic properties of canine ventricular muscle.

Effects of CM7857 on electrophysiologic properties in canine Purkinje fibers and inotropic effects in canine ventricular muscle were studied. As CM7857 is a derivative of disopyramide phosphate, the effects of CM7857 (5 mg/L, 1.5 X 10(-5) M) were compared with those of disopyramide phosphate (5 mg/L, 1.4 X 10(-5) M). CM7857 significantly lowered the maximum rate of rise of phase 0 (Vmax) from 351.5 +/- 50.6 V/s (mean +/- SE, n = 5) to 283.6 +/- 33.0 V/s, and conduction velocity from 2.68 +/- 0.56 m/s to 1.70 +/- 0.28 m/s. The automaticity of Purkinje fibers was depressed by CM7857 as the result of reduction in the slope of phase 4. These effects were comparable to those of disopyramide. A marked difference between CM7857 and disopyramide was observed in the effect on action potential duration. APD90 was significantly shortened from 327.4 +/- 14.8 ms (n = 8) to 279.9 +/- 12.9 ms by CM7857, whereas disopyramide did not show any significant changes in APD90. As the CM7857-induced shortening of APD disappeared in low [Na+]o or low [K+]o concentration, it may be attributed to the lowering effect of "window current," a steady-state sodium current, maintaining action potential plateau. Effective refractory period (ERP) did not show any significant change. An acetylstrophanthidin-induced oscillatory afterpotential was significantly depressed by disopyramide, but not by CM7857. Isotonic contraction and isometric contraction of the right ventricular trabecullae were depressed by both drugs.

Action Potentials↗
PubMed2000

Direct vasodilating effects of the new dopaminergic agonist Z1046 in human arteries.

Dopaminergic agonists remain of interest in the treatment of heart failure; however, concomitant stimulation of alpha- and beta-receptors should be avoided. This study evaluates the dopaminergic and adrenergic (vasodilating) properties of Z1046, epinine (the active metabolite of ibopamine), and dopamine. Isotonic contraction experiments were performed on human internal mammary artery rings in vitro. alpha1-Antagonistic effects of Z1046 were demonstrated by performing cumulative dose-response curves with the selective alpha1-agonist phenylephrine in the presence of Z1046. Furthermore, both alpha1- and dopamine-mediated receptor effects of Z1046, epinine, and dopamine were studied by performing cumulative dose-response relations both at baseline and in precontracted artery rings both with and without the D1-like antagonist SCH23390. In contrast to both epinine and dopamine, Z1046 is devoid of alpha1-receptor-mediated contraction. Furthermore, Z1046, epinine, and dopamine induced direct dopamine receptor-mediated vasodilation when interfering alpha1 effects were blocked. In contrast to epinine and dopamine, Z1046 is devoid of vasoconstricting properties at higher dosages. Because of its D1-like agonistic and alpha1-antagonistic properties, Z1046 is an effective vasodilator in the whole dosage range. Because of its total receptor profile, Z1046 appears to be more favorable for treatment of heart failure than is ibopamine.

Adult↗
PubMed2000

Effects of back extensor strength training versus balance training on postural control.

PURPOSE: Aim of this study was to investigate effects of 1) regular back extensor strength training as opposed to balance training, and 2) the influence of the sequence of both training types on postural control, force, and muscle efficiency. METHODS: Twenty-six young, healthy subjects were investigated at baseline, 1 month and 2 months later. At each examination, subjects completed a posturographic, balance skill, and isometric maximum voluntary (MVC) back extension testing, including surface electromyographic (SEMG) recordings. After baseline evaluation, subjects were assigned to either daily strength training or balance training. After 1 month, the type of training was exchanged between groups. RESULTS: After 1 month, back extensor strengthening led to decreased postural stability on hard surface, whereas there were no change after balance skill training. Analysis of the low- and high-frequency components of the sway signal revealed that strength training increased control efforts as indicated by an increased high-frequency component in order to maintain postural stability and unchanged low-frequency component. Balance skill training, however, increased postural stability as indicated by a decreased low-frequency component. The control effort remained unchanged. After completing either sequence of training, all postural parameters remained unchanged in both groups. Muscular efficiency as measured by SEMG root mean square during a standardized motor skill task revealed improved muscle economy regardless of the type of training. Back extension torque improved in both groups. CONCLUSION: To avoid reduction of postural stability in rehabilitation processes, we recommend to include antagonist muscles in a comprehensive strength training regime or balance skill training.

Adult↗
PubMed2002

Motor output is more variable during eccentric compared with concentric contractions.

PURPOSE: This study examined the ability of 10 young (25.3 +/- 2.8 yr) healthy individuals to control knee-extension force during several discrete concentric and eccentric contractions. METHODS: Subjects performed maximal and submaximal tasks on a KIN-COM isokinetic dynamometer. The submaximal tasks were to match a force-time parabola with a time to peak force of 200 ms at five target-forces (50, 100, 150, 200, and 250 N). RESULTS: Mean peak force produced by the subjects at each target-force during concentric and eccentric contractions was similar. Mean time to peak force, however, was much shorter for eccentric contractions and was not influenced by increases in the level of force. The standard deviation (SD) and coefficient of variation (CV) of peak force was greater during eccentric compared with concentric contractions. The SD of time to peak force was greater for concentric contractions; however, when normalized to the mean time to peak force produced (CV), eccentric contractions were more variable. CONCLUSIONS: Results provide evidence that even in young adults the control of motor output is different for eccentric compared with concentric contractions.

Adult↗
PubMed1997

A fresh cadaveric study of the paratubal muscles: implications for eustachian tube function in cleft palate.

The aims of this anatomic investigation were to examine the levator veli palatini, tensor veli palatini, and salpingopharyngeus muscles in relation to normal eustachian tube function and to analyze the clinical implications of these data for tubal physiology in cleft palate individuals. Detailed dissections under 3.2x loupe magnification were conducted on the paratubal muscles of 15 fresh human adult cadaveric head specimens, paying particular attention to their cranial base anatomy. Each half of the cadaveric heads was examined separately, giving a sample size of 30. The cranial base origin of the levator veli palatini was the junction of the cartilaginous and bony parts of the eustachian tube. Contrary to statements in the existing literature, it had no origin from the quadrate area of the petrous temporal bone. In its path toward the velum, it was related inferiorly and lay almost parallel to the tube. The tensor veli palatini originated from the scaphoid fossa of the sphenoid bone and the tube. In contrast to previous descriptions, it was found to consist of a single sheet of muscle with no bilaminar structure. Its axis was oblique to that of the tube. The salpingopharyngeus was a slender muscle attached to the posteroinferior aspect of the pharyngeal end of the tube. It inserted into the palatopharyngeus inferiorly. These morphologic characteristics and anatomic relationships suggest that (1) the levator veli palatini opens the eustachian tube by isotonic contraction that results in displacement of the medial tubal cartilage and the tubal membrane, (2) the tensor veli palatini opens the tube directly by traction on the lateral tubal membrane and indirectly by rotation of the medial tubal cartilage by means of traction on the lateral tubal cartilage, (3) because of its consistently small size, the salpingopharyngeus is probably functionally the least important of the paratubal muscles, (4) the levator veli palatini is unable to cause tubal dilatation in cleft palate because it can only contract isometrically, and (5) tensor veli palatini function is probably unaffected by clefting. However, its mechanism of action may be disrupted iatrogenically by complete hamular fracture or division of its tendon.

Aged↗
PubMed1987

Normal trunk muscle strength and endurance in women and the effect of exercises and electrical stimulation. Part 1: Normal endurance and trunk muscle strength in 101 women.

The lack of trunk muscle strength and endurance has frequently been cited as a suspected factor in the etiology of low-back pain. Several investigators have suggested that asymptomatic patients have stronger trunk muscles than patients with low-back pain. People who are physically fit appear to have a decreased incidence of low-back pain. Increased trunk muscle endurance also have been observed to decrease the incidence of low-back pain. The objective evaluation of the strength and endurance of trunk musculature may, therefore, be significant. Part 1 of this study was designed to develop a reproducible strength-endurance screening procedure and to establish normal isometric-isokinetic trunk muscle strength and endurance parameters for women. This study showed that isometric trunk flexion varied from 19-109 Nm and trunk extension from 38-168 Nm. Peak values for isokinetic trunk flexion at two speeds (30 degrees per second and 60 degrees per second) varied from 17-191 Nm and isokinetic trunk extension from 14-208 Nm. The average endurance time for trunk extensors tested with the Sorensen test was 196 seconds.

Adolescent↗
PubMed1987

Normal trunk muscle strength and endurance in women and the effect of exercises and electrical stimulation. Part 2: Comparative analysis of electrical stimulation and exercises to increase trunk muscle strength and endurance.

Several studies have shown positive correlations between muscle strength, flexibility, and the frequency of low-back pain. Weak trunk musculature and decreased endurance have thereby come to be identified as significant risk factors in the development of occupational back problems. Because it is widely accepted that exercise plays an important role in the conservative treatment and prevention of low-back pain, the goals of most rehabilitative programs involves improving the strength and endurance of the low-back pain patient. Whereas electrical stimulation has been shown to increase the muscle strength of the lower extremities, this effect has not been demonstrated for the trunk muscles. Part 2 is a prospective controlled study designed to document and to compare objectively the effects of electrical stimulation and exercise on trunk muscle strength. A total of 117 healthy women were divided randomly into four groups. Two groups received electrical stimulation with different electrical parameters, one group received exercises, and one group acted as a control group. The results showed that low-frequency electrical stimulation and exercises significantly (P less than .05) increased isokinetic back-muscle strength compared to the control and medium-high-frequency electrical stimulation groups. Both types of electrical stimulation, however, significantly increased (P less than .05) the endurance in the back muscles compared with the control and the exercise groups. This study showed that electrical stimulation may be a valuable treatment in the early care of low-back pain patients in maintaining and increasing strength and endurance of back muscles when a more active exercise program is too painful to perform.

Adolescent↗
PubMed1997

Axial rotation strength in seated neutral and prerotated postures of young adults.

STUDY DESIGN: To determine the trunk-twisting capability from neutral and prerotated postures, a study was designed to measure torque generated in isometric and isokinetic activities of 50 young adults. OBJECTIVES: To determine the isometric and isokinetic axial rotation strengths of male and female subjects in neutral and asymmetric postures and to quantify the effect of velocity of rotation on the isokinetic trunk strength profile. METHODS: A specially designed axial rotation tester was employed using specially written modular software for data collection and analysis. The isometric strengths were measured in neutral, 15 degrees, and 30 degrees prerotated trunk postures. The isokinetic strength was measured in activities starting from the neutral position to fully rotated and from a fully rotated position to neutral positions at 10 degrees, 20 degrees, and 40 degrees per second angular velocity. The data obtained were subjected to multivariate and univariate analyses of variances with multiple comparisons and multiple regression analyses. RESULTS: All study participants were significantly stronger in isometric twisting activities than in the isokinetic activities. In isometric activities, participants were 20-25% weaker in prerotated postures when twisting in the direction of prerotation and were approximately 30% stronger in the opposite direction. For isokinetic activities, the trunk rotation from neutral to asymmetric positions produced lesser torques compared with torques from rotated positions to the neutral position. The torque-producing capability declined with increasing velocity of activity. CONCLUSION: This study adds to the data base of rotational strength.

Adolescent↗
PubMedDate not supplied

A controlled trial of circuit weight training on aerobic capacity and myocardial oxygen demand in men after coronary artery bypass surgery.

BACKGROUND: Cardiovascular benefits of resistance training in cardiac patients have been suggested but not studied in a randomized, controlled trial of circuit weight training (CWT) without an aerobic exercise component. The purpose of the current study was to examine the effects of 10 weeks of CWT on muscular strength, peak oxygen consumption (peak VO2), and myocardial oxygen demand (mVO2) in men after coronary artery bypass surgery. METHODS: Twenty-six, post-coronary bypass male subjects (mean 19 months after bypass), aged 60 +/- 8.5 years, were randomly allocated to 10 weeks of CWT at 40 to 60% of maximum voluntary contraction (n = 12) or to a control group (n = 14). Muscular strength was assessed using a modified one repetition maximum technique. Peak VO2 was recorded during symptom-limited treadmill exercise. Rate pressure product, as an indirect measure of mVO2, was measured during isometric, isodynamic, and dynamic exercise. RESULTS: No ischemic symptoms nor electrocardiographic changes were recorded during testing or training. Strength increased by 18% (P < 0.005) in five out of seven exercises in the training group, but was unchanged in the control group. Training did not improve peak VO2. Rate pressure product during isometric and isodynamic exercise decreased from pre- to post-testing (P < 0.05) but was equivalent to that seen in the control group. CONCLUSIONS: Moderate intensity CWT is safe and can improve strength in selected low-risk patients after coronary artery bypass surgery. However, it does not significantly increase peak VO2 nor reduce mVO2 during isometric, isodynamic, and dynamic exercise.

Aerobiosis↗
PubMed2003

Functional and electromyographic results after open rotator cuff repair.

Fifty-one patients treated for full-thickness rotator cuff tears were followed up an average of 4 years after surgery (range, 2-6.4 years). The shoulder function was assessed according to the Constant classification, each patient did strength measurements, and had electromyographic evaluation of the supraspinatus and infraspinatus muscles. The mean value of the Constant score for the surgically treated shoulder was 2.7 points. Forty-five patients (88.2%) had satisfactory scores and six patients (11.8%) had unsatisfactory scores. The result of treatment was significantly correlated to the size of the tear and the time elapsed from injury to surgery. However, no correlation was found between the result of the treatment and the type of surgery, mode of postoperative rehabilitation, and age. The strength measurement of abduction and of external rotation indicated significantly reduced power in surgically treated shoulders compared with contralateral shoulders. There was a significant difference of the infraspinatus motor unit potential interference pattern reduction between surgically treated and the contralateral shoulder. There was a positive correlation between electromyographic findings and the results of rotator cuff reconstruction.

Adult↗
PubMed1984

Myosin isoenzymes in single muscle fibres of Xenopus laevis: analysis of five different functional types.

An analysis has been performed of the native myosin isoenzyme composition of isolated skeletal muscle fibres from Xenopus laevis with well-defined isotonic contraction properties. Fast twitch 'white' (type 1) fibres contained three isomyosins; fast twitch 'red' (type 2) fibres showed two major myosin bands with migration velocities very similar to those of the two slower bands in type 1. Slow twitch (type 3) fibres yielded a single, slowly migrating band as did slow tonic (type 5) fibres, whereas the myosin from type 4 (very slow twitch, 'intermediate') fibres migrated with a somewhat higher mobility. The results suggest that amphibian skeletal muscle may possess the principal fibre types found in mammals and birds.

Adenosine Triphosphatases↗
PubMed1993

A new strategy for multifunction myoelectric control.

This paper describes a novel approach to the control of a multifunction prosthesis based on the classification of myoelectric patterns. It is shown that the myoelectric signal exhibits a deterministic structure during the initial phase of a muscle contraction. Features are extracted from several time segments of the myoelectric signal to preserve pattern structure. These features are then classified using an artificial neural network. The control signals are derived from natural contraction patterns which can be produced reliably with little subject training. The new control scheme increases the number of functions which can be controlled by a single channel of myoelectric signal but does so in a way which does not increase the effort required by the amputee. Results are presented to support this approach.

Amputation, Surgical↗
PubMed1975

Fibrin-blood platelet interaction in a contracting clot.

The interaction of fibrin and blood platelets was studied by measuring tension development in clots containing different ratios of these two components. Isometric tension attained a saturation value (MT) when plotted as a function of the concentration of either component at a constant concentration of the other. The value of MT increases linearly with the minimal platelet concentration (Ps) required in order to reach saturation at various different fibrin concentrations. A linear relationship also holds in a plot of Ps versus the logarithm of the corresponding fibrin concentration. When the cylindrical clots contracted isotonically, the velocity, normalized with respect to the momentary length, was found to be constant. This velocity decreased in an hyperbolic manner with increasing fibrin concentration at a constant concentration of blood platelets. The results are interpreted in terms of a three-dimensional network in which the blood platelets serve as contractile cross-bridges connecting fibrin fibres. Tension development is assumed to be accompanied by the reduction of the angle between fibrin fibres. An attempt was made to calculate the isometric tension developed by a platelet.

Blood Coagulation↗
PubMed1976

The influence of percussion, occlusion and mastication on the occurrence of silent periods in masseter muscle activity.

The occurrence of silent periods in masseter muscle activity was investigated during percussion of the bony structures of the head and neck, during occlusion of the teeth on surfaces of varying hardness, and during chewing of different food-stuffs. Silent periods were demonstrated on percussion during isometric and isotonic contraction of the masseter muscles and the occurrence of silent periods was influenced by the force of occlusion and by the nature of the surface contacted. Mandibular velocity was investigated during tapping and chewing sequences by ultra-high-speed cinematography, but it was not found possible to identify a critical change in mandibular velocity associated with the occurrence of silent periods. More silent periods were observed during the chewing of hard foods than of soft foods and there were more silent periods near the beginning of chewing sequences than towards the end. Differences in latency and duration of silent periods were observed in relation to artificial changes in the occlusion.

Dental Occlusion↗
PubMed1989

Characterization of single heart cell contractility by rapid imaging.

1. A rapid imaging technique with temporal resolution of about 1 ms was employed to describe cell-length changes during the isotonic contraction cycle of adult rat ventricular myocytes at 22 degrees C. 2. Parameters of cell contraction and relaxation were defined and values obtained under control conditions and after treatment with 5 mumol/L verapamil. 3. Over 15 min, verapamil dramatically reduced the maximum shortening attained. This was associated with delay in both excitation-contraction coupling latency and the time at which maximum rate of shortening occurred. However, peak shortening was recorded earlier in the contraction cycle. Total cell-cycle time was abbreviated under the influence of verapamil and maximum rates of shortening and lengthening were depressed in a similar manner. 4. The results highlight the value of improved temporal precision in describing myocyte contractility and validate the use of the parameters defined in the single-cell model for the study of the mechanisms of action of cardiotonic agents.

Animals↗
PubMed2000

The capacity of mdx mouse diaphragm muscle to do oscillatory work.

1. Mdx mice were used as a model for Duchenne muscular dystrophy; both lack dystrophin. It was hypothesized that the mdx condition would have a marked effect on the ability of diaphragm muscle from mdx mice to do active net work and generate power. This hypothesis was tested using the work-loop technique. 2. Specific twitch force, specific tetanic force and maximum power were all significantly less in diaphragm strips from mdx mice than those from control mice. 3. In all preparations muscle length at which maximum power was achieved (Lw) was about 8% less than that at which maximum tetanic force was achieved (L0), both in mdx and control muscle. 4. The isometric force-length curve for mdx muscle was steeper on both sides of the plateau. Similarly, the curve relating net work per cycle to muscle length was steeper for mdx muscle on both sides of the plateau. 5. Maximum power of mdx muscle was achieved at a lower strain than for control muscle; maximum power occurred at a strain of 10.2% for mdx and 14.7% for control. Further increases in strain caused a marked decrease of power production in mdx muscle, whereas they caused a smaller decrease in control muscle. 6. In summary, at muscle lengths longer than Lw and at high strains, performance of mdx muscle was compromised relative to that of control muscle. Work and power were compromised more than isometric force.

Animals↗