Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Isotonic Contraction”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources
PubMed2006

Sex differences in single muscle fiber power in older adults.

PURPOSE: This study was conducted to determine whether differences in power at the single muscle fiber level contribute to sex differences in whole muscle power production in the elderly. METHODS: A total of 16 sedentary older persons (10 women, 6 men), mean age 72 yr, had percutaneous needle biopsy of musculus vastus lateralis. Chemically skinned single muscle fibers were activated with Ca for maximal isometric force measurement (Po). The slack test was performed to determine maximal unloaded shortening velocity (Vo). Force-velocity and power curves were generated via a series of isotonic contractions, allowing measurement of peak power and specific power. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to determine myosin heavy chain composition of single muscle fibers. Whole muscle strength, velocity, and power were measured for knee extension and double leg press. RESULTS: Men had greater whole muscle strength, power, and velocity compared with women. Studied were 274 type I and 33 type IIa single fibers. No significant sex differences were found for fiber size, Po, specific force, Vo, power, or specific power in type I or IIa fibers. CONCLUSIONS: Single muscle fiber quality in older women is equivalent to that in older men and can not explain the differences seen in whole muscle strength, power, or function.

Aged↗
PubMed1991

[Plasticity and remodeling of the myocardium in hypertensive patients. The inotropic effect].

Systolic function of normal hearts is characterised by the sequence isometric-isotonic contraction and dominated by the force-time relationship which, more than the pressure graph, determines myocardial oxygen consumption. It is the main factor of heat production whether or not related to mechanical activity. Apart from the loading conditions, there are two important biological factors during contraction: the structure of the myosin and the quantity of free intracytoplasmic calcium on which the membrane proteins depend. In cardiac hypertrophy, the decrease of Vmax allows the fibre to develop a normal active tension more economically at the expense of its velocity. Depending on the species and tissues, this decrease may be due to a sarcoplasmic and/or a membrane protein modification. The therapeutic inotropic effect is obviously deleterious at fibre level but it may, on the contrary, be economically beneficial from the thermodynamic point of view to the heart as a whole.

Calcium Channels↗
PubMed1984

[Comparative characteristics of the mechanical activity of atria and ventricles].

Differences between parameters of isometric and isotonic contractions of atria and ventricles were studied in warm-blooded and cold-blooded animals. The maximal shortening velocity of contractile element was determined from isometric contraction using a two-component Hill's model as well as from the strength-velocity ratio. The atrial Vmax was about twice as high as that of ventricles. The rate constant of delayed activation in atrium was 10.6 +/- 0.4 s-1, in the rabbit ventricles 4.42 +/- 0.60 s-1. The data suggest differences of ATP hydrolysis velocity with actomyosin ATP-ase of atrium and ventricles.

Adenosine Triphosphatases↗
PubMed1978

Transient force responses in blood-perfused papillary muscle after step changes in load.

In in situ canine papillary muscles, we studied transient responses in peak isometric force at control length, after contraction was suddenly switched from isotonic contractions at various forces and isometric contractions at different lengths. Peak isometric force rapidly decreased after isotonic contractions at relatively low forces and isometric contractions at shorter lengths. In contrast, peak isometric force rapidly increased after isotonic contractions at relatively high forces and isometric contractions at longer lengths. There was no transient response when the preceding isotonic force was about half of the present peak isometric force. Magnitude and direction of the transient force response depended on magnitude and direction of the change in the mean muscle force level produced by the sudden switch of loading conditions. Transient force responses were accompanied by simultaneous changes in time to peak isometric force in the same direction. We proposed that, in the blood-perfused papillary muscle, a sudden change in the mean muscle force causes an abrupt change in coronary flow supply-demand relation which in turn causes a transient change in contractile force.

Animals↗
PubMed2002

The effects of timing and application of vibration on muscular contractions.

BACKGROUND: The effect of vibration stimulation on muscular strength is an emerging field of research and very little comprehensive work has been conducted at this stage. HYPOTHESIS: There will be no effects of timing or application of vibration stimulation on muscular strength and activation across isometric, isokinetic and concentric isotonic contractions. METHODS: There were 28 recreational athletes who participated in this study. Their characteristics were: (mean +/- SD) age, 22.8 +/- 5.6 yr; height, 174.1 +/- 8.8 cm; and body mass, 78.0 +/- 13.6 kg. The vibration stimulation was delivered at 50.42 +/- 1.16 Hz with an acceleration of 13.24 +/- 0.18 ms(-2). RESULTS: A series of one-way ANOVAs revealed significant (p < 0.05) improvements of 14.7 +/- 2.9% and 15.3 +/- 3.1% above normal contraction levels for concentric isotonic strength during and after the vibration stimulation, respectively. No significant improvements in isometric and isokinetic strength were evident. Concurrent measurement of electromyography (EMG) presented significant improvements during stimulation of 30.1 +/- 14.6%, 43.0 +/- 13.0%, and 107.1 +/- 44.4% in mean activation of rectus femoris (RF) for the isometric, isokinetic, and concentric isotonic contractions, respectively. Synchronous collection of vibromyography (VMG) during stimulation displayed a significant decrease of -6.4 +/- 1.5%, -5.1 +/- 1.2%, and -4.1 +/- 1.7% in mean VMG activity of RF for the isometric, isokinetic, and concentric isotonic contractions, respectively. CONCLUSIONS: Significant improvements in muscular strength and activation for concentric isotonic contractions performed during an applied vibration suggest that the optimal timing of a vibratory stimulation would be while the participant is contracting isotonically. However, further research needs to be conducted to establish the exact mechanism behind these improvements.

Adolescent↗
PubMed2001

Potentiation of shortening and velocity of shortening during repeated isotonic tetanic contractions in mammalian skeletal muscle.

The purpose of this study was to investigate the enhancement of shortening and of the velocity of shortening during repeated incompletely fused isotonic tetanic contractions. The medial gastrocnemius muscle of anesthetized rats was isolated in situ and the motor nerve stimulated with supramaximal pulses, 50 micros duration, at optimal length. Estimated maximal velocity of shortening (V(max)) was 210 +/- 6 mm x s(-1) (mean +/- SEM). Repeated incompletely fused tetanic contractions (three pulses at 80 Hz) resulted in initial shortening which was 1.5 +/- 0.1 mm, and this increased to 2.7 +/- 0.2 mm after 7 s of 4 s(-1) contractions. Peak velocity of shortening for intermittent 80 Hz stimulation increased from 60.5 +/- 4 mm x s(-1) to 91.8 +/- plus minus 6 mm x s(-1). The initial velocity of shortening for 80 Hz stimulation was substantially less than the velocity of shortening observed with 200 Hz stimulation, but increased to 72 +/- 3% of the load-specific value for 200 Hz stimulation. Myosin regulatory light chain phosphorylation increased from 11.1 +/- 1.5% at rest to 32.9 +/- 5.4% after 4 s of intermittent 80 Hz stimulation and 50.4 +/- 8.8% after 7 s ( P<0.01). The ascending limb of the length-force relationship was determined with tetanic contractions, 200 Hz for 100 ms. At the length corresponding to peak shortening after 7 s of repeated 80 Hz contractions, the maximal isometric force was five times greater than the isotonic load. The rate of phosphorylation was sustained from 4 to 7 s, but the rate of increase in shortening and velocity decreased. The slower rate of change in shortening and velocity may be due to approaching maximal velocity for this short duration of contraction, but is not due to slowing of the rate of phosphorylation of the myosin regulatory light chains.

Animals↗
PubMed1994

Preload release increases blood flow and decreases fatigue during repetitive isotonic muscle contractions.

The effects of preload on blood flow (Q), O2 uptake (VO2), and fatigue were investigated in the canine gastrocnemius-plantaris muscle in situ. Repetitive (1 contraction/s, 200 ms duration) afterloaded (0.25-0.3 maximal active isometric tension) isotonic tetanic contractions were performed in high-preload (HP; 69 g/g, n = 5), low-preload (LP; 35 g/g, n = 6), and preload-release (PR; 0 g/g, n = 5) experiments. Maximal Q values (1.0, 1.6, and 2.1 ml.min-1.g-1, P < 0.05 for all comparisons) and Q2 delivery (8, 13, and 17 mumol.min-1.g-1, P < 0.05 for all comparisons) increased significantly with decreasing preload. The maximal VO2 of HP was 7.2 mumol.min-1.g-1, which is significantly lower than both LP (10.5 mumol.min-1.g-1, P < 0.05) and PR values (11.4 mumol.min-1.g-1, P < 0.05); these differences were sustained through 20 min of contractions. Fatigue, measured as a loss of power production, was 63, 37, and 23% at 20 min of contractions in HP, LP, and PR, respectively, indicating significantly less fatigue with decreasing preload (P < 0.05 for all comparisons). These data demonstrate that the preload, present as the level of passive tension maintained between contractions, can influence Q, VO2, and fatigue during repetitive isotonic tetanic contractions of muscle in situ by a mechanically determined metabolic modulation of dynamic muscle performance.

Animals↗
PubMed1983

Systolic time intervals: assessment by isolated cardiac muscle studies.

To document the independent effects of acute changes in preload, afterload and inotropic state on the systolic time intervals, 10 isolated rat left ventricular muscle preparations were studied. Experiments were performed using physiologically sequenced contractions that simulate the loading conditions of the intact left ventricle. The preshortening period was measured from the time of the electrical stimulus to the onset of muscle shortening, and the isotonic contraction time was measured as the duration of shortening. These variables are analogous to the preejection period and the left ventricular ejection time in the intact heart. It was found that an isolated increase in preload shortened the preshortening period and prolonged the isotonic contraction time, whereas an increase in afterload prolonged the former and shortened the latter. Isoproterenol shortened both the preshortening period and the isotonic contraction time, while an increase in calcium shortened the preshortening period and lengthened the isotonic contraction time. All changes were significant (p less than 0.01) by analysis of variance. Thus, the similar dependence of preshortening period, isotonic contraction time and clinical systolic time intervals on changes in preload, afterload and inotropic state supports the derivation of systolic time intervals from fundamental principles of myocardial mechanics. These data provide an improved basis for the rational interpretation of systolic time intervals in patients with and without heart disease.

Animals↗
PubMed1980

Isotonic vocalis contraction as a means of producing rapid decreases in Fo.

In a first experiment, subjects were presented with frequency modulated tones and instructed to vary their own vocal pitch to match what they were hearing. It was found that the faster a subject modulated his voice, the higher the carrier frequency he produced became relative to that specified as his target. In a second experiment, subjects were presented with one or two target tones. After one was presented, they were required to reproduce its pitch with their own voice. They did so accurately. After two were presented, they were asked to oscillate the pitch of their voice as rapidly as possible between them. In this case, it was found that the tones which were produced were higher than those specified by the targets. It is argued that the results from both experiments indicate that fast decreases in voice pitch are produced by isotonic contraction of the vocalis muscles.

Adult↗
PubMed1997

Antagonistic effects of trifluoperazine, imipramine, and chlorpromazine against acetylcholine-induced contractions in isolated rat uterus.

AIM: To examine the effects and affinity of some phenothizines (trifluoperazine, Tri and chlorpromazine, Chl) and antidepressant (imipramine, Imi) drugs on acetylcholine (ACh)-induced uterine contraction. METHODS: Isotonic contractions of rat uterine strips were recorded. ACh was administrated to induce maximal contraction before exchange of nutrient solution. ACh was added 5 min after the testing drugs. The nutrient solution was exchanged 4 times after each agonist (ACh or other agents) to produce maximal contraction. RESULTS: Atropine (Atr, 0.029-2.9 mumol.L-1), 4-DAMP (3.6-360 nmol.L-1), pirenzepine (Pir, 0.23-23.5 mumol.L-1), and AF-DX 116 (0.7-35.6 mumol.L-1) competitively antagonized the muscular uterine concentration induced by ACh (0.068-36068 mumol.L-1). The Schild plot was linear (r = 1.00). The pKB and slopes values (95% confidence limits) were 9.28 +/- 0.12 and 1.00 +/- 0.10 to Atr, 9.06 +/- 0.10 and 1.10 +/- 0.08 to 4-DAMP, 7.03 +/- 0.15 and 0.99 +/- 0.12 to Pir, and 5.60 +/- 0.08 and 1.00 +/- 0.19 to AF-DX 116. Tri 0.01-2 mumol.L-1 (pKB = 8.39 +/- 0.04) and Imi 94-940 nmol.L-1 (pKB = 7.21 +/- 0.10) produced also a competitive antagonism of the muscular uterine contraction induced by ACh (r = 1.00), but the slope was only 0.60 +/- 0.03 to Tri or 0.83 +/- 0.16 to Imi. Chl 2.8-5.6 mumol.L-1 produced a weak antagonism on amplitude of muscular contraction induced by the cholinomimetic. CONCLUSION: The muscarinic receptors on uterus behaved as M3 subtype. Tri and Imi, but not Chl, were competitive antagonist of muscarinic receptors of uterus. Imi behaved a simple competitive antagonist at a single site on myometrium, but Tri was not a simple competitive agent at a single site.

Acetylcholine↗
PubMed2001

The effect of hypoxia on shortening contractions in rat diaphragm muscle.

Hypoxia is known to reduce isometric contractile properties of isolated rat diaphragm bundles. Its effect on isotonic contractile properties (i.e. force-velocity relationship and power output) has not been studied. We hypothesized that hypoxia reduces velocity of shortening and consequently power output of the unfatigued muscle, and shortens endurance time during isotonic contractions. Force-velocity relationship, power output, and fatigue resistance of rat diaphragm muscle bundles were measured during hypoxia (PO2: 6.6 +/- 0.2 kPa) and compared with hyperoxia (PO2: 91.8 +/- 0.7 kPa). Force was clamped from 1 to 100% of maximal tetanic force (Po). Fatigue during isotonic contractions was induced by repeated stimulation every 2 s at a clamp level of 33% of Po. Hypoxia did not affect isometric force generation compared with hyperoxia, nor contraction or relaxation time. In contrast, maximum shortening velocity decreased significantly (hypoxia: 4.2 +/- 0.3, hyperoxia: 6.0 +/- 0.2 Lo/s, P < 0.05). The force-velocity curve shifted downwards (P < 0.05). Hypoxia lowered power output at each load compared with hyperoxia (P < 0.05). The isotonic endurance time was shorter during hypoxia compared with hyperoxia (80 +/- 2 vs. 130 +/- 3 s, P < 0.05). These data show that hypoxia depresses isotonic contractile properties and power output, and reduces endurance time during repeated isotonic contractions.

Animals↗
PubMed1993

Myocardial mechanics and the Fenn effect determined from a cardiac muscle crossbridge model.

A three-element cardiac muscle fibre model, utilising Huxley's sliding filament theory for the contractile element and coupled with parallel and series elastic components, was simulated to see if it were possible to predict the cardiac Fenn effect. The force/length energy (FLE) was computed in both isometric and isotonic contractions, as a function of muscle fibre length (preload) in the isometric case and afterload in the isotonic contraction case. Simulation results demonstrated that isotonic contractions produced a greater FLE than isometric contractions at every corresponding afterload, with the difference being equal to the work produced in the isotonic case, which is characteristic of the Fenn effect. The maximum energy utilisation was observed at maximum force isometric contractions, as has been experimentally observed in cardiac muscle. Changing the stiffness of the series elastic component did not change the Fenn-effect behaviour. Fenn-effect plots using crossbridge energy predictions showed behaviour similar to the FLE plots, but the FLE: crossbridge energy ratio declined with decreasing force even though the efficiency has been experimentally found to be constant.

Adenosine Triphosphate↗
PubMed1990

Mechanics of K(+)-induced isotonic and isometric contractions in isolated canine coronary microarteries.

The effects of shortening in isotonic contractions on the mechanics of microvascular smooth muscle were investigated. Intramyocardial canine coronary microarteries (in situ diameter 60 +/- 3 microns) were mounted as rings, connected to a newly developed photoelectromagnetic force-length transducer, and activated with 125 mM K+. Shortening during isotonic contractions depressed the length-force relation (shortening deactivation) compared with the length-force relation obtained from isometric contractions; the effect was present at the earliest moments after activation, suggesting that a fundamental mechanism associated with the actual sliding of contractile filaments delayed onset of contractile activity in isotonic contractions compared with isometric contractions. Force-velocity relations were obtained by isotonic quick releases from isotonic and isometric contractions at various times. Isotonic shortening before the quick releases reduced the constants of the apparent hyperbolic force-velocity relations and maximal velocity of shortening (Vmax) compared with isometric contractions released at the same time. Increasing contraction duration reduced Vmax but more so in isotonic than in isometric contractions. Vmax also decreased with decreasing instantaneous length. A possible effect of force development on Vmax before the isotonic quick release was also described. Quick increments of load during isotonic contractions were sustained during active shortening in the phasic part, but during the tonic part loading resulted in a pronounced transient relaxation. Thus, in microvascular preparations, active isotonic shortening altered the length-force, force-velocity, and velocity-time relations and uncovered a time-dependent sensitivity to loading conditions. These experiments suggested that the mechanics of smooth muscle contraction may contribute significantly to the mechanisms of the physiological control of coronary microvascular diameter.

Animals↗
PubMed1978

Acetylcholine-like activity in the fruit of the black nightshade (Solanaceae).

The presence of acetylcholine in aqueous extracts of the fruit of Solanum nigrum Linn. (black nightshade) has been established based upon the following pharmacological tests: a) isotonic contraction of the isolated toad rectus abdominis; b) negative chronotropic and inotropic action on the isolated toad heart; c) isotonic contraction of the isolated guinea pig's ileum; d) isotonic contraction of the rat's isolated jejunum; 3) decrease on the cat's arterial blood pressure; f) secretory effects on the rat's submaxillary gland. These actions were selectively blocked by curate or atropine and disappeared after incubation of the extract at 37 C with plasma. Further evidence showing that the fruit of the black nightshade contains acetylcholine was obtained by chromatographic separation of the aqueous extract. The average content of acetylcholine was found to be 250 micrograms/g of fruit.

Acetylcholine↗
PubMed1986

Aerobic and anaerobic correlates of mechanical work by gastrocnemius muscles of the aquatic amphibian Xenopus laevis.

Isolated, saline-perfused gastrocnemius muscles of Xenopus laevis were used to assess the relationships between aerobic and anaerobic metabolism during conditions of rest, isotonic contraction and recovery. The major part (85%) of the energy used during 25 min of isotonic contractions in the saline-perfused muscles was from anaerobic rather than aerobic sources. However, the small contribution made by oxidative metabolism during activity can be attributed, in part at least, to limitations imposed by the rate of perfusion and the low O2 capacity of the perfusate. The respiratory exchange ratio (R = VCO2/VO2) of saline-perfused gastrocnemius muscles of Xenopus was 0.82 at rest, increasing to values well above 1.0 during activity. The elevated R value is consistent with liberation of CO2 by metabolic acid titration of the bicarbonate buffer system of the saline perfusate. Recovery from exercise was characterized as a period of net CO2 retention (R values of 0.4) presumably reflecting a replenishment of depleted CO2 stores. Depending on the acid-base status of the venous outflow from the isotonically contracting muscles, hydrogen ions were found to be released at either a greater rate (alkalosis) or slower rate (acidosis) than that of lactate.

Aerobiosis↗
PubMed1993

Changes in the heart rate and electromyogram beyond the limit time of an isotonic isometric contraction.

Nine men [24.6 (SEM 1.1) years] carried out isometric contractions (IC) of the right elbow flexors at 50% and 100% of the maximal voluntary contraction (MVC). At 50% MVC they had to maintain IC until the limit time (isotonic IC: IIC50) and beyond for as long as possible (anisotonic IC: AIC50). At 100% MVC, IC was anisotonic since the decrease in force was immediate (AIC100). Measurements of the force, the integrated electromyogram (iEMG) and the heart rate (fc) were made during the entire period of contraction. There was a linear relationship between the iEMG increase and the fc increase for IIC50 and AIC100. This relationship was not found for AIC50. The role played by the peripheral information would seem to have become more important in fc regulation when the isotonic IC preceding the anisotonic IC was sufficiently long (submaximal IIC). It would seem that the idea of muscle exhaustion at the limit time was only relative, and depended greatly on the subject's motivation and his capacity to endure a certain degree of pain.

Adult↗
PubMed2002

Plasma-renin response to isotonic volume contraction in young salt-sensitive normotensive men.

Salt-sensitive persons have lower plasma renin activity than salt-resistant persons and their plasma renin activity increases less with a low sodium diet or volume depletion, compared to salt-resistant individuals. However, the time course of the renin response to acute volume contraction has not been studied in humans. Therefore, we designed an acute study in salt-sensitive and salt-resistant normotensive volunteers, in which we examined the renin response to isotonic volume contraction. Twenty-four previously characterized salt-resistant (n = 13) and salt-sensitive (n = 11) persons were placed on a high salt diet containing 280 mmol NaCl/day for 3 days. After an overnight stay, volume depletion (total, 300 mmol Na) was induced by furosemide infusion. Free water deficits were replaced by 5% isotonic glucose infusion. Blood was obtained for electrolytes, plasma renin activity, and plasma aldosterone concentration. Blood pressure (BP) and heart rate were monitored during the experiment. Intravascular volume depletion resulted in a progressive increase in plasma renin activity that was both steeper and higher in salt-resistant than in the salt-sensitive subjects (P < .001). There was a slight increase in BP in response to volume contraction in both groups. Although heart rate did not change in salt-sensitive persons, it increased significantly (P < .001) in the salt-resistant group. These findings point to an intrinsic difference in the regulation of renin release between salt-sensitive and salt-resistant subjects that may account for the different BP responses to changes in dietary sodium intake.

Adult↗
PubMed1975

Mechanical control of the time-course of contraction of the frog heart.

Changes in load during most phases of an isotonic contraction of the frog and turtle heart increased or decreased the duration of the twitch. It was abbreviated by a maintained increase or by a brief decrease in load. The relaxing effect of these procedures developed with a delay lasting more than a second under some conditions and will be called lengthening deactivation. The reverse procedures, a maintained diminution or a brief increase in load, increased the duration of the twitch. This effect will be called shortening activation. Although the termination of relaxation may be delayed or advanced by the mechanical interventions mentioned, the normal time-course of isotonic relaxation was always resumed later, regardless of the starting level of the load, making it possible to measure accurately changes in the duration of the twitch. The responses to changes in load produce positive feedback during the isotonic contraction and explain, at least in part, the difference in the time-course of isotonic and isometric contraction. The effects of changes in load were much smaller and briefer in the atrium than the ventricle.

Animals↗