scholarly journals Mechanical control of the rising phase of contraction of frog skeletal and cardiac muscle.

1977 ◽  
Vol 70 (6) ◽  
pp. 697-705 ◽  
Author(s):  
E Bozler
Keyword(s):  
Isometric Contraction ◽  
Time Course ◽  
Contractile Activity ◽  
Muscle Length ◽  
Isometric Contractions ◽  
Activation Process ◽  
Control Activity ◽  
Isotonic Contraction ◽  
Fenn Effect ◽  
Isotonic Shortening

The effect of shortening on contractile activity was studied in experiments in which shortening during the rising phase of an isotonic contraction was suddenly stopped. At the same muscle length and the same time after stimulation the rise in tension was much faster, if preceded by shortening, than during an isometric contraction, demonstrating an increase in contractile activity. In this experiment the rate of tension rise determined in various phases of contraction was proportional to the rate of isotonic shortening at the same time after stimulation. Therefore, the time course of the isotonic rising phase could be derived from the tension rise after shortening. The rate of isotonic shortening was found to be unrelated to the tension generated at various lengths and to correspond closely to the activation process induced by shortening. The length response explains differences between isotonic and isometric contractions with regard to energy release (Fenn effect) and time relations. These results extend previous work which showed that shortening during later phases of a twitch prolongs, while lengthening abbreviates contraction. Thus the length responses, which have been called shortening activation and lengthening deactivation, control activity throughout an isotonic twitch.

Influence of submaximal isometric contractions of the hamstrings on electromyography activity and force while functioning as hip extensors

2020 ◽  
pp. 1-8
Author(s):  
Dasom Oh ◽  
Wootaek Lim
Keyword(s):  
Prone Position ◽  
Supine Position ◽  
Isometric Contraction ◽  
Muscle Length ◽  
Biceps Femoris ◽  
Emg Activity ◽  
Isometric Contractions ◽  
Significant Difference ◽  
Extension Force ◽  
Long Head

BACKGROUND: Although the medial and lateral hamstrings are clearly distinct anatomically and have different functions in the transverse plane, they are often considered as one muscle during rehabilitation. OBJECTIVE: The purpose of the study was to compare the electromyographic (EMG) activity between the prone position and the supine position during maximal isometric contraction and to additionally confirm the effect of submaximal isometric contractions on EMG activity of medial and lateral hamstrings, and force. METHODS: In the prone position, EMG activities of the long head of biceps femoris (BFLH) and semitendinosus (ST) were measured during the maximal isometric contraction. In the supine position, hip extension force with EMG activity were measured during the maximal and the submaximal isometric contractions. RESULTS: EMG activity in the prone position was significantly decreased in the supine position. In the supine position, there was a significant difference between the BFLH and ST during the maximal isometric contraction, but not during the submaximal isometric contractions. CONCLUSIONS: The dependence on the hamstrings could be relatively lower during hip extensions. When the medial and lateral hamstrings are considered separately, the lateral hamstrings may show a more active response, with increased muscle length, in clinical practice.

scholarly journals The time-course of energy balance in an isometric tetanus.

1979 ◽  
Vol 73 (5) ◽  
pp. 553-567 ◽  
Author(s):  
E Homsher ◽  
C J Kean ◽  
A Wallner ◽  
V Garibian-Sarian
Keyword(s):  
Energy Balance ◽  
Chemical Reaction ◽  
Isometric Contraction ◽  
Time Course ◽  
Rana Temporaria ◽  
Isometric Contractions ◽  
Chemical Changes ◽  
Rate Of Evolution ◽  
Work Production

Unpoisoned sartorius muscles of Rana temporaria were stimulated tetanically in isometric contractions lasting up to 20 s at 0 degrees C. The observed enthalpy (heat + work) production and the chemical changes in these contractions were measured, and a comparison was made between the observed enthalpy and the enthalpy that could be explained by the chemical changes. Like earlier workers, we found that the only net known reaction of energetic significance that occurred was dephosphorylation of n-phosphoryl creatine (PC), and we found a significant evolution of unexplained enthalpy (UE), a portion of the observed enthalpy which could not be explained by the extent of PC dephosphorylation. We measured the total quantity and the rate of production of the UE, and we found that its rate of evolution, which was most rapid during the first 750 ms of contraction, fell progressively to zero by the 8th s of contraction: i.e., after 8 s of contraction, all the observed enthalpy is adequately explained by PC dephosphorylation. The time-course of evolution of the UE was slower than that of the labile enthalpy (a component of the enthalpy evolved in isometric contraction whose rate of production declines exponentially at approximately 1 s-1). We conclude that, although the magnitudes of these enthalpy quantities may be similar, they are not derived from the same chemical reaction in muscle.

Length Range, Morphology and Mechanical Behaviour of Rat Gastrocnemius Muscle During Isometric Contraction At the Level of the Muscle and Muscle Tendon Complex

1984 ◽  
Vol 35 (3) ◽  
pp. 505-516 ◽  
Author(s):  
R.D. Woittiez ◽  
P.A. Huijing
Keyword(s):  
Isometric Contraction ◽  
Fibre Length ◽  
Muscle Length ◽  
Muscle Fibres ◽  
Isometric Contractions ◽  
Force Relation ◽  
Length Range ◽  
Equilibrium Length ◽  
Fibre Angle

Fibre length, fibre angle and muscle length were quantified for rat m. gastrocnemius medialis with the muscle passive as well as fully activated during isometric contraction. This was done with the muscle in situ still attached with intact origin and insertion as well as with the calcaneus cut for simultaneous force measurements. Comparison of muscle lengths in maximal plantar and dorsal flexion with the physiological length range of the muscle, as defined by the limits of the length force relation, indicated that approximately the lower 75% of this range may be used between the extreme ankle angles, while the knee is kept at 90° of flexion. It is likely that simultaneous knee extentension would take the muscle through the remainder of its physiological length range. During isometric contractions at the level of the muscle, fibres shorten and fibre angles increase (with values exceeding 12 % and 45 % respectively at short muscle lengths). At short lengths fibre angle may reach values exceeding 40°, thereby creating sizable differences between force exerted by the muscle and that of its fibres. Changes of fibre length and fibre angle increase with decreasing muscle length and are ascribed to compliance effects of the aponeuroses above muscle equilibrium length while below muscle equilibrium length a taking up of slack present in these structures occurs prior to these compliance effects. During isometric contractions at the level of the muscle-tendon complex work will be performed by the muscle on the achilles tendon. This work was estimated from tendon length-force characteristics. Its peak value does not exceed 1.35 mJ for any of the muscles at anv length, which is small ( < 2 % ) relative to estimated total energv expenditure of the isometric contractions.

Potentiation of smooth muscle contractility after rapid changes in isotonic force

1996 ◽  
Vol 271 (2) ◽  
pp. C511-C523 ◽  
Author(s):  
R. A. Meiss
Keyword(s):  
Smooth Muscle ◽  
Time Course ◽  
Muscle Length ◽  
Muscle Contractility ◽  
Smooth Muscle Contractility ◽  
Contractile System ◽  
Rapid Changes ◽  
Step Duration ◽  
Cytoskeletal Elements ◽  
Isotonic Shortening

The sudden application of step increases in afterload (0.4-3.0 s in duration) arrested the isotonic shortening of electrically stimulated ovarian ligament smooth muscle strips from rabbits. Force steps were chosen to produce, after initial rapid yielding, a quasi-steady state in which muscle length and force remained constant. Removal of the extra afterload allowed renewed shortening that began with a velocity transiently greater than that measured before the force step (at same muscle length). The rate of force redevelopment was also transiently potentiated under isometric conditions after the removal of the extra load. Both types of potentiation depended on force-step duration, and the transients decayed exponentially with a time constant of approximately 0.25 s. The stiffness of the muscle during the force step was initially depressed but then increased along an exponential time course while force and length remained constant. These observations are consistent with an initial detachment of a portion of the cross-bridge array, which then reattached during the course of the force step, with potentiation being due to either a transient increase in cycling rate or a time-dependent reconfiguration of cytoskeletal elements supporting the contractile system.

scholarly journals Correlation between the clinical phonoaudiological assessment and electromyographic activity of the masseter muscle

2005 ◽  
Vol 13 (4) ◽  
pp. 424-430 ◽  
Author(s):  
Daiana Cristina Biasotto ◽  
Daniela Ap. Biasotto-Gonzalez ◽  
Ivone Panhoca
Keyword(s):  
Statistical Analysis ◽  
Isometric Contraction ◽  
Masseter Muscle ◽  
Speech Therapy ◽  
Young Female ◽  
Isometric Contractions ◽  
Electromyographic Activity ◽  
Masticatory Muscle ◽  
Mean Square ◽  
Isotonic Contraction

OBJECTIVE: The objective of this paper was to evaluate the specificity of masseter muscle palpation when compared to its electromyographic activity. MATERIALS AND METHODS: Twenty-one young female adults, aged between 17 and 25, participated in this research. The speech therapy evaluation data were obtained by two speech therapists through masseter muscle palpation during isometric contraction, and the electromyographic exam was achieved by using bipolar superficial electrodes, positioned on the masseter muscle. The volunteers were instructed to chew the Parafilm M® material bilaterally and simultaneously. The capture of the electromiographic signals occurred during masseter muscle isometric contractions. The electrical activity study of the masticatory muscle was analyzed through the Root Mean Square value during its isotonic contraction. STATISTICAL ANALYSIS: All data were then submitted to Kappa statistical analysis. RESULTS: The results of this study have shown a low correlation between palpation and electromyography (25%), as well as between evaluators (40%). CONCLUSION: According to the findings of the present study, it could be observed that the correlation between masseter muscle palpation and its electromyographic activity was very low, which allows to conclude that muscular palpation cannot effectively replace the eletromyographical exam, but complement it instead.

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

1990 ◽  
Vol 258 (3) ◽  
pp. C512-C523 ◽  
Author(s):  
P. J. Boels ◽  
V. A. Claes ◽  
D. L. Brutsaert
Keyword(s):  
Smooth Muscle ◽  
Contractile Activity ◽  
Smooth Muscle Contraction ◽  
Isometric Contractions ◽  
Maximal Velocity ◽  
Physiological Control ◽  
Force Relation ◽  
Force Velocity ◽  
Isotonic Contractions ◽  
Isotonic Shortening

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.

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

1975 ◽  
Vol 65 (3) ◽  
pp. 329-344 ◽  
Author(s):  
E Bozler
Keyword(s):  
Isometric Contraction ◽  
Positive Feedback ◽  
Time Course ◽  
Frog Heart ◽  
Isotonic Contraction ◽  
Mechanical Control ◽  
The Difference ◽  
Relaxing Effect ◽  
Turtle 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.

scholarly journals Muscle length and joint angle influence spinal but not corticospinal excitability to the biceps brachii across forearm postures

2019 ◽  
Vol 122 (1) ◽  
pp. 413-423 ◽  
Author(s):  
Davis A. Forman ◽  
Daniel Abdel-Malek ◽  
Christopher M. F. Bunce ◽  
Michael W. R. Holmes
Keyword(s):  
Isometric Contraction ◽  
Elbow Joint ◽  
Joint Angle ◽  
Biceps Brachii ◽  
Motor Evoked Potentials ◽  
Muscle Length ◽  
Elbow Flexion ◽  
Corticospinal Excitability ◽  
Biceps Brachii Muscle ◽  
Spinal Excitability

Forearm rotation (supination/pronation) alters corticospinal excitability to the biceps brachii, but it is unclear whether corticospinal excitability is influenced by joint angle, muscle length, or both. Thus the purpose of this study was to separately examine elbow joint angle and muscle length on corticospinal excitability. Corticospinal excitability to the biceps and triceps brachii was measured using motor evoked potentials (MEPs) elicited via transcranial magnetic stimulation. Spinal excitability was measured using cervicomedullary motor evoked potentials (CMEPs) elicited via transmastoid electrical stimulation. Elbow angles were manipulated with a fixed biceps brachii muscle length (and vice versa) across five unique postures: 1) forearm neutral, elbow flexion 90°; 2) forearm supinated, elbow flexion 90°; 3) forearm pronated, elbow flexion 90°; 4) forearm supinated, elbow flexion 78°; and 5) forearm pronated, elbow flexion 113°. A musculoskeletal model determined biceps brachii muscle length for postures 1–3, and elbow joint angles ( postures 4–5) were selected to maintain biceps length across forearm orientations. MEPs and CMEPs were elicited at rest and during an isometric contraction of 10% of maximal biceps muscle activity. At rest, MEP amplitudes to the biceps were largest during supination, which was independent of elbow joint angle. CMEP amplitudes were not different when the elbow was fixed at 90° but were largest in pronation when muscle length was controlled. During an isometric contraction, there were no significant differences across forearm postures for either MEP or CMEP amplitudes. These results highlight that elbow joint angle and biceps brachii muscle length can each independently influence spinal excitability. NEW & NOTEWORTHY Changes in upper limb posture can influence the responsiveness of the central nervous system to artificial stimulations. We established a novel approach integrating neurophysiology techniques with biomechanical modeling. Through this approach, the effects of elbow joint angle and biceps brachii muscle length on corticospinal and spinal excitability were assessed. We demonstrate that spinal excitability is uniquely influenced by joint angle and muscle length, and this highlights the importance of accounting for muscle length in neurophysiological studies.

Gastrointestinal motor effects of erythromycin

1990 ◽  
Vol 259 (3) ◽  
pp. G355-G363 ◽  
Author(s):  
M. F. Otterson ◽  
S. K. Sarna
Keyword(s):  
Small Intestine ◽  
Cycle Length ◽  
Amplitude Ratio ◽  
Contractile Activity ◽  
Low Doses ◽  
Control Activity ◽  
Distal Small Intestine ◽  
Gastrointestinal Motor ◽  
High Doses ◽  
Motor Effects

We studied the small intestinal motor effects of oral and intravenous (iv) erythromycin in 10 conscious dogs. After control recordings with placebo, oral or iv erythromycin was given at 40% of the migrating motor complex (MMC) cycle. Recordings were made after administration until normal contractile activity had returned or 12 h postdrug administration. Low doses initiated a premature MMC. High doses, however, prolonged the MMC cycle length. Erythromycin reduced the MMC propagation velocity at all doses. Both oral and iv erythromycin induced amyogenesia. During this pattern, electrical control activity was obliterated in the proximal and destabilized in the distal small intestine. Erythromycin also increased the incidence of retrograde giant contractions (RGCs) and vomiting. These effects occurred within the first 2 h after oral and within the first 30 min after iv administration. The incidence of giant migrating contractions (GMCs) increased significantly from 5 to 12 h but not from 0 to 5 h after administration. The distance of origination of GMCs from the ileocolonic junction was significantly increased from 5 to 12 h. The amplitude ratio, duration, and velocity of migration of GMCs induced after erythromycin were similar to control values. Clusters of coordinated antral and duodenal contractions also occurred early after administration. Our findings suggest that erythromycin has multiple motor effects on the stomach and small intestine. Diarrhea, abdominal cramping, and vomiting associated with erythromycin may be related to increased incidence of GMCs and RGCs. Erythromycin has a biphasic effect on MMC cycle length, initiating premature MMCs at low doses and prolonging their cycle length at higher doses.(ABSTRACT TRUNCATED AT 250 WORDS)

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