SEARCH · PubMed Health

Results for “Isometric Contraction”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 235 records · Page 13Linked to original sources

PubMed1988

Negative inotropic effects of ATP on the isometric contractions of isolated rat heart muscle.

The effects of ATP on the isometric contractions of isolated rat left ventricular papillary muscle were studied. Exogenously administered ATP had an immediate onset, an abrupt response, progressive recovery and produced dose-related depression in the peak developed tension, maximum rate of tension development and relaxation, which were statistically significant. There were no significant changes in the resting tension, time to peak tension and relaxation time, except for a significantly prolonged relaxation time at the highest concentration of ATP. In the studies of interactions of ATP and either epinephrine or Ca(++), we observed that ATP seemed to interfere with the inotropic effect of epinephrine, while Ca(++) antagonized the negative inotropic action of ATP. We conclude that the site of negative inotropic action of ATP is most likely on the cell membrane, where ATP interferes with Ca(++) flux, and that ATP interferes with the positive inotropic action of epinephrine.

Journal Article↗

PubMed1997

Joined effects of pennation angle and tendon compliance on fibre length in isometric contractions: a simulation study.

The main purpose of this study was to investigate the joined behaviours of tendon and pennation angle during maximal isometric contractions. A musculotendon model of the human soleus muscle was simulated as a function of ankle joint position, which determines the soleus length. Analysis of the respective values of tendon length and pennation angle for various musculotendon lengths showed that the primary effects of tendon elasticity and pennation angle variation were to reduce the fibre length variations by absorption of the musculotendon lengthening. The efficiency of this reduction process was the highest at short soleus lengths and principally related to tendon length variations. Finally, it was suggested that the optimal solution for musculotendon actuators acting in high lengthening ranges were long tendon units and great pennation angles. The heuristic model used in this study highlighted the existence of some dynamic phenomena inside the actuator. However, it did not pretend to represent the overall complexity of the mechanical interactions between the different elements composing the soleus architecture.

Ankle Joint↗

PubMed1991

EMG power spectra of elbow extensors during ramp and step isometric contractions.

The goal of the present study was to compare electromyogram (EMG) power spectra obtained from step (constant force level) and ramp (progressive increase in the force level) isometric contractions. Data windows of different durations were also analysed for the step contractions, in order to evaluate the stability of EMG power spectrum statistics. Fourteen normal subjects performed (1) five ramp elbow extensions ranging from 0 to 100% of the maximum voluntary contraction (MVC) and (2) three stepwise elbow extensions maintained at five different levels of MVC. Spectral analysis of surface EMG signals obtained from triceps brachii and anconeus was performed. The mean power frequency (MPF) and the median frequency (MF) of each power spectrum were obtained from 256-ms windows taken at 10, 20, 40, 60 and 80% MVC for each type of contraction and in addition on 512-, 1024- and 2048-ms windows for the step contractions. No significant differences (P greater than 0.05) were found in the values of both spectral statistics between the different window lengths. Even though no significant differences (P greater than 0.05) were found between the ramp and the step contractions, significant interactions (P less than 0.05) between these two types of contraction and the force level were found for both the MPF and the MF data. These interactions point out the existence of different behaviours for both the MPF and the MF across force levels between the two types of contraction.

Adult↗

PubMed2003

Electrical impedance of muscle during isometric contraction.

Non-invasive measurements of the 50 kHz impedance of the anterior forearm show that the resistance and reactance increase under voluntary isometric contraction of the finger flexor muscles. The relationship between impedance and force is nonlinear, dependent on the type of test, the history of prior exercise, and the health status of the subject. Nevertheless, useful dynamic response parameters betaR = deltaR/R0deltaF and betax = deltaX/X0deltaF can be defined, typically a few hundredths of a per cent per newton. Evidence is presented for the view that these effects reflect dominantly physiological as opposed to morphological changes in the muscle. In particular, (a) the impedance changes many milliseconds before the force is generated, (b) betaR and betaX change substantially during a series of repetitions of the same exercise, and (c) the impedance does not return to its original value following relaxation of the muscle. Supporting data are presented for six healthy men and women, with ages ranging from 19 to 70 years. A preliminary study of patients with various neuromuscular diseases was also performed, amongst whom marked quantitative and qualitative contrasts with the healthy group were found. Further research aimed at assessing the clinical potential of such measurements is discussed, as are studies to elucidate the underlying mechanisms for the impedance changes. We propose the name 'dynamic electrical impedance myography' for this new technique.

Aged↗

PubMed1994

Mechanical and geometrical properties of the rat semimembranosus lateralis muscle during isometric contractions.

The orientation of the line of pull and geometrical characteristics of rat semimembranosus lateralis muscle (SM1) were measured in a plane during isometric contractions at different muscle lengths. The orientation of the line of pull was always similar in our plane of analysis. It was always aligned with the external tendon but not with the aponeurosis. Muscle and fiber length changes were similar. Aponeurosis length changes were very small. Angular changes of aponeurosis with respect to the line of pull were larger than those of muscle fibers. Functional implications of angular effects on muscle length changes were negligible in SM1. The muscle fiber was modelled as a slanted cylinder to test the hypothesis whether angular changes of fibers with the attachment area during muscle shortening are related to the constancy of fiber volume. Accommodation of the change in fiber cross-sectional area which accompanies fiber shortening was insufficient at the bony attachment area. It is concluded that during muscle shortening fiber volume displacement toward the bony origin is reduced as a smaller cross-sectional area needs to be accommodated. Angular changes of fibers with the proximal and distal part of the aponeurosis were so large that they cannot be related to the constancy of volume of a fiber with a homogeneous cross-sectional area. When angular changes of fibers are related to their length changes it is suggested that volume displacement and inhomogeneous length changes along the aponeurosis can explain the experimental results at the aponeurosis.

Analysis of Variance↗

PubMed2000

Sarcomere length changes during end-held (isometric) contractions in intact mammalian (rat) fast and slow muscle fibres.

The sarcomere length change, within a 2 mm region, during end-held isometric contractions in intact rat fast and slow muscle fibre bundles was investigated at 20 degrees C and an initial sarcomere length of 2.68 microm using He-Ne laser diffraction. In some experiments, the fibre segment displacement was monitored with markers (pieces of human hair) placed at regular intervals on the surface of the muscle fibre bundles. The sarcomere length changes, monitored near the proximal end of the bundle (transducer end), during tetanic contractions were similar to those previously reported in frog muscle fibres. Thus, throughout the tension plateau, sarcomere length remained constant (and shortened) but showed evidence of non-uniform sarcomere behaviour (further shortening) during the rapid tension relaxation phase. Such non-uniform behaviour was not seen during twitch contractions. During a twitch contraction, sarcomeres at the proximal end shortened rapidly at first and continued to shorten--or remained shortened--until the tension had relaxed to between 20-23% of its peak value before lengthening back to the original length. The maximum twitch sarcomere shortening (mean +/- SEM) was 5.9 +/- 0.2% (n = 16) in fast and 5.4 +/- 0.3% (n = 14) in slow fibre bundles at 20 degrees C; sarcomere shortening near body temperature (approximately 35 degrees C) was greater, 8.8 +/- 0.2% (n = 7) in fast and 8.1 +/- 0.2% (n = 5) in slow fibre bundles. Increasing the initial sarcomere length of a preparation decreased the extent of sarcomere shortening and reducing the amount of sarcomere shortening, by sarcomere length clamping, markedly increased the peak twitch tension without significantly altering the twitch time course. When examined at different positions along muscle fibres, a sarcomere shortening was observed along much of the fibre length in most preparations. However, in about a third of the preparations some sarcomere lengthening was recorded in the distal end, but its amplitude was too small to accommodate the fibre shortening elsewhere. Complementary data were obtained using the surface marker technique. The displacement was largest and in opposite--but fibre shortening--direction in the markers placed approximately 0.5-1.0 mm away from the two tendon attachments; the markers placed at or near the centre of the fibre bundle showed the least amount of displacement. The findings suggest that the compliant region, where lengthening occurs, is at fibre ends, i.e. near myotendinous junction.

Animals↗

PubMed1977

Lactate in fast and slow twitch skeletal muscle fibres of man during isometric contraction.

Concentration of lactate in fast and slow twitch fibres, respectively, were determined in m. quadriceps femoris after sustained contractions at 25%, 50%, and 75% of maximal voluntary isometric contraction (MVC) until exhaustion as well as after interrupted exercises at 25% and 50% MVC. Maximal lactate concentrations were only found at 50% of MVC performed to exhaustion. Lactate concentration was higher in slow twitch (ST) fibres at 50% MVC compared to in ST fibres at 25% MVC, and higher in fast twitch (FT) fibres at 50% MVC compared to in FT fibres at 75% MVC. After short time isometric exercise (i.e. 75% to exhaustion and 50% and 25% performed for the same period of time as 75% MVC) lactate concentration, expressed as lactate ratio (lactate concentration in FT fibres/lactate concentration in ST fibres) was found to be positively correlated to percent FT fibres (r=0.89). Lactate ratio ranged 0.5-2.0, i.e. at onset of isometric exercise, lactate concentration increase was faster in ST fibres in the muscle rich in ST fibres and faster in FT fibres when the muscle wasrich in FT fibres.

Age Factors↗

PubMed1985

[Muscle exercise after the anterior cruciate ligament reconstruction of the knee--Part I: The force given to the anterior cruciate ligament by separate isometric contraction of the quadriceps or the hamstrings].

UNLABELLED: An attempt was made to investigate the force of the anterior cruciate ligament (ACL) in separate isometric contraction (IMC) of the quadriceps and the hamstrings by means of the analysis of two-dimensional models. In IMC of the quadriceps, the average value of the anterior drawer force (ADF) was equal to 14% of the quadriceps tension at the knee flexion of 5 degrees. The ADF decreased as the flexion angle increased. The average value of the angles, where the ADF became zero, was 45.3 degrees, and the standard deviation was 12.5 degrees. In IMC of the hamstrings, the posterior drawer force was given at the every flexion angle. CLINICAL RELEVANCE: In the early stage of the rehabilitation after the ACL reconstruction, the quadriceps exercise by IMC should be performed at the knee flexion of more than 70 degrees (average + 1.96 X S.D.). The hamstrings exercise by IMC can be carried out regardless of flexion angle.

Adult↗

PubMed1994

Pulse control during rapid isometric contractions of the elbow joint.

Normal subjects exerted isometric torque at a rapid rate of contraction with different amplitude targets, and at different rates with a constant target. In the fastest contractions, the agonist triceps and antagonist biceps muscles showed an electromyographic volley characterized by a slow wave with an initial negative and subsequent positive phases. The duration of each phase was relatively constant for different target amplitudes. In the agonist, the area comprised by the negative or positive waveform increased with increasing target amplitude and correlated with the peak of the first time derivative of torque. The relationship of the antagonist volley to the target amplitude varied among subjects both in the area and the interval of the agonist-antagonist volley. With a decreasing contraction rate, the agonist volley decreased in the area in correlation with the peak of the torque derivative, retaining a constant duration, while the antagonist volley disappeared. These results suggest that rapid isometric contractions are controlled by an amplitude-modulated pulse of agonist activation, which is associated with a pulse of antagonist activation, while the pulse of the antagonist activation is variably utilized among subjects.

Adolescent↗

PubMed1991

Cortical post-spike facilitations in elbow muscles during isometric contraction.

Averaged responses of elbow muscles to action potentials of 37 single motor cortex cells were analyzed in two Macaca fascicularis monkeys during performance of a submaximal but high level isometric contraction. Post-spike facilitations (PSFs) of the rectified electromyographic activity (EMG) were frequently (72%) observed. They consisted of PSFs largely distributed in agonistic (biceps brachii and brachioradialis) and antagonistic (triceps brachii) muscles. Some post-spike inhibitions (7%) were also noted. As compared with distal muscles PSFs, most of the proximal PSFs were of lower amplitude, probably because of the higher level of the contractions. These PSFs were also of longer latency. The data indicate functional connectivity between motor cortical cells and proximal limb muscles. Cortical cells with oligosynaptic and even, for a few of them, with monosynaptic connections to the alpha-motoneurones may contribute to recruitment of motor units (MUs) involved in proximal limb muscle contraction.

Action Potentials↗

PubMed1991

Simultaneous potentiation and fatigue in quadriceps after a 60-second maximal voluntary isometric contraction.

Potential mechanisms of fatigue (metabolic factors) and potentiation (phosphate incorporation by myosin phosphorylatable light chains) were investigated during recovery from a 60-s maximal voluntary isometric contraction (MVC) in the quadriceps muscle of 12 subjects. On separate days before and for 2 h after the 60-s MVC, either a 1-s MVC or electrically stimulated contractions were used as indexes to test muscle performance. Torque at the end of the 60-s MVC was 57% of the initial level, whereas torques from a 1-s MVC and 50-Hz stimulation were most depressed in the immediate recovery period. At this time, muscle biopsy analyses revealed significant decreases in ATP and phosphocreatine and a 19-fold increase in muscle lactate. Conversely, isometric twitch torque and torque from a 10-Hz stimulus were the least depressed of six contractile indexes and demonstrated potentiation of 25 and 34%, respectively, by 4 min of recovery (P less than 0.05). At this time, muscle lactate concentration was still 16 times greater than at rest. An increased phosphate content of the myosin phosphorylatable light chains (P less than 0.05) was also evident both immediately and 4 min after the 60-s MVC. We conclude that the 60-s MVC produced marked force decreases likely due to metabolic displacement, while the limited decline in the twitch and 10-Hz torques and their significant potentiation suggested that myosin phosphorylation may provide a mechanism to enhance contractile force under conditions of submaximal activation during fatigue.

Adenosine Triphosphate↗

PubMed1989

Muscular sound and force relationship during isometric contraction in man.

The contracting muscle generates a low frequency sound detectable at the belly surface, ranging from 11 to 40 Hz. To study the relationship between the muscular sound and the intensity of the contraction a sound myogram (SMG) was recorded by a contact sensor from the biceps brachii of seven young healthy males performing 4-s isometric contractions from 10% to 100% of the maximal voluntary contraction (MVC), in 10% steps. Simultaneously, the electromyogram (EMG) was recorded as an index of muscle activity. SMG and EMG were integrated by conventional methods (iSMG and iEMG). The relationship between iSMG and iEMG vs MVC% is described by parabolic functions up to 80% and 100% MVC respectively. Beyond 80% MVC the iSMG decreases, being about half of its maximal value at 100% MVC. Our results indicate that the motor unit recruitment and firing rate affect the iSMG and iEMG in the same way up to 80% MVC. From 80% to 100% MVC the high motor units' discharge rate and the muscular stiffness together limit the pressure waves generated by the dimensional changes of the active fibres. The muscular sound seems to reflect the intramuscular visco-elastic characteristics and the motor unit activation pattern of a contracting muscle.

Adult↗

PubMed1985

[Muscle exercise after anterior cruciate ligament reconstruction of the knee--Part II: The development of the exercise method by simultaneous isometric contraction of the quadriceps and the hamstrings, and its biomechanics].

UNLABELLED: An attempt was made to investigate the stress of the ACL in the simultaneous isometric contraction (IMC) of the quadriceps and the hamstrings by means of analysis of two-dimensional models, and to estimate electromyographically the forces of those muscles in that contraction. The anterior drawer force (ADF) in the simultaneous IMC decreased as the flexion angle of the knee increased. The average value of the angles, where the ADF became zero, was 7.4 degrees. The integrated EMGs of the quadriceps and the hamstrings in the simultaneous maximum IMC were equal to 30-60% of those in separate maximum IMC. CLINICAL RELEVANCE: In the early stage of the rehabilitation after the ACL reconstruction, the simultaneous IMC of the quadriceps and the hamstrings is useful as one of the muscle exercise method, because that can be performed at the knee position near the full extension and can generate sufficient muscle force for exercise.

Adult↗

PubMed1999

Regulation of energy consumption in cardiac muscle: analysis of isometric contractions.

The well-known linear relationship between oxygen consumption and force-length area or the force-time integral is analyzed here for isometric contractions. The analysis, which is based on a biochemical model that couples calcium kinetics with cross-bridge cycling, indicates that the change in the number of force-generating cross bridges with the change in the sarcomere length depends on the force generated by the cross bridges. This positive-feedback phenomenon is consistent with our reported cooperativity mechanism, whereby the affinity of the troponin for calcium and, hence, cross-bridge recruitment depends on the number of force-generating cross bridges. Moreover, it is demonstrated that a model that does not include a feedback mechanism cannot describe the dependence of energy consumption on the loading conditions. The cooperativity mechanism, which has been shown to determine the force-length relationship and the related Frank-Starling law, is shown here to provide the basis for the regulation of energy consumption in the cardiac muscle.

Animals↗

PubMed1996

Diurnal rhythm of the muscular performance of elbow flexors during isometric contractions.

The influence of time of day on elbow flexion torque was studied. Thirteen physical education students, 7 males and 6 females, made maximal and submaximal isometric contractions at 90 degrees of elbow flexors using a dynamometer. The torque developed was measured on each contraction. The myoelectric activity of the biceps muscle was also measured at the same time by surface electromyography (EMG) and quantified from the root mean square (RMS) activity. Torque and surface EMGs were measured at 6:00, 9:00, 12:00, 15:00, 18:00, 21:00, and 24:00 h over the same day. Oral temperature before each test session was measured on each occasion after a 30-min rest period. We observed a diurnal rhythm in elbow flexor torque with an acrophase at 18:00 h and a bathyphase at 6:00 h, in phase with the diurnal rhythm in oral temperature. However, the diurnal rhythm of temperature did not appear to have any influence on the torque. Links between neuromuscular efficiency and RMS/torque ratio were evaluated by measuring muscle activity along with torque. We also assessed variations in the level of maximal activity of the muscle under maximal voluntary contraction. Neuromuscular efficiency fluctuated during the day, with maximal and minimal efficiency at 18:00 h and 9:00 h, respectively, whereas activation level was maximal at 18:00 h and minimal at 9:00 h. The diurnal rhythm of torque was accounted for by variations in both central nervous system command and the contractile state of the muscle.

Adult↗

PubMed1989

The human pressor response during and following voluntary and evoked isometric contraction with occluded local blood supply.

1. Changes in heart rate and blood pressure were observed, in nine healthy subjects, during and after voluntary and electrically evoked isometric contractions of the triceps surae under conditions of local circulatory arrest. 2. The progressive increases in heart rate and blood pressure seen during 2 min voluntary and evoked contractions at 30% of maximal voluntary contraction were not significantly different in the two conditions. On cessation of contraction but with circulatory arrest maintained, heart rate fell to control levels while blood pressure fell to a similar though still significantly elevated level in both conditions. Elevated blood pressure was maintained for 2 min until the circulatory occlusion was removed; however it was maintained at a significantly higher level for the last 60-90 s of occlusion following electrically evoked contractions compared to voluntary contraction. 3. Comparison of the responses to voluntary and involuntary electrically evoked contractions suggest that 'central command' is not necessary for the initial increases in heart rate and blood pressure to occur. In addition the removal of central command on cessation of contraction need not account for the return of heart rate to control levels or the drop in blood pressure at that time. Maintained blood pressure elevation during circulatory occlusion would seem to be due to the trapping of chemical substances within the muscle interstitium.

Adult↗

PubMed1998

Immediate response of retinal vessels to isometric muscle contraction.

Isometric muscle contraction results in a rise in systemic blood pressure (BP) and constriction of retinal arterioles. The responses in the anaesthetised cat have been studied to provide further insight into the results of human studies. Constriction (median 3.43% of control values) and dilatation (median 4.17% of control values) were observed; the onset of constriction was delayed by 4 s compared with dilatation. There was spatial and temporal variation in the observed calibre changes, and inter-experimental variation in the calibre change/BP ratio. It is concluded that the response of retinal arterioles of measurable size is not unified, and that the two modes of response differ in mechanism.

Animals↗

PubMed1987

Relationship between average muscle fibre conduction velocity and EMG power spectra during isometric contraction, recovery and applied ischemia.

The relationship between muscle fibre conduction velocity (MFCV) and the power spectrum of surface EMGs in 3 human volunteers was studied during isometric contractions at 40% maximum voluntary contraction. In addition, the recovery of these two parameters was measured during short lasting contractions at the same force level every 30 s. The recovery phase was also studied during ischaemia, thereby preventing the recovery of MFCV. The mean MFCV was calculated by the cross-correlation method. The measurements were facilitated by a real-time estimation of the cross-correlation and the MFCV and by a graphic display of the digitised signal. During contraction a nearly linear relation was found between MFCV and the median frequency of the power spectrum (MPF). During recovery this relationship was lost in one subject: MPF restored much faster then MFCV. During recovery under ischemia MFCV did not recover, but MPF recovered partially in all subjects. It is concluded that the shift of the power spectrum to lower frequencies during fatigue cannot be explained by changes in MFCV alone. Central mechanisms also influence the power spectrum and studying the recovery of local muscle fatigue during ischemia may separate these influences from that of MFCV on the power spectrum during fatigue.

Adult↗