PubMed Health⌕ Search

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 721 records · Page 40Linked to original sources
PubMed1995

Electromechanical delay in isometric muscle contractions evoked by voluntary, reflex and electrical stimulation.

Electromechanical delay (EMD) in isometric contractions of knee extensors evoked by voluntary, tendon reflex (TR) and electrical stimulation (ES) was investigated in 21 healthy young subjects. The subject performed voluntary knee extensions with maximum effort (maximal voluntary contraction, MVC), and at 30%, 60% and 80% MVC. Patellar tendon reflexes were evoked with the reflex hammer being dropped from 60 degrees, 75 degrees and 90 degrees positions. In the percutaneous ES evoked contractions, single switches were triggered with pulses of duration 1.0 ms and of intensities 90, 120 and 150 V. Electromyograms of the vastus lateralis and rectus femoris muscles were recorded using surface electrodes. The isometric knee extension force was recorded using a load cell force transducer connected to the subject's lower leg. The major finding of this study was that EMD of the involuntary contractions [e.g. mean 22.1 (SEM 1.32) ms in TR 90 degrees; mean 17.2 (SEM 0.62) ms in ES 150 V] was significantly shorter than that of the voluntary contractions [e.g. mean 38.7 (SEM 1.18) ms in MVC, P < 0.05]. The relationships between EMD, muscle contractile properties and muscle fibre conduction velocity were also investigated. Further study is needed to explain fully the EMD differences found between the voluntary and involuntary contractions.

Adult↗
PubMed2000

A mathematical model of forces in the knee under isometric quadriceps contractions.

OBJECTIVE: To predict the knee's response to isometric quadriceps contractions against a fixed tibial restraint.Design. Mathematical modelling of the human knee joint. BACKGROUND: Isometric quadriceps contraction is commonly used for leg muscle strengthening following ligament injury or reconstruction. It is desirable to know the ligament forces induced but direct measurement is difficult. METHODS: The model, previously applied to the Lachmann or 'drawer' tests, combines an extensible fibre-array representation of the cruciate ligaments with a compressible 'thin-layer' representation of the cartilage. The model allows the knee configuration and force system to be calculated, given flexion angle, restraint position and loading. RESULTS: Inclusion of cartilage deformation increases relative tibio-femoral translation and decreases the ligament forces generated. For each restraint position, a range of flexion angles is found in which no ligament force is required, as opposed to a single flexion angle in the case of incompressible cartilage layers. CONCLUSIONS: Knee geometry and ligament elasticity are found to be the most important factors governing the joint's response to isometric quadriceps contractions, but cartilage deformation is found to be more important than in the Lachmann test. RELEVANCE: Estimation of knee ligament forces is important when devising exercise regimes following ligament injury or reconstruction. The finding of a 'neutral zone' of zero ligament force may have implications for rehabilitation of the ligament-injured knee.

Cartilage↗
PubMed1996

Isometric muscle contractions after double pulse stimulation. comparison of healthy subjects and patients with myotonic dystrophy.

Isometric contractions of the adductor pollicis muscle were studied in healthy subjects and patients with myotonic dystrophy after single and double stimuli of the ulnar nerve using a wide range of interstimulus intervals (ISI, 0.4-180 ms). In healthy subjects, the force contributed by a second stimulus was greater than the single twitch force being maximal (mean + 140%) at 12-ms ISI. In myotonic dystrophy, the force contributed by the second stimulus was (relative to a reduced twitch amplitude) increased (mean + 204%) with a maximum at 4.8-ms ISI. An abnormal increase of force was only recorded if the single twitch force was clearly reduced. The absolute refractory period of muscle contraction (normal range 1.2-1.6 ms, mean 1.35 ms) was shortened in all patients (mean 1.01 ms) except one (1.2 ms). The ISI showing the maximal force were related to those showing the maximal prolongation of the contraction time in healthy subjects (r = 0.71) but not in patients. The rate of force development contributed by a second stimulus was slower than expected from the summation of two single twitches with short stimulus intervals (3-40 ms) a phenomenon called early depression. In patients, the early depression was reduced or abolished within this range of ISI as has been found in dystrophic mouse muscles. The optimal ISI in patients was shifted towards very short times and together with the other disturbances it is suggested that activation of diseased muscle by motoneurons may be less effective, being an additional factor leading to weakness in myotonic dystrophy.

Adult↗
PubMed1991

Ventricular pressure-area loop characteristics in the stage 16 to 24 chick embryo.

The accurate description of embryonic cardiovascular function requires the adaption of standard measurement techniques to the small scale of the developing heart. In the mature heart, the analysis of ventricular pressure and volume accurately defines function. Because in vivo measures of volume are not feasible in the embryonic heart, we tested the hypothesis that ventricular pressure-area loops accurately define ventricular function in the stage 16 to stage 24 white Leghorn chick embryo. We simultaneously measured ventricular pressure with a servo-null pressure system and recorded video images at 60 Hz. The pressure waveform was superimposed onto the video image in real time. Video fields were planimetered for epicardial ventricular cross-sectional area and ventricular pressure. Pressure and area data were smoothed using a fast Fourier transform filter and plotted. Data are reported as mean +/- SEM, n greater than or equal to 4, and were tested by regression analysis and analysis of variance (p less than 0.05). Heart rate increased from 90 +/- 7 beats/min at stage 16 to 130 +/- 13 beats/min at stage 24. All pressure-area loops displayed diastolic filling, isometric contraction, ejection, and isometric relaxation, similar to pressure-volume loops of the mature heart. Isometric contraction time increased from 42 +/- 5 to 62 +/- 4 msec (p less than 0.05), while isometric relaxation time was 124 +/- 12 and 120 +/- 10 msec (p greater than 0.05) between stages 16 and 24, respectively. The maximum ratio of instantaneous ventricular pressure to area identified end systole better than peak ventricular pressure or minimum ventricular area. Thus, pressure-area relations define ventricular function in the embryonic chick heart.

Animals↗
PubMed2005

Contribution of prostaglandins to the dilation that follows isometric forearm contraction in human subjects: effects of aspirin and hyperoxia.

In 11 healthy volunteers, we evaluated, in a double-blind crossover study, whether the vasodilation that follows isometric contraction is mediated by prostaglandins (PGs) and/or is O2 dependent. Subjects performed isometric handgrip for 2 min at 60% maximal voluntary contraction (MVC), after pretreatment with placebo or aspirin (600 mg orally), when breathing air or 40% O2. Forearm blood flow was measured in the dominant forearm by venous occlusion plethysmography. Arterial blood pressure was also recorded, allowing calculation of forearm vascular conductance (FVC; forearm blood flow/arterial blood pressure). During air breathing, aspirin significantly reduced the increase in FVC that followed contraction at 60% MVC: from a baseline of 0.09 +/- 0.011 [mean +/- SE, conductance units (CU)], the peak value was reduced from 0.24 +/- 0.03 to 0.14 +/- 0.01 CU. Breathing 40% O2 similarly reduced the increase in FVC relative to that evoked when breathing air; the peak value was 0.24 +/- 0.03 vs. 0.15 +/- 0.02 CU. However, after aspirin, breathing 40% O2 had no further effect on the contraction-evoked increase in FVC (the peak value was 0.15 +/- 0.02 vs. 0.16 +/- 0.02 CU). Thus the present study indicates that prostaglandins make a substantial contribution to the peak of the vasodilation that follows isometric contraction of forearm muscles at 60% MVC. Given that hyperoxia similarly reduced the vasodilation and attenuated the effect of aspirin, we propose that the stimulus for prostaglandin synthesis and release is hypoxia of the endothelium.

Adult↗
PubMed1992

Factors affecting blood pressure during heavy weight lifting and static contractions.

Brachial arterial pressure was directly recorded in 31 healthy male volunteers through protocols examining the effects of the Valsalva maneuver, muscle size and strength, contraction force, contraction type (concentric, isometric, eccentric), changes in joint angle, and muscle fatigue on the blood pressure response to resistance exercise. Weight lifting at the same relative intensity produced similar increases in blood pressure, regardless of individual differences in muscle size or strength. Concentric, isometric, or eccentric exercise at the same relative intensity caused similar increases despite differences in force production. In weight lifting, the greatest increase in blood pressure occurred at the joint angle corresponding to the weakest point in the strength curve and the least at the angle corresponding to the strongest point. Isometric contractions of the same relative intensity at different joint angles produced identical blood pressures despite differences in absolute force production. When subjects attempted to maintain a maximum isometric contraction for 45 s, the blood pressure increase remained the same despite a marked diminution in force. Thus the magnitude of the blood pressure response depends on the degree of effort or central command and not actual force production. A brief Valsalva maneuver, which exaggerates the increase in blood pressure, is unavoidable when desired force production exceeds approximately 80% maximum voluntary contraction.

Adult↗
PubMed1992

Neurally mediated renal vasoconstriction during isometric muscle contraction in cats.

The aim of this study was to determine if the reflex increase in renal sympathetic nerve activity (RSNA) during static (isometric) muscle contraction evokes renal vasoconstriction and decreases renal blood flow. RSNA, renal blood flow velocity, and arterial pressure were measured simultaneously during isometric contraction of the hindlimb triceps surae muscle in eight chloralose-anesthetized cats. A 1-min contraction was evoked by stimulating the peripheral ends of the cut L7 and S1 ventral roots. RSNA and mean arterial pressure (MAP) increased 41 +/- 14% (SE) and 50 +/- 10 mmHg during static contraction, whereas mean renal blood flow velocity (MRBV) decreased 14 +/- 5%. Calculated renal vascular resistance increased 73 +/- 20% during the contraction. The increase in RSNA preceded the decrease in MRBV by 20 s. Passive mechanical stretch of the muscle increased RSNA 21 +/- 12% but did not alter MRBV. Renal denervation abolished the decrease in MRBV during isometric contraction but only attenuated the rise in MAP. Cutting the L4-S1 dorsal roots or muscle paralysis abolished the MRBV and MAP responses. Thus reflex stimulation of RSNA from the contracting muscle can induce renal vasoconstriction and decrease renal blood flow.

Animals↗
PubMed1984

Alterations in ankle dorsiflexion torque as a result of continuous ultrasound to the anterior tibial compartment.

Although considerable documentation of the physiologic effects of ultrasound (US) exists, little information is available concerning direct effects of US on muscle, particularly when the US is applied immediately before muscle performance. The purpose of this study was to determine the effect of continuous US to the anterior tibial muscle compartment on ankle dorsiflexion torque assessed immediately posttreatment, at 30 minutes, and at 60 minutes posttreatment. Seventeen healthy subjects were tested performing isometric contractions at dynamometer velocities of 60 and 180 degrees/sec. Subjects first received either a placebo or a 1.5 W/cm2 15-minute US treatment. One week later, the protocol was repeated with the administration of a second treatment. Analysis of variance showed no significant interactions for time and treatment for any contraction; time, for isometric contraction, was the only significant main effect. Follow-up analyses were all nonsignificant for comparisons of pretreatment to posttreatment and posttreatment to 30- and 60-minute intervals within treatment groups. The study concludes that in spite of known physiologic effects, one treatment of US does not have an immediate or latent effect on peak torque.

Adult↗
PubMedDate not supplied

[The force of an isometric twitch contraction and the phases of tetanus].

The isometric twitch contractions of human flexor digitrum sublimis muscle were recorded after the unfused 9.5 pps tetani of different durations. The peak twitch force was plotted against the number of preceding pulses both for this experimental situation and for the usual staircase phenomenon on the frequencies of 2-4 pps. The dependence of the twitch force on the number of the preceding pulses in tetanus differs from that in staircase. In the staircase twitch reaches maximal level after 100-120 repetitions and remains fully potentiated during 800-1000 repetitions more. In 9,5 pps trains potentiation begins to decline immediately after reaching peak on 100th-120th pulse and the decline is accompanied by the slowing of twitch relaxation. So we can speak of the two stages of the post-train twitch potentiation. This has some implications to the process of the force maintenance in unfused tetanus. Initial stage of increased twitch force and quick relaxation corresponds to that phase of prolonged unfused tetanus which is characterized by big oscillations of tension. Second stage of decreasing twitch force and slowing relaxation give rise to the gradual increase of tetanic tension and to the diminishing of its oscillations. It is supposed that sustained tetanic contraction leads to the slowing of the cross-bridges cycling thus impairing the ability of muscle to develop sufficient tension in twitches.

Electric Stimulation↗
PubMed2002

Expiratory resistive loaded breathing in humans increases fluctuations of force production in submaximal isometric quadriceps contractions.

This study demonstrated that expiratory resistive loading (ERL) induced an increase in force fluctuation during a unilateral, submaximal isometric contraction of the non-dominant left vastus lateralis (VL), but did not effect force fluctuation during complex bilateral contractions. The increase in force fluctuation in the unilateral left VL contraction during ERL was not accompanied by alterations of average force production, motor unit activation (median power frequency) or airflow rate when compared to the bilateral contraction. Inspiratory RL (IRL) did not significantly affect force fluctuation in unilateral or bilateral contractions. The results concur with previous reports of ERL, but not IRL, effecting VL function and suggest that patients with obstructive diseases may also be vulnerable to reduced fine motor control.

Adult↗
PubMed1994

Coherent modulations of human motor unit discharges during quasi-sinusoidal isometric muscle contractions.

Spectral analysis of single-unit discharges, multi-unit EMG and muscle force during voluntary quasi-sinusoidal isometric contractions of two hand muscles revealed corresponding modulations of the firing rates of motor units at the frequency of the force oscillation. These rate modulations were correlated; and they showed a phase advance over the force oscillation, which is consistent with a cause-effect relationship between changes in firing rate and variations in force. These effects, observed over wide ranges of modulation amplitudes and frequencies, confirm the role of rate coding in the generation of time-varying muscle contractions; and they support the idea that during voluntary contraction of a given muscle, the motoneuron pool is subject to a common drive.

Adult↗
PubMed2000

Cortico-muscular synchronization during isometric muscle contraction in humans as revealed by magnetoencephalography.

Magnetoencephalographic (MEG) and electromyographic (EMG) signals were recorded from six subjects during isometric contraction of four different muscles. Cortical sources were located from the MEG signal which was averaged time-locked to the onset of motor unit potentials. A spatial filtering algorithm was used to estimate the source activity. Sources were found in the primary motor cortex (M1) contralateral to the contracted muscle. Significant coherence between rectified EMG and M1 activity was seen in the 20 Hz frequency range in all subjects. Interactions between the motor cortex and spinal motoneuron pool were investigated by separately studying the non-stationary phase and amplitude dynamics of M1 and EMG signals. Delays between M1 and EMG signals, computed from their phase difference, were found to be in agreement with conduction times from the primary motor cortex to the respective muscle. The time-dependent cortico-muscular phase synchronization was found to be correlated with the time course of both M1 and EMG signals. The findings demonstrate that the coupling between the primary motor cortex and motoneuron pool is at least partly due to phase synchronization of 20 Hz oscillations which varies over time. Furthermore, the consistent phase lag between M1 and EMG signals, compatible with conduction time between M1 and the respective muscle with the M1 activity preceding EMG activity, supports the conjecture that the motor cortex drives the motoneuron pool.

Adult↗
PubMed1988

Activity levels during isometric test contractions of neck and shoulder muscles.

In order to analyse isometric muscle test contractions in the neck and shoulder region, an electromyographic (EMG) study of ten healthy females was undertaken. A series of 13 standardized isometric contractions with manual resistance was performed in the sitting position. Rectified time-averaged EMG was recorded, using surface electrodes. All tests activated all muscles studied to some extent and at various levels, but four different patterns of activation could be identified. Maximum level of activity was obtained: 1) in the cervical erector spinae muscles during neck extension, 2) in the splenius and levator scapulae muscles during lateral flexion of the cervical spine, 3) in the trapezius, pars descendens muscle during abduction of the arm in the plane of the scapula, 4) in the thoracic erector spinae/rhomboids muscles during shoulder elevation or scapular retraction/elevation.

Adult↗
PubMed1981

Human motor unit activity during the onset of muscle fatigue in submaximal isometric isotonic contraction.

The onset of fatigue has been studied by relating motor unit activity and surface myoelectric activity during constant force isometric contraction in man. The surface (global) EMG of the biceps brachii was recorded using bipolar electrodes. The global EMGs of the other elbow flexors were also recorded. Motor unit activity was recorded simultaneously at three points of the biceps brachii by using wire electrodes. The time course of the integrated surface EMG showed that fatigue occurred right at the beginning of the contraction. The increase of the integrated EMG was especially important when the value of the force maintenance was high. The time course of this increase was close to that of the output of the spikes recorded by the wire electrodes. No matter what the value of the force maintenance, MU recruitment occurred throughout the contraction. The existence of an increase in the MU firing frequently depended on the value of this force. Contractile element fatigue is believed to provide the explanation of these results, while neuromuscular junction fatigue may perhaps be more important near the time limit.

Action Potentials↗
PubMed2000

Asynchronous muscle: a primer.

The asynchronous muscles of insects are characterized by asynchrony between muscle electrical and mechanical activity, a fibrillar organization with poorly developed sarcoplasmic reticulum, a slow time course of isometric contraction, low isometric force, high passive stiffness and delayed stretch activation and shortening deactivation. These properties are illustrated by comparing an asynchronous muscle, the basalar flight muscle of the beetle Cotinus mutabilis, with synchronous wing muscles from the locust, Schistocerca americana. Because of delayed stretch activation and shortening deactivation, a tetanically stimulated beetle muscle can do work when subjected to repetitive lengthening and shortening. The synchronous locust muscle, subjected to similar stimulation and length change, absorbs rather than produces work.

Animals↗
PubMed2005

Somatosensory-evoked potentials are influenced differently by isometric muscle contraction of stimulated and non-stimulated hand in humans.

Chronic pain is associated with motor dysfunctions, and stimulation of the motor cortex has been shown to alleviate chronic pain. Recently Nakata et al. [Pain 107 (2004) 91-98] showed differentiated patterns of neuromagnetic evoked fields following painful laser stimulation during phasic movements of stimulated and non-stimulated hand. Phasic movements and static contractions differ in their functional activation of the motor cortices. Therefore, we decided to analyze the effects of isometric contractions of intrinsic right and left hand muscles on cortical sources of somatic-evoked potentials related to a painful galvanic stimulation of the right middle finger. Using spatio-temporal source dipole analysis of 111 electroencephalographic signals in 10 right-handed men, source activities were evaluated in the left primary somatosensory cortex (S1), left (S2(L)) and right (S2(R)) secondary somatosensory cortex, anterior cingulate cortex (ACC) and posterior cingulate cortex (PCC). Ipsilateral hand muscle contraction was associated with a decrease of source activity in S1 and with subsequent increases in S2(L) and the PCC. Contralateral hand muscle contraction was accompanied by a decrease of source activity in bilateral S2 cortices followed by decreases in the S1 and anterior cingulate cortex. Results suggest early suppression of source activity in S1 during ipsilateral hand muscle contractions and in bilateral S2 during contralateral hand muscle contractions.

Adult↗
PubMed1979

EMG, bite force, and elongation of the masseter muscle under isometric voluntary contractions and variations of vertical dimension.

The relation EMG activity, bite force, and muscular elongation was studied in eight subjects with complete natural dentition during isometric contractions of the masseter muscle, measured from 7 mm to almost maximum jaw opening. EMG was registered with superficial electrodes and bite force with a gnathodynamometer. In series 1, recordings of EMG activity maintaining bite force constant (10 and 20 kg) show that EMG is high when the bite opening is 7 mm, decreases from 15 to 20 mm, and then increases again as jaw opening approaches maximum opening. In series 2, recordings of bite force maintaining EMG constant show that bite force increases up to a certain range of jaw opening (around 15 to 20 mm) and then decreases as we approach maximum jaw opening. Results show that there is for each experimental subject a physiologically optimum muscular elongation of major efficiency where the masseter develops highest muscular force with least EMG activity.

Adult↗