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Results for “Isometric Contraction”

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PubMed2000

Differential effects of muscle contraction from various body parts on neuromagnetic somatosensory responses.

We studied eight healthy subjects with a whole-scalp 306-channel neuromagnetometer to explore the effect of motor activity from different body parts on somatosensory responses to left median nerve stimulation. The stimuli produced clear tactile sensation without any motor movement. In the rest condition, the subject had no task. During contraction conditions, the subject had to maintain submaximal isometric contraction in masseter, left deltoid, left thenar, or left tibialis muscles. Short-latency responses from the primary somatosensory cortex did not change during contraction. Responses from both the right (contralateral) and left second somatosensory cortices (SII) were significantly enhanced during contraction of the left thenar muscles. Responses from the left SII were significantly enhanced also during contraction of the left deltoid muscles, but they were decreased during contraction of the masseter and left tibialis anterior muscles. This study implies that SII activation is modulated by motor activity and that the effect depends on the topographical proximity of the stimulated and contracted body parts.

Adult↗

PubMed1997

Selegiline diminishes cardiovascular autonomic responses in Parkinson's disease.

Selegiline (L-deprenyl), a selective inhibitor of monoamine oxidase type B, is an established adjuvant to levodopa therapy in Parkinson's disease (PD). To evaluate whether selegiline also effects the severity and progression of autonomic nervous system dysfunction in PD, we studied autonomic functions by measuring cardiovascular responses to normal breathing, deep breathing, the Valsalva maneuver, the tilting test, and the isometric contraction test prospectively in 52 PD patients receiving either selegiline (n = 27) or placebo (n = 25) in randomized order in a double-blind parallel trial. The study also continued double-blind after the introduction of levodopa. Recordings of cardiovascular responses were carried out annually, with the median follow-up period being 6 years. Cardiovascular autonomic reflexes were diminished in the patient groups compared with those of healthy control subjects (n = 45). There was no progression (except age-related) in dysautonomia in patients on placebo, but there was a decrease in cardiovascular responses in the selegiline group. The heart rate variability in normal breathing, in the Valsalva maneuver, and in the tilting test was clearly diminished during the selegiline treatment. In addition, in the tilting test, the fall in diastolic blood pressure immediately after tilting and in systolic blood pressure 2 minutes after standing up was more pronounced in the selegiline group than in the placebo group. Levodopa treatment had no effect on the measured autonomic responses. In the isometric contraction test, the two treatment groups showed no difference. We conclude that selegiline treatment diminishes autonomic responses, especially those of the sympathetic division. This sympatholytic effect may signal an increased risk of orthostatic hypotension.

Analysis of Variance↗

PubMed1979

Relaxation rate of constituent muscle-fibre types in human quadriceps.

1. Muscle fibres may be subdivided into type I (with slow-twitch contractile properties) and type II (fast-twitch) depending on their myosin adenosine triphosphatase activity. In voluntary isometric contractions type I fibres are utilized at low forces (less than 20% of maximum) whereas type II fibres are recruited in addition at high forces. This physiological recruitment order has enabled us to measure the relaxtion rate of type I and II fibres in vivo in normal human subjects. 2. Relaxation rate was measured in 16 subjects from low (10% of maximum) and maximum isometric quadriceps contractions and the muscle-fibre type composition determined from needle-biopsy specimens in 10 subjects. The relaxation rate of type II fibres was calculated to be twice as fast as that of type I. 3. It was not possible to estimate, from studies in 33 quadriceps muscles (25 normal subjects), the contribution of type II fibres to overall fibre area from the relaxation rate as determined from electrically stimulated isometric contractions.

Adenosine Triphosphatases↗

PubMed1975

Effect of alterations of arterial blood pressure and heart rate on segmental dyskinesis during acute myocardial ischemia and following coronary reperfusion.

The effect of alterations of blood pressure and heart rate on segmental dyskinesis induced by coronary artery ligation and the influence of such manipulations on the magnitude of recovery of the syskinetic segment during subsequent coronary artery reperfusion were evaluated in 77 open-chest dogs. Wall motion was recorded by ultrasound reflected directly from the ischemic myocardial segment. Acute ischemia produced characteristic regional abnormalities in wall motion: aneurysmal bulging occurred during isometric contraction and wall velocity was markedly reduced during ventricular ejection. During 69 minutes of ischemia, a control group of dogs underwent no interventions and showed no further changes in wall motion. Tachycardia induced by atrial pacing during ischemia had no significant effect. Arterial hypertension during ischemia caused a marked reduction in wall velocity when methoxamine was used: 14 plus or minus 2 (SE) mm/sec (ischemia alone) to 6 plus or minus 1 mm/sec (ischemia + drug). In contrast, norepinephrine improved wall velocity: 11 plus or minus 2 mm/sec (ischemia alone) to 25 plus or minus 4 mm/sec (ischemia + drug). Hypertension caused by infusion of phenylephrine gave intermediate results, as did hypotension induced by either nitroprusside or hemorrhage during the ischemic period. After 60 minutes the drugs were stopped, the coronary ligation released, and the ischemic myocardium reperfused. The relative order of improvement of wall velocity with reperfusion was 11 plus or minus 2 mm/sec (ischemia alone) to 24 plus or minus 3 mm/sec (reperfusion) in the group that received norepinephrine, 12 plus or minus 3 mm/sec to 20 plus or minus 3 mm/sec in the control group with no intervention durin ischemia, 13 plus or minus 2 mm/sec to 20 plus or minus 1 mm/sec in the nitroprusside group, 9 plus or minus 2 mm/sec in the phenylephrine group, and 14 plus or minus 2 mm/sec to 12 plus or minus 1 mm/sec in the methoxamine group. The aneurysmal bulging during isometric contraction also was reduced to a greater degree by reperfusion in the group that received norepinephrine during the ischemic period than it was in the groups undergoing other interventions during ischemia. We conclude that drug-induced elevations in arterial blood pressure can have different effects on the syskinetic motion of acutely ischemic myocardium and on the degree of recovery following reperfusion depending on the particular agent used.

Animals↗

PubMed2003

Habitual level of physical activity and muscle fatigue of the elbow flexor muscles in older men.

Reduced muscle performance, related to the loss of muscle mass and strength, is a common and natural part of ageing. Nevertheless, it is generally believed that regular participation in activities of moderate intensity may slow down these age-related changes. This study investigated the relationship between the habitual level of physical activity (PA), assessed by the modified Baecke Questionnaire, and the mechanical and fatigue characteristics of the right elbow flexor muscles, m. biceps brachii and m. brachioradialis, in men over the age of 55 years. Muscle fatigue was quantified both by measuring the maximal voluntary contraction (MVC) torque before and after a sustained isometric contraction at 25% MVC until exhaustion, and also by the temporal changes observed in the surface electromyographic (EMG) signal recorded during the fatigue task. Results showed a decreased MVC torque at the end of the fatiguing contraction. After 20 min of recovery, the MVC force was still significantly lower than the pre-fatigue value, except for the most active subjects. Typical myoelectrical indications of fatigue were also observed: a shift in the frequency spectrum of the signal towards lower frequencies accompanied by an increase in the EMG amplitude. We concluded from this study that the level of PA was related to the absolute isometric MVC values and the measurement of neuromuscular efficiency after 20 min of recovery, but did not influence the indications of muscle fatigue during an isometric fatigue task.

Aged↗

PubMed1994

Neomycin inhibition of hormone-stimulated smooth muscle contractions in myometrial tissue.

These studies sought to determine the effects of neomycin, a phospholipase C inhibitor, on hormone-stimulated myometrial contractions. For these studies, computer digitalized in vitro isometric contraction data were analyzed for changes in contractile activity in response to oxytocin and aluminum fluoride with and without neomycin. Neomycin (1-5 mM) produced dose-related inhibition of oxytocin and aluminum fluoride-stimulated myometrial contractions. This neomycin effect was apparent within 2-3 minutes of addition and was completely reversible, with resolution of its inhibitory effects within 6-8 minutes of washout. This study is the first to demonstrate the functional effect of neomycin inhibition of the phosphatidylinositol signaling pathway in myometrial smooth muscle tissue.

Aluminum Compounds↗

PubMed2005

Correlation between right ventricular indices and clinical improvement in epoprostenol treated pulmonary hypertension patients.

The aim of this study was to evaluate which parameter of right ventricular (RV) echocardiographic best mirrors the clinical status of patients with pulmonary arterial hypertension. Patients with pulmonary arterial hypertension on epoprostenol therapy were identified via hospital registry. Twenty patients, (16 females, 4 males) were included in the study, 9 with primary pulmonary hypertension and 11 with other diseases. Echocardiograms before therapy and at 22.7 (+/-9.3) months into therapy were compared. The right ventricular myocardial performance index (RVMPI) was measured as the sum of the isometric contraction time and the isometric relaxation time divided by right ventricular ejection time. Other measures included peak tricuspid regurgitation jet velocity (TRV), pulmonary artery systolic pressure (PASP), pulmonary valve velocity time integral (PVVTI), PASP/PVVTI (as an index of total pulmonary resistance) and symptoms by New York Heart Association (NYHA) functional class. Echo parameters of right ventricular function were analyzed in patients, before and during therapy. There was significant improvement of NYHA class in patients following epoprostenol therapy (P < 0.0001). Peak tricuspid regurgitant jet velocity (pre 4.2 +/- 0.6 m/sec, post 3.8 +/- 0.7 m/sec, P = 0.02) and PASP/PVVTI (pre 6.7 +/- 3.3 mmHg/m per second, post 4.8 +/- 2.2 mmHg/m per second, P < 0.0001) were significantly improved during treatment. RVMPI did not improve (pre 0.6 +/- 0.3, post 0.6 +/- 0.3, P = 0.54). Changes in NYHA class did not correlate with changes in RVMPI (P = 0.33) or changes in PASP/PVVTI (P = 0.58). Despite significant improvements in TRV, PASP/PVVTI, and NYHA class, there was no significant change in RVMPI on epoprostenol therapy. Changes in right ventricular indices were not correlated with changes in NYHA class.

Antihypertensive Agents↗

PubMed2004

Isoproterenol-produced damage in amphibian heart could be mediated by adrenergic receptors located in the heart muscle.

In mammals, isoproterenol may produce heart damage in part by binding to adrenergic receptors in the coronary arteries. Previously we showed evidence that isoproterenol produces cellular necrosis and interstitial fibrosis in the ventricle of the heart of an amphibian, which has no coronary arteries. The present study examines responses to 3-adrenergic receptor stimulation in the heart of urodele amphibians. The hearts from three amphibians; Ambystoma mexicanum, A. tigrinum and A. dumerilii were mounted in an organ bath at 16+/-2 degrees C. The spontaneous isometric contractions (heart rate and isometric tension) were recorded using a tension transducer connected to polygraph. Concentration-response to isoproterenol in the presence and absence of propranolol (10(-6)) was recorded. The basal heart rate in the A. mexicanum heart was 19+/-2 beats/min and in A. tigrinum and A. dumerilii was 14+/-2 beats/min. The auricular tension was 284+/-15, 190+/-10, 140+/-8 mg, while the ventricular tension was of 62+/-3, 55+/-2 and 29+/-2 mg for A. mexicanum, A. tigrinum and A. dumenrilii respectively. Isoproterenol (10(-9), 10(-6), 10(-3) M) increased the heart rate and tension in a dose-dependent manner, and the effect was reversed in presence of propranolol. Our results indicate that isoproterenol-induced heart damage in urodele amphibians can be mediated by beta-adrenergic receptors located in the heart muscle. In the future, it will be necessary to characterize adrenergic receptor subtypes directly in these species, in order to understand the mechanism underlying the use of isoproterenol in experimental models of cardiac injury in non- mammalian vertebrates.

Adrenergic beta-Agonists↗

PubMed1979

Treatment of hypertonicity in muscles of lip retraction.

An EMG biofeedback program was developed for a 56-year-old Parkinsonism patient who exhibited pathological lip hypertonia and retraction. The program was designed to achieve the following goals: (1) to demonstrate a reduction in postural lip hypertonicity and (2) to demonstrate a reduction in lip hypertonicity during a series of increasingly complex speech activities. To achieve the first goal, contrastive tasks of full contraction and relaxation were utilized. Each posture was sustained while voltage measurements were made at specific intervals. Procedures to modify lip retraction during speech included five tasks in which the patient was to monitor the audio feedback signal. The tasks involved: prolongation of a neutral vowel, consonant-vowel combinations, monosyllabic words, sentences, and a paragraph-reading task. Data collected over six biofeedback sessions are presented. Trend analyses showed consistent muscular reduction within each task. The following explanations for the decrease in the patient's hypertonicity were discussed: (1) reduction of anisometric contraction, (2) reduction of isometric contraction, (3) relearning of agonistic-antagonistic muscle balance.

Biofeedback, Psychology↗

PubMed1985

The mechanical response of the active human triceps brachii muscle to very rapid stretch and shortening.

Very rapid, small amplitude, ramp-and-hold rotations were imposed on the braced forearms of three normal adult male subjects who were isometrically contracting their elbow extensors. By carefully accounting for inertial and viscoelastic coupling effects in the experimental system it was possible to compute the time course of the muscle-moment evoked by these mechanical perturbations. The muscle-moment responses, and their dependence on rotation amplitude and direction, as well as tonic contraction level, are described. These responses are also compared to the predictions of a simple muscle model which we have proposed previously on the basis of frequency-response tests. The results indicate that: at a given tonic contraction level, triceps may be stiffer in an isometric state than in an oscillatory steady state, and high frequency fluctuations in the myoelectric activity are very ineffective in generating corresponding muscle-force fluctuations.

Adult↗

PubMed1969

Isometric muscle contraction and the active state: an analog computer study.

From Sandow's excitation-contraction coupling hypothesis and reasonable assumptions I obtain the kinetics of the active state, (AS), and thence, via empirical equations for series elastic and contractile components for frog sartorius around 20 degrees C, the tension, P, and dP/dt vs. time. Assumptions: (a) Rate of Ca(+2) injection is proportional to the Ca gradient, and a permeability, which increases from zero to a limit as the membrane potential rises above a threshold. (b) Released Ca(+2) is bound by the "muscle machinery," M, and removed by a carrier pump. (c) The AS is proportional to the concentration of Ca-M. The kinetic pattern depends mainly upon the mechanism; the time scale was fixed by the amount of Ca(+2) injected. Depending upon the time course and repetition pattern chosen for the action potential, I obtain P and dP/dt, that agree well with experiment, for normal, potentiated, and summed twitches, tetani, and tension redevelopment after a quick release. Upon excitation the AS rises rapidly to 88%, declines thereafter in twitches, but rises slowly in unfused fashion toward 100% in tetani. The knee in dP/dt marks the first maximum in the AS. Potentiators should raise it in tetani as well as in twitches. Velocity and dP/dt show a much higher fusion frequency than P. The model integrates diverse observations. It may be tested by measuring tension and intramyofibrillar Ca(+2) under controlled depolarization.

Animals↗

PubMed2001

Activation of the VMO and VL during dynamic mini-squat exercises with and without isometric hip adduction.

OBJECTIVE: the purpose of this study was to compare vastus medialis obliquus (VMO) and vastus lateralis (VL) activity while performing a mini-squat with and without isometric hip adduction. DESIGN AND SETTING: a repeated measures within subjects design was used. Subjects performed two sets of three repetitions of a traditional mini-squat and a mini-squat with concurrent hip adduction (squeeze). SUBJECTS: 20 recreationally active subjects (10 men, 10 women age=28.10+/-5.91 years, height=170.94+/-11.03 cm, mass=72.32+/-16.66 kg) with no history of patellofemoral pain (PFP), quadriceps injury, or other knee injury participated in the study. MEASUREMENTS: the EMG signal of the VMO and VL was recorded bilaterally during both exercises. EMG data were normalized to the maximal voluntary isometric contraction (MVIC) of the quadriceps produced during seated, isometric knee extension. RESULTS: results of repeated measures ANOVA's revealed that the squeeze squat produced significantly greater VMO and VL activity than the traditional squat (p=0.02). For both the traditional and squeeze squats, intrasession reliability from the first to the second set was calculated using intraclass correlation coefficient (ICC) formula (3:1) bilaterally for both the VMO and the VL. All ICC values were greater than 0.9. CONCLUSION: combining isometric hip adduction with a mini-squat exercise significantly increases the activity of the quadriceps. Performing mini-squats with isometric hip adduction will be beneficial to patellofemoral patients as they increase quadriceps activity, however, based on our data we cannot conclude that this exercise preferentially recruits the VMO. Further research is needed to determine the exact mechanism by which quadriceps function is altered.

Adult↗

PubMed1964