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PubMed2005

Haemodynamic responses to salbutamol and isometric exercise are altered in young adults with mild asthma.

OBJECTIVES: Tolerance to the haemodynamic effects of regularly inhaled beta(2) agonists has been reported in a research setting. It is unclear whether cardiovascular responses in adults with asthma are influenced by their use in routine clinical practice. This study aimed to characterise the effects of acute salbutamol administration on systemic haemodynamics in adults with mild asthma who were receiving intermittent beta(2) agonist treatment. METHODS: Ten patients with mild asthma and ten healthy age and sex-matched controls were recruited to a randomised placebo-controlled double-blind two-way crossover study. Each received salbutamol 200 mug or placebo, then performed sustained isometric handgrip exercise as an adrenergic cardiovascular stimulus. Heart rate and blood pressure responses were observed during rest and exercise, and cardiac index and systemic vascular resistance index were measured using non-invasive impedance cardiography. RESULTS: Isometric exercise caused a greater increase in heart rate (12+/-3 vs. 8+/-3 bpm, P<0.01) and diastolic blood pressure (19+/-3 vs. 12+/-3 mmHg, P<0.01) in patients with asthma compared with healthy controls. Salbutamol administration significantly increased heart rate, blood pressure and cardiac index in healthy controls, but these responses were attenuated in patients with asthma. CONCLUSION: These findings indicate that adults with asthma, who are receiving intermittent beta(2) agonist treatment, have a greater cardiovascular responses to sympathetic stimulation, and haemodynamic tolerance to acute salbutamol administration.

Administration, Inhalation↗

PubMed2000

Blood pressure and heart rate responses during a fatiguing isometric exercise in paraplegic men with hypertension.

A group of 45 male subjects were examined in a cross-sectional study to compare the blood pressure response that occurs during isometric exercise maintained to fatigue among control subjects and paraplegic patients with (PH) and without essential hypertension (PN). Two muscle groups were examined: the handgrip muscles (voluntary effort) and the quadriceps muscles. The tension chosen for the contraction was 40% of the muscles maximum strength for both muscle groups. While the paraplegic groups had more strength in their handgrip muscles than that found for the controls, the control subjects had more strength in their quadriceps muscles than either of the paraplegic groups. During the fatiguing isometric contractions, the rate of rise and absolute systolic blood pressure was higher in the PH than the other groups of subjects. The diastolic pressure of the PH group, while elevated during exercise, was only elevated to the same degree as the increase in resting diastolic pressure above normal. Heart rate changes during exercise was the same in all groups of subjects for handgrip contractions. The controls had the same heart rate response to handgrip as to leg exercise. The paraplegic groups showed no heart rate change during fatiguing contractions of their quadriceps muscles. The PH group actually showed a reduction in heart rate during the leg exercise.

Blood Pressure↗

PubMed1999

Cardiovascular responses to light isometric and aerobic exercise in 21- and 59-year-old males.

The effects of aging on the cardiovascular response to continuous light isometric and aerobic exercise remains to be determined. Thus, the purpose of this study was to compare the cardiovascular response of young and older males during light handgrip and cycle ergometry exercise. Blood pressure, heart rate, rate pressure product, as well as pre-ejection period (derived from impedance cardiography) were obtained for 15 young [mean (SE) age: 21 (0.7) years] and 15 older males [59 (0.8) years] during and after light handgrip exercise and cycle ergometry. The parasympathetic influence on the heart was also assessed through a time-series analysis of heart period variability (HPVts). Both during and when recovering from the handgrip exercise and cycle ergometry, the older subjects exhibited a significantly higher absolute systolic and diastolic blood pressure, and rate pressure product, and a lower HRVts than the young subjects. Relative to baseline, the change in pre-ejection period was lower for the young subjects during the handgrip and cycle ergometry, tasks. These results indicate that although the sympathetic influence on both the myocardium and the vasculature was less pronounced in the older males, the aging cardiovasculature was under greater hemodynamic stress both during rest and during exposure to light isometric and aerobic challenge.

Adult↗

PubMed1999

A comparison of models explaining muscle activation patterns for isometric contractions.

One of the main problems in motor-control research is the muscle load sharing problem, which originates from the fact that the number of muscles spanning a joint exceeds the number of degrees of freedom of the joint. As a consequence, many different possibilities exist for the activation of muscles in order to produce a desired joint torque. Several models describing muscle activation have been hypothesized over the last few decades to solve this problem. This study presents theoretical analyses of the various models and compares the predictions of these models with new data on muscle activation patterns for isometric contractions in various directions. None of the existing models fitted the experimental data in all aspects. The best fit was obtained by models based on minimization of the squared sum of muscle forces ( summation operator(m)φ(2)(m), which is almost equivalent to the Moore-Penrose pseudo-inverse solution), muscle stress sigma ( summation operator(m)sigma(m)(2)) or muscle activation alpha ( summation operator(m)alpha(m)(2)). Since muscle activation patterns are different for isometric contractions and for movements, it could well be that other models or optimization criteria are better suited to describe muscle activation patterns for movements. The results of our simulations demonstrate that the predicted muscle activation patterns do not depend critically on the parameters in the model. This may explain why muscle activation patterns are highly stereotyped for all subjects irrespective of differences between subjects in many neuro-anatomical aspects, such as, for example, in the physiological cross-sectional area of muscle.

Models, Biological↗

PubMed1991

Two-dimensional Doppler echocardiographic correlation of dipyridamole-thallium stress testing with isometric handgrip.

To determine how frequently new wall-motion abnormalities that are indicative of ischemia accompany thallium redistribution, 47 consecutive patients underwent two-dimensional echocardiography during routine dipyridamole-thallium stress testing. A secondary aim of the study was to determine whether the addition of isometric handgrip exercises to the standard dipyridamole imaging protocol increased the frequency of wall-motion abnormalities or thallium redistribution. Echocardiograms and thallium scans were independently interpreted, and wall-motion abnormalities that appeared with dipyridamole, handgrip exercise, or both were compared with results of thallium imaging. Five of 24 patients with thallium redistribution had new wall-motion abnormalities, and the extent (number of segments) of thallium redistribution in these five patients was significantly greater than in those who did not have well-motion abnormalities (p less than 0.03). The addition of isometric handgrip exercises to the imaging protocol did not distinguish between patients with and without new wall-motion abnormalities or thallium redistribution. Thus new wall-motion abnormalities infrequently accompany thallium redistribution in routine dipyridamole stress testing in spite of the addition of handgrip exercises, but when new wall-motion abnormalities are present, they are associated with a greater area of thallium redistribution.

Coronary Disease↗

PubMed1993

A randomized comparison between the hemodynamic effects of hydralazine and nitroglycerin alone and in combination at rest and during isometric exercise in patients with chronic mitral regurgitation.

Both arteriolar vasodilation with hydralazine and venodilation with nitroglycerin have been shown to favorably alter the hemodynamic profile in patients with chronic mitral regurgitation. Since these therapeutic modalities exert their effects by different mechanisms, this study was designed to assess hemodynamic response to both drugs given individually and in combination at rest and during isometric exercise in patients with chronic mitral regurgitation of various etiologies. When used individually, hydralazine caused larger increase in heart rate, cardiac index, stroke volume index, and systemic vascular resistance both at rest and during exercise. In contrast, nitroglycerin administration was associated with a superior effect on mean pulmonary artery pressure and V wave amplitude at rest and on mean right atrial and mean pulmonary artery wedge pressures at rest and during isometric exercise. In comparison with hydralazine alone, combination therapy enhanced the reduction in right atrial pressure (4 +/- 1 versus 0 +/- 2 mm Hg, p < 0.05), mean pulmonary arterial pressure (11 +/- 5 versus 1 +/- 3 mm Hg, p < 0.05), and the V wave amplitude (15 +/- 6 versus -5 +/- 3 mm Hg, p < 0.05) at rest and resulted in a larger reduction in exercise values of mean pulmonary artery pressure (-11 +/- 7 versus -3 +/- 5 mm Hg, p < 0.05) and mean pulmonary arterial wedge pressure (-11 +/- 5 versus -5 +/- 3 mm Hg, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1988

Blood pressure at rest and during maximal dynamic and isometric exercise as predictors of systemic hypertension.

This study sought to verify evidence that transient high blood pressure (BP) at rest and during dynamic and isometric exercise is often predictive of later hypertension. In addition these 3 predictors were compared. One hundred office patients (all men) with BPs less than 140/90 mm Hg, ages 28 to 79 years, who had little or no heart disease and were not taking medication, had BPs taken at rest and during treadmill and handgrip dynamometer. Within 14 years, 16 subjects developed hypertension and 84 remained normotensive. Multivariate statistical comparisons for systolic and diastolic BPs and their interactions were used to discriminate between later hypertensive and normotensive subjects. The best single predictor was resting diastolic BP, classifying 88% of hypertensive and 69% of normotensive subjects correctly, followed closely by handgrip and treadmill diastolic BP and resting, treadmill and handgrip systolic BP. The best prediction was by the interaction between resting diastolic BP X handgrip diastolic BP; this classified 88% of hypertensive and 80% of normotensive subjects correctly. Of the few known precursors of hypertension, high BP at rest and during dynamic and isometric stress provides a means of alerting to careful follow-up and early treatment.

Adult↗

PubMed1992

Efficacy of intravenous sotalol for suppressing inducibility of supraventricular tachycardias at rest and during isometric exercise.

The efficacy of intravenous sotalol (1 mg/kg) for suppressing inducibility of supraventricular tachycardias (SVT) with different electrophysiologic mechanisms was studied in 30 consecutive patients referred for an electrophysiologic study because of paroxysmal SVT. Orthodromic SVT using accessory atrioventricular (AV) connection was inducible in 14 patients, AV nodal reentrant SVT in 8, and intraatrial SVT in 8 before administration of sotalol, Isometric handgrip exercise facilitated the inducibility of SVT in 8 patients who were noninducible at rest. After intravenous sotalol, 7 of 14 patients (50%) with orthodromic SVT, 8 of 8 (100%) with AV nodal reentrant SVT, and 8 of 8 (100%) with intraatrial reentrant SVT became noninducible into sustained SVT, Isometric exercise facilitated the inducibility of only 3 nonsustained SVT runs after sotalol infusion, and exercise did not reverse the prolongation of refractory periods of the atrium, AV node, accessory pathway and ventricle caused by sotalol. During a mean follow-up period of 18 +/- 7 months, none of the 14 patients who remained noninducible into sustained SVT during the stress test after intravenous sotalol and tolerated long-term oral sotalol therapy had recurrence of symptomatic SVT. Thus, sotalol is efficacious for suppressing SVT with AV nodal or intraatrial reentrant mechanism, but less efficacious in patients with accessory AV pathway. The beta-blocking and cellular antiarrhythmic effects of sotalol are not significantly reversed by exercise.

Adult↗

PubMed1982

Force sensation in isometric contractions: a relative force effect.

A contralateral limb matching paradigm was employed to investigate the perception of isometric forces. Both force and brachial biceps and triceps EMG were recorded from each arm as subjects matched isometric contractions on the basis of equal sensation. It was found that smaller forces were consistently overestimated in magnitude and that the most accurate estimation of force occurred around the middle of the force domain. It is proposed that these results reflect the properties of the biceps muscle which is predominantly involved in gross motor activity.

Arm↗

PubMed1979

Effect of estradiol and progesterone on the isometric tension developed by longitudinal and circular isthmus of rabbit fallopian tube.

The effect of estradiol and progesterone on the isometric tension developed by longitudinal and circular muscle of isthmus of rabbit fallopian tube to various agonists was studied. The isometric tension developed was reduced by about 50% under progesterone dominance as compared to estrogen dominance. This inhibition was of non-specific nature and did not involve adrenergic receptors. The non-specific effect of progesterone may have a role in regulating the entry of ova into the isthmus after their initial retention at the ampullary--isthmic junction.

Animals↗

PubMed1983

Changes in isometric contractile properties of fast-twitch and slow-twitch skeletal muscle of C57BL/6J dy2J/dy2J dystrophic mice during postnatal development.

Our primary aim was to determine if there exists a preferential involvement of the fast-twitch or slow-twitch skeletal muscle fibers in the dy2J/dy2J strain of murine dystrophy. The changes in the contractile properties of the slow-twitch soleus (SOL) and the fast-twitch extensor digitorum longus (EDL) muscles of normal and dystrophic mice were studied at 4, 8, 12, and 32 weeks of age. Isometric twitch and tetanus tension were decreased in the 4- and 8-week-old dystrophic EDL compared with controls, this situation being reversed in the older animals. At 12 weeks, the dystrophic EDL generated 15% more tetanic tension than normal EDL and by 32 weeks no significant difference was seen between normal and dystrophic EDL twitch or tetanus tension. By 8 weeks, dystrophic EDL exhibited a prolonged time-to-peak twitch tension (TTP) and half-relaxation time (1/2RT) of the isometric twitch which continued to 32 weeks. For the dystrophic SOL, decreased twitch and tetanus tension was observed from 4 to 32 weeks. At 8 and 12 weeks, TTP and 1/2RT of dystrophic SOL were prolonged. However, by 32 weeks there was no longer a significant difference seen in TTP or 1/2RT between normal and dystrophic SOL. Our results appear to indicate that a loss of the primary control which is determining the fiber composition of the individual muscles is occurring as the dystrophic process advances.

Animals↗

PubMedDate not supplied

Response of plasma immunoreactive beta-endorphin and corticotropin to isometric exercise in uncomplicated pregnancy and in pregnancy-induced hypertension.

The response of plasma immunoreactive beta-endorphin (ir-beta E) and corticotropin to isometric exercise was studied in 10 women with pregnancy-induced hypertension (PIH) and in nine healthy women subjected to a handgrip test in the third trimester of gestation. The mean basal concentration of corticotropin was higher in the PIH than in the control group, 3.8 +/- 0.3 (SE) pmol/l and 2.2 +/- 0.2 pmol/l, respectively (p = 0.002). No significant difference was found in the basal ir-beta E level, 6.9 +/- 0.9 pmol/l and 6.1 +/- 1.0 pmol/l, respectively. In response to the handgrip test, the corticotropin and ir-beta E concentrations rose significantly in all subjects (p = 0.001 and p = 0.02, respectively) without any significant differences between the groups. These findings indicate that an isometric exercise is sufficient to increase the secretion of ir-beta E and corticotropin during pregnancy. Increased basal concentration of corticotropin in women with PIH may be explained by significantly increased circulating corticotropin-releasing hormone, 1451 +/- 323 pmol/l, as compared to 528 +/- 190 pmol/l in the control group.

Adrenocorticotropic Hormone↗

PubMed1978

The structural organization of DNA packaged within the heads of T4 wild-type, isometric and giant bacteriophages.

We present electron microscopic and X-ray diffraction evidence concerning the structural organization of condensed DNA within a series of T4 bacteriophage with the following head morphologies: prolate (wild-type), isometric and giant (with greatly increased axial ratio). In all cases, the DNA helix segments are locally parallel and 27 A apart. For the giant particles, we show that the DNA forms a large coil whose axis is perpendicular to the axis of the phage tail. This evidence, combined with previous results from a series of isometric bacteriophages (Earnshaw and Harrison, 1977), leads to a model for the organization of condensed DNA that may apply to most dsDNA-containing bacteriophages.

Coliphages↗

PubMed1990

An isometric method to study respiratory smooth muscle responses in mice.

An isometric method to measure the smooth muscle tone of murine tracheas in vitro was developed. Nine trachea rings from just beneath the larynx were prepared free of excess tissue with the help of a binocular microscope. These trachea parts were slipped onto supports in an organ bath containing Krebs' solution. Isometric tension was measured with a force displacement transducer connected to the upper-trachea support, and is expressed as changes in grams force. The cholinergic agonist carbachol contracted isolated tracheas. Serotonin also induced contractions, but was less potent than carbachol. Histamine induced tracheal contractions only at very high concentrations. Sympathomimetic beta adrenergic agonists relaxed carbachol-precontracted tracheas with the following order of potency: isoprenaline (beta 1 and beta 2 adrenoceptor agonist) greater than salbutamol (beta 2 adrenoceptor agonist) greater than prenalterol (beta 1 adrenoceptor agonist). Adrenaline and noradrenaline relaxed carbachol-precontracted tracheas, with adrenaline being the more potent relaxant. For the study of airway reactivity, this mouse trachea model has several advantages over immunopharmacologic models: The immune system of the mouse has been characterized extensively, and many reagents are available to study the immune system and, thus, possible interactions of this system with pharmacological mechanisms. Other animal models used in pharmacology are generally less well defined immunologically.

Adrenergic beta-Agonists↗

PubMed2005

Co-contraction recruitment and spinal load during isometric trunk flexion and extension.

BACKGROUND: Pushing and pulling tasks account for 20% of occupational low-back injury claims. Primary torso muscle groups recruited during pushing tasks include rectus abdominis and the external obliques. However, analyses suggest that antagonistic co-contraction of the paraspinal muscles is necessary to stabilize the spine during flexion exertions. The study quantified co-contraction and spinal load differences during isometric flexion and extension exertions. The goal was to provide insight into the mechanisms requiring greater co-contraction during trunk flexion exertions compared to extension exertions. METHODS: Electromyographic (EMG) signals were recorded from the trunk muscles of healthy volunteers during isometric trunk flexion and extension exertions. A biomechanical model was implemented to estimate total muscle force from the measured EMG and trunk moment data. A similar model estimated the muscle forces necessary to achieve equilibrium while minimizing the sum of squared muscle forces. The difference in these forces represented co-contraction. Spinal load attributed to co-contraction was computed. RESULTS: Average co-contraction during flexion exertions was approximately twice the value of co-contraction during extension, i.e. 28% and 13% of total muscle forces respectively. Co-contraction accounted for up to 47% of the total spinal load during flexion exertions. Consequently, spinal compression during the flexion tasks was nearly 50% greater than during extension exertions despite similar levels of trunk moment. INTERPRETATION: Co-contraction must be considered when evaluating spinal load during pushing exertions. Results underscore the need to consider neuromuscular control of spinal stability when evaluating the biomechanical risks.

Adult↗

PubMed2004

Activation of shoulder muscles in healthy men and women under isometric conditions.

PURPOSE: Due to the low osseous lead of the shoulder joint a large portion of the shoulder muscles, in addition to executing movements, deals with stabilising tasks. This requires a permanent readjustment of the intermuscular co-ordination of all involved muscles. The aim of the study was to verify the existence of gender dependent differences in intramuscular co-ordination patterns of shoulder muscles. METHOD: Fifteen healthy men and nine healthy women, who executed 24 isometric exercises in sagittal, frontal and horizontal planes with a loading of 50% of their individual isometric maximum force, were investigated. In every plane, four angular positions were chosen and both opposite force directions were measured, respectively. SEMG was taken from 13 muscles of the shoulder and the upper arm. Due to inter-individual differences SEMG amplitudes were normalised. RESULTS: Gender specific differences of functional intermuscular co-ordination patterns could be proven systematically. Women showed less activation of muscles acting in the main force direction. In addition, those muscles less necessary for the actual force production were more activated in women than in men. CONCLUSIONS: Functionally comparable shoulder function showed a gender dependency in terms of functional intermuscular co-ordination.

Adult↗

PubMed2004

Simultaneous surface electromyography (SEMG) and 31P-MR spectroscopy measurements of the lumbar back muscle during isometric exercise.

The aim of this study was to demonstrate the feasibility of simultaneous surface electromyography (SEMG) and 31P-MR spectroscopy (31P-MRS) measurements on the back muscle of volunteers during the performance of an isometric exercise. Six volunteers (three male, three female) performed a modified Biering-Sörensen test inside a 1.5 T MR scanner while simultaneously recording SEMG signals. A surface coil was used for 31P-MRS with a CSI sequence. Spectra were collected with a voxel resolution of 40 mm x 40 mm x 100 mm and a temporal resolution of 30 s during periods of rest, sustained muscle contraction and recovery. The duration of muscle contraction was 150 s. SEMG analysis yielded a decrease of the mean SEMG frequency of approximately 20%. The SEMG amplitudes were constant or increased up to approximately 150% during exercise. 31P-MRS showed a maximum decrease of the phosphocreatine (PCr) amplitude down to approximately 32% of its initial value. Simultaneously, a doubling of the inorganic phosphate (Pi) signal was observed. The present study demonstrates that simultaneous SEMG and 31P-MRS measurements of the back muscle are feasible during isometric exercises.

Adult↗

PubMed1998

Isometric pull forces in the sagittal plane.

This paper investigates the differences in maximal isometric horizontal pull forces in the sagittal plane about a frontal plane work envelope. Eight subjects produced maximal isometric horizontal pulls about 32 positions in the frontal for each of three different postural conditions: free standing, fixed standing and seated. Four horizontal positions (0, 200, 400, 600 mm relative to the mid-line of the body) in the sagittal plane at four vertical heights in two standing postures (1070, 1470, 1610, 2000 mm from the floor) and one sitting posture (220, 620, 760, 1150 mm from a seated reference position) were tested for both the left and right hand under all three postural conditions. Experimental findings reveal that the largest horizontal forces were produced at a height of 1070 mm in the standing postures and 220 mm in the sitting posture and were within 200 mm to the left and right of the mid-line of the body. These findings confirm that work-station designs should position heavy materials near the mid-line of the body, at or about elbow height to take advantage of operator's force-producing capabilities in the sagittal plane.

Adult↗