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PubMed1985

Quantification of lumbar function. Part 4: Isometric and isokinetic lifting simulation in normal subjects and low-back dysfunction patients.

The present study collected the first normative data on a new dynamic isokinetic lifting device and compared a normal subject sample (n = 65) with a chronic low-back pain patient sample (n = 68) on this device. In addition, a comparison was made between isometric lifting measures collected for these controls and patients, and a normative industrial sample used in an earlier isometric testing protocol. Results demonstrated significant differences between controls and patients on all measures. An unanticipated finding was the greater lifting capacity levels of the present normal sample relative to those reported in the earlier isometric testing. These findings demonstrate that dynamic lifting simulation offers an important new tool for medical and industrial assessment, and conservative medical management.

Adult↗

PubMed1978

Correction of metabolic acidosis by the kidney during isometric expansion of extracellular fluid volume.

In dogs with chronic hypochloremic metabolic alkalosis associated with ECFV contraction, plasma [HCO-3] ([HCO-3]p) normalizes during expansion of ECFV with a solution containing Cl- and HCO-3 in concentrations duplicating those in the plasma before expansion (isometric expansion). The kidney selectively rejects administered HCO-3 and retains Cl-. If this preferential Cl- less than HCO-3 reabsorptive selectivity were a characteristic renal response to ECFV expansion, isometric expansion during hyperchloremic acidosis would exacerbate the acid-base disturbance rather than correct it as it does in alkalosis. We examined the effect of isometric expansion in dogs with chronic hyperchloremic metabolic acidosis induced by HCl feeding or mineralocorticoid hormone deficiency. During expansion, as the expected decrease occurred in the fractional reabsorption of Na+, a lesser decrease occurred in fractional reabsorption of HCO-3, whereas a greater decrease occurred in fractional reabsorption of Cl-. The kidney selectively retained administered HCO3 and rejected Cl-. [HCO-3]p normalized. The shift to bicarbonate-selective from chloride-selective anion reabsorption during ECFV expansion in metabolic acidosis vs. metabolic alkalosis indicates that in response to ECFV expansion- the kidney selectively alters the ratio of bicarbonate to chloride concentration in the tubular reabsorbate in the direction that tends to normalize plasma acid-base composition, irrespective of the direction of deviation of the initial plasma bicarbonate concentration. The signal that initiates the shift in anion reabsorptive selectivity remains to be identified.

Acidosis↗

PubMed1986

Comparative effect of propranolol and labetalol on isometric exercise and cold stress induced increase in arterial blood pressure.

The effect of propranolol and labetalol on cold stress and isometric exercise induced rise of blood pressure was studied in 7 patients with essential hypertension and 14 normal volunteers in a controlled, double blind, randomized, cross-over trial design. The subjects received either propranolol (40 mg) or labetalol (100 mg) orally after breakfast. In patients of mild to moderate essential hypertension, labetalol reduced significantly both systolic as well as diastolic rise of blood pressure induced by both types of exercises. Propranolol only reduced the rise of systolic blood pressure significantly. In normotensive subjects, labetalol reduced significantly the rise in systolic as well as diastolic blood pressure induced by cold stress, but not by the isometric exercise, while propranolol only reduced significantly the rise in systolic blood pressure induced by both the tests. The rise in heart rate was more with isometric exercise than with cold stress both in hypertensive patients and control subjects. The heart rate rise was significantly reduced by propranolol in all the experiments except for the rise induced by cold stress in hypertensive patients. The changes in heart rate produced by labetalol were not significant.

Adult↗

PubMedDate not supplied

Effect of captopril and propranolol, alone and in combination, on the responses to isometric and dynamic exercise in normotensive and hypertensive men.

This study evaluated the effects of single doses of the angiotensin converting enzyme inhibitor captopril and the beta-adrenergic blocking agent propranolol, alone or in combination, on the blood pressure, heart rate and humoral responses to both isometric (handgrip) and dynamic (ergometric) exercise in normotensive and hypertensive men. Single oral doses of either placebo, captopril 50 mg, propranolol 80 mg, or the latter two in combination were administered to age-matched groups (n = 5) of normotensive and hypertensive men in a random, double-blind manner. Captopril alone was indistinguishable from placebo after both isometric and ergometric exercise. Propranolol suppressed heart rate after both types of exercise and tended to decrease systolic blood pressure only in the hypertensive group; combination with captopril did not alter these responses. These data suggest that in sodium-replete subjects undergoing short-term vigorous exercise, the renin-angiotensin system, as measured by captopril inhibition, is less important than the sympathoadrenal system, as measured by propranolol inhibition, in the reflex cardiovascular adjustments accompanying acute isometric and dynamic exercise in both normotensive and hypertensive men.

Adult↗

PubMed1984

Isometric exercise following myocardial infarction.

Twenty-six consecutive patients had measurement of ejection fraction by gated blood-pool imaging at rest and during isometric exercise, following recovery from an uncomplicated myocardial infarction. We found there was a highly significant fall in ejection fraction at rest from 56 +/- 3% to 43 +/- 3% during isometric exercise (p less than 0.0001). There was a dramatic fall in ejection fraction during isometric exercise in some patients with a normal resting value. These patients may be a cause for concern. Our preliminary findings suggest these latter patients are at risk for future cardiac events such as, unstable angina, further myocardial infarction and future coronary bypass surgery.

Adult↗

PubMed1983

Isometric muscle force response of the human lower limb.

This paper deals with isometric muscle force response of the human lower limb when the leg is subjected to various external forces applied on the knee and ankle joints. The major components of the research apparatus are a subject restraint system, a force application device which employs three sonic emitters, and an upper leg cuff with four sonic emitters. The sonic emitters are used to determine the direction and the location of the force application on the lower limb and the orientation of the upper leg with respect to the torso. The numerical results are presented from experiments conducted on three male and three female subjects to determine their isometric muscle resistance against external forces trying to dislodge their lower limbs from several initial configurations. Quantitative results on the isometric muscle force capability of the subjects, when their lower limbs are dislodged from the initial stowed position, are also presented. It is concluded that, although there are intra- and inter-subject variations for the maximum values of the resistive muscle forces of the lower limb, there are some trends in the behavior of their magnitudes. Incorporating the results of the present research into multi-segmented models of the human body should improve the long-time response capabilities of these models so that they can simulate more realistically the biodynamic events which take place when the human body is subjected to high magnitudes of external forces lasting more than a fraction of a second.

Adult↗

PubMed1982

Cardiac output and cardiac load during isometric exercise in man.

Cardiac output, heart rate, arterial pressure and indirect left ventricular oxygen consumption have been measured in three subjects during isometric contractions (50-170 kg) of the plantar flexors until fatigue was reached and during walking on a treadmill. Cardiac output was linearly related to VO2 for both exercises. However, for the same VO2, Q was four times higher during isometric effort than during walking. In the last 15 s of static tasks, HR was linearly increasing to VO2 and AP reached values of 160 and 125 Torr (systolic and diastolic respectively) independently of VO2. For comparable VO2 in static and isotonic exercises myocardial O2 uptake was doubled during isometric rather than during the isotonic exercise.

Blood Pressure↗

PubMed1997

Choroidal blood flow during isometric exercises.

PURPOSE: To investigate the response of choroidal blood flow in the foveal region of the human eye to increases in mean perfusion pressure (PPm = mean ophthalmic artery pressure - intraocular pressure; IOP) induced by isometric exercises. METHODS: Using laser-Doppler flowmetry, changes in velocity (ChBVel), number (ChBVol), and flux (ChBF) of red blood cells in the choroidal vascular system in the foveal region of the fundus were measured in both eyes of 11 normal subjects (ages 18 to 57 years) during isometric exercises. RESULTS: During 90 seconds of squatting, PPm increased by an average of 67%, from 46 to 77 mm Hg. This resulted in a significant increase of 12% in ChBFm (the mean of ChBF during the heart cycle), mainly caused by an increase in ChBVelm. A further increase in PPm to a value approximately 85% above baseline resulted in a 40% increase in ChBFm. A significant negative correlation was found between the changes in ChBVelm and ChBVolm, during squatting. CONCLUSIONS: Previous studies have demonstrated that during isometric exercise, blood pressures in the ophthalmic and brachial arteries rise in parallel. These observations and the current results indicate that an increase in PPm up to 67% induces an increase in choroidal vascular resistance that limits the increase in choroidal blood flow to approximately 12%. This regulatory process fails when PPm is further increased.

Adolescent↗

PubMed1999

Comparison of isometric contractile properties of the tongue muscles in three species of frogs, Litoria caerulea, Dyscophus guinetti, and Bufo marinus.

Previous studies show that anurans feed in at least three different ways. Basal frogs have a broad tongue that shortens during protraction and emerges only a short distance from the mouth. Some frogs have long, narrow tongues that elongate dramatically due primarily to inertia from mouth opening, which is transferred to the tongue. A few species have a hydrostatic mechanism that produces tongue elongation during protraction. This functional diversity occurs among frogs that share the same two pairs of tongue muscles. Our study compares the isometric contractile properties of these tongue muscles among three frog species that represent each feeding mechanism. Nerves to the paired protractors and retractors were stimulated electrically in each species to record the force properties, contraction speeds, and fatigabilites of these muscles. Few differences were found in the isometric contractile properties of tongue muscles, and the greatest differences were found in the retractors, not the protractors. We propose that the unique arrangement of the tongue muscles in frogs results in a retractor that may also be coactivated with the protractor in order to produce normal tongue protraction. Inertial effects from body, head, and jaw movements, along with clear differences that we found in passive resistance of the tongues to elongation, may explain much of the behavioral variation in tongue use among species.

Animals↗

PubMed1982

The relationship between left ventricular functional response to isometric exercise and asynergic contraction and diastolic stiffness.

Either augmentation or impairment of left ventricular function has previously been reported in different patients, in response to isometric exercise. To identify the mechanisms associated with these disparate responses, the effects of submaximal sustained handgrip upon left ventricular systolic and diastolic properties were studied in 29 patients during diagnostic catheterization. In 16 patients (group I), ejection fraction, mean Vcf, and the mean systolic ejection rate remained constant, while the ratio of peak systolic pressure to end systolic volume increased significantly from 2.81 +/- 0.6 to 3.17 +/- 0.6 ml/mm Hg. In 13 patients (group II) ejection fraction declined from 0.6 +/- 0.03 to 0.51 +/- 0.03, Vcf from 0.96 +/- 0.09 to 0.85 +/- 0.09 circ/sec, mean normalized systolic ejection rate from 1.79 +/- 0.1 to 1.50 +/- 0.09 sec-1, and the peak systolic pressure to end systolic volume ratio from 2.23 +/- 0.3 to 1.99 +/- 0.3 (p less than 0.05 for each). Systemic arterial mean pressure increased similarly by 19% and 21% in groups I and II, respectively (p less than 0.05 for each). Systemic vascular resistance increased significantly by 23% in group I and by 5% in group II (p less than 0.05). Left ventricular end diastolic volume declined from 85.4 +/- 7 to 77.3 +/- 11 ml/m2 in group I, while end diastolic and end systolic volumes increased by 13% and 35%, respectively in group II (p less than 0.05 for each). In both groups, baseline exponential pressure-volume relations were similar, though higher intercepts on the pressure-volume relations upon the Y-axis suggested greater "diastolic tone," and steeper volume-normalized pressure-volume elasticity relations indicated "stiffer" left ventricular chambers in group II patients. While the incidence of coronary artery disease was similar, both the severity and extent of left ventricular asynergy were greater in group II patients. We conclude that dilatation and deterioration of left ventricular ejection function in response to isometric exercise are causally related to, and comprise a useful predictor of, severe underlying left ventricular asynergy and impaired chamber distensibility.

Adult↗

PubMed1988

Nitroglycerin-induced coronary vasodilatory responses in patients during isometric handgrip exercise.

Intracoronary nitroglycerin is frequently administered during invasive procedures such as coronary angioplasty or thrombolysis which may be associated with pain and sympathetic neural stimulation. Whether sympathetic-mediated reflex vasoconstriction interferes with nitroglycerin-induced augmentation of coronary blood flow is unknown. Therefore, coronary and systemic hemodynamics were measured in 19 patients during isometric handgrip exercise (3 min x 25% maximal effort), during intracoronary nitroglycerin, and during handgrip plus intracoronary nitroglycerin. Nine patients had no significant left anterior descending coronary artery stenosis (group 1) and ten patients had greater than 70% left anterior descending coronary artery stenosis (group 2). Handgrip exercise increased heart rate, mean arterial pressure, and coronary sinus and great vein flow 15% while increasing coronary resistance 10%. Intracoronary nitroglycerin (200 micrograms) reduced mean arterial pressure -4 +/- 6% and increased great cardiac vein flow 35-72%. Anterior left ventricular regional coronary flow responses to intracoronary nitroglycerin were unaffected by sympathetic stimulation for group 1. Group 2 had a greater increase in great vein flow with intracoronary nitroglycerin plus handgrip compared to nitroglycerin alone due to increased mean arterial pressure with no change in the great vein resistance. These data indicate that sympathetic stimulation does not alter the nitroglycerin-induced augmentation of coronary sinus and great vein blood flow in patients with and without significant left anterior descending coronary artery stenosis. In patients undergoing invasive interventions who may have increased circulating catecholamines, mild sympathetic (isometric) stimulation does not appear to interfere with the coronary vasodilatory responses to intracoronary nitroglycerin.

Cardiac Catheterization↗

PubMed1987

Effects of verapamil on left ventricular diastolic function at rest and during isometric exercise in patients with hypertrophic cardiomyopathy.

Ten patients with hypertrophic cardiomyopathy were examined with echocardiography before and during verapamil treatment to evaluate short-term and long-term effects of verapamil on left ventricular diastolic function. All patients were in sinus rhythm and in NYHA functional class I. Effects on filling and myocardial relaxation were documented by digitized echocardiography obtained at rest and during isometric exercise before treatment, after two weeks (short-term) and four months (long-term) treatment, respectively. At rest a significant decrease of the myocardial relaxation time was found during verapamil treatment. A few patients, however, returned to almost baseline conditions after an initial improvement. A small increase in the peak rate of dimension change, a parameter of filling, reached statistical significance at the end of the long-term treatment period. Isometric exercise did not induce any changes in the diastolic parameters during verapamil treatment. A positive effect of verapamil was thus seen on both myocardial relaxation and left ventricular filling, but only in resting conditions.

Adult↗

PubMed1987

Left ventricular diastolic and systolic function during isometric exercise: an echocardiographic study.

Normal subjects of both sexes between 20 and 63 years were examined with M-mode echocardiography. Blood pressure (BP), heart rate (HR), and left ventricular (LV) diastolic and systolic function were measured at rest and at the end of a standardized maximal isometric handgrip test. BP and HR increased about 25%. This increase in cardiac work had no significant influence on LV systolic function. Diastolic function (myocardial relaxation and maximum rate of LV filling), however, improved significantly. Isometric handgrip test is a suitable exercise test in combination with M-mode echocardiography. Studies on LV function during exercise may improve the sensitivity for detection of mild LV dysfunction.

Adult↗

PubMed1988

Effect of ibopamine on the failing heart at rest and during isometric exercise: a noninvasive study.

Eleven patients suffering from heart failure were treated with oral ibopamine, a di-isobutyric ester of N-methyldopamine, 100 mg three times a day for 1 week and 200 mg three times a day for 3 weeks. Therapy was discontinued by one patient because of tachycardia. Left ventricular performance was evaluated with echocardiography and systolic time intervals at rest and after 3 minutes of isometric exercise using a handgrip. Six of 10 patients completing the study were in New York Heart Association (NYHA) functional class III, 2 in class IV, and 2 in class II. All patients, except one who remained stable in class II, improved their subjective condition by one functional class during 4 weeks of therapy (p less than 0.01). There were no changes in heart rate, blood pressure, rate-pressure product, cardiac index, or total peripheral vascular resistance. The left ventricular end-systolic diameter decreased after four weeks from 71.2 +/- 12.7 (SD) to 65.9 +/- 13.0 mm (p less than 0.001); the left ventricular end-diastolic diameter did not change. The ejection fraction increased from 26 +/- 8 to 32 +/- 9% (p less than 0.01). Afterload, that is, left ventricular circumferential systolic wall stress, declined as a result of decreased systolic diameter. Systolic time intervals did not vary. There were no changes due to ibopamine during isometric exercise probably owing to increased beta-adrenergic stimulation induced by the handgrip. Neither urine volume nor body weight changed. Side effects were mild except for tachycardia of one patient.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2003

Isometric handgrip exercise during dobutamine-atropine stress echocardiography increases heart rate acceleration and decreases study duration and dobutamine and atropine dosage.

BACKGROUND: Dobutamine-atropine stress echocardiography (DASE) is an established test for the diagnosis and risk stratification of patients with coronary artery disease. Atropine use to attain target heart rate prolongs test time. HYPOTHESIS: The aim of this study was to assess the utility of isometric handgrip exercise (33% maximal voluntary contraction x 4 min) with DASE. METHODS: We prospectively evaluated 131 patients undergoing DASE randomized to handgrip exercise or no handgrip. Effect of handgrip exercise on endpoints: time to target heart rate (85% maximum predicted), recovery time, total test time, mean dobutamine and atropine dosage, and the number of ischemic responses were assessed. Effect of current beta-blocker medication use was also evaluated. RESULTS: Heart rate rose more quickly in the handgrip group. At 6-10 min (peak handgrip), mean heart rate rose 51 +/- 14 beats/min in the handgrip group compared with 38 +/- 18 beats/min in the no handgrip group (p < 0.0001). With handgrip, overall dobutamine study time was reduced by a mean of 4.3 min (16.4 +/- 6.9 vs. 20.7 +/- 8.4, p = 0.004) in all patients, and by a mean of 5.9 min in patients not on beta-blocker medication (p = 0.001). The handgrip group also had a lower mean dose of dobutamine (25.8 +/- 13.5 vs. 32.4 +/- 16.4 mg, p = 0.025). The mean atropine dose was also lower (0.2 +/- 0.4 vs. 0.4 +/- 0.5 mg, p = 0.04). Handgrip exercise, however, did not decrease endpoints in patients on beta-blocker medication. CONCLUSIONS: Use of isometric handgrip exercise with DASE decreases time to target heart rate, recovery time, overall study time, and mean dosage of dobutamine and atropine. In patients not on beta-blocker medication, handgrip exercise should be routinely incorporated into all DASE protocols.

Adrenergic beta-Antagonists↗

PubMed2006

Influence of structure on the tissue dynamics of the human soleus muscle observed in MRI studies during isometric contractions.

This article investigates how the internal structure of muscle and its relationship with tendon and even skeletal structures influence the translation of muscle fiber contractions into movement of a limb. Reconstructions of the anatomy of the human soleus muscle from the Visible Human Dataset (available from the National Library of Medicine), magnetic resonance images (MRI), and cadaver studies revealed a complex 3D connective tissue structure populated with pennate muscle fibers. The posterior aponeurosis and the median septum of the soleus form the insertion of the muscle and are continuous with the Achilles tendon. The distal extremities of the pennate muscle fibers attach to these structures. The anterior aponeurosis is located intramuscularly, between the posterior aponeurosis and the median septum. It forms the origin of the muscle and contacts the proximal extremities of the soleus muscle fibers. MRI measurements of in vivo tissue velocities during isometric contractions (20% and 40% maximum voluntary contractions) revealed a similarly complex 3D distribution of tissue movements. The distribution of velocities was similar to the distribution of major connective tissue structures within the muscle. During an isometric contraction, muscle fiber contractions move the median septum and posterior aponeurosis proximally, relative to the anterior aponeurosis. The pennate arrangement of muscle fibers probably amplifies muscle fiber length changes but not sufficiently to account for the twofold difference in muscle fiber length changes relative to excursion of the calcaneus. The discrepancy may be accounted for by an additional gain mechanism operating directly on the Achilles tendon by constraining the posterior movement of the tendon, which would otherwise occur due to the increasingly posterior location of the calcaneus in plantarflexeion.

Achilles Tendon↗

PubMed1995

Mechanical properties of aponeurosis and tendon of the cat soleus muscle during whole-muscle isometric contractions.

Recent studies have suggested that the mechanical properties of aponeurosis are not similar to the properties of external tendon. In the present study, the lengths of aponeurosis, tendon, and muscle fascicles were recorded individually, using piezoelectric crystals attached to the surface of each structure during isometric contractions in the cat soleus muscle. We used a surgical microscope to observe the surface of the aponeurosis, which revealed a confounding effect on measures of aponeurosis length due to sliding of a thin layer of epimysium over the proximal aponeurosis. After correcting for this artifact, the stiffness computed for aponeurosis was similar to tendon, with both increasing from around 8 F0/Lc (F0 is maximum isometric force and Lc is tissue length) at 0.1 F0 to 30 F0/Lc at forces greater than 0.4 F0. At low force levels only (0.1 F0), aponeurotic stiffness increased somewhat as fascicle length increased. There was a gradient in the thickness of the aponeurosis along its length: its thickness was minimal at the proximal end and maximal at the distal end, where it converged to form the external tendon. This gradient in thickness appeared to match the gradient in tension transmitted along this structure. We conclude that the specific mechanical properties of aponeurosis are similar to those of tendon.

Animals↗

PubMed1997

Muscle activation at the human knee during isometric flexion-extension and varus-valgus loads.

We examined the role of muscles in counteracting static loads in the transverse plane at the knee to determine if (a) knee muscles are activated to counteract isometric varus or valgus loads, (b) muscle activity during varus and valgus loads changes with the angle of knee flexion, and (c) the direction of a muscle's activation can be predicted by its moment arm orientations. For seven subjects, muscle activity was recorded during isometric tasks using surface and intramuscular electrodes from 10 muscles that span the knee. A six-degree-of-freedom load cell was rigidly attached to each subject's lower leg just above the ankle, and the subjects were instructed to push against the load cell so as to produce moments in the flexion-extension-varus-valgus plane at the knee. Moments in this plane were all of equal magnitude and varied in direction the full 360 degrees in 20 degrees increments. Most muscles were not activated to stabilize the knee against varus-valgus loads, but the sartorius, gracilis, and tensor fasciae latae showed substantial electromyographic activation in these directions. The load directions where muscles were principally active were observed to be dependent on joint angle for some muscles. In particular, the principal directions of activation for these three muscles changed as the angle of knee flexion changed. Similarly, a muscle's moment arm orientation was a good predictor of direction of activation for some muscles and a poor one for others. These results suggest that different muscles may play different roles in providing joint stability and that these roles are complex functions of muscle moment arm orientations, joint angles, external load directions, and possibly other undetermined parameters.

Adult↗