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PubMed1990

Hemodynamic effects of pindolol and atenolol at rest and during isometric exercise: a noninvasive study with healthy volunteers.

Hemodynamic effects of intravenous and oral pindolol and atenolol were assessed in ten healthy volunteers by left ventricular echocardiography and systolic time intervals. Measurements were made at rest and during hand-grip-induced isometric exercise. Drug doses were pindolol 0.015 mg/kg intravenously and 10 mg/day orally, atenolol 0.1 mg/kg intravenously, and 50 mg/day orally. Heart rate at rest was reduced by both drugs. The reduction caused by atenolol during oral treatment was significantly greater (p less than 0.01). Intravenously only pindolol reduced mean arterial pressure. During oral treatment atenolol reduced the mean arterial pressure nonsignificantly. Both drugs lowered heart rate during isometric exercise, atenolol being significantly more effective. During oral treatment atenolol blunted the heart-rate reaction to exercise. Mean arterial pressure during isometric exercise rose slightly with both drugs after intravenous administration. During oral treatment only atenolol reduced the mean arterial pressure significantly. Intravenous atenolol reduced cardiac contractility at rest, indicated by significant decreases in fractional shortening, ejection fraction, and the mean velocity of circumferential fiber shortening. In contrast, intravenous pindolol and oral therapy with either drug did not change contractility. Intravenous atenolol raised total peripheral resistance. The preejection period/left ventricular ejection time ratio decreased with intravenous pindolol, while atenolol increased it. In conclusion, atenolol had more negative inotropic and chronotropic effects, especially after acute intravenous administration. Only atenolol reduced cardiac output and increased peripheral resistance. After repeated oral administration, these effects were less apparent.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗

PubMed2006

Anatomical two-bundle versus Rosenberg's isometric bi-socket ACL reconstruction: a biomechanical comparison in laxity match pretension.

It is not well known how much tension should be applied to ACL graft at the time of graft fixation. As a step to determine the optimal initial tension, it is indispensable to know the graft tension to restore normal anterior-posterior (A-P) laxity (laxity match pretension, LMP). The objective was to determine the LMP in ACL reconstruction for the anatomical two-bundle technique and for the Rosenberg's isometric bi-socket one, and to compare these two techniques in LMP. Twenty-four patients with unilateral chronic ACL insufficiency were divided into the following two groups. The anatomical two-bundle technique was performed on 12 patients via two femoral tunnels at 9 and 10 o'clock or 2 and 3 o'clock on the posterior margin of the notch and two tibial tunnels (Group A), while the Rosenberg's isometric bi-socket reconstruction was performed on the remaining 12 patients through two femoral tunnels at 10 and 11 o'clock or 1 and 2 o'clock and one wider tibial tunnel (Group B). After two doubled semitendinosus grafts were fixed with two EndoButton-CL s on the femur, they were temporarily fixed to the tension-adjustable force gauge on the tibia, respectively. The total tension applied to grafts was set at 10, 20, 30, 40, or 50 N at 20 degrees of knee flexion, and the A-P laxity was measured by applying A-P drawer load of 134 N at 20 degrees of flexion. By comparing the measured laxity with that for the opposite healthy knee, the tension to restore the normal A-P laxity (LMP) was estimated. The mean LMP of 7.3 N in Group A was significantly smaller than that of 25.8 N in Group B. The anatomical two-bundle technique makes it possible to more effectively restore A-P stability with lower initial tension than the isometric Rosenberg's bi-socket reconstruction.

Adolescent↗

PubMed2003

Local tissue temperature effects on peak torque and muscular endurance during isometric knee extension.

The aim of the study was to investigate the relationship between local tissue temperature, peak torque and time to fatigue during isometric knee extensions. Nine males performed maximum voluntary contractions (MVCs) and isometric knee extensions at 70% MVC to exhaustion after 30 min of hot [H, 47.7 (1.3) degrees C; mean (SD)], warm [W, 34.6 (0.4) degrees C], temperate [T, 24.5 (1.3) degrees C], and cold [C, -11.9 (1.8) degrees C] localized temperature applications. Isometric peak torque was not significantly affected by temperature. Time to fatigue was strongly and negatively correlated ( r=-0.98) to temperature, with endurance after H [46.99 (4.98) s] and W [54.36 (9.18) s] significantly shorter than after C [73.27 (13.43) s]. We conclude that local tissue temperature does not impair peak force production but may change muscular endurance through local factors.

Adult↗

PubMed2004

Strategies that improve human skeletal muscle performance during repetitive, non-isometric contractions.

Previous studies have suggested that during sustained maximal voluntary and evoked contractions, decreasing activation rates may minimize fatigue. The idea of gradually decreasing stimulation frequency to preserve force during fatiguing isometric contractions has, however, recently been challenged. The primary purpose of this study was to test the effectiveness of decreasing or increasing electrical stimulation rates during evoked, repetitive, submaximal, non-isometric contractions of healthy human quadriceps femoris muscles. The ability of the muscles to produce a 50 degrees knee excursion repetitively was evaluated using low-frequency trains, high-frequency trains, and a combination of these trains. Results showed that stimulating the muscles with high-frequency trains followed by low-frequency trains produced the worst performance and starting with low-frequency trains followed by high-frequency trains produced the best performance. Present results cast doubt on the applicability of decreasing stimulation rates during non-isometric contractions and suggest that a combination of trains that begin at a low frequency and then switch to a higher-frequency may improve performance during functional electrical stimulation.

Adult↗

PubMed1991

Effect of autonomic blockade, postural changes and isometric exercise on Doppler indexes of diastolic left ventricular function.

Previous studies have demonstrated substantial changes in Doppler-derived indexes of left ventricular (LV) diastolic function in response to changes in loading conditions. To assess the influence of autonomic reflexes on these indexes, 2-dimensional and Doppler echophonocardiography were performed in 8 normal male subjects before and during autonomic blockade (0.2 mg/kg of propranolol and 0.04 mg/kg of atropine, intravenously) in the supine, passive upright 80 degree tilt and passive leg-raised positions, and during supine isometric exercise. During autonomic blockade in the supine position, there were significant increases in transmitral peak late filling velocity (A) (mean +/- standard error of the mean +34 +/- 7%) and isovolumic relaxation time (+18 +/- 9%), and significant decreases in transmitral peak early filling velocity (E) (-20 +/- 7%), deceleration time (-35 +/- 7%) and E/A ratio (-40 +/- 5%). E/A ratio decreased from 2.0 +/- 0.1 to 1.2 +/- 0.1 with autonomic blockade. When either upright tilt or isometric handgrip exercise was combined with autonomic blockade, the pattern of diastolic filling became distinctly "abnormal," with E/A ratio decreasing to 0.9 +/- 0.1. The effect of volume loading (increased end-diastolic volume and increased peak E) was seen in the legs-raised position only during autonomic blockade. It is concluded that autonomic blockade substantially alters the Doppler indexes of LV diastolic filling and modifies both hemodynamic response and Doppler indexes produced by positional changes and by isometric exercise.

Adult↗

PubMed1981

Comparative actions of substances affecting cyclic AMP metabolism on the isometric contractions of fast and slow skeletal muscle during single-pulse and subtetanic stimulation.

Increasing concentrations of isoprenaline (0.5-4 muM) produced a dose-dependent increase in both TD and dT/dtmax during direct single-pulse stimulation of hemidiaphragm of the rat. The same drug during the same type of stimulation produced an insignificant change in these parameters of the isometric contraction of the isolated guinea-pig soleus muscle. On the contrary, isoprenaline produced a dose-dependent decrease of the isometric contraction during subtetanic stimulation of the soleus muscle. Contrary to the results obtained on hemidiaphragm, there was no interaction between halothane and aminophylline on the soleus muscle. In the soleus muscle, aminophylline (0.3-3.2 mM) produced a dose-dependent increase in TD and dT/dtmax during single-pulse stimulation, whereas isoprenaline failed to do so under the same experimental conditions, in spite of the fact that both substances are activators of cyclic AMP system. The beta2-selective adrenoceptor agonist terbutaline acted in the same way as isoprenaline. During subtetanic stimulation aminophylline (0.3-3.2 mM) produced a dose-dependent decrease of both parameters of the isometric contraction of hemidiaphragm, which is opposite to the results obtained during single-pulse stimulation. It is concluded that various types of electrical stimulation can produce different responses in slow and fast-contracting muscles, depending on the fundamental biochemical differences of two types of muscle, but some of these responses are the same irrespective of the method of muscle activation.

4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone↗

PubMed1989

The importance of 'lumbar lordosis measurement device' application during pregnancy, and post-partum isometric exercise.

In this study, we measured the lumbar lordosis of normal pregnant women throughout their pregnancies and studied the efficacy and importance of the postpartum isometric exercise. 40 healthy primigravid patients were randomly assigned to one of the control and exercise groups. The lumbar lordotic deviation increased significantly throughout the pregnancy (p less than 0.05). Second postpartum day values of lumbar lordotic deviation and depth decreased compared to the third trimester values (p less than 0.05). Sixth postpartum week values of lumbar lordotic deviation and depth were found to be increased when compared to the first trimester values in the control and exercise group (p less than 0.05). On the other hand, the sixth week values in the exercise group are significantly lower compared to the control group (p less than 0.05). For these measurements we have used a 'Lumbar Lordosis Measurement Device' which was constructed in our institute. Muscle testing showed that isometric exercise improves the functional status of the affected muscles during pregnancy. We therefore conclude that the usage of 'LLMD' during the follow-up examination of pregnant women is essential to evaluate the posture of the patients. Isometric exercise is very important in order to obtain a normal posture and muscle tonus postpartumly.

Anthropometry↗

PubMed1987

Comparison of isometric and isotonic responses of human small airway smooth muscle in vitro.

The difference between isometric and isotonic responses of human small airway smooth muscle to a number of pharmacological agonists was studied. The isotonically measured sensitivity to methacholine was 1.4 times less than the isometrically measured value (p less than 0.05), and similar small discrepancies were found for histamine, leukotriene, prostaglandin F2 alpha, isoproterenol, and theophylline. Maximal isometric force and isotonic shortening after methacholine were linearly related (p less than 0.01). The between-methods difference is relatively small. Because the difference was of similar magnitude and in the same direction in all tissues studied, it is of little practical importance for conventional pharmacological experiments.

Bronchi↗

PubMed2006

Reliability of the assessment of lumbar range of motion and maximal isometric strength.

OBJECTIVE: To examine the interobserver reliability and intrasubject variability of the assessment of lumbar range of motion (ROM) and maximal isometric strength in asymptomatic subjects by using commercially available equipment. DESIGN: A cross-sectional repeated-measures design. SETTING: Ambulatory care in a university hospital. PARTICIPANTS: Convenience sample of 61 asymptomatic healthy subjects aged 20 to 55 years. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Six movements of the lumbar spine were assessed with commercially available equipment. Both the ROM and the maximal isometric strength for flexion, extension, lateroflexion, and rotation of the lumbar spine were assessed by 2 investigators who were blinded to the outcome of the assessment performed by their colleague. RESULTS: The intraclass correlation coefficient (ICC) was above .95 for all the strength measurements. For the assessment of the ROM of the lumbar spine, the ICC varied between .77 and .94. There was a significant intrasubject variability for 8 of 12 measurements. CONCLUSIONS: The interobserver reliability is excellent for the measurement of the maximal isometric strength and good for the assessment of the ROM of the lumbar spine. There is a significant intrasubject variability, which requires the use of the mean or the best value of different trials.

Adult↗

PubMed2004

Differences between measured and resultant joint moments during voluntary and artificially elicited isometric knee extension contractions.

OBJECTIVE: Examine two hypotheses: (a) during isometric knee extension contractions the moment measured at the dynamometer is different from the resultant moment in the same plane around the knee joint and (b) during isometric contractions, at the same given resultant moment the knee angle while loading is different from the knee angle while unloading. DESIGN: Comparative study in which the geometrical and the kinetic differences between joint and dynamometer were determined. BACKGROUND: It is usually assumed that the moment measured by the dynamometer is equivalent to the resultant joint moment. The non-rigidity of the dynamometer-leg system can influence the equivalence of these two moments. METHOD: Twenty seven subjects performed isometric maximal knee extension contractions and contractions induced by electrostimulation on a dynamometer. The kinematics of the leg were recorded using 8 cameras (120 Hz). RESULTS: The resultant moment at the knee joint and the moment measured by the dynamometer are different. During a knee extension effort the knee angle changes significantly. At identical resultant knee joint moments the knee angles are different when comparing the loading and the unloading phases. CONCLUSIONS: The differences between the measured and the resultant joint moments might influence the estimation of parameters as: muscle forces, moment-angle relationship and strain and hysteresis of tendons and aponeuroses. RELEVANCE: Torque dynamometers have been often used to estimate muscle forces, to examine neuromuscular processes and to determine the mechanical properties of tendons and aponeuroses.

Biomechanical Phenomena↗

PubMed2006

The effects of breath control on maximum force and IAP during a maximum isometric lifting task.

BACKGROUND: Evidence exists linking breath control to increases in intra-abdominal pressure and lumbar stability. Weight-lifting experts use this evidence as a rationale to suggest that increases in lumbar stability afforded by specific forms of breath control can influence the amount of force produced by the trunk. No studies have examined this issue. Therefore, this study determined whether voluntary control of the breath is related to maximal trunk extension force and if maximal force is correlated to intra-abdominal pressure. METHODS: Thirteen men and 20 women (mean age: 25.6 years (5.5)) performed a maximal isometric trunk exertion in a knee bent posture using voluntary breath conditions: (1) inhalation prior to exertion with hold during exertion; (2) exhalation prior to exertion with hold during the exertion; (3) inhalation prior to the exertion with exhalation during the exertion. A subset of subjects (n=11) were also simultaneously measured for intra-abdominal pressure. Separate repeated measures ANOVA were used to determine the effects of breath conditions on force and intra-abdominal pressure. Pearson coefficients were used to determine the correlation between force and intra-abdominal pressure. FINDINGS: Breath control did not significantly affect isometric force production (P=.089) but did affect intra-abdominal pressure (P=.003). Correlations between force and intra-abdominal pressure in each breath condition were low (range: 0.152-0.583). INTERPRETATION: Although breath control was shown to influence intra-abdominal pressure, it does not appear to influence isometric trunk extension force in a knees bent position. Further, the intra-abdominal pressure produced in such efforts appears to be unrelated to the amount of force produced.

Abdomen↗

PubMed2005

Effects of isometric exercise on the diastolic function in patients with severe aortic stenosis with or without coronary lesion.

BACKGROUND: There is no literature evaluating the effect of exercise on patients with aortic stenosis, in which patients with and without coronary artery disease were assessed separately. OBJECTIVE: To assess the effects of isometric exercise on the diastolic function in patients with aortic stenosis (AS). METHODS: 18 patients with AS, and 5 control patients were studied (group 1, G1). Patients with AS were divided in: group 2 (G2, n=10), without coronary lesion, and group 3 (G3, n=8), with coronary lesion. All patients underwent cardiac catheterization and performed isometric exercise until heart rate increased 32+/-9%. Left ventricular systolic pressure and end diastolic pressure (LVEDP), t1/2 (relaxation index), and the +dP/dt(max) were all measured. RESULTS: The +dP/dt(max) increased in G1, G2, and G3 during exercise returning to their basal values once exercise had concluded. While exercising, the LVEDP increased in G1, G2 and G3, returning to its original baseline value only in G1 and G2. The t1/2 increased, while exercising, in G2 and G3, and continued to be elevated after the exercise in both groups although it was only statistically significant in G3. The control group did not show significant changes. CONCLUSIONS: Isometric exercise decreases relaxation rate and increases LVEDP in patients with AS. After exercise, relaxation and LVEDP remained altered only in the patients with coronary lesion. The alteration in lusitropism and increased LVEDP after exercising suggest the presence of stunned myocardium.

Aged↗

PubMedDate not supplied

The impact of rotator cuff pathology on isometric and isokinetic strength, function, and quality of life.

The purposes of this study were to determine the reliability of strength and self-reporting measures, the relationship of different strength measures to function, and the impact of rotator cuff pathology on patients' quality of life. Patients with nonoperated rotator cuff pathology (n = 36) and unaffected control subjects (n = 48) were assessed by use of the LIDO dynamometer to determine isometric and isokinetic (concentric and eccentric) strength of the shoulder rotators. The Shoulder Pain and Disability Index and Short Form-36 were self-reported by patients. Intraclass correlation coefficients (ICCs) were used to assess reliability, and Pearson correlations and multiple linear regression were used to determine the relationship between strength and function. The findings of this study include the following: (1) measures of self-reported physical disability had high reliability (ICC = 0.89); (2) the LIDO dynamometer reliably measured internal and external shoulder rotation strength in both concentric and isometric modes of testing (ICC = 0.78-0.94), whereas eccentric muscle actions had lower reliability; (3) all shoulder rotation strength measures were predictive of disability, with isometric external rotation strength being the most predictive (r = 0.56); and (4) the presence of rotator cuff pathology was highly predictive of impaired physical health quality of life (R(2) = 0.71, P < .001).

Adult↗

PubMedDate not supplied

The effect of scapular protraction on isometric shoulder rotation strength in normal subjects.

To measure the effect of scapular protraction on isometric shoulder rotation strength, 20 normal subjects completed 2 maximal isometric internal and external rotation contractions in 2 scapular positions (scapula neutral [SN] and scapula protracted [SP]) from 3 arm positions (90 degrees internal rotation [IR], 45 degrees internal rotation [MR], and 90 degrees external rotation [ER]). Scapular protraction reduced shoulder rotation strength in 5 of 6 test positions (P < .0004), with significant interactions between scapular position and arm position (P < .001) and between scapular position and contraction type (P < .0001). Protraction significantly reduced IR strength by 13% to 24% relative to SN. The effect of SP on ER strength was more position-dependent, increasing strength by 6% in the IR position and decreasing it by 7% in the MR position and 20% in the ER position. In conclusion, acute changes in scapular position affect shoulder isometric IR and ER strength. The potential adverse effects of scapular protraction on shoulder rotation strength should be considered during the evaluation and treatment of shoulder pain.

Adolescent↗

PubMed1997

Comparison of left ventricular function using isometric exercise Doppler echocardiography in competitive runners and weightlifters versus sedentary individuals.

It is unclear whether cardiovascular responses to heavy isometric exercise are changed by intensive training. We evaluated the effects of this type of exercise on left ventricular (LV) function in athletes engaged in static and dynamic sport, compared with sedentary persons, and looked for peculiarities in static athletes' responses that might reflect adaptive mechanisms to their specific activity. The study population comprised 45 men (age 24 +/- 5 years): 29 dynamic and 16 static athletes (runners and weightlifters, respectively). The control group consisted of 20 age and gender-matched healthy sedentary persons. All performed 50% of maximal voluntary contraction on a whole-body isometric exercise device for 2 minutes. Echocardiographic calculations were determined at rest and exercise. Upon exercise, stroke volume, cardiac output, end-diastolic volume, and ejection fraction increased significantly in athletes, while end-systolic volume and systemic vascular resistance decreased. In sedentary persons, stroke volume and resistance remained unchanged, cardiac output and LV volumes increased, and ejection fraction decreased from 67 +/- 5% to 60 +/- 5% (p <0.01 compared with rest; p <0.0001 compared with athletes). Whereas peak flow velocity decreased from 103 +/- 10 to 81 +/- 6 cm/s in sedentary persons, it increased from 112 +/- 9 to 126 +/- 8 cm/s in the static group and from 120 +/-3 to 126 +/- 9 cm/s in the dynamic athletes (p <0.0001 compared with the sedentary group). Mean acceleration decreased in the sedentary group, remained unchanged among the dynamic athletes, and increased among the static athletes. We conclude that cardiovascular responses to heavy isometric exercise are modified by intensive training. Athletes, taken as a group, react differently and adapt better than sedentary individuals. Moreover, among them, those involved in static sport show an improved cardiovascular adaptation to this type of exercise.

Adult↗

PubMed1999

Mechanochemical coupling in spin-labeled, active, isometric muscle.

Observed effects of inorganic phosphate (P(i)) on active isometric muscle may provide the answer to one of the fundamental questions in muscle biophysics: how are the free energies of the chemical species in the myosin-catalyzed ATP hydrolysis (ATPase) reaction coupled to muscle force? Pate and Cooke (1989. Pflugers Arch. 414:73-81) showed that active, isometric muscle force varies logarithmically with [P(i)]. Here, by simultaneously measuring electron paramagnetic resonance and the force of spin-labeled muscle fibers, we show that, in active, isometric muscle, the fraction of myosin heads in any given biochemical state is independent of both [P(i)] and force. These direct observations of mechanochemical coupling in muscle are immediately described by a muscle equation of state containing muscle force as a state variable. These results challenge the conventional assumption mechanochemical coupling is localized to individual myosin heads in muscle.

Animals↗

PubMed2001

Differential gating of slow postsynaptic and high-frequency spike-like components in human somatosensory evoked potentials under isometric motor interference.

Human cortical somatosensory evoked potentials (SEP) can be modified by concomitant motor tasks ('gating'), through peripheral occlusion and/or central mechanisms. The present study aimed (1) at refining earlier results concerning motor-gating of the primary cortical EPSP-related N20 response after electric median nerve stimulation, and (2) at providing first data on motor-gating of the 600 Hz SEP wavelet burst which occurs superimposed onto N20 and primarily reflects repetitive cerebral population spikes. In 12 healthy subjects median nerve SEP were elicited, using electrical stimuli with intensities below, at and above motor threshold, under either rest or an isometric fist clenching task. Amplitude and latency modifications were analysed for the peripheral compound action potential (CAP), low-frequency SEP components (N20, P25, N35 and P70) and the high-frequency burst. While the peripheral CAP remained unchanged, isometric motor innervation significantly attenuated N20, P25 and P70 amplitudes and shortened peak latencies progressively for all components after N20. In contrast, the high-frequency 600 Hz burst was modulated neither in amplitude nor in latency. Regular amplitude recruitment occurred for all components independent from the motor task, excluding channel saturation as an explanation for gating. We suggest that SEP gating under isometric motor innervation is a central process which selectively operates on specific SEP components and could partly reflect an "efference copy" mechanism.

Action Potentials↗

PubMed1998

Influence of parasympathetic dysfunction and hyperinsulinemia on the hemodynamic response to an isometric exercise in non-insulin-dependent diabetic patients.

The handgrip test has long been used as a test for investigating cardiac autonomic neuropathy in diabetic patients. However, the factors involved in the hemodynamic response to the handgrip test have not been thoroughly studied. The aim of this study was to investigate blood pressure (BP) and heart rate (HR) responses to an isometric test in non-insulin-dependent diabetics (NIDDs) and to correlate the results with vagal function evaluated by three standardized tests and with plasma insulin levels. Fifty-five NIDDs, 35 of whom had one to three abnormal parasympathetic tests (PS+), were compared with 10 healthy control subjects. Fasting and postprandial plasma insulin levels were significantly higher in the PS+ than in the PS- patients. Resting HR correlated significantly with log fasting and postprandial insulin. In PS+ NIDDs, resting HR was significantly higher than in PS- patients. Age-matched comparisons also showed that resting systolic BP was significantly higher in PS+ patients than in controls. In PS- patients, the mean acceleration of HR was significantly higher than in the control group from the second to the fifth minute, and the BP response was also higher than in controls. These data suggest that (1) sympathetic response to an isometric exercise is increased in PS- NIDDs; (2) cardiac parasympathetic dysfunction is associated with a more severe insulin resistance; and (3) the subsequent higher plasma insulin level may contribute to the increase in resting HR and BP through sympathetic activation while limiting the hemodynamic response to an isometric exercise through its vasodilative effect.

Blood Pressure↗