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PubMed1978

[Echocardiographic determination of left ventricular function during isometric muscle exertion and the Valsalva maneuver].

Left ventricular dimensions and function were estimated in 11 healthy volunteers by means of echocardiography during isometric exercise and the Valsalva manoeuvre. Isometric exercise induces a rise of heart rate and Vcf by 14% and of cardiac output as well as of the cardiac index by 12%. Stroke volume remains unchanged. During Valsalva's manoeuvre a marked decrease in left ventricular dimensions is observed. A reduction of the stroke volume by 29% was not compensated by increasing heart rate. However, cardiac output and cardiac index is found 10% below control values.

Adult↗

PubMed1995

The quantitative measurements of hip isometric muscle torques in Chinese young adults--a preliminary report.

A standard procedure for measurement of hip muscle strength (maximal isometric torque) with the Cybex 340 isokinetic dynamometer is presented. Twenty-two healthy males aged 30-40 years (average 34.3 years) were tested on hip flexors, extensors and abductors; in which the factors as sex, age, dominant side and testing session were all eliminated. The test was redone two weeks later on the same 10 males to evaluate its reproducibility. The results disclosed the maximal isometric torque of the hip flexors was stronger than that of extensors and abductors in both sides hips. The comparison between two sides hips showed only the abductors of right side hip significantly stronger than that of left side (P = 0.0259). The tests between the two different periods were quite compatible. The results have clinical implications for objective assessment of preoperative and postoperative hip strengths in patients with hip arthropathy and thus giving a reasonable guidance for physiotherapeutic management.

Adult↗

PubMed1995

The efficacy of isokinetic, isometric and vertical jump tests in exercise science.

This research examined the efficacy of several tests of muscular strength and power in their capacity to be related to performance, their ability to effectively discriminate between individuals of different performance levels and their sensitivity in detecting training induced changes to performance. Thirty healthy active subjects performed the following maximal tests of muscular function: (1) Vertical jump; (2) Isokinetic knee extension at 1.05, 3.14 and 5.24 rads s-1; and (3) Isometric rate of force development. Performance was assessed by the peak power output achieved on a cycle test. In addition, subjects participated in a 10 week resistance training program. The isokinetic and vertical jump tests were significantly related to performance (r = 0.5-0.73) and could be used to discriminate between subjects of differing performance levels. However, the isometric rate of force development test was an ineffective assessment modality. None of the tests were able to effectively monitor training induced changes in performance, as evidenced by non-significant correlations between the pre- to post-percentage changes in cycling performance and the test variables. Consequently, alterations to training programs for athletes should be based on changes in actual performance, as opposed to muscular function tests.

Adult↗

PubMed1993

A modified isometric test to evaluate blood pressure control with once-daily slow-release verapamil.

Blood pressure at rest is not predictive of round-the-clock values. Blood pressure should therefore be measured during effort to evaluate hypertension and its response to treatment. The effect of sustained-release verapamil (240 mg taken once a day) on blood pressure at rest and during isometric effort was therefore investigated. Overall, verapamil reduced blood pressure significantly in 41 of 45 hypertensive patients: the mean systolic blood pressure at rest (+/- SD) fell from 151 +/- 35 mmHg to 137 +/- 13 mmHg (P < 0.001) and the diastolic blood pressure from 97 +/- 21 mmHg to 83 +/- 7 mmHg (P < 0.001), while the systolic blood pressure during isometric effort fell from 186 +/- 23 mmHg to 156 +/- 13 mmHg (P < 0.001) and the diastolic blood pressure from 118 +/- 14 mmHg to 95 +/- 8 mmHg (P < 0.001). The simple, inexpensive handgrip method described is cost-effective and strongly recommended as an integral part of the evaluation of hypertensive patients. The combination of a drug to which compliance is good and a simple method of blood pressure evaluation should result in improved effectiveness of treatment in the long term.

Adult↗

PubMed1994

Muscular fatigue and recovery following alternating isometric contractions at different levels of force.

The purpose of this study was to document the amount and rate of muscular fatigue during alternating levels of isometric contraction similar to that found during the Simulated Aerial Combat Maneuver (SACM). In addition, the time needed to recover from such an exercise was examined. Twenty males between the ages of 22 and 35 years performed an isometric contraction of their right quadriceps muscle at alternating levels of tension (20 and 50% maximum voluntary contraction) until exhaustion. The time at each contraction level was 10 s. After each exhaustive exercise bout, subjects were assigned to one of six recovery intervals (10, 20, 40, 60, 120, and 240 min) followed by a repeat of the exhaustive exercise. All subjects were tested under each of the six recovery intervals. Results showed that the amplitude (RMS) of the myoelectric signal increased while the frequency content of the signal (MPF) decreased over the course of the fatiguing activity. Endurance time (ET) was found to be significantly (p < 0.05) recovered (90.96%) within 60 min after stopping the exercise. Although MPF returned to its prefatigue value within 10 min of rest, the RMS value had still not recovered after 4 h.

Adult↗

PubMed1994

Isometric shoulder torque in subjects with spinal cord injury.

The etiology of shoulder pain in spinal cord injured (SCI) patients has been attributed to overuse, with dysfunction being more prevalent as the time since injury increases. Impingement syndrome, the most common diagnosis in this population, may be related to weakness of the rotator cuff and shoulder girdle musculature. Shoulder dysfunction is greater in subjects with SCI than in able-bodied patients; consequently, this study compares isometric strength of quadriplegic and paraplegic subjects to able-bodied controls. Peak isometric torque for internal rotation, external rotation, and scapular elevation was assessed using a Lido isokinetic dynamometer. The strength (torque) values of the quadriplegic group were significantly lower than the control group and paraplegic group for all motions tested (p < .0005). The only significant difference between the paraplegic and able-bodied groups was found with internal rotation (p < .0001). These results indicate that quadriplegic patients may be at greater risk for shoulder pathology because of both muscular limitation and increased functional demand.

Adult↗

PubMed1993

Correlation of myosin light chain phosphorylation with isometric contraction of fibroblasts.

In vitro studies have indicated that the enzymatic activity of myosin II from non-muscle cells is controlled by phosphorylation of its regulatory light chain (LC20). We have studied one likely functional consequence of phosphorylating LC20 in living chick embryo fibroblasts (CEF) by measuring contractile force developed by these cells. Using a recently developed method, we recorded quantitative changes in isometric force generated by a population of cells following mitogenic stimulation. Fetal bovine serum, thrombin, and lysophosphatidic acid stimulate rapid isometric contraction of CEF. Cells stimulated with thrombin develop maximal force within 5-10 min. Force development correlates temporally with a 3-5-fold increase in the overall fraction of LC20 phosphorylated and with the fractions of LC20 in both the monophosphorylated and diphosphorylated states. Unloaded shortening velocity also increases after thrombin stimulation. Although both force and phosphorylation begin to decline 10 min after stimulation, the level of phosphorylation declined more rapidly than the force. These results suggest that the role of LC20 phosphorylation in regulating fibroblast contractility is analogous to its well established role in regulating smooth muscle contraction and that quantitative measurements of the force developed by populations of fibroblasts (or other cultured cells) can be used to study the regulation of non-sarcomeric myosin at the molecular level in vivo.

Animals↗

PubMed1993

Isometric exercise increases strength and does not produce sustained creatinine phosphokinase increases in a patient with polymyositis.

A patient with active stable idiopathic polymyositis received a 4-week supervised right quadriceps and biceps isometric strengthening program. He demonstrated a significant increase in isometric peak torque without a sustained rise in creatinine phosphokinase (CPK). A significant decrease in postexercise CPK occurred at the end of the exercise program. We conclude a randomized clinical trial using a nonexercised patient group vs an exercised patient group may be useful.

Creatine Kinase↗

PubMed1996

[Recruitment of the bi-articular gastrocnemius muscles during maximal isometric contractions in humans].

The main purpose of this study was to investigate the maximal isometric plantarflexion moment as a function of the triceps surae's length. As the gastrocnemius are bi-articular actuators, their respective lengths were modified by variations of the ankle and knee joints angles. The mechanical results agreed ones previously published in the literature. The maximal and minimal isometric moments were attained at maximal lengthening and shortening of the gastrocnemius respectively. The gastrocnemius electromyographic (EMG) activities showed paradoxal results. Their EMG activities decreased with their lengthening when this was induced by ankle joint angle variations. Inversely, their EMG activities increased with their lengthening when this was induced by knee joint angle variations. These results allowed the authors to hypothesize the existence of specific recruitment of neuro-muscular compartments of the gastrocnemius with knee extension.

Ankle Joint↗

PubMed1975

Isometric, three-dimensional viewing of ultrasonograms.

This report describes a system that allows amplitude information to be used as a third dimension or aspect of display on B-scan ultrasonograms. The relative strength of reflected echoes can be shown on B-scan by means of gray scale, color coding, or on A-scan with amplitude deflection. With this new technique, called isometric display, superimposition of the A-scan trace on the B-scan allows preservation of these amplitude characteristics. The three-dimensional presentation can be rotated around any azimuth to provide isometric viewing of the ultrasonogram. Tissue may then be characterized on a more reliable basis than is permitted by independent analysis of outline and amplitude features.

Eye Diseases↗

PubMed1976

Effects of isometric exercise on serum creatine phosphokinase activity.

The effect of isometric exercise on serum creatinine phosphokinase (CPK) activity in 14 psychotic patients in remission and ten normal controls was studied. The increases in serum CPK activity at 18 and 42 hours after exercise were no significantly different in patients and controls. The postexercise serum CPK activities in the patients were significantly less than the peak serum CPK levels when they were psychotic. There were no significant correlations between postexercise serum CPK activity and preexercise or peak serum CPK activity in the patient group. It is unlikely that increased isometric muscle tension is a major causative factor in the increased serum CPK levels frequently found in psychotic patients.

Acute Disease↗

PubMed1990

Length-dependence of isometric twitch tension potentiation and myosin phosphorylation in mouse skeletal muscle.

The effect of changes in muscle length on post-tetanic isometric twitch tension potentiation and myosin P-light chain phosphorylation was studied at 23 degrees C in the mouse extensor digitorum longus muscle. The length-tension relationship was determined for the same muscles after a 30 min period of quiescence and between 30 s and 3 min after a 1.5 s tetanus at L0. Isometric twitch tension is increased at all muscle lengths after the tetanus; however, the fractional increase in twitch tension rises from 0.2 at L0 to a maximum of 0.3 at 1.2 L0. The fractional increase in twitch tension measured at any fixed muscle length is constant between 30 s and 3 min post-tetanus. P-light chain phosphorylation remains constant between 30 s and 3 min post-tetanus followed by a slow decline to basal values. Under fixed length conditions, there is linear relationship between the relative magnitude of the twitch tension and the extent of P-light chain phosphorylation. Net myosin phosphorylation measured after a 1.5 s tetanus at 1.23 L0 is 35% less than that obtained under the same conditions at L0. Thus, contraction-induced phosphorylation of P-light chain decreases with increased muscle length and post-tetanic potentiation at a constant level of P-light chain phosphorylation increases with increasing muscle length. These observations may be consistent with alterations in the sarcoplasmic Ca2+ ion transient as the muscle is lengthened.

Animals↗

PubMed1994

EMG changes in respiratory and skeletal muscles during isometric contraction under normoxic, hypoxemic, or ischemic conditions.

The consequences of general hypoxemia (PaO2 = 51 mmHg) on two muscle groups (adductor pollicis and diaphragm) sustaining 80% maximal isometric voluntary contraction were studied in healthy individuals. For adductor pollicis, contractions were also executed after 10-s or 3-min rest ischemia. Compared to control, i.e., normoxic, sustained isometric workloads, significant shortening of endurance time occurred only when adductor pollicis contracted under hypoxemic conditions. In both muscle groups, a 3-min ischemia test as well as hypoxemia reduced the rate of changes in integrated surface EMG in a low frequency band and lowered, or did not modify, the rate of change in the high above low frequency ratio. Recovery of normal patterns of EMG changes was prolonged only after the adductor pollicis contracted under hypoxemic conditions. The present data show that both hypoxemia and prolonged rest ischemia reduced the rate of changes in quantitative EMG activity, with the more significant effects being measured under hypoxemia.

Adult↗

PubMed1998

Myosin head movements during isometric contraction studied by X-ray diffraction of single frog muscle fibres.

Time resolved X-ray diffraction experiments in single muscle fibres of the frog at 2.15 microns sarcomere length and 4 degrees C were performed at ID2 (SAXS), ESRF, Grenoble (France) to investigate the structural aspects of cross-bridge action during the development of the isometric tetanic tension (T0). Changes in the low angle myosin-based reflections were measured with 5 ms time resolution by signal averaging data collected with a 10 m camera length and a 2D gas-filled detector. Upon activation the intensity of the first order myosin layer line reflection, I(M1), and the intensity of the second order meridional reflection, I(M2), reduced practically to zero with a half-time which leads the tension rise by 15-20 ms. The complex changes of the intensity of the third order myosin meridional reflection, I(M3), and the increase of its axial spacing from 14.34 nm (at rest) to 14.57 nm (at T0) could be analysed by assuming that they were the result of the combination of the time dependent modulation in intensity of two closely spaced periodicities, one at 14.34 nm, characteristics of the myosin molecule at rest and the other at 14.57 nm, assumed by the myosin as a consequence of the activation and force production. I(14.34) drops monotonically in advance to isometric tension development with a half-time similar to that of I(M1) and I(M2), while I(14.57) rises from zero to a maximum in parallel with tension.

Animals↗

PubMed1988

Isometric exercise for the evaluation of vasodilatory therapy in severe congestive heart failure.

There are few data available about the hemodynamic effects of isometric handgrip in severe congestive heart failure and its role in the evaluation of vasodilatory therapy. Therefore, we studied 20 patients with dilated cardiomyopathy at rest, during isometric handgrip, and during supine bicycle exercise before and after a single 25-mg dose of captopril. During handgrip, heart rate (p less than 0.001); systemic vascular resistance (p less than 0.01); systolic, mean, and diastolic pulmonary artery pressure (p less than 0.01) increased significantly; stroke volume index fell (p less than 0.05); whereas mean arterial pressure showed only a small increase, and cardiac index did not change. In contrast, mean arterial pressure and cardiac index increased during dynamic exercise (p less than 0.001), and peripheral resistance decreased (p less than 001). During both handgrip and bicycle exercise, captopril induced a decrease of arterial pressure (p less than 0.01 and p less than 0.001; respectively), peripheral resistance (p less than 0.001 and p less than 0.01; respectively), and systolic (p less than 0.01 and p less than 0.001, respectively) mean (p less than 0.001), and diastolic pulmonary artery pressure (p less than 0.001). Captopril induced and increase in stroke volume index (p less than 0.01) and cardiac index (p less than 0.001 and p less than 0.01 respectively) during both types of exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

Comparison of blood pressure and heart rate responses to isometric exercise and passive muscle stretch in humans.

The responses of mean arterial blood pressure (BPa) and heart rate (fc) to isometric contraction and passive stretch were compared in seven healthy male subjects at identical external forces. They were investigated in the sitting position with the hip and knee joint flexed to 90 degrees. Each subject performed two tests, separated by a day, in which the stimuli were applied in random order. After 5 min of rest they performed either 10-min static plantar flexion of one calf (200 N) or 10 min of passive calf muscle stretch at the same load. After 5-min rest, the second stimulus was applied for a further 10 min followed by 5-min rest. The second test was identical except for the sequence of the stimuli. The BPa was measured by a noninvasive and continuous method. Contraction of the vastus lateralis, gastrocnemius lateralis, and soleus muscles were determined by the myo-electric activity (electromyogram, EMG) by means of surface electrodes. The EMG activity of the vastus lateralis muscle remained at resting values throughout the experiments. Increases in EMG activity could only be detected for the triceps surae muscles during isometric contraction. During the initial 2 min of stimulation the BPa and fc responses to active contraction and passive stretch were comparable. Thereafter, both parameters showed significantly higher values during contraction. It was concluded that mechanical stress may have contributed to the early response of BPa during both passive stretch and voluntary contraction but that chemical stimuli were needed to maintain the peripheral cardiovascular drive.

Blood Pressure↗

PubMed1995

The relationship between voluntary electromyogram, endurance time and intensity of effort in isometric handgrip exercise.

The relationship between relative force, electromyogram (EMG) and time to fatigue was examined in seven male and seven female subjects [mean (SD) age, 21.7 (3.2) years] during isometric handgrip exercise. Subjects performed sustained submaximal contractions of the right handgrip at three different intensities: 30%, 50%, and 75% of the pretrial maximum voluntary contraction (MVC). EMG was sampled in 1-s epochs every 15 s during the contractions, and the integrated EMG (IEMG) values were then normalized to that of the pretrial MVC. As expected, time to fatigue was longest at 30% MVC and shortest at 75% MVC, but women performed consistently longer than men at each of the three intensities [woman vs men; 400.7 (35.8) vs 364.3 (34.4) s, 205.1 (15.6) vs 139.4 (13) s, and 89.9 (11.4) vs 66.4 (6.4) s, for 30%, 50%, and 75% MVC, respectively; P < 0.05)]. IEMG increased in a non-linear fashion over time during each trial, with the magnitude of IEMG being proportional to the intensity of the contraction. At the endurance limit, IEMG was greatest in the 75% MVC trial, however, no IEMG values reached those obtained in the related MVC [30%, 57.2 (6.9)%, 50%, 84.6 (5.7)%; 75%, 92.8 (7.4)%]. In conclusion, endurance time during sustained submaximal isometric handgrip exercise is dependent up on the intensity of the effort, with women having significantly larger endurance times than men. The related increase in IEMG is also proportional to the intensity of effort, however, the factors causing force to fail prior to the final IEMG reaching its predicted maximum remain to be elucidated.

Adult↗

PubMed1995

EMG activation patterns during force production in precision grip. I. Contribution of 15 finger muscles to isometric force.

Electromyographic (EMG) activity was examined in six normal subjects, producing low isometric forces between thumb and index finger in a visually guided step-tracking task. Target forces ranged between 0.5 and 3.0 N. EMG activity of all 15 muscles acting on thumb or index finger was screened with simultaneous recordings of up to 8 muscles. Linear regression was applied to quantify the EMG activity as a function of force. The intrinsic muscles and the long flexors of the index finger had a tight relation to force, as indicated by the high correlation coefficient, as did the adductor and short flexor of the thumb. In contrast, the long extensors of the index finger did not show force-related activity. The other muscles, including the long flexor and extensor of the thumb, had varying, on average moderate, correlations to force. The slope of the regression lines, a measure for the amount of EMG modulation with increasing force, revealed the same trends. Thus the majority of the intrinsic muscles were as closely related to force as the long flexors, suggesting a more important role in production of low isometric forces in the grip than previously believed, perhaps even a primary role. Systematic interindividual differences were rarely observed. Analysis of the trial-by-trial variability of EMG activity revealed that for most muscles the observed scatter was produced by varying background activity and was not a random fluctuation of relative increases in activity from one force level to the next.

Adult↗