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PubMed1992

[Reconstructive interventions of the posterior cruciate ligament--experimental studies of isometric aspects. Part I: Studies of a string model].

In six intact cadaveric knees, we measured how the distance between six selected points in and around the femoral and tibial attachment area of the posterior cruciate ligament (PCL) changes with knee flexion. After complete removal of the PCL, 2-mm drill holes were made at the selected points. Each femoral point was measured against each tibial point using a heavy suture that was passed through the drill holes. The proximal end of the suture was fixed to the lateral aspect of the femur. The distal end of the suture was attached to a measuring unit. The changes in femorotibial distance were measured during flexion from 0 degrees to 110 degrees in 10 degrees steps. The tibial drill hole locations had only a minor effect on the changes in femorotibial distance. The most isometric point was located in the centre of the posterior intercondylar area. The femoral locations of the drill holes were the primary determinant of whether the distance increased, decreased or remained nearly constant. According to our results the most isometric femoral point is located at the posterosuperior margin of the anatomical PCL attachment. Using the tibial isometric point as a reference, the femoral points positioned anterior or posterior to the isometric point produced considerable changes in the femorotibial distance upon knee flexion. The anterior point led to an increase of about 7-8 mm at 110 degrees of flexion, the posterior point to a decrease of the same extent. Much smaller changes in femorotibial distance resulted from the points located superior or inferior to the femoral isometric point.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed2006

The reliability of isokinetic and isometric leg strength measures among individuals with symptoms of mild osteoarthritis.

AIM: The aim of the study is to evaluate the test-retest reliability of measures of isokinetic and isometric leg strength and joint function among individuals exhibiting symptoms of mild osteoarthritis. Reliable procedures are needed to assess the effectiveness of an intervention on osteoarthritic symptoms. METHODS: Test-retest reliability of two leg strength protocols was assessed using the intraclass correlation coefficient (R). Testing was completed on two occasions separated by 7 days. Eighteen subjects (9 male and 9 female; 54.1+/-11 years) completed an isokinetic testing trial, which consisted of a set of 5 maximal repetitions of the quadriceps and hamstrings at 60 deg/s followed by a set of 15 maximal contractions at 180 deg/s with a 2-min rest between sets and an isometric testing trial, which consist of 3 maximal contractions of the quadriceps for 6 s with a 30-s rest between contractions at 30, 45, and 80 degrees of knee flexion for a total of 9 isometric contractions. A 90-s rest occurred between angles. RESULTS: Most of the isokinetic variables showed moderate to high intraclass reliability (ICC). Two of the calculated isokinetic variables (work fatigue at 180 degrees /s for extension and for flexion) showed low intraclass reliability (ICC=0.78, resp. ICC=0.6). All calculated ICC values of the isometric variables were moderate to high. CONCLUSIONS: Test-retest reliability of isokinetic and isometric leg strength was high, allowing the intervention protocol to monitor changes in leg strength and joint function among those exhibiting symptoms of mild osteoarthritis.

Biomechanical Phenomena↗

PubMed1990

The relationship between ATPase activity, isometric force, and myosin light-chain phosphorylation and thiophosphorylation in skinned smooth muscle fiber bundles from chicken gizzard.

Isometric force developed by skinned gizzard muscle fiber bundles and levels of phosphorylation and thiophosphorylation of the 20,000-dalton myosin light chain were determined. These data showed a highly non-linear relationship between isometric force and myosin light-chain phosphorylation. Maximum force was developed at approximately 0.2 mol of phosphate/mol of light chain as reported previously (Hoar, P. E., Kerrick, W. G. L., and Cassidy, P. S. (1979) Science 204, 503-506). In contrast, the relationship between isometric force and myosin light-chain thiophosphorylation was linear, with maximum force occurring at 1.0 mol of thiophosphate/mol of myosin light chain. These observations are consistent with the latch-bridge hypothesis for conditions of varying myosin light-chain phosphatase/myosin light-chain kinase activity ratios as discussed by Hai and Murphy [1988) Am. J. Physiol. 254, C99-C106). To further test the latch-bridge hypothesis, ATPase activity was also measured during isometric force development in these fiber bundles. The relationship between isometric force and ATPase activity was linear whether the myosin light chains were phosphorylated or thiophosphorylated. Thus the number of cycling myosin cross-bridges, as measured by ATPase activity, was directly proportional to the force the muscle developed, not to the level of myosin light-chain phosphorylation. This finding that high levels of tension generated at low levels of light-chain phosphorylation are associated with high levels of ATPase activity is inconsistent with the latch-bridge model (Hai and Murphy, 1988).

Adenosine Triphosphatases↗

PubMed1989

The stability of isometric trunk flexion measurements.

The purpose of this study was to determine (a) the number of isometric trunk flexions needed to obtain a stable measure of exertion, (b) the least variable parameter to be used to quantify maximum isometric trunk flexion, and (c) the time interval needed to obtain the least variable measure of maximum isometric flexion. Ten adult males served as subjects. Each subject performed five trials of one maximum isometric trunk flexion. Each trial lasted for 5 s. The results showed (a) only one trial is required to obtain a stable measure of the maximum torque generated during isometric flexion, (b) more than one trial is required to obtain a stable measure of the average torques, (c) maximum torques are more stable measures than average torques, (d) the first second of a 5-s exertion does not yield stable measurements, and (e) individuals adopt different exertion strategies during each trial.

Adult↗

PubMed1989

Isometric and isokinetic knee extension and flexion torque in men and women aged 20-70.

An investigation was made of the influence of age and sex on peak muscle torque in knee extension and flexion during maximal isokinetic and isometric contraction. The study was performed on both legs of 139 clinically healthy men and 141 clinically healthy women aged 20, 30, 40, 50, 60 or 70 years. Maximum knee extension and flexion muscle torque (Newtonmetre, Nm) was measured isokinetically at various angles of velocity (12, 90 and 150 degrees/s) and isometrically under standardized conditions (Cybex II). No significant differences were found between the right and the left leg in the whole material. Muscle torque was higher in men than in women in all age groups (p less than 0.001). Both isokinetic and isometric torque decreased with age in both sexes. Isokinetic torque decreased significantly (p less than 0.05) between 20 and 30 years of age in men and between 40 and 50 years of age in women (at all velocities studied; p less than 0.05). A significant decrease (p less than 0.05) was found between the ages of 60 and 70 years in both sexes. Maximum isometric torque showed a significant decrease (p less than 0.05) between 60 and 70 years in men and women. There were no significant differences in isokinetic or isometric torque between moderately active and inactive men or women. Significant correlations were found between muscle torque and body weight, height and body surface area.

Adult↗

PubMed1985

Discharge characteristics of motor units and the surface EMG during fatiguing isometric contractions at submaximal tensions.

The RMS amplitude of the surface electromyogram (EMG) and the frequency of discharge of motor units was examined throughout the duration of isometric contractions of the adductor pollicis muscles sustained to fatigue at tensions of 25, 40, and 55% of the maximum voluntary strength (MVC) of eight male subjects during fatiguing isometric contractions. The maximum strength of the muscle and the EMG above the adductor pollicis muscles was also assessed during 3 s of voluntary and electrically induced isometric contractions interposed at 25, 50, 75, and 100% of the duration of the fatiguing contractions. At the point of fatigue from submaximal isometric contractions, the RMS amplitude of the surface EMG was highest for contractions at 55 as compared to 40 and 25% MVC. The lower RMS amplitude of the EMG during contractions at lower as compared to higher tensions at the point of fatigue was paralleled by a lower discharge frequency of the alpha motor neurons in the fatigued muscle during contractions at 25% as compared to 40 and 70% MVC. The reduction in discharge frequency was probably of a sufficient order of magnitude to account for the lower amplitude of the EMG at the end of fatiguing isometric contractions at lower tensions.

Aerospace Medicine↗

PubMed1988

Antihypertensive therapy and cardiovascular reactivity during isometric stress.

The cardiovascular reactivity to isometric stress test before and after antihypertensive therapy was evaluated by invasive haemodynamic techniques in 23 patients with mild to moderate essential hypertension. A beta-blocking agent (atenolol 50 to 100 mg daily) was given to 11 patients; 12 patients received calcium entry blockers (diltiazem 240 to 360 mg daily or verapamil 240 to 480 mg per day). The pressor response to isometric stress before therapy consisted of an increase in systolic, diastolic, and mean arterial pressure (all P less than 0.01) that was similar in both treatment groups. The rise in arterial pressure was mainly due to an increase in cardiac output (P less than 0.01), as total peripheral resistance did not change significantly. After treatment with the beta-blocker, the increase in total peripheral resistance during isometric stress was exaggerated (P less than 0.01), and, conversely, the increase in cardiac output was attenuated (P less than 0.01). In contrast, treatment with calcium entry blockers preserved the haemodynamic reactivity pattern of the untreated state: arterial pressure increased during isometric stress through an increase in cardiac output, while total peripheral resistance remained unchanged. Since the haemodynamic culprit of essential hypertension is an elevated peripheral resistance, a drug that numerically increases this culprit under conditions of resting and isometric stress becomes less attractive than one that lowers peripheral resistance and preserves the physiologic response pattern.

Adult↗

PubMed1988

Relationship between smooth muscle volume and contractile response in airway tissue. Isometric versus isotonic measurement.

Two different methods of recording contractile response (isometric and isotonic) were used in both spirally cut and intact ring preparations of rabbit airways. The volume of smooth muscle in each airway preparation was compared with the amount of contraction induced by histamine and carbachol. There were significant relationships between smooth muscle volume and carbachol-induced contraction measured isometrically in spiral and ring preparations. There also was a significant relationship between the proportion of airway smooth muscle and the histamine-induced contraction measured isometrically on ring preparations. There were no significant relationships between smooth muscle volume or proportion of airway smooth muscle and the carbachol or histamine contraction measured isotonically. It is concluded that isometric measurements may provide a more accurate representation of smooth muscle changes in response to agonists in vitro. This may indicate that hyper-responsiveness of airway smooth muscle in vitro is more likely to be detected by isometric rather than isotonic measurements.

Animals↗

PubMed1987

Muscle exercise after anterior cruciate ligament reconstruction. Biomechanics of the simultaneous isometric contraction method of the quadriceps and the hamstrings.

Biomechanical analysis of two-dimensional models composed from roentgenographic pictures and electromyographic analysis on simultaneous isometric contraction exercises of the quadriceps and hamstrings were conducted in 20 healthy adult males. During simultaneous isometric contraction at 5 degrees knee flexion, an anterior drawer force equivalent to 15% of the tension of the quadriceps was exerted to the tibia, and decreased with increased angle of flexion. The mean angle at which this force became zero was 7.4 degrees, with a standard deviation of 5.0 degrees. When the angle increased further, a posterior drawer force to the tibia occurred and gradually increased. Each tension of the quadriceps or hamstrings during maximum simultaneous isometric contraction of the quadriceps and hamstrings was estimated as 30%-60% of that during separate isometric contractions of each muscle. In the early stage of the rehabilitation after the anterior cruciate ligament reconstruction, the simultaneous isometric contraction of the quadriceps and the hamstrings is useful as one of the muscle exercise methods because it can be performed safely with the knee position near the full extension and can generate sufficient muscle force to be an effective exercise.

Adult↗

PubMed1987

Exercise after anterior cruciate ligament reconstruction. The force exerted on the tibia by the separate isometric contractions of the quadriceps or the hamstrings.

The anterior or posterior drawer force exerted on the tibia by the separate isometric contractions of the quadriceps or hamstrings at various angles of knee flexion was examined in 20 healthy males. A two-dimensional model was analyzed using roentgenographic films. In separate isometric contractions of the quadriceps, the mean value of the anterior drawer force was equivalent to 14% of the tension of the quadriceps at 5 degrees knee flexion. The value decreased with the increase in the angle of knee flexion. The mean angle at which the anterior drawer force became zero was 45.3 degrees +/- 12.5 degrees. When the angle was increased further, the posterior drawer force gradually increased. In separate isometric contractions of the hamstrings, the posterior drawer force was exerted at all angles of flexion. Thus, during the early stage of rehabilitation after the anterior cruciate ligament injury, the quadriceps exercise by isometric muscle contraction should be performed with the knee flexion at more than 70 degrees (mean +/- 1.96). Exercise of the hamstrings by isometric muscle contractions can be carried out regardless of flexion angle.

Adult↗

PubMed1986

[Importance of isometric training in the rehabilitation of myocardial infarct patients].

A method of isometric exercise was developed for myocardial infarction patients, and its efficiency was evaluated in the course of rehabilitation after acute myocardial infarction in 48 patients aged 39 to 57 years. The trained patients showed significantly increased tolerance to arm and leg isometric exercise and better systemic hemodynamic response to isometric exercise, manifested in a lower cost of one isometric tension unit, and increased minute blood volume, a result of increased stroke volume. It is concluded that isometric exercise has a favorable effect on cardiovascular function and physical working capacity of postmyocardial-infarction patients.

Adult↗

PubMed1985

[Effect of beta-receptor block on QT/QS2 behavior during isometric and dynamic exercise].

Our study is aimed to evaluate the change of QT/QS2 ratio in normal subjects during both isometric and dynamic exercise before and after propranolol administration. We studied 10 young volunteers healthy subjects who performed an isometric exercise by squeezing a grip dynamometer at 70% of their maximal voluntary contraction as long as possible. They also performed a dynamic exercise undergoing a submaximal bicycle stress test. Both tests were performed before and after administration of propranolol (0.15 mg/Kg e.v.) QT and QS2 intervals were measured at rest, during exercise and in the recovery period. Heart rate and blood pressure were also determined. Isometric exercise induces a significant shortening of both intervals although minor for QT so that the ratio significantly increases in comparison to baseline (p less than .001). At rest propranolol induces a significant decrease of heart rate and only a slight lengthening of QT and QS2 so that the ratio is unchanged. During exercise propranolol does not influence the increase of heart rate and blood pressure and the shortening of QT interval but prevent exercise-induced QS2 shortening so that the ratio after beta-blockade is significantly reduced at the peak of exercise (p less than .005). During dynamic exercise QT and QS2 behaviour is similar to that of isometric exercise; in fact both intervals are shortened and QS2 decrease is major than QT so that the ratio increases (p less than .001). These results confirm that QT/QS2 ratio can monitor the effects of adrenergic stimulation on the heart during physiological manoeuvres enhancing sympathetic discharge like occurs during both isometric and dynamic exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1981

Cardiovascular responses to handgrip isometric exercise in patients following cardiac transplantation.

The effects of cardiac denervation on the hemodynamic responses to isometric handgrip contraction were studied in patients 1--5 years after allograft cardiac transplantation. The objective of these studies was to determine the role of cardioacceleration and myocardial contractility on the increase in systemic arterial pressure during isometric exercise. Initially, noninvasive measurement of brachial artery pressure and heart rate during 60 seconds of isometric exercise at 50% of maximal voluntary contraction (50% MVC) were recorded in 23 cardiac transplant patients, 18 ischemic heart disease patients, and 15 healthy controls. While the increases in arterial pressure were not significantly different among the three groups and the heart rate response for the healthy controls and ischemic heart disease patients were similar, the transplant patient's heart rate remained essentially unchanged. In an attempt to determine the mechanisms for the increase in arterial pressure, despite any increase in heart rate in transplant patients, we recorded left ventricular volumes before and at the end of 50% MVC using fluoroscopy of tantalum midwall myocardial markers in seven cardiac transplant recipients and seven nontransplant cardiac surgery patients. The rise in arterial pressure during isometric exercise in both groups of patients resulted from a significant increase in peripheral vascular resistance but not in stroke volume or cardiac output. These data demonstrate that the rise in arterial pressure observed during isometric exercise can be achieved by increased peripheral vascular resistance alone in patients who lack the capacity to increase heart rate or stroke volume.

Adolescent↗

PubMed1994

[The behavior of central and peripheral hemodynamics in isometric and dynamic stress in hypertensive patients treatment with regular sauna therapy].

Effective treatment of hypertension includes decrease of blood pressure at rest, dynamic and isometric exercise. Therefore, we investigated the hemodynamic changes by radiocardiography (central hemodynamic) and Xenon-133-muscle clearance (peripheral hemodynamic) before and after a sauna treatment during a period of 3 months. 46 hypertensive men (WHO I-II, aged 41 +/- 11 years) participated in the study. Systolic and diastolic blood pressure at rest and during dynamic exercise were decreased significantly (p < or = 0.01) by sauna therapy. Change of blood pressure at isometric exercise was not significant (from 157.5 +/- 16.5 mmHg to 155.0 +/- 15.4 mmHg). The changes of cardiac output and total peripheral resistance were also not significant. Half-time of muscle clearance decreased significantly (from 4.4 +/- 1.9 min to 3.2 +/- 1.2 min, p < or = 0.01) and functional cross-section A increased significantly (from 3.8 +/- 0.9 mm2.c to 4.4 +/- 0.9 mm2.c, p < or = 0.01) after the sauna therapy at dynamic exercise, but not at isometric exercise. These results show the changes between isometric and dynamic exercise, which can only be explained well by a study of peripheral hemodynamic. Contrary to dynamic exercise, sauna therapy did not significantly decrease blood pressure at isometric exercise.

Adult↗

PubMedDate not supplied

Inhibition of EMG activity in isometrically loaded agonist muscle preceding a rapid contraction.

It was recently suggested that a premotion silent period in isometrically loaded agonist muscle reflects transition process in switching motor program from an isometric to an isotonic condition. To test this hypothesis we investigated changes in EMG activity of a biceps muscle during motor preparatory phase in an entirely isometric paradigm. Five healthy volunteers produced rapid isometric elbow flexions superimposed on a slightly sustained contraction during self-paced and reaction time conditions. In addition to surface EMG, single motor units were recorded in agonist muscle prior to a rapid contraction. Silent period was found in responses of three out of five subjects, whereas inhibition of some but not all tonically active motor units was observed in all studied subjects prior to the phasic EMG burst. Inhibition of motor unit activity occurred more often in self-paced than reaction time contractions. Our results indicate that inhibition is not always powerful enough to produce a complete electrical silence, and weaker inhibitory effects were observed as a declining number of firing motor units. We conclude that the silent period or depression of the EMG activity is associated with changes in motor program from tonic to phasic muscle activation and is not merely a consequence of changes from an isometric to an isotonic condition.

Action Potentials↗

PubMedDate not supplied

Muscle activation and force production during bilateral and unilateral concentric and isometric contractions of the knee extensors in men and women at different ages.

In experiment I ten young men (29 +/- 3 yrs; M30), 12 middle-aged men (50 +/- 4 yrs; M50) and 12 women (48 +/- 5 yrs; W50), 12 elderly men (67 +/- 4 yrs; M70) and 12 women (68 +/- 4 yrs; W70) volunteered for subjects for examination of maximal 1 RM strength and electromyographic activity of the knee extensor muscles during the bilateral and unilateral concentric contraction on a variable resistance knee extension dynamometer. In experiment II 10 young (Y) men (29 +/- 5 yrs) and 10 older (O) men (61 +/- 4 yrs) were examined for their maximal voluntary isometric force and force-time curves and electromyographic activity of the knee extensor muscles during the bilateral and unilateral contractions. The bilateral 1 RM of 165.5 +/- 25.5 kg in M30 was greater (p < 0.01) than that of 127.7 +/- 24.5 kg recorded for M50 the latter being also greater (p < 0.05) than that of 109.0 +/- 17.7 kg recorded for M70. The bilateral value of 87.4 +/- 13.4 kg in W50 was greater (p < 0.05) than that of 69.9 +/- 15.0 kg recorded for W70. The bilateral 1 RM values were slightly greater than the summed unilateral 1 RM values in all groups M50, W50 and W70 showing a significant (p < 0.05) difference. All groups showed slightly (ns.) greater mean maximal integrated EMG values during the bilateral conditions in comparison to that of the corresponding unilateral condition. The maximal isometric forces in Y men were 25% greater (p < 0.001) than in O men. In both groups the bilateral forces were somewhat greater (p < 0.05) than the summed unilateral forces and the bilateral IEMG values slightly (ns.) greater than the corresponding unilateral IEMG values. The early forces on the force-time curve were much greater (p < 0.05-0.001) in Y than O men in both conditions. The present findings suggest that both maximal voluntary isometric and concentric force, and especially explosive strength of the knee extensors decrease greatly with increasing age probably due to selective muscle atrophy and/or possible decreases in the amount or rate of voluntary activation of the muscles. However, no bilateral deficit could be found indicating that the central nervous system in a simple single joint isometric and maximal 1 RM concentric force production of the knee extensors was capable of activation of the two bilateral muscle groups simultaneously independent of age and sex of the subject. To which extent the activation and force production of the muscles would be different in terms of the bilateral deficit during various multijoint exercises utilizing isometric and higher velocity concentric, eccentric and various stretch shortening cycle exercise needs to be examined in the future.

Adult↗

PubMed1985

Regulation of isometric force and isotonic shortening velocity by phosphorylation of the 20,000 dalton myosin light chain of rat uterine smooth muscle.

The regulation of isometric force maintenance and isotonic shortening velocity by phosphorylation of the 20,000 dalton light chain of myosin has been examined for potassium-depolarized rat uterine smooth muscle. Following a transient peak in myosin light chain (LC20) phosphorylation at 20 s of contraction (0.46 mol PO4/mol LC20), phosphorylation declined to a steady-state by 2 min (0.28 mol PO4/mol LC20) with no significant change from 2-90 min of contraction. Isometric force developed more slowly, reaching a maximum at 2 min with no further change out to 90 min. Lightly-loaded (0.1 F0) shortening velocity, like LC20 phosphorylation, increased initially to a peak of 0.034 L0/s at 20 s of contraction and then declined to 0.023 L0/s by 2 min. However, unlike LC20 phosphorylation and isometric force, shortening velocity decreased approximately 4-fold from 0.023 L0/s at 2 min to 0.006 L0/s at 90 min of contraction. Graded activation with reduced extracellular calcium was associated with proportional changes in steady-state isometric force and LC20 phosphorylation. Shortening velocity was also decreased with reduced calcium, however, unlike LC20 phosphorylation, the greatest changes in velocity occurred at low levels of developed force. Moreover, in contrast to the large reductions in shortening velocity observed during 90 min contractions where force and LC20 phosphorylation were unchanged, similar reductions in shortening velocity did not occur with graded activation in spite of significant (greater than 3-fold) decreases in both force and LC20 phosphorylation. These results suggest that factors other than light chain phosphorylation are involved in the regulation of isotonic shortening velocity during extended isometric contractions of uterine smooth muscle.

Animals↗

PubMed1989

Effect of isometric exercise on cardiac performance and mitral regurgitation in patients with severe congestive heart failure.

Left ventricular performance was studied during isometric exercise in 17 patients with severe congestive heart failure, combining invasive hemodynamic and echo-Doppler techniques. Isometric exercise at 30% of maximum resulted in a decrease in stroke volume index (27.4 +/- 7.1 to 22.7 +/- 7.4 ml/m2), with a significant increase in heart rate from 81 +/- 10 to 92 +/- 14 beats/min and in systemic vascular resistance from 1827 +/- 527 to 2372 +/- 737 dyne.sec.cm-5. A significant rise in pulmonary capillary wedge pressure (18 +/- 9 to 31 +/- 10 mm Hg) was associated with a marked increase in mitral regurgitant volume (14 +/- 11 to 27 +/- 15 ml), calculated as the difference between total stroke volume obtained by two-dimensional echocardiography and forward stroke volume measured by pulsed Doppler at the aortic anulus. During isometric exercise, left ventricular end-diastolic and end-systolic volumes did not change markedly, but the total stroke volume tended to increase from 62 +/- 13 to 67 +/- 13 ml. The increase in mitral regurgitant volume induced by isometric exercise was correlated with the fall in forward stroke volume (r = 0.7, p less than 0.01). Thus a rise in systemic arterial pressure induced by isometric exercise is associated with a decrease in cardiac performance attributable to redistribution of total left ventricular output with an increase in mitral regurgitation and a simultaneous decrease in forward cardiac output.

Aged↗