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PubMedDate not supplied

Local venous lactate changes and spectral analysis of surface EMG during fatiguing isometric efforts in intrinsic hand muscles.

In this study relationships between local venous lactate concentrations and power spectrum changes in surface EMG due to fatiguing isometric contractions were investigated. Two different isometric efforts of the opponents pollicis muscle, 25% and 50% of maximum voluntary contraction, were examined. In 25% of maximum voluntary contraction no changes in local venous lactate were observed, whereas mean power frequency values of surface EMG shifted significantly towards lower frequencies. On the contrary, in 50% of maximum voluntary contraction lactate significantly increased and was related to the mean power frequency shifts of the surface EMG. These data suggest that lactate plays a role in muscle fatigue only in a limited intensity range of isometric muscle contractions.

Adult↗

PubMed1990

A technique for quantifying and determining the site of isometric muscle fatigue in the clinical setting.

We investigated a clinically applicable technique for quantifying and determining the site of fatigue during isometric contraction. We measured torque in the right knee extensors of 17 able-bodied subjects during an isometric contraction for 60sec at 100%, 75%, 50%, and 25% of maximal effort. During contractions, a 0.5-sec train of 50-Hz stimulation was applied at 15, 30, and 45sec. We measured the percent decline in force over 60 sec (fatigue index) and average augmentation in torque during stimulation (AVAUGTORQ). The mean fatigue index at full effort was 25.1%. The mean AVAUGTORQ at 100%, 75%, 50%, and 25% of maximal effort was 12.1%, 26.3%, 40.5%, and 69.7% of values at complete relaxation, respectively. These methods should be clinically useful for quantifying the level of isometric fatigue, determining the site of fatigue, and measuring the level of effort in subjects without neuromuscular disease. The results agree with previous studies reporting a peripheral site of fatigue in healthy, well-motivated subjects.

Adolescent↗

PubMed1990

Comparisons between surface electrodes and intramuscular wire electrodes in isometric and dynamic conditions.

The purpose of this study was to compare EMG surface electrodes (SE) and intramuscular wire electrodes (IWE) for isometric and dynamic contractions during an occupational cervico-brachial working task (OCWT). Six normal adult male subjects were tested on two days (two conditions with three trials each). Raw EMG signals from middle deltoid, anterior deltoid and trapezius muscles were recorded by both IWE and SE for two conditions (isometric and dynamic contractions). Full wave rectified and low pass filtered EMG, and integrated EMG were processed from raw EMG signals. The statistical analysis performed on the integrated EMG was a factorial analysis model with repeated measures. Statistical results confirmed that EMG signals, from both SE and IWE, are reliable between trials on the same day. These statistical results also confirmed that SE are more reliable than IWE on day-to-day investigations. Both electrodes recorded statistically similar signals, although the coefficient of variability between electrodes was very high (STDE%; 48% and 84%, for isometric and dynamic conditions respectively).

Adolescent↗

PubMed1990

[Cardiac effects of exhausting isometric muscular contraction in trained and endurance athletes].

The effect of exhausting isometric contraction (60% of the maximal voluntary contraction) on left ventricular function has been investigated using echocardiography (M and B mode) in 4 groups, each of 8 subjects (27 +/- 5 years; mean +/- SD): weight lifters, 2 years of training; amateur cyclists, 4 years of training; sedentary controls, and hypertensive subjects, 1st WHO class. Heart rate, arterial pressure, ventricular diameters (diastolic and systolic), wall thickness, wall stress and the double product (heart rate x arterial pressure) were determined at rest, at exhaustion and after 30, 90 and 180 s of recovery. Maximal voluntary contraction was 48 +/- 9 kg in weight lifters; 32 +/- 5 kg in amateur cyclists; 32 +/- 4 kg in sedentary control and 36 +/- 7 kg in 1st WHO class. Exhaustion time ranged from 80 s to 120 s. Our results showed that: 1) in all subjects at exhaustion, arterial pressure and heart rate increased significantly and the index of ventricular function was decreased but not significantly; 2) after 180 s of recovery both arterial pressure and heart rate returned to the pre-exercise value; 3) wall stress was significantly lower in weight lifters than in sedentary controls; 4) the double product (index of myocardiac oxygen consumption) resulted lower in amateur cyclists that in sedentary controls. The hypertrophy of the heart could justify the slight increase in wall stress observed in weight lifters during isometric exercise. However, the low index of myocardiac oxygen consumption in amateur cyclists probably reflects the changes in cardiovascular function due to the endurance training. In hypertensive subjects, the isometric contraction causes significant and substantial increase of the wall stress and the double product.

Adult↗

PubMed1989

[Effects of isometric exercise on left ventricular function assessed with polycardiography in patients with early type I diabetes].

15 patients with controlled type 1 diabetes lasting up to 24 months underwent the study. The control group consisted of 22 healthy men. Noninvasive examinations were carried out at rest and during a 3-minute isometric exercise of a load equal to 30% maximal effort. Rest systolic and diastolic blood pressures (SBP and DBP) were almost the same in both groups. Also exercise peak SBP and DBP did not significantly differ in examined groups. Rest PEP/LVET ratio were significantly lower in diabetics (means = 0.313 vs means = 0.348 in the control group; p less than 0.002). Peak isometric exercise PEP/LVET ratio significantly increased to 0.333 in diabetics, comparing with its rest value, whereas significantly decreased to 0.333 in the control group. Results indicate increased resting left ventricular contractility in patients with early, type 1 diabetes and impairment of a left ventricular adaptation for the isometric exercise in comparison with the control group.

Adult↗

PubMed1989

[The effect isometric exertion on left ventricular function in patients after myocardial infarct].

24 patients, after transmural cardiac infarction, were exposed to isometric exercise ("handgrip"). The haemodynamic response was checked by means of impedance plethysmography. The stroke volume decreased on average from 64 +/- 14 to 60 +/- 15 ml (p less than 0.05), cardiac output increased from 4.8 +/- 1.0 to 5.4 +/- 1.2 l/min. (p less than 0.01). Peripheral resistance significantly increased and left ventricular performance was non-significantly reduced. Compared with a group of healthy control, their stroke and cardiac output and cardiac work kept increasing during isometric exercise. Isometric exercise is an adequate means of checking left ventricular performance.

Blood Pressure↗

PubMed1989

[Effect of molsidomine preparations on the contractile function of the myocardium and coronary circulation in patients with ischemic heart disease complicated by heart failure after isometric load].

Isometric stress tests were conducted in 95 coronary patients and 15 normal subjects. Load tests were repeated 1 hr after a single dose administration and at the end of a two-week treatment course. Left-ventricular contractility was found to be impaired at isometric stress in 66.7% of patients showing no clinical signs of heart failure, and coronary insufficiency was detected in 44.1%. A single molsidomin dose reduced diastolic and systolic left-ventricular volume by an average of 10.9 and 13.3%, respectively. At repeated isometric stress after molsidomin administration, only 15.7% of patients showed ischemic ST displacement on the electrocardiogram. Eleven (32.4%) of 34 patients with early phases of heart failure showed increased ejection fraction and a higher myocardial fibre circular shortening rate (by 4.9 and 11.7%, respectively) during hand grip under molsidomin effect. Long-term treatment with molsidomin preparations produced general improvement in 84.4% of patients, as reflected in the reduction of the signs of heart failure as well as the rate and intensity of anginal attacks.

Administration, Oral↗

PubMedDate not supplied

Length-force characteristics of aponeurosis in passive muscle and during isometric and slow dynamic contractions of rat gastrocnemius muscle.

Length-force characteristics of aponeurosis of rat gastrocnemius medialis muscle and achilles tendon were studied for passive and active muscle. Active muscle performed isometric as well as slow concentric and eccentric contractions at low velocity. For isometric conditions, different aponeurosis and tendon length-force characteristics were found between passive and active muscle: At comparable low levels of force longer aponeuroses were encountered in passive than in active muscle. Similar results were found for achilles tendon, but the magnitude of the length change involved was smaller than for aponeurosis. For active muscle, no differences of aponeurosis length- force characteristics could be distinguished between the isometric contractions and a slow concentric contraction. Indications that such differences of aponeurosis length-force characteristics may exist between slow concentric and eccentric contractions were found. It is concluded that, for gastrocnemius medialis muscle, aponeurosis and tendon length - force characteristics may be quite variable depending on recent history of muscle length and activity.

Animals↗

PubMed1987

Isometric and isokinetic muscle strength in patients with fibrositis syndrome. New characteristics for a difficult definable category of patients.

A common complaint among patients with fibrositis syndrome is exhaustion and fatique. It was therefore felt desirable to evaluate the muscle strength of these patients compared with normal subjects. Maximum isometric and isokinetic strength of knee extension was measured in 15 patients and 15 healthy matched subjects, using an isokinetic dynamometer (Cybex II). Maximum isometric strength at various knee extension angles (90 degrees, 60 degrees and 30 degrees degrees) was significantly (p less than 0.001) lower in the fibrositis group than in controls, a reduction of approximately 58-66%. Maximum isokinetic strength at various knee extension velocities (30-240 degrees per second) was also significantly (p less than 0.01) lower in the fibrositis group than in controls, the reduction being approximately 41-51%. In conclusion, isometric and isokinetic muscle strength is found to be lower in patients with fibrositis syndrome than in healthy subjects.

Female↗

PubMed1987

Respiratory response and muscle function during isometric handgrip exercise at high altitude.

The purpose of this investigation was to determine if the hyperventilatory response to fatiguing isometric exercise at sea level could predict resting ventilation and acute mountain sickness (AMS) at 4300 m altitude. Exercise consisted of four successive endurance handgrips held to complete fatigue at 40% of maximum isometric handgrip strength (MHS). There was no relationship between the magnitude or pattern of exercise-induced hyperventilation at sea level and the severity of AMS later at altitude. Sea level hyperventilatory response was not predictive of resting ventilation at altitude. Altitude exposure progressively increased both the incidence and magnitude of the hyperventilatory response to exercise and prolonged it for 60-90 s into the recovery period, providing support for the "central command" theory of ventilatory control during isometric exercise. MHS was significantly increased at altitude--by 11% on day 2 and 16% on day 6. Endurance times to fatigue were reduced, but not always significantly so. A follow-up study involving more practice at sea level demonstrated MHS to be significantly increased throughout an entire 18-d stay at 4300 m and for 3, but not 5, days after descent. Significant changes in endurance could not be demonstrated. Neither AMS nor changes in body weight or circulating norepinephrine levels can account for the temporal pattern of increased grip strength, but the respiratory alkalosis occurring at altitude appears to be a likely mechanism.

Adult↗

PubMed1985

Work-rest periods: their effects on normal physiologic response to isometric and dynamic work.

Heart rate (HR) and blood pressure (BP) responses to repeated dynamic and combined dynamic and isometric work bouts of 30 sec, 2 min, and 6 min with equal rest periods at 40% and 80% of Vo2max was studied in five healthy men and five healthy women. Total work duration for each experimental condition was 24 min. The treadmill was used for dynamic work. Subjects pushed a bar horizontally while on the treadmill at 20% of their maximal voluntary strength for isometric work. Results showed that work performed at 40% of Vo2max in 30 sec bouts compared to 6 min bouts reduced HR, BP and the double product (BP X HR) by 11%, 4%, and 14%, respectively. Work performed at 80% of Vo2max in 30 sec bouts of repeated work or rest compared to the 6 min bouts resulted in reducing HR, BP, and double product 28%, 15%, and 39%, respectively. Addition of the isometric load did not significantly change the results. This study suggests that cardiac patients may be able to perform more work safely if it is carried out in short periods alternating with rest periods of equal duration.

Adult↗

PubMed1979

Increase of muscle strength from isometric quadriceps exercises at different knee angles.

Isometric quadriceps exercises were performed at two different knee angles, 15 and 60 degrees respectively. The maximal torque was measured in both positions before and after training in 10 healthy females. Both legs were exercised, one at each position. The purpose was to develop practical recommendations for choice of training position. The strength increase was mainly specific according to the angle at which the knee was exercised. It was suggested that isometric exercise would preferably be performed at different knee angles to secure an optimal total strength increase. Isometric exercises improved dynamic strength at a low velocity but not at a high velocity.

Adult↗

PubMed1979

[Effects of isometric exercise on the right ventricular function and on the pulmonary circulation, in normal subjects (author's transl)].

The pulmonary circulatory response and right ventricular haemodynamics were assessed in normal subjects who sustained hand-grip exercise (HG) at 50% of the maximum voluntary contraction (M.V.C.) for 3 minutes. Ten normal subjects, aged 25 to 66 years, who underwent full right catheterization were studied. The following parameters were taken into consideration: heart rate (HR), end diastolic right ventricular pressure (EDRVP) end diastolic right ventricular volume (EDRVV), mean pulmonary arterial pressure (PAP), pulmonary wedge pressure (PWP), total pulmonary resistance (TPR), cardiac output (CO) and right ventricular sistolic work minute index (RVSWMI). These data were obtained by means of a tip-micromanometer connected with an polygraphic recorder and by means of thermodilution cardiac output computer. The statistical significance of the difference between the resting control values and those after isometric exercise was calculated with the Student's paired t test. A comparison of the control data with those obtained after isometric exercise, demonstrate a statistical significant (p less than 0,001) increase of the HR, PAP, PWP, TRP, CO, RVSWMI, a less significant (p less than 0.01) increase RVEDP. Our findings show that the HG causes changes in the pulmonary circulation and the right ventricular function. Our data seem to sustain that the pulmonary circulation respondes differently under isometric stress than it does under isotonic stress. The use of HG can thus be postulated as a useful means of evaluation of the response of the pulmonary circulation and right ventricular function.

Adult↗

PubMed1984

Reliability of isometric strength testing. Temporal factors and strength variation.

Isometric strength measurements of grip, pronation, supination, and elbow extension and flexion on dominant and nondominant sides were made on 40 normal subjects (age range, 40-70 years) to investigate the variability of isometric strength at different times of the day. Statistically significant differences were found in certain pronation, supination, and grip comparisons. No statistically significant difference was found in extension and flexion. Although significant, the absolute change in strength at different times of the day was small and showed no consistent trend. On the basis of these data, it appears that this variation can probably not be routinely detected in the normal clinical setting. However, the study further defines the reliability of isometric strength testing and should be considered in further attempts at more accurate measurement of elbow function. The small variations of strength, approximately 5%, that can be measured universally with sensitive testing equipment, are clinically relevant. However, when attempting to determine an impairment state in order not to place too much importance on small differences, care should be exercised in interpreting strength measurements. This investigation demonstrates how the application of sophisticated biomechanical techniques may be employed to provide useful objective information in the difficult clinical area of disability assessment. Disability judgments may be made more accurate as more is learned of the normal variables influencing objective measurement.

Adult↗

PubMed1984

[Changes in hemodynamics during isometric loading in healthy subjects].

The hemodynamic response and changes in myocardial contractility during leg isometric exercise with maximal exertion were studied in 30 healthy males. The exercise lasted for 6 to 8 minutes. An analysis of the results showed that the major cause of the increased arterial pressure was an increase in the stroke volume, with the systemic vascular resistance being virtually unaltered. An increased myocardial contractility was shown to be largely responsible for the elevation and the maintenance of the stroke volume at a high level. The prolongation of the sustained isometric exercise was attended by some decrease in the heart rate as compared with the first minutes and the involvement of Frank-Starling mechanism which maintains the stroke volume at the adequate level. The above isometric exercise was associated with no complications, which allows us to consider it safe for patients with heart diseases.

Adult↗

PubMed1984

[Changes in hemodynamics during isometric loading in ischemic heart disease].

The hemodynamics and contractility of the myocardium were investigated in 38 men with coronary heart disease using maximal leg isometric load. It was shown that the systemic response to the isometric load in CHD patients unlike in normal subjects was mediated through increased total peripheral resistance rather than through an increase in myocardial contractility and stroke volume. The degree of these changes corresponded to the exercise tolerance as determined by bicycle ergometry. Leg isometric load is an accessible method for evaluating myocardial contractility in CHD which makes it possible to detect its disorders at the earliest stages in functional class I patients.

Adult↗

PubMed1984

[Value of the isometric exercise test in objectively evaluating the effectiveness of hyperbaric oxygenation in ischemic heart disease].

The isometric test was conducted prior to and after a hyperbaric oxygenation (HBO) session in 31 coronary heart disease (CHD) patients. The results were compared with the findings provided by the examination of 138 coronary patients and 23 normal subjects receiving no HBO treatment. It was shown that the isometric test makes it possible to objectively assess the HBO effect in CHD patients. The results of the test reflect reduction in the severity of angina pectoris or cardiac failure following hyperbarotherpy. The results obtained justify the recommendation of the isometric test for the individual evaluation of the hyperbaric treatment in CHD.

Adult↗

PubMed1980

[Changes in left ventricular function induced by isometric exercise in coronary disease].

The effects of isometric exercise on left ventricular function in 16 patients with chronic coronary heart disease were assessed by measuring left ventricular pressures and volumes under basal conditions and during a sustained effort of 2 minutes 30 seconds at 50% of the maximal effort. In 7 patients (Group I) with abnormal elevation of left ventricular end diastolic pressure (LVEDP) (over 4 mmHg) the end diastolic volume remained unchanged and the diastolic pressure-volume curve was displaced upwards. The ejection fraction fell together with the percentage filling during the first part of diastole with 50% filling occurring after 61% instead of 45% of diastole. The time constant T also increased showing abnormal relaxation. In 9 patients without abnormal elevation of LVEDP on exercise no changes in the other parameters studies were observed. Our results show that pathological elevation of LVEDP during isometric exercise is associated with a decreased ejection fraction and an abnormality of left ventricular relaxation with a reduced rate of filling during protodiastole and an upward displacement of the diastolic pressure-volume curve. The LVEDP alone is therefore an important index of the haemodynamic behaviour of the left ventricle during isometric exercise.

Coronary Disease↗