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PubMed1981

Intravenous dipyridamole combined with isometric handgrip for near maximal acute increase in coronary flow in patients with coronary artery disease.

Twenty-four patients with coronary artery disease were studied during cardiac catheterization to determine the effects of sustained isometric handgrip exercise and intravenous dipyridamole and their combination on coronary and systemic hemodynamics and measured coronary luminal caliber. During 4 to 5 minutes of 25 percent maximal handgrip, blood pressure and heart rate increased 24 and 19 percent, respectively, coronary sinus flow increased to 1.7 x baseline value, and epicardial coronary arteries constricted to increase predicted flow resistance by 40 percent in 36 diseased arterial segments. After a 4 minute intravenous infusion of dipyridamole (0.56 mg/kg body weight), systemic pressure decreased 8 percent, heart rate increased 23 percent, coronary sinus flow increased to 2.4 x baseline value and coronary luminal caliber was unchanged. During isometric handgrip initiated 6 minutes after the infusion of dipyridamole, systemic pressure and heart rate increased to 14 and 31 percent, respectively, above control values, coronary sinus flow increased to 3.3 x baseline value (3.8 x baseline value in patients with normal anterior perfusion) and stenotic flow resistance increased by 36 percent. The response of coronary flow to the combined stresses was 68 percent greater than the response to dipyridamole alone (p less than 0.02); these flow levels exceed values previously reported for the human coronary circulation. Aminophylline plus nitroglycerin appears to assure patient safety.

Acute Disease↗

PubMed1981

Coronary sinus blood flow at rest and during isometric exercise in patients with aortic valve disease. Mechanism of angina pectoris in presence of normal coronary arteries.

In 46 patients with aortic valve disease, coronary sinus blood flow was measured using a continuous thermodilution method both at rest and during isometric handgrip exercise. All patients had normal coronary angiograms. The patients were separated into three groups: Group I, 12 patients with aortic stenosis (systolic gradient 72 +/- 12 mm Hg); Group II, 15 patients with both aortic stenosis and regurgitation; Group III, 19 patients with aortic regurgitation. At rest, the coronary sinus blood flow was two to three times normal. However, when corrected for left ventricular mass (ml/100 g), flow was within normal limits. The ratio diastolic pressure-time index/systolic pressure-time index (DPTI/SPTI) was decreased in all three groups at rest. During isometric exercise, coronary sinus blood flow increased significantly: by 60 percent in Group I, by 88 percent in Group II and by 118 percent in Group III. There was a significant reduction of the DPTI/SPTI ratio. Of the 18 patients with angina on effort during the test, 7 were in Group I, 6 in Group II and 5 in Group III. There were no differences in the coronary sinus blood flow between the patients with angina and those who were pain-free, either at rest or during exercise. Angina pectoris does not appear to be caused by a failure of coronary blood flow to increase. There was no discrepancy between myocardial demand, as measured by the pressure-time index and coronary blood flow. However, the DPTI/SPTI ratio was significantly lower during exercise in the patients with angina than in those who were pain-free. Underperfusion of the subendocardial muscle seems to be a causative factor in the patients with angina.

Angina Pectoris↗

PubMed1984

Effect of coronary artery bypass grafting on left ventricular response to isometric exercise.

The left ventricular (LV) response to isometric exercise was evaluated in 20 patients who performed handgrip exercise tests before and 3 months after coronary artery bypass grafting. Preoperative LV ejection fraction (EF) decreased during the handgrip test from 0.57 +/- 0.08 to 0.49 +/- 0.09 (p less than 0.001); the ratio between the LV peak systolic pressure (PSP) and end-systolic volume index (ESVI) did not change. In 12 patients with patent grafts, the LVEF after operation did not change (0.54 +/- 0.06 at rest and 0.56 +/- 0.06 during handgrip exercise) and PSP/ESVI ratio increased from 4.5 +/- 1.5 to 5.6 +/- 2.1 mm Hg/ml X m-2 (p less than 0.001) during exercise. In 8 patients with occluded grafts, the LVEF after operation decreased from 0.56 +/- 0.10 to 0.48 +/- 0.06 (p less than 0.02), whereas PSP/ESVI did not change during handgrip exercise. Thus, the LV response to isometric handgrip exercise appears to improve after coronary artery bypass grafting in patients with patent grafts, but not in patients with 1 or more occluded grafts.

Adult↗

PubMed1984

Effects of topical cooling on isometric contractions of the human masseter muscle.

Six adult males performed tooth clenching for 10 and 80 s at maximum voluntary contraction strength (MVC). Motor activity in the right and left masseter muscles was monitored by surface electromyography. Local temperatures of both cheeks were monitored by a thermocouple. MVC activity for 80 s induced pain and fatigue in both muscles; 10 s of clenching caused no muscle discomfort. Ice, subsequently applied to the right cheek for 30 min, lowered the temperature of the cheek and masseter muscle. The isometric MVC exercises were then repeated. During 10 s of isometric contraction, MVC motor activity in the cooled masseter muscle was significantly increased by 29 per cent; that of the non-cooled contralateral muscle was insignificantly reduced by 12 per cent. During 80 s of clenching, MVC motor activity in the cooled muscle was significantly increased by 30 per cent; that of the non-cooled muscle was insignificantly reduced by 4 per cent. MVC activity for 80 s by the cooled muscle caused no pain and fatigue, but the discomforts continued in the non-cooled muscle. Increased MVC alpha motor activity in the cooled masseter muscle might have resulted from motor facilitation that was mediated by cutaneous, muscular or mucosal cold receptors, or it might have been due to the absence of pain and fatigue.

Adult↗

PubMed1988

Analysis of electromyographic signals in human jaw closing muscles at various isometric force levels.

The effect of sustained isometric contraction on surface electromyograph (EMG) and force signals derived from these muscles was examined. Premolar-molar region force was measured with a small unilaterally positioned force transducer. Subjects produced and sustained 25, 50, 75 and 100 per cent isometric force levels, and measurements were made at the beginning and end of these efforts. There was no significant change in the resulting EMG/force ratio at any of the force levels. The EMG signal did exhibit a significant shift in its frequency both as the force level increased and during the sustained effort. Neuromuscular fatigue, when defined as a change in the EMG/force ratio, was not demonstrated even though there was a consistent change in the frequency of the EMG signal.

Adult↗

PubMed1989

Comparison of 133Xe clearance and laser Doppler flowmetry in assessment of blood flow changes in human masseter muscle induced by isometric contraction.

Changes induced by 30 s of isometric contraction at 10% and 50% of the maximum voluntary contraction were assessed in 10 healthy subjects; there was a median increase of 1.8 and 0.3 times in 133Xe clearance and 5.3 and 2.7 times in laser Doppler flowmetry. In the first minute after 10% maximum voluntary contraction, 133Xe clearance increased 12.1 times in relation to the initial resting level, and flowmetry values decreased to become 3.5 times higher than the basal flow; corresponding values after 50% maximum voluntary contraction were 24.3 times and 3.7 times. From the second minute after contraction, there was a rapid decrease in 133Xe clearance and a slow decrease in flowmetry values. Five minutes after biting at 10% maximum voluntary contraction, both methods showed a total net increase of about 15 times; after biting at 50% maximum voluntary contraction the corresponding values were 38 and 23 times. Thus laser Doppler flowmetry can be used to assess changes in blood flow in the masseter; it registers a greater increase in flow during isometric contraction than does 133Xe clearance. The significant difference between methods immediately after either chosen level of contraction disappears when the total net post-contraction hyperaemia is assessed over a period of 2 and 5 min, respectively.

Adult↗

PubMed1993

Electromyographic turns analysis of sustained contraction in human masseter muscles at various isometric force levels.

The jaw-closing muscles differ from peripheral limb muscles in that the maximum attainable force does not decline following a sustained isometric contraction. Also, the averaged electromyographic (EMG)/force ratio in these muscles does not change with sustained contraction, whereas it increases in fatiguing limb muscles. The present study analysed EMG records from masseters in healthy male subjects. No statistically significant difference was seen between average rectified EMG signals at the beginning or the end of a sustained isometric contraction at 25-100% of maximum voluntary contraction (MVC). However, when the number of turns, or reversals of direction, was taken at various percentage MVC levels, a significant decrease was seen after 60s or at the end of the contraction. The turns/force ratio decreased monotonically with percentage MVC, but the ratio was not significantly different at the end of a contraction from that at the beginning. This result confirms an earlier suggestion that neuromuscular fatigue does not accompany sustained contractions of these muscles.

Adult↗

PubMed1996

Haemodynamic changes induced by submaximal isometric contraction in painful and non-painful human masseter using near-infra-red spectroscopy.

Although mechanisms underlying chronic muscle pain are poorly understood, one prevalent theory is that it is due, in part, to localized hypoxia. The purpose of this study was to evaluate this theory using non-invasive near-infra-red spectroscopy that monitors relative changes in intramuscular haemoglobin (Hb) concentration and oxygen saturation levels. Data were collected for the human masseter muscle during and following three isometric 30-s trials at 50% maximum voluntary contraction. Ten females, with a history of chronic muscle pain in the jaw, and eight matched healthy females without muscle pain (controls) participated. Results showed that, upon initiation of masseter muscle contraction, there was a rapid reduction in the intramuscular Hb concentration concomitant with a reduction in oxygen saturation levels. After cessation of the contraction, the Hb concentration increased rapidly and then fell toward the baseline. Significant differences in the recovery profile for oxygen saturation were found between the first trial and the following two trials for both the muscle pain- and control group. Looking at the first trial only, and adjusting for covariates of height, weight and bite-force in the analysis, revealed a marginally significant postcontraction difference between the two groups with a lower level of oxygen saturation during recovery in the group with chronic muscle pain. Significant group differences were found in Hb concentrations without any significant trial effect. It is likely that the well-known changes in intramuscular blood flow that occur during and after contraction in human muscles are reflected in these altered relative Hb concentrations. The group with chronic muscle pain showed a clearly reduced magnitude of the Hb concentration change in the postcontraction recovery period. The results support the concept that patients with chronic muscle pain have a slower intramuscular reperfusion during the recovery phase after sustained isometric contractions.

Adult↗

PubMed1986

Electrical and mechanical changes in human soleus muscle during sustained maximum isometric contractions.

Experiments were designed to evaluate changes in the electrical activation and force generating capabilities of human soleus muscle during sustained, maximum isometric contractions. Eighteen experiments were conducted on 7 healthy subjects. Surface EMG, and in select cases, intramuscular fine wire EMG recordings, were made to assess the electrical activation of soleus. Subjects performed maximum isometric plantarflexion contractions of 1-3 min during which time supramaximal electrical pulses were delivered to the tibial nerve at 5-s intervals to elicit maximum M waves. M wave areas were assessed for evidence of neuromuscular junction failure. The results revealed that, on average, maximum force declined to 80% of unfatigued maximum by 60 s of effort, 74% by 90 and 120 s, and 70% by 180 s. M waves were stable for efforts up to 3 min, thereby providing little evidence for neuromuscular junction failure. In 3 experiments, total spike counts from intramuscular recordings displayed a 50% reduction in firing by 30 s of effort, with little additional slowing for up to 3 min. Although all of the fatigue-induced electrical and mechanical alterations in muscle activation reported earlier for intrinsic hand and foot muscles were verified in these experiments on soleus, the magnitudes and time courses of these changes were quite different. All changes were consistent with a muscle designed to optimally resist fatigue.

Action Potentials↗

PubMed1996

Firing rate modulation of human motor units in different muscles during isometric contraction with various forces.

To examine the factors affecting the control of human motor units, rate coding strategies of the motor units were investigated in upper limb and intrinsic hand muscles during voluntary isometric contraction of steady force levels up to 80% of maximal voluntary contraction. Numerous spike trains from single motor units were recorded from the m. first dorsal interosseous (FDI) and the m. biceps brachii (BB) of eight human subjects by means of tungsten micro-electrodes, and the mean firing rate (MFR) was calculated for each subject and inter-individual comparisons made. The MFRs of the FDI were larger than that of the BB at the higher force level, and substantial differences were not found between these muscles at the lower force level. The slope of the linear regression line of MFRs vs. exerted forces for the FDI was more than twice that for the BB. Therefore, isometric force control of the FDI depends more on the rate coding strategy. The difference in rate coding between the FDI and BB motor units may be determined by factors other than muscle fiber composition, because both muscles are known to possess a similar composition of fiber types. Possible mechanisms underlying these characteristics of rate coding strategy are considered in this report.

Adult↗

PubMed1994

The calcium sensitizer EMD 53998 antagonizes phosphate-induced increases in energy cost of isometric tension in cardiac skinned fibres.

We have investigated whether a Ca(2+)-sensitizing substance, the thiadiazinone derivative EMD 53998, can alter the ratio of ATPase activity to force, i.e. the tension cost in skinned fibres of swine cardiac trabecula in which the tension cost was increased by inorganic phosphate. In the presence of 10 mM inorganic phosphate (Pi) and thapsigargin 20 microM, EMD 53998 reduced the energy cost of isometric tension over the entire range of activating Ca2+ concentrations, resulting in a consistent change in slope (approximately 20% decrease) of the ATPase/force relation. We confirmed that in the absence of added phosphate and at maximal Ca2+ activation EMD 53998 had little if any effect on tension cost. We had previously reported that the effects of EMD 53998 and Pi on calcium sensitivity and maximum isometric tension are mutually antagonistic and our new energy data now support the proposal that EMD 53998 functionally antagonizes the effects of Pi on crossbridges. The decrease in the slope of the relation between ATPase and force caused by EMD 53998 may be interpreted to reflect either a decrease in the rate of 'detachment' (g(app)) of crossbridges or an increase in average force per crossbridge, as predicted by classical crossbridge models. Since the Pi release step of the crossbridge cycle is associated with the rate of 'attachment' (f(app)) rather than g(app), we conclude that the decrease in tension cost with EMD 53998 most likely reflects an increased force per crossbridge.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate↗

PubMed1988

Effects of immobilization on the isometric contractile properties of embryonic avian skeletal muscle.

Chicken embryos were chronically immobilized by applying a neuromuscular blocking agent, curare, to the chorioallantoic membrane from day 8 through day 16 of incubation to study the effects of a deficit in motor activity on the development of contractile properties of skeletal muscle. Compared with control embryos, spontaneous embryonic motor activity was depressed by 60 to 90% in the curare-treated animals during the treatment period. Growth of the posterior latissimus dorsi muscle, a fast-twitch muscle in the adult, was greatly affected by immobilization. The average blotted mass of the muscles from curare-treated 18- to 19-day embryos was approximately 20% of that from control embryos. The isometric contractile properties of posterior latissimus dorsi muscles isolated from control and curare-treated embryos were compared at 18 to 19 days of incubation. The times to peak tension and to one-half relaxation of the twitch and tetanic responses were significantly greater for the muscles from the immobilized embryos. The peak twitch and tetanic tensions, normalized for muscle cross-sectional area, were significantly less than control values for the muscles from curare-treated embryos. The maximal rate of tetanic tension production was, however, unaffected by immobilization. The results of this study demonstrate that the development of isometric contractile properties of embryonic skeletal muscle is significantly altered by an experimentally induced reduction of spontaneous motor activity. A disruption in the functional development of the sarcoplasmic reticulum following a similar decrease in motor activity, as reported by others, is discussed as a potential mechanism for the altered contractile properties of muscles from the curare-treated embryos.

Animals↗

PubMed1988

In vivo muscular force analysis during the isometric flexion on a monkey's elbow.

An experimental method has been developed to analyse muscular forces and torques in vivo during isometric flexion of the elbow in small monkeys (Macaca fascicularis). A mini-transducer was built with a view to measure forces in situ, without cutting tendons. The positions of tendon insertions were measured on anatomical parts, then integrated in a series of calculations aiming of deducing the lever arms of forces to be included in a torque equilibrium relationship. Muscle activity of the three main flexors was measured for five angles of isometric flexion between 70 degrees and 110 degrees, 0 degrees corresponding to the full extended forearm. The analysed signals were selected using physiological and biomechanical criteria. Then, results corresponding to force participation, and torque participations, were worked out; they are presented and discussed in the present paper.

Animals↗

PubMedDate not supplied

Estimation of muscle forces about the wrist joint during isometric tasks using an EMG coefficient method.

A technique for estimating isometric muscle forces based on EMGs and anatomical parameters is presented. In the present study, we record EMGs from five muscles acting at the wrist, during a series of isometric contractions in flexion, extension, ulnar deviation and radial deviation. The method then uses these EMG signals and the necessary anatomical data to estimate individual muscle forces. For one subject, complete anatomical parameters were estimated by MRI reconstruction of muscle moment arms and lines of muscle action. In all subjects, the errors associated with variability in the EMG signals were reduced through the use of signal processing techniques and intensive subject training. These EMG-based force estimates were then validated by evaluations at torque directions in which no mechanical redundancy existed. The stability of the solution space was examined using Monte Carlo simulations. The results of our study show that individual muscle forces at the wrist can be estimated with considerable accuracy, without assuming any control strategy (as is done with optimization theories). However, due to the limited mechanical redundancy of the wrist, it is uncertain whether the method can be used to estimate muscle forces in more highly redundant systems.

Adult↗

PubMed1996

Simulation of in situ soleus isometric force output as a function of neural excitation.

The purpose of this study was to investigate the behaviour of the human soleus muscle during isometric contraction. A model taking into account the musculoskeletal geometry, the musculotendon architecture and the neural excitation input has been developed. The neural excitation input was simulated using a recruitment and firing rate organisation model. The musculotendon actuator was modelled as a tendon inserted in series with fibres defined by a contractile component in parallel with an elastic component. At maximal neural excitation, the model highlighted the functional significance of tendon stiffness and pennation angle. These architectural parameters tended to increase the operative ankle joint angle range of the soleus actuator, either to the maximal plantarflexion positions for the pennation angle or to the maximal dorsiflexion positions for tendon elasticity. When the model was simulated under various neural excitation levels, it predicted a displacement of the soleus fibre optimal length towards the soleus long length (maximal dorsiflexion position) with increasing neural excitation. The study concluded that the effect of muscular architecture should be taken into account to analyse the effect of neural excitation level on isometric force output.

Ankle Joint↗

PubMed1991

Acoustic myographic activity increases linearly up to maximal voluntary isometric force in the human quadriceps muscle.

Sounds produced during voluntary isometric contractions of the quadriceps muscle were recorded by acoustic myography (AMG) in seven healthy adults. With the subject seated, surface AMG and electromyography (EMG) were recorded over rectus femoris (RF) during isometric contractions, at different levels of maximum voluntary force. The AMG and EMG signals were amplified and integrated (IAMG and IEMG). The relationships between force and IAMG (r = 0.98 +/- 0.01, mean +/- 1 SD) and force and IEMG (r = 0.99 +/- 0) were linear in all subjects. The results for EMG confirm previous reports but those for AMG differ from the relationships reported for other muscles. Physiological and technical explanations are proposed for these differences and the necessity for further validation of the AMG technique is stressed.

Acoustics↗

PubMed1985

Maintenance of low isometric forces during prehensile grasping.

A specially designed microcomputer-controlled force measurement system was tested in 24 normal adults. The task was to maintain a prescribed low isometric grip-force (2.5 Newton) under different visual feedback conditions. The performance variability across subjects and conditions was surprisingly low. Normal adults can maintain low isometric forces with great accuracy. No left/right hand differences could be found in the subjects investigated. These results seem to qualify our procedure for the clinical examination of neurologically impaired patients.

Adult↗

PubMed1996

Effects of early plasmin digests of fibrinogen on isometric tension development in isolated rings of rat pulmonary artery.

The purpose of the study was to determine the effects of early plasmin-mediated digests of rat fibrinogen on the vascular tone of rat pulmonary artery in order to compare with reported vasoactive effects of high levels of isolated human peptides in various rat vascular beds. Isometric tension was monitored in isolated rings of rat pulmonary artery precontracted with phenylephrine (4 x 10(-8) mol). Fibrinogen degradation products (FgDPs) were produced by digestion of rat fibrinogen with plasmin to 1, 2, 3 and 60 minutes whereupon the digestion was stopped by addition of Trasylol. These FgDPs were added to the tissue bath to achieve final concentrations of 6.7, 13.3, 26.7 and 53.3 micrograms/mL i.e. values similar to those found in vivo during thrombolytic therapy for myocardial infarction. Results were expressed as a percentage of a maximal contraction elicited in each ring in response to phenylephrine (10(-5) M). The early FgDP fractions, at these pathophysiological concentrations, did not induce significant change in isometric tension in the isolated pulmonary arterial rings (P > 0.05, ANOVA).

Animals↗