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Results for “Isometric Contraction”

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PubMed1986

Reduced alpha 1-adrenoreceptor mediated responsiveness in vas deferens from spontaneously hypertensive rats.

alpha-adrenoreceptor-mediated responses were investigated in isolated vasa deferentia from spontaneously hypertensive rats (SHR), Wistar Kyoto rats (WKY) and normotensive rats (NWR). There was no significant difference between NWR, WKY and SHR in the inhibition of the isometric contraction to single pulse field stimulation by the alpha 2-selective agonist xylazine in prostatic portions, nor by xylazine and the alpha 1-selective agonist amidephrine in epididymal portions in the presence of nifedipine to prevent postjunctional actions of alpha 1-selective agonists. There was no significant difference between NWR, WKY and SHR in the potency of amidephrine in causing a postjunctionally mediated potentiation of the isometric contraction to single pulse field stimulation in prostatic portions but the maximum potentiation was significantly reduced in SHR. However contraction by the calcium entry facilitator, Bay K 8644, was not significantly different between NWR, WKY and SHR. The maximum direct contraction to amidephrine, but not to Bay K 8644, was also significantly reduced in SHR. It is concluded that the altered alpha 1-adrenoreceptor-mediated responsiveness in SHR is due not to genetic strain, but is presumably linked to development of hypertension.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1993

Increased amplitude of cutaneous reflexes during human running as compared to standing.

The amplitude of H-reflexes is decreased during walking as compared to standing and a further reduction is seen during running as compared to walking. Does a similar reduction occur for reflexes elicited by cutaneous stimulation? To answer this question, the electromyographic (EMG) responses in biceps femoris (BF) and tibialis anterior (TA) to a 20 ms train of 5 electrical pulses, were recorded. This stimulus was applied to the sural nerve at the ankle, either at 16 different phases of the step cycle in human volunteers running on a treadmill at 8 km/h or at different isometric contraction levels of TA and BF in the same subjects during standing, imitating the postures of different phases of the step cycle. The mean latency of the main responses in BF of all subjects was 76 ms. Similar responses (P2), with a latency of 79 ms were seen in TA in 6 of the 10 subjects. For a constant strength of stimulation (2 times perception threshold) during isometric contractions at different levels in early stance imitation, the mean reflex ratio's (reflex/background) of BF and TA responses were 1.07 and 0.53, respectively, while the ratio's for these 2 muscles during running were 1.78 and 1.1. The higher reflex ratio's in running were primarily due to the large facilitatory responses, which were present during most of the step cycle but rarely during voluntary contractions in the subjects during standing. At the end of the swing phase, however, the responses in BF and TA were predominantly suppressive, as were most of the responses to stimulation applied to the standing subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1975

Excitation overflow: an electromyographic investigation.

The amount of excitation overflow into a nonactive upper limb can be predicted when the active limb is isometrically contracted during a standardized exercise. Bilateral electromyographic recordings from the biceps brachii and brachialis demonstrated that the amount of excitation overflow in the nonactive limb is between 10 percent and 20 percent of the maximal intensity of activity measured in the exercised limb. This amount appears to be independent of the position of the active limb (supination, neutral, or pronation) and the amount of force used during the isometric contraction exercise. Excitation overflow, using the exercise described, should be considered as a reliable rehabilitation technique for maintaining a degree of muscle tone and tissue turgor in a limb that is temporarily immobilized.

Adolescent↗

PubMed1976

Postcontractile motoneuronal discharge produced by muscle afferent activation.

Muscle afferent activity is markedly enhanced following isometric contractions in hindlimb musculature of various vertebrates. Such increased and persistent postcontractile sensory discharge (PCSD) consists for the most part of potentiated firing of muscle spindle primary afferents. To determine if a positive feedback function is served, involving recruitment of homonymous and synergistic motor units, 62 motoneurons were isolated in L7 ventral root filaments, categorized according to their reflex response to triceps surae stretch, and monitored before and after isometric contraction for variations in spike frequency. Motoneurons found reflexly coupled to triceps surae stretch receptors significantly increased (P less than .01) their firing frequency during PCSD. Tonic motoneurons, believed to be primarily of alpha origin, accounted for most of the observations. This latter finding is consistent with known effects of spindle afferent input on motoneuronal recruitment. Functionally, this autogenetic control circuit should enhance "muscle stifness" and stabilize the muscle against minor perturbations.

Animals↗

PubMed1999

Gender differences in muscle strength & endurance in young Indian adults.

Muscle strength was studied in 70 males and 53 females between the ages of 17-30 yr, using a handgrip dynamometer. In a subset group of 31 males and 20 females, muscle endurance during sustained isometric contraction was studied using a load cell based handgrip dynamometer coupled to a polygraph. The males had a significantly greater muscle mass and lower body fat as compared to the females. Males had close to twice the handgrip strength of females in absolute terms (P < 0.01) and this difference persisted after correction for forearm muscle area (P < 0.05). In contrast, the rate of decline of muscle strength during sustained isometric contraction was lower in females as compared to males (P < 0.05), suggestive of greater skeletal muscle endurance in females. Physical activity patterns were not a determinant of skeletal muscle function. These findings are consistent with gender specific muscle fibre characteristics reported in literature in other racial groups.

Adolescent↗

PubMed2006

Combinatory effects of high-intensity-strength training and sensorimotor training on muscle strength.

It has been shown in classical strength training studies using high loads that improvements in rate of force development are mainly due to adaptations in the intramuscular coordination. Adaptations following sensorimotor training were also characterized by improvements in the rate of force development during maximum voluntary isometric contraction. The purpose of the present study was to investigate neuromuscular adaptations of combined sensorimotor and classical strength training. Eighteen subjects were randomly assigned to two groups. Group 1 (SMT-HST) had to perform a period of sensorimotor training at first and a high-intensity strength training afterwards. Group 2 (HST-SMT) performed the high intensity strength training at first and the sensorimotor training after. Maximum voluntary isometric contraction and neuromuscular activation were measured at three occasions: Before training, after the first, and after the second period. The results after the first period confirmed the positive effects of both training regimen on rate of force development (13 % [SMT-HST] and 27 % [HST-SMT], p < 0.05) and on maximum strength (9 % [HST-SMT] and 12 % [SMT-HST], p < 0.05) during maximum voluntary contraction. Improvements caused by sensorimotor training could only be achieved, when it was performed at first. It is supposed that classical strength training with high loads basically improves the mechanical efficiency of the effectors, whereas sensorimotor training alters the afferent input on the central nervous system. In combination, the sensorimotor training can have preconditioning effects on the strength training. A combination of both training methods can thus be recommended, if the sensorimotor training is performed at first.

Adaptation, Physiological↗

PubMed1981

Muscle fiber recruitment and blood pressure response to isometric exercise.

Blood pressure was recorded during fatiguing and nonfatiguing isometric contractions of a slow-twitch muscle (the soleus) and a mixed muscle (the medial gastrocnemius) of the cat. Four tensions were examined in each muscle; 10, 25, 40, and 70% of the muscle's initial strength (tetanic tension of the unfatigued muscle). All experiments were also repeated at two muscle temperatures, 28 and 38 degrees C. For the soleus muscle, there was no change in the blood pressure during isometric contractions. For the medial gastrocnemius muscle, both the systolic and diastolic blood pressure increased markedly when either all or just the fast-twitch motor units were stimulated; however, when only the slow-twitch motor units were stimulated, a lower pressor response was observed. Venous blood samples were drawn before, during, and after fatiguing and nonfatiguing contractions of both muscles to determine the K+ concentration in the venous blood. The mean increase in the K+ concentration during contractions was 0.6 meq/l for the slow-twitch motor units of the soleus and 5.1 meq/l for the motor units in the medial gastrocnemius.

Animals↗

PubMed1983

[Effect of staphylococcal toxin and antistaphylococcal gamma-globulin on the electrical and contractile activity of the guinea pig myocardium].

A study was made of the action of staphylococcal toxin (ST) and its combination with antistaphylococcal gamma-globulin (ASGG) on intracellular potentials (rest potential--RP, and action potential--AP), and isometric contractions of guinea-pig auricle. ST (initial concentration 18.10(-2)Lh) diluted with normal Tyrode's solution at 1:1000, 1:100 and 1:10 (spontaneously active preparations), and Tyrode's solution with 13.5 mM KCl (evoked activity of preparations), significantly increased the duration of AP of myocardial cells. In evoked activity of preparations, RP and the amplitude of AP declined as the concentration of ST was raised. The amplitude of isometric contractions and maximal rates of their growth and fall increased under the effect of ST (1:1000) and decreased at 1:100 and 1:10. ASGG combined with ST (1:100) did not produce any protective effect on the myocardium. On the contrary, it provoked a still greater inhibition of contractility. The inhibitory action of combined ST and ASGG was seen at all ratios of ST to ASGG (use was made of ASGG shortage, equivalent amount and excess as regards ST) and reached 50% for all study characteristics of contractility. Anatoxin (inactivated toxin) combined with ASGG also produced a cardiodepressant action which was manifested in an approximately 50% decrease in the maximal rate of the growth and fall of contractions in the absence of significant changes in the contraction amplitude.

Action Potentials↗

PubMed1978

The effect of norgestrel and clogestone on the spontaneous motility of the human fallopian tube.

Spontaneous isometric contractions in vitro of both isthmic and ampullary parts of the human fallopian tube were studied. The tubes were obtained during the early luteal phase of the menstrual cycle from patients undergoing abdominal hysterectomy and who had ingested clogestone acetate or norgestrel, either 1 or 12 hours prior to the experiment. A dose of 150 microgram dl-norgestrel given orally 12 hours preoperatively caused a significant increase in the frequency of spontaneous isometric contractions together with a significant reduction in the area under the curve for each contraction. The possible effect of this altered pattern of motility is discussed.

Fallopian Tubes↗

PubMed1975

Correlation between echocardiographically demonstrated segmental dyskinesis and regional myocardial perfusion.

In order to evaluate the relationship between regional myocardial perfusion and segmental dyskinesis, 22 open chest dogs were studied using ultrasound to register cardiac wall motion and radioactive labeled microspheres to determine myocardial perfusion. In six dogs, motion and perfusion were correlated at two levels of partial circumflex coronary artery occlusion followed by complete occlusion. A good correlation between declining myocardial perfusion of all the ischemic segments and development of aneurysmal bulging (during isometric contraction) was seen: r = minus 0.80. A similar correlation between myocardial perfusion and endocardial wall velocity (during systolic ejection) was observed: r = 0.92. In nine dogs, the effect of 45 minutes of complete coronary occlusion followed by 30 minutes of reperfusion was evaluated with respect to perfusion and motion. After coronary reperfusion myocardial perfusion of the ischemic area returned to control levels (from 32.6 +/- 3.5 to 130.3 +/- 13.3 ml/100 g/min), but aneurysmal bulging during isometric contraction persisted. Endocardial wall velocity during systolic ejection showed a variable response to reperfusion, achieving values ranging from 32% to 162% of the preocclusion levels. In seven dogs the ultrasound beam was reflected off nonischemic myocardium adjacent to areas of ischemia resulting from coronary occlusion. Despite preservation of normal myocardial perfusion in these nonischemic areas wall motion abnormalities were evident: endocardial wall velocity declined from 25.8 +/- 5.8 to 14.0 +/- 4.9 mm/sec (P less than 0.01), and aneurysmal bulging in three animals. These changes may be due to transient undetected ischemia in the segments struck by the ultrasound beam, or to passive alteration of the motion of the normally perfused areas by the severe dyskinesis of the adjacent ischemic myocardium.

Animals↗

PubMed1990

Failure of glutamate dehydrogenase system to predict oxygenation state of human skeletal muscle.

In a recent study, the total tissue contents of glutamate (Glu), ammonium (NH+4), and 2-oxoglutarate (2-OG) were used to estimate changes in the mitochondrial redox state ([NAD+]/[NADH]) of contracting skeletal muscle with intact circulation [Am. J. Physiol. 253 (Cell Physiol. 22): C263-C268, 1987]. These metabolites participate in the glutamate dehydrogenase (GDH) reaction, which, based on a number of assumptions, theoretically enables calculation of the mitochondrial redox state as follows (brackets indicate concentrations): [NAD+]/[NADH] = ([NH+4] [2-OG])/[( Glu]Kapp), where Kapp is the apparent equilibrium constant for GDH. The purpose of this study was to determine whether changes in the total tissue contents of Glu, NH+4, and 2-OG could be used to predict a reduction of the mitochondrial redox state in anoxic skeletal muscle. Anoxia was induced in the quadriceps femoris muscle by 10 min of circulatory occlusion (low metabolic rate) and isometric contraction to fatigue (high metabolic rate). The mean (+/- SE) value for the metabolite ratio ([NH+4][2-OG]/[Glu]) at rest was 6 +/- 3 mmol/kg dry wt (x 10(-4]. No significant change occurred after circulatory occlusion (4 +/- 2 x 10(-4); P greater than 0.05), whereas an almost 60-fold increase was observed after isometric contraction (P less than 0.05). Because the muscle was anoxic under both conditions, a significant decrease in the metabolite ratio should have occurred. These data demonstrate that changes in total tissue contents of Glu, NH+4, and 2-OG cannot be used to estimate changes in the redox and oxygenation state of mitochondria in intact human skeletal muscle.

Adenosine Triphosphate↗

PubMed2006

Role of the right dorsal premotor cortex in "physiological" mirror EMG activity.

A distributed cortical network enables the lateralization of intended unimanual movements, i.e., the transformation from a default mirror movement to a unimanual movement. Little is known about the exact functional organization of this "non-mirror transformation" network. Involvement of the right dorsal premotor cortex (dPMC) was suggested because its virtual lesion by high-frequency repetitive transcranial magnetic stimulation (rTMS) increased the excitability of the left primary motor cortex (M1) during unilateral isometric contraction of a left hand muscle (Cincotta et al., Neurosci Lett 367: 189-93, 2004). However, no behavioural effects were observed in that experimental protocol. Here we tested behaviourally twelve healthy volunteers to find out whether focal disruption of the right dPMC by "off-line" One Hz rTMS (900 pulses, 115% of resting motor threshold) enhances "physiological" mirroring. This was measured by an established protocol (Mayston et al., Ann Neurol 45: 583-94, 1999) that quantifies the mirror increase in the electromyographic (EMG) level in the isometrically contracting abductor pollicis brevis (APB) muscle of one hand during brief phasic contractions performed with the APB of the other hand. Mirroring in the right APB significantly increased after real rTMS of the right dPMC. In contrast, no change in mirroring was seen with sham rTMS of the right dPMC, real rTMS of the right M1, or real rTMS of the left dPMC. These findings strongly support the hypothesis that the right dPMC is part of the non-mirror transformation cortical network.

Action Potentials↗

PubMedDate not supplied

Low-load eversion force sense, self-reported ankle instability, and frequency of giving way.

CONTEXT: Functional ankle instability has been attributed to proprioceptive loss. However, in previous studies of proprioception,authors have not investigated the ability to sense force at the ankle. Additionally, previous investigators have viewed functional ankle instability as either a present or absent condition,rather than a continuum. OBJECTIVE: To determine the relationship of ankle giving-way frequency and perceived ankle instability to ankle eversion force sense. DESIGN: Cohort design. SETTING: Sports medicine research laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty individuals (5 men,15 women) with a history of unilateral ankle instability. INTERVENTION(S): We tested subjects with 2 loads: 10% and 30% of maximal voluntary isometric contraction. MAIN OUTCOME MEASURE(S): We measured eversion force sense by calculating absolute, constant, and variable errors from a 3-trial force-matching procedure. Furthermore, subjects reported their frequency of giving way in units of times per day,week, or month, and these data were extrapolated to estimate annual giving-way frequency. Finally, subjects answers to 6 questions about ankle stability during typical daily or sports activities were summed to create a perceived ankle instability index. RESULTS: Significant relationships were found for only the 10% maximal voluntary isometric contraction. For absolute error,a positive relationship existed between the number of self reported episodes of giving way and eversion force sense for both ipsilateral (r .58) and contralateral (r .49) testing of the injured ankle. Constant error was correlated with giving way(r = -.56) for ipsilateral testing of the injured ankle. The ankle instability index was also positively correlated with eversion force sense absolute error (r .51) for ipsilateral testing only. CONCLUSIONS: Our results suggest that subjects with ankle instability had difficulty replicating eversion forces. Specifically,larger errors were related to both self-reported giving-way episodes and perceived ankle instability.

Journal Article↗

PubMed2003

Hindlimb unloading-induced muscle atrophy and loss of function: protective effect of isometric exercise.

The primary objective of this study was to determine the effectiveness of isometric exercise (IE) as a countermeasure to hindlimb unloading (HU)-induced atrophy of the slow (soleus) and fast (plantaris and gastrocnemius) muscles. Rats were assigned to either weight-bearing control, 7-day HU (H7), H7 plus IE (I7), 14-day HU (H14), or H14 plus IE (I14) groups. IE consisted of ten 5-s maximal isometric contractions separated by 90 s, administered three times daily. Contractile properties of the soleus and plantaris muscles were measured in situ. The IE attenuated the HU-induced decline in the mass and fiber diameter of the slow-twitch soleus muscle, whereas the gastrocnemius and plantaris mass were not protected. These results are consistent with the mean electromyograph recordings during IE that indicated preferential recruitment of the soleus over the gastrocnemius and plantaris muscles. Functionally, the IE significantly protected the soleus from the HU-induced decline in peak isometric force (I14, 1.49 +/- 0.12 vs. H14, 1.15 +/- 0.07 N) and peak power (I14, 163 +/- 17 vs. H14, 75 +/- 11 mN.fiber length.s-1). The exercise protocol showed protection of the plantaris peak isometric force at H7 but not H14. The IE also prevented the HU-induced decline in the soleus isometric contraction time, which allowed the muscle to produce greater tension at physiological motoneuron firing frequencies. In summary, IE resulted in greater protection from HU-induced atrophy in the slow soleus than in the fast gastrocnemius or plantaris.

Animals↗

PubMed2004

Femoro-tibial and menisco-tibial translation patterns in patients with unilateral anterior cruciate ligament deficiency--a potential cause of secondary meniscal tears.

OBJECTIVE: To analyze menisco-tibial and femoro-tibial translation patterns in healthy and ACL-deficient knees in different knee flexion angles under muscle activity. METHODS: The ACL-deficient and contralateral healthy knees of 10 patients were examined with an open MRI system at 30 degrees and 90 degrees of knee flexion, under isometric contraction of the extensors or flexor muscle groups. Translations between the tibia, the femoral condyles and the menisci were analyzed by three-dimensional image postprocessing. RESULTS: Posterior translation of the femur and menisci relative to the tibia occurred during knee flexion (30-90 degrees) in all knees. In ACL-deficient knees, posterior translation of the medial femoral condyle (+1.3 +/- 3.8 mm) was significantly larger than in healthy knee (-0.9 +/- 2.9 mm; p<0.05), while the translation pattern of the menisci was similar (med. meniscus 0.6 +/- 2.3 mm vs. 0.6 +/- 2.7 mm). Under isometric contraction of the extensors (relative to the flexor muscle group), an increased posterior position of the femur and menisci was observed at 30 degrees knee flexion, but not at 90 degrees. This applied to ACL-deficient and healthy knees. CONCLUSIONS: This study shows a significant increase of translation of the medial femoral condyle in ACL-deficient knees, whereas menisco-tibial translation remains almost unchanged. This difference in translation patterns indicates that the posterior horn of the medial meniscus might encounter shear, potentially explaining the high rate of secondary medial meniscal tears in patients with ACL-deficiency.

Adolescent↗

PubMed1988

Muscle stretching and motoneuron excitability.

Change of motoneuron excitability has been studied during the three basic modalities of slow or static stretching of the human soleus muscle. Tendon (T) and Hoffmann (H) reflexes were analyzed during static stretching (SS). The H response was compared in SS, in SS preceded by a maximal isometric contraction of the muscle or contraction-relaxation (CR) and during stretching of the muscle by contracting the antagonistic muscles (AC). During progressive dorsiflexion of the foot there is a significant difference (p less than 0.05) between T and H reflexes during SS, although the amplitude of direct motor (M) response, evoked by a maximal stimulation of the motor nerve, is not changed. The maximal joint mobilization during SS, CR and AC modalities appears to be closely related to the decrease in the H response during stretching. This decrease is significantly (p less than 0.05) smaller in SS than in AC or CR. In this last method, the duration of the maximal isometric contraction does not affect the results. In these three basic stretching procedures, the H reflex quickly recovers as soon as the manoeuvre is interrupted. It is suggested that changes in muscle motoneuron pool excitability closely control joint mobilization during slow or static stretching. The inhibition of the motoneurons observed during SS, CR and AC modalities is limited to the duration of the stretching manoeuvre.

Adult↗

PubMed1994

Pressure generation in a contracting myocyte.

The central hypothesis of this investigation is that a shortening myocyte generates a time-varying transmural pressure, or intracellular pressure. A mathematical model was formulated for a single myocyte, consisting of a fluid-filled cylindrical shell with axially arranged contractile filaments, to quantitate the fiber-fluid interaction. In this model, the intracellular pressure mediates the interaction between myofilament force, cell shortening, and the mechanical properties of the sarcolemma. Shortening of myofibrils, which are embedded in the fluid-filled myocytes, deforms the myocyte, thereby altering its transmural fluid pressure. This increase in transmural pressure counteracts fiber shortening, hence constituting an internal load to shortening. The shortening of the myocyte is accompanied by thickening, due to the incompressible nature of its contents. Consequently, the overall contractile performance of the cell is integrally linked to the generation of intracellular pressure. The model manifests a positive transmural pressure during shortening, but not without shortening. The pressure in the myocyte, therefore, is not a direct function of the force generated, but rather of shortening. Intracellular pressure was measured through a fluid-filled glass micropipette (5 mu ID) employing a servo-nulling pressure transducer in a standard micropuncture technique. Measured intracellular pressure in a contracting isolated skeletal myocyte of the giant barnacle is observed to be dynamically related to shortening, but not to tension without shortening. The relation between the force of contraction, cell shortening, and intracellular pressure was assessed during both isotonic and isometric contractions. The results support the prediction that isometric, or nondeforming, contractions will not develop intracellular pressure and identify a reason for relengthening of the myocytes during relaxation.

Animals↗

PubMed1988

Diminished cardiac hypertrophy and muscle performance in older compared with younger adult rats with chronic atrioventricular block.

The combined effect of advancing age and hemodynamic overload on cardiac muscle function has received little attention. In male, Sprague-Dawley rats, we studied the interaction of chronic atrioventricular heart block induced by transvenous electrocautery for 4-12 months (mean, 7 months) and age at study (12, 19 +/- 0.7, and 24 +/- 0.2 months) on cardiac hypertrophy and muscle function compared with age-matched, sham-operated controls. Hypertrophy was determined by the ratio of heart weight to tibial length. Muscle function was first determined from the mechanical variables of the isometric contraction of an excised, thin, left ventricular trabecular muscle bathed at 29 degrees C under a variety of calcium concentrations and stimulation patterns. Then, in the same muscles after disruption of membranes with Triton X-100, the force-pCa curve of the myofibrils was obtained. No hypertrophy occurred with aging in the control group, but alteration in hypertrophy with age occurred in the block group such that the youngest animals with block had the most hypertrophy (170%) and the oldest animals with block the least hypertrophy (120%). The tension developed by cardiac muscle and the duration of the isometric contraction were not affected by age in the control group but were significantly affected by age in the block group. The young animals with block had a markedly prolonged contraction duration and almost twice the developed tension compared with the older animals with block or with controls. The age-related difference in muscle contraction duration in the block group was associated with, and may have only been secondary to, the age-related difference in the extent of cardiac hypertrophy. For developed tension, the age-related difference in the block group could not be explained by differences in the extent of cardiac hypertrophy. Rather, this difference was attributable to both an increased myofibrillar force-generating capacity in the young block and to an impairment in excitation-contraction coupling in the old block. The results show that during long-term block, age exerted not only a significant effect on the extent of cardiac hypertrophy but also an independent effect on the developed tension of cardiac muscle.

Aging↗