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PubMedDate not supplied

Reliability of SEMG spike parameters during concentric contractions.

This study examined the reliability of four surface electromyographic (SEMG) spike parameters during concentric (isotonic) contractions: mean spike amplitude, mean spike frequency, mean spike slope, and the mean number of peaks per spike. Eighteen subjects performed rapid elbow flexion on a horizontal angular displacement device that was used to measure joint torque. The SEMG activity of the biceps brachii was monitored with Beckman Ag/AgCl electrodes. The testing schedule consisted of four hundred trials distributed equally over four sessions. The stability of the means across sessions and the consistency of scores within subjects was determined for the first five (1-5) and last five (96-100) trials of each session to examine the possible influence of a "warm up" effect. All measures exhibited a significant (p < 0.01) increase across test days. However, the intraclass correlation coefficients for the first five (1-5) trials ranged from 0.76 to 0.83, which was quite good. The stability and consistency for most of the criterion measures increased for the last five (96-100) trials of each session. This resulted in a higher range of coefficients from 0.85 to 0.93. Subjects became more homogeneous with respect to the mean number of peaks per spike and the R decreased to 0.65. It was concluded that the four SEMG spike parameters could be reliably measured to assess changes in muscle activity patterns. The adaptations in SEMG spike activity suggest that repetitive dynamic contractions enhanced the ability to recruit more fast-twitch motor units across test days.

Adult↗
PubMed1982

A comparison of the mechanical properties of oesophageal striated muscle with skeletal muscles of the guinea pig.

An in vitro comparative study has been made of the contractile properties of guinea pig oesophageal striated muscle with fast twitch (extensor digitorum longus) and slow twitch (soleus) muscles. Histochemical analysis of sections showed oesophageal fibres to react in a manner typical of fast twitch muscles. Isometric measurements made at 23 and 37 degrees C indicated that oesophageal striated muscle contracts at speeds similar to, but still significantly faster than soleus. Isotonic measurements of oesophageal preparations made at 23 degrees C gave an intrinsic speed of shortening and an a/Po value derived from Hill's equation, comparable with that obtained for soleus. The reason for the contradiction between the results from histochemistry, and the results from isometric and isotonic contractions are not apparent, but may be due to differences in fibre arrangement between oesophagus and the two skeletal muscles.

Adenosine Triphosphatases↗
PubMedDate not supplied

Inhibition of contractility during the early phase of total ischaemia in the working heart. Recovery during reperfusion.

Total global ischaemia of the normothermic working rat heart caused an initial positive inotropic response characterized by vigorous contractions. After +/- 15 s this response reached a peak whereafter the isotonic contraction amplitude started to decline. After +/- 3.5 min the heart ceased to beat. The low level of high energy phosphates (HEP), determined 3 min after the onset of ischaemia, indicated that these phases of contractility during ischaemia might play a significant role in depleting HEP. This was substantiated by the observation that inhibition of the contractions during ischaemia by low calcium or high potassium solutions resulted in conservation of myocardial adenosine triphosphate (ATP) and creatine phosphate (CP) stores. It also resulted in the prevention of contracture development during ischaemia and improved mechanical recovery during reperfusion. It was therefore concluded that inhibition of contractility immediately after the onset of total global ischaemia of the normothermic working rat heart is of prime importance in mechanical recovery during reperfusion.

Adenosine Triphosphate↗
PubMed1986

Endurance exercise training reduces lactate production.

In situ muscle stimulation in trained and untrained rats was used to reevaluate whether adaptations induced by endurance exercise training result in decreased lactate production by contracting muscles. The gastrocnemius-plantaris-soleus muscle group was stimulated to perform isotonic contractions. After 3 min of stimulation with 100-ms trains at 50 Hz at 60/min, the increases in lactate concentration in the plantaris, soleus, and fast-twitch red muscle (deep portion of lateral head of gastrocnemius) were only approximately 50% as great in trained as in sedentary rats. In the predominantly fast-twitch white superficial portion of the medial head of the gastrocnemius the increase in lactate concentration was 28% less in the trained than in the sedentary group. The decreases in muscle glycogen concentration seen after 3 min of stimulation at 60 trains/min were smaller in the trained than in the untrained group. The reduction in lactate accumulation that occurred in the different muscles in response to training was roughly proportional to the degree of glycogen sparing. These results show that endurance training induces adaptations that result in a slower production of lactate by muscle during contractile activity.

Adaptation, Physiological↗
PubMed1981

Studies on isolated smooth muscle cells. VII. Response to agonists and the contraction velocity of taenia coli of guinea pig and the single smooth muscle cells.

Single smooth muscle cells were isolated from taenia coli of guinea pigs and degrees of responses of acetylcholine, histamine and prostaglandin E2, and velocity of acetylcholine-contraction were compared with those of whole tissue. The contraction of single cells by these agonists were dose-dependent and ED50 of acetylcholine, histamine and prostaglandin E2 were 0.3 - 1.1 x 10(-6), 5-11 x 10(-7) and 1-3 x 10(-9) M, respectively. These values were quite similar to those obtained with whole tissue. It took 2.0 +/- 0.2 s for the single cells to be contracted completely by 10(-4) M acetylcholine while it took 6.9 +/- 0.2 s for the isotonic contraction of whole tissue. Times for a half maximum contraction, assuming that the whole tissue and the single cells were contracted at the maximum velocity, were 1.43 +/- 0.05 and 0.92 +/- 0.12 s, respectively when 10(-4) M acetylcholine was applied. These results revealed the response of muscle cells in the tissue to agonists was reflected on magnitude of the contraction of whole tissue and suggested that pharmacological properties of smooth muscle cells of taenia coli were not changed during the isolation procedure, whereas velocity of contraction of single cells was faster than that of whole tissue. Reasons for the difference in velocity were discussed.

Acetylcholine↗
PubMedDate not supplied

Electromyography tension and frequency spectrum analysis of some masticatory muscles at rest, isotonic and isometric contractions.

On a population of 52 subjects surface electromyographic recordings of temporals and masseters, simultaneously with mandible dynamic of closure and clenching, were performed, in order to study tension and frequency behaviour in three postural conditions: rest, isotonic and isometric contractions. Frequency was studied using the median resulting from FFT calculation, and a new computing method, which presents the proportion of frequencies making up the whole EMG signal, by steps of 50 Hz. Tension was calculated as well. The results permit us to draw the following conclusions: 1. a period of EMG silence was present in 51 of 52 subjects at mandible closure (SPA--Silent Period Area); 2. SPA onset was before teeth contact (22.5 msec., during the motion of the mandible), while its end was after closure (10.2 msec., during motionless phase of clenching). This allowed to use the SPA as a tool to clearly distinguish isotonic from isometric contraction; 3. the comparison of tension and frequency, expressed as median, showed that at rest a muscle presents low frequency and low tension. In active contraction both increase their values. Nevertheless, in active contraction, while no differences were found in frequency behaviour, tension showed a difference: although higher than at rest, isotonic contraction presented lower values than during isometric contraction; 4. the study performed by the new program showed that the low frequency at rest was due to the high proportion (30-40%) of frequencies of less than 50 Hz, while the increase at function was due to the parallel increase of frequencies comprised between 100 and 250 Hz. Because it is known that muscles are composed of fibers at low frequency and at high frequency of discharge, which play different functional roles, the last finding suggests that the mathematical analysis of the spectrum of frequencies, could provide a functional-histological image of the muscle.

Adolescent↗
PubMed1984

Rabbit atrial myocardium in hypoxic conditions: rate dependent variation of contraction.

The dependence of contraction in the atrial myocardium on the stimulation pattern was studied in normoxic and hypoxic conditions. Isotonic contractions were measured from left atrial muscle strips of the rabbit. At rapid stimulation hypoxia produced a negative inotropic effect which disappeared at slower stimulation and became a positive inotropic one. The potentiation of a first beat after a pause in stimulation was enhanced by hypoxia because the contractions were stronger depressed at steady state than after a pause. At all pacing patterns the relative maximum rate of shortening and re-lengthening were independent of the oxygen-supply. After application of epinephrine in hypoxia they were enhanced and so was peak shortening. The findings suggest an impaired or altered function of the sarcolemma only under the degrees of hypoxia chosen.

Animals↗
PubMed1997

The influence of age on isometric and isotonic rat detrusor contractions.

BACKGROUND: Reductions in detrusor shortening velocity and detrusor contractility have been observed in association with aging. The reasons for these changes are unclear. METHODS: We examined the isometric and isotonic responses of detrusor, taken from the bladder body, to adenosine 5'-triphosphate (ATP), noradrenaline (NA), serotonin, and acetylcholine (Ach) in vitro, using bladders from young (30 days) and old (365 days) Sprague-Dawley rats, to determine whether there were any significant age-related differences. RESULTS: Isometric contractions with ATP at doses of 10(-3) to 10(-2) molar concentrations produced greater contractile forces in old rats when compared to young rats (p = .0136 at 10(-2) mole of ATP). Isotonic contractions at similar concentrations also produced significant differences between the young and the old rats, the latter being faster (p = .0225). Isometric contraction with noradrenaline produced significant differences between young and old rats, the latter being stronger. This became apparent at 10(-4) molar concentration of noradrenaline (p = .0043). Isometric contractions with serotonin also produced significantly greater contractions in the old rats when compared to young rats. The differences became apparent at 10(-4) molar concentration of serotonin (p = .045). There were no age-related differences in isotonic and isometric contractile responses to acetylcholine in the doses used in our experimental setup. CONCLUSIONS: Age-related differences in isometric function were detected in response to ATP, NA, and serotonin. Differences in isotonic function were only found in response to ATP and Ach.

Acetylcholine↗
PubMed1985

The effects of ADP and phosphate on the contraction of muscle fibers.

The products of MgATP hydrolysis bind to the nucleotide site of myosin and thus may be expected to inhibit the contraction of muscle fibers. We measured the effects of phosphate and MgADP on the isometric tensions and isotonic contraction velocities of glycerinated rabbit psoas muscle at 10 degrees C. Addition of phosphate decreased isometric force but did not affect the maximum velocity of shortening. To characterize the effects of ADP on fiber contractions, force-velocity curves were measured for fibers bathed in media containing various concentrations of MgATP (1.5-4 mM) and various concentrations of MgADP (1-4 mM). As the [MgADP]/[MgATP] ratio in the fiber increases, the maximum velocity achieved by the fiber decreases while the isometric tension increases. The inhibition of fiber velocities and the potentiation of fiber tension by MgADP is not altered by the presence of 12 mM phosphate. The concentration of both MgADP and MgATP within the fiber was calculated from the diffusion coefficient for nucleotides within the fiber, and the rate of MgADP production within the fiber. Using the calculated values for the nucleotide concentration inside the fiber, observed values of the maximum contraction velocity could be described, within experimental accuracy, by a model in which MgADP competed with MgATP and inhibited fiber velocity with an effective Ki of 0.2-0.3 mM. The average MgADP level generated by the fiber ATPase activity within the fiber was approximately 0.9 mM. In fatigued fibers MgADP and phosphate levels are known to be elevated, and tension and the maximum velocity of contraction are depressed. The results obtained here suggest that levels of MgADP in fatigued fibers play no role in these decreases in function, but the elevation of both phosphate and H+ is sufficient to account for much of the decrease in tension.

Adenosine Diphosphate↗
PubMed1975

Mechanics of guinea pig taenia coli smooth muscle during anoxia and rigor.

Potassium-contracted guinea pig taenia coli relaxed when exposed to hypoxic glucose-free conditions, and this was followed by a second contraction. During this second contraction, which was not inhibited by ethylene glycol-his-(beta-aminoethylether)-N,N'-tetracetic acid (EGTA) the muscle was in rigor. After development of this contraction the muscle did not have an active state and was less extensible than a muscle normally contracted with KCl. Tension during rigor in an isometrically contracting muscle was short-lived in contrast to shortening during rigor development in a lightly loaded isotonically contracting muscle. These findings, together with the observation of irreversible lengthening of a muscle in rigor on stretching, suggest that rigor linkages can be broken. Glucose removal under aerobic conditions did not produce rigor, but oxygen removal in the presence of glucose resulted in relaxation followed by secondary contraction. This later contraction, unlike that accompanying rigor, was reversed by removal of calcium with EGTA. These data imply that in the absence of oxygen the removal of cytoplasmic free-Ca2+ is inhibited.

Animals↗
PubMed1975

[The relationships between left ventricular volumes and ejection fraction in mitral and aortic regurgitation (author's transl)].

In 2 groups of patients with mitral valvular incompetence (MI, n equals 20) and aortic valvular incompetence (AI, n equals 22) intracardiac pressures as well as left ventricular volumes (enddiastolic volume, endsystolic volume, stroke volume, ejection fraction, regurgitant volume) were determined during routine left heart catheterization and left ventriculography. Data obtained were compared with a normal group (N, n equals 20). 1. Enddiastolic volume was increased by 32 per cent (MI) and 180 per cent (AI) respectively in comparison to normal. Endsystolic volume was increased by 85 per cent (MI) and 113 per cent (AI). Total stroke volume exhibited increases by 11 per cent (MI) and 86 per cent (AI) respectively. Regurgitant volume averaged 64 per cent (AI) of total stroke volume, and 47 per cent in MI. Left ventricular ejection fraction was reduced in both groups by about 12-14 per cent. 2. enddiastolic volume was significantly dependent on the amount of regurgitant volume in both groups (MI, AI). Likewise total stroke volume increased with increments in enddiastolic volume. This increase was far mor pronounced (up to 250 per cent of normal) in AI in comparison to MI and may be referred to an effective contribution of the Frank-Starling-Straub-mechanism, induced by increased preload following regurgitation. There existed no correlation between enddiastolic volume or regurgitant volume and the effective forward stroke volume and other parameters of forward pump function (effective cardiac output, cardiac index, external cardiac work). Left ventricular compliance, as determined by diastolic pressure-volume relationships, was nearly the same in the 3 groups (N, MI, AI). 3. Left ventricular ejection fraction was nearly unchanged with increments in enddiastolic volume over a range of enddiastolic volumes up to 400 ml. At higher enddiastolic volume (is greater than 400 ml) decreases were found. In the failing heart with AI left ventricular ejection fraction was reduced even at low enddiastolic volume, exerted by decreases of fibre shortening and contractility. In contrast, in MI ejection fraction decreased with increments of enddiastolic volume over the whole range investigated. The increase in total stroke volume in both groups therefore was produced by increases of enddiastolic volume and to a very small extent by an increase of the ejection fraction. 4. The large contractility reserve in compensated AI may be referred to the altered contraction mechanism in aortic valvular regurgitation associated with i) decrese of isovolumic pressure development and increase of isotonic contraction, ii) increase of diastolic fibre stretch (preload) and iii) decrease of mean wall tension. Contractility reserve was essentially influenced by myocardial contractility. With decreases of contractility consecutively decreases of the total and the effective pump function of the left ventricle may occur despite unchanged contraction form and left ventricular dimensions.

Animals↗
PubMed1987

Crossed facilitation and post-contraction depression of abductor pollicis brevis motor neurons.

Crossed facilitation of abductor pollicis brevis (APB) motor neurons by voluntary contraction of the contralateral APB was investigated using F response analysis. The integrated F response EMG showed a mean 4-fold increase during contraction. This enhancement was maintained until the onset of subjective fatigue and then declined. After isometric or isotonic contraction of the ipsilateral APB there was a significant depression of F responses with a progressive return to baseline values over a 6 minute period. The significance of the findings is discussed.

Adult↗
PubMed1989

[Correlation between somatosensory evoked potentials and long loop reflexes--basic investigation and its application for multiple sclerosis].

Somatosensory evoked potentials (SEPs) and long loop reflexes (LLRs) to the median nerve stimulation were investigated on 25 normal controls and 25 patients with multiple sclerosis (MS). Fifteen normal controls were also subjected to LLR study by the common peroneal nerve stimulation. The mean height were 159 +/- 8.2 cm in normal controls and 160 +/- 8.9 cm in MS, respectively. LLRs were obtained with 100% reproducibility in all cases. Upper limb LLRs were recorded from m. abductor pollicis brevis by trigger stimulation during isotonic contraction of the thumb, while lower limb LLRs were recorded from m. peroneus longus by trigger stimulation during isotonic eversion of the foot. The threshold of LLR was lower than that of short latency reflex (H-wave) with the mean latency of 40.4 +/- 1.5 ms. The height of subjects revealed an obvious positive correlation not only with the latency of LLR but also with N 20 of SEP, whereas central conduction time was not. Furthermore, a significant correlation was present between the latencies of LLR and N 20, showing a twofold gradient of LLR against N20. There was a significantly prolonged latency difference between H-wave and LLR of lower limb as compared with that of upper limb. When the stimulation site was changed from the wrist to the elbow, the latency difference between M-wave and H-wave shortened. This fact, therefore, appears to be against "resonance hypothesis" that LLR is set off according to the intrinsic mechanical oscillation given to the muscle concerned.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1998

Intramuscular pressure, force and blood flow in rabbit tibialis anterior muscles during single and repetitive contractions.

The elevated intramuscular pressure (IMP) associated with sustained muscle contraction can affect blood flow, and could influence the long-term viability of functional skeletal muscle grafts. We therefore examined the relationship between force, peak IMP and blood flow in the tibialis anterior muscle of the anaesthetized rabbit. During isometric contractions. IMP was related linearly to force, and only the slope of the relationship varied between animals. During isotonic contractions, however, the highest values of IMP were found at the lowest force levels, and IMP appeared to be related to the amount and speed of shortening. During repeated isometric contractions, the ratio of IMP to force varied with time, stimulation pattern and subject. Mean blood flow did not differ appreciably between repetitive isometric contractions at duty cycles of 10-40%, and was unrelated to integrated pressure, integrated force, or depth from the surface. We conclude: (1) that IMP is unlikely to affect mean blood flow during cyclic activity that has a duty cycle less than 40%; and (2) that the clinical use of IMP as a predictor of muscle force appears to be justified only for single isometric contractions, and needs to be interpreted cautiously when contractions involve shortening or fatigue.

Animals↗
PubMed2006

Pharmacological effects of Eugenia punicifolia (Myrtaceae) in cholinergic nicotinic neurotransmission.

The effects of the aqueous crude extract (5%) of Eugenia punicifolia on cholinergic nicotinic neurotransmission were investigated. Actions of aqueous crude extract over the inhibitory effect of the cholinergic nicotinic antagonists gallamine or pancuronium, on contractions induced by electrical stimulation of phrenic nerve of rat diaphragm, were studied. Tissues were mounted as for isotonic contractions and stimulation was delivered at submaximal voltage. Addition of Eugenia punicifolia did not alter the amplitude of twitch contraction. Gallamine (IC(50): 28.8+/-0.51 microM) or pancuronium (IC(50): 3.16+/-0.11 microM) completely inhibited twitch contractions. After the maximum effect of the antagonists was achieved, addition of the aqueous crude extract (0.5-1.0 mL) totally recovered the responses to electrical stimulation. Neostigmine, a reversible acethylcholinesterase inhibitor, partially recovered responses (49.70+/-6.90% at 1 microM). In another series of experiments, previous incubation of the extract (0.5 mL) shifted to the right inhibitory concentration-response curves for the antagonists gallamine (IC(50) before E. punicifolia: 35.8+/-1.61 microM; IC(50), after E. punicifolia: 2.24+/-0.04 mM) and pancuronium (IC(50), before E. punicifolia: 3.55+/-0.13 microM; IC(50), after E. punicifolia: 0.39+/-0.01 mM). Our results show that the aqueous extract of E. punicifolia recovered the action of competitive nicotinic antagonists at the neuromuscular junction. A receptor-mediated mechanism or the possibilities of interactions of the extract with the enzyme acethylcholinesterase, however, remain to be investigated.

Animals↗
PubMed1994

A simple technique for on-line measurement of contractions of single smooth muscle fibers under current or voltage clamp.

This paper describes a simple technique for routine on-line measurement of length and unloaded, isotonic contractions of single smooth muscle fibers during electrophysiological experiments. The fiber is held by the recording electrode itself, stretched straight in a fast-flowing stream of solution. The video image of the fiber is measured on-line by a simple computer program. Unlike other optical methods of tracking fiber length, the technique does not require a rigid one-dimensional contraction of the fiber. The technique is reliable and easy to use, and readily compatible with current clamp, voltage clamp, and rapid reversible application of neurotransmitters and drugs.

Algorithms↗
PubMedDate not supplied

Bit-mapped somatosensory evoked potentials and muscular reflex responses in man: comparative analysis in different experimental protocols.

Bit-colour maps of somatosensory evoked potentials (SEPs) and muscular responses from forearm and hand muscles were simultaneously recorded after median nerve stimulation. Subjects were asked either to relax totally (A), or to contract the examined muscle continuously and isometrically at 10-20% (B) and 80-100% (C) of the maximal strength. Isotonic contractions ipsilateral (D) and contralateral to the stimulus (E) were also examined. Both SEPs and EMG responses were elicited by individual near-motor threshold pulses delivered at 0.2/sec to the median nerve at the elbow. SEPs were maximal in amplitude during complete relaxation, whilst all the components following the parietal N20 were depressed by muscle contraction. Such decrements affected predominantly the parietal and frontal peaks of positive polarity during condition B, whilst the frontal negative component (wave N30) dropped remarkably in conditions C and D. Early EMG responses (V1 = spinal circuitry) were usually absent in condition A; they were present together with later components (= V2 possibly long-loop, transcortical circuitry) in C and D, whilst they were alone recordable in B and E. The amplitudes of the frontal wave N30 in SEPs and of V2 in LLRs were inversely correlated. This observation is consistent with the hypothesis that a change in the reactivity of the sensorimotor brain areas to afferent impulses is coupled to LLR elicitation in forearm and hand muscles.

Adult↗