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PubMed2005

Contractile properties of inner and outer smooth muscle bundles from pig urinary detrusor.

Like in the human detrusor, the pig urinary detrusor muscle consists of two layers: compactly arranged smooth muscle bundles on the mucosal side (inner layer) and loosely arranged smooth muscle bundles on the serosal side (outer layer). The contractile properties of muscle bundles of both layers were measured using the stop test followed by an isometric contraction. Total and passive forces were measured in ten muscle bundles from the inner and outer muscle layers. Active force was defined as the difference between total and passive force. The curvature and the unloaded shortening velocity of the force-velocity relation were calculated from the shortening forces measured during the stop test. The rate of force development was calculated from the isometric contraction. Differences in contractile properties between both layers were pairwise tested using the Wilcoxon Signed Ranks test. Percentage wise, the outer layer muscle bundles produced the highest active isometric force. The shortening forces were also higher in the outer layer bundles. As a result, both the curvature and the unloaded shortening velocity, derived from the average force-velocity relations fitted to the data sets, were higher in the muscle bundles from this layer. Finally, the outer layer muscle bundles contracted significantly faster than those of the inner layer. Muscle bundles from the outer layer of pig detrusor were found to be faster and stronger (more phasic) than the weaker and slower (more tonic) bundles from the inner layer, suggesting that during bladder contraction the outer layer of the detrusor does more work than the inner layer.

Animals↗
PubMed1976

Action of anaphylaxis and histamine on isolated mammalian ventricles: contractile hyperactivation and changes of membrane potentials.

The effects of anaphylaxis and histamine on the action potential and the isometric contraction of isolated guinea-pig papillary muscles have been investigated. The anaphylactic reaction was found to affect directly ventricular muscle fibers. The anaphylactic alterations of membrane and contraction parameters were very similar to effects of histamine and were not affected by pretreatment with reserpine. Isometric contraction developed typical features of contractile hyperactivation, characterized by a marked increase of peak force associated with shortening of time to peak of contraction and the appearance of oscillatory contractions and aftercontractions. Mechanical alternans and electrical alternans were also observed. Oscillatory contractions occurring during membrane depolarization were increased with prolongation of the action potential duration. After contractions developed after complete repolarization of the membrane and increased at higher stimulation rates. The anaphylactic reaction and histamine caused shortening of the action potential. Resting potential, overshoot and maximum rate of rise of action potential were not significantly changed. A common mechanism of contractile hyperactivation based on a multicompartment model of the intracellular Ca movements in discussed.

Anaphylaxis↗
PubMed1979

[Effect of hypokinesia on the contractile function of the myocardium].

Rats were subjected to hypokinesia for two months and the contractile function of isolated papillary muscles was studied. Hypokinesia reduced significantly the isotonic contraction velocity which depended on the ATPase activity of the myofibrils; it also reduced the velocity and index of relaxation which depended on the functional capacity of the Ca++-pump of the sarcoplasmic reticulum. The maximum force of isometric contraction determined by the quantity of actomyosine bridges in the myofibrils did not change after hypokinesia. This complex of changes is contrary to that observed in adaptation to exercise, when the velocity of isotonic contraction and relaxation increases while the force of isometric contraction does not change. The possible mechanism of this stability of the contractile force during adaptation and readaptation of the heart is discussed.

Animals↗
PubMed1997

Forearm muscle oxygenation decreases with low levels of voluntary contraction.

The purpose of our investigation was to determine if the near infrared spectroscopy technique was sensitive to changes in tissue oxygenation at low levels of isometric contraction in the extensor carpi radialis brevis muscle. Nine subjects were seated with the right arm abducted to 45 degrees, elbow flexed to 85 degrees, forearm pronated 45 degrees, and wrist and forearm supported on an armrest throughout the protocol. Altered tissue oxygenation was measured noninvasively with near infrared spectroscopy. The near infrared spectroscopy probe was placed over the extensor carpi radialis brevis of the subject's right forearm and secured with an elastic wrap. After 1 minute of baseline measurements taken with the muscle relaxed, four different loads were applied just proximal to the metacarpophalangeal joint such that the subjects isometrically contracted the extensor carpi radialis brevis at 5, 10, 15, and 50% of the maximum voluntary contraction for 1 minute each. A 3-minute recovery period followed each level of contraction. At the end of the protocol, with the probe still in place, a value for ischemic tissue oxygenation was obtained for each subject. This value was considered the physiological zero and hence 0% tissue oxygenation. Mean tissue oxygenation (+/-SE) decreased from resting baseline (100% tissue oxygenation) to 89 +/- 4, 81 +/- 8, 78 +/- 8, and 47 +/- 8% at 5, 10, 15, and 50% of the maximum voluntary contraction, respectively. Tissue oxygenation levels at 10, 15, and 50% of the maximum voluntary contraction were significantly lower (p < 0.05) than the baseline value. Our results indicate that tissue oxygenation significantly decreases during brief, low levels of static muscle contraction and that near infrared spectroscopy is a sensitive technique for detecting deoxygenation noninvasively at low levels of forearm muscle contraction. Our findings have important implications in occupational medicine because oxygen depletion induced by low levels of muscle contraction may be directly linked to muscle fatigue.

Adult↗
PubMed1983

Does atropine block antigen-induced contraction in canine bronchial rings? A preliminary report.

Isometric contractions recorded with a strain gauge, were elicited with cumulative doses of ascaris suum antigen on fresh canine bronchial rings from 8 dogs. Fifteen rings from 2 spontaneously sensitized dogs reacted with contractions to the antigen, while 11 rings from other dogs did not react. Seven sensitized rings were re-challenged after atropine, which significantly prevented the antigen from contracting these rings at a time when antigen contracted 3 non-atropinized, simultaneously tested rings from the same bronchi. Acetylcholine may play a part in the smooth-muscle contraction induced by antigen, or atropine may inhibit early activation of the "arachidonic acid cascade". The findings may be of interest in the interpretation of anti-muscarinic drugs as inhibitors of reflex cholinergic activity versus local anti-allergic effect.

Animals↗
PubMed2004

Combining isometric knee extension exercises with hip adduction or abduction does not increase quadriceps EMG activity.

OBJECTIVE: To determine if the combined isometric contractions of knee extension/hip adduction and knee extension/hip abduction will elicit a different quadriceps and gluteus medius electromyographic (EMG) pattern as compared to isometric contraction of a uniplanar knee extension exercise. METHODS: Eight healthy young adult volunteers without history of knee or quadriceps injury participated. Surface EMG data were collected from the vastus medialis oblique (VMO), vastus lateralis (VL), and gluteus medius (Gmed) muscles of the dominant leg of each subject during three single leg, weight bearing, isometric exercises (uniplanar knee extension, knee extension/hip adduction, knee extension/hip abduction). All exercises were performed at a position of 60 degrees knee flexion. Three trials lasting 5 s each were performed for each of the three exercises. EMG data from each muscle were integrated and the maximum root mean square activity over a 0.5 s window for each trial was averaged. Analyses of variance were performed with exercise (straight extension, extension/adduction, extension/abduction) as the independent variable and VMO, VL, and Gmed activity and VMO:VL ratio as dependent variables. RESULTS: A significant main effect for exercise was found for the VMO (p = 0.006) and VL (p = 0.02), but not the Gmed (p = 0.25) or the VMO:VL ratio (p = 0.13). For the VMO and VL, the uniplanar knee extension task produced significantly more EMG activity than the extension/adduction or extension/abduction tasks. CONCLUSIONS: Uniplanar knee extension exercises may be more appropriate than combining isometric knee extension exercises with hip adduction or abduction when eliciting maximal VMO and VL contractions.

Adult↗
PubMed1981

The effect of 5-hydroxytryptamine on the slow inward current of bullfrog atrium.

The effect of 5-hydroxytryptamine (5-HT) on the isometric contraction, membrane potential, and membrane current of isolated bullfrog (Rama catesbeiana) atrium was investigated. 5-HT depressed the isometric contraction and this negative inotropism was atropine-resistant. 5-HT reduced both peak amplitude and duration of the action potential, but caused no detectable changes in the resting membrane potential and membrane input resistance. The final, or "secondary depolarization phase"1) in the rising phase of the action potential was found to be selectively depressed by 5-HT. These inhibitory effects on the action potential was also atropine-resistant. A single sucrose-gap voltage-clamp experiment revealed that 5-HT caused a reduction of the slow inward (Ca++/Na+) current. The membrane slope conductance near the resting membrane potential and the degree of activation of the of the time-dependent potassium current showed no detectable change in the presence of 5-HT. It was concluded on the basis of the present results that 5-HT directly controlled the action potential by selectively depressing the slow inward (Ca++/Na+) current. This may be responsible for the negative inotropic effect of 5-HT on bullfrog atrium.

Acetylcholine↗
PubMed2001

Knee Extensor Electromyographic Activity-to-Work Ratio is Greater With Isotonic Than Isokinetic Contractions.

OBJECTIVE: To determine whether isotonic or isokinetic contractions produced greater electromyographic (EMG) activity per unit of work during isotonic and isokinetic knee-extension exercise. DESIGN AND SETTING: Subjects performed three 3-second maximal voluntary isometric contractions of the dominant knee extensors for EMG normalization. Exercise testing performed on the Biodex System 3 Dynamometer involved 10 isokinetic contractions at 180 degrees.s(-1) and 10 isotonic contractions with the resistance set at 50% of the previously recorded maximal voluntary isometric contraction. SUBJECTS: Recreationally active college students (10 men and 11 women). MEASUREMENTS: Surface EMG signals were collected from the vastus medialis and lateralis muscles and then integrated (IEMG) over the concentric phase of each repetition for both exercises. The IEMG was divided by the total work performed during the concentric phase for each exercise (IEMG/W). RESULTS: We analyzed the IEMG/W data using a 1-between (sex), 2-within (exercise and muscle) repeated-measures analysis of variance. There was a significant main effect for exercise, with the isotonic IEMG/W value being significantly greater than the isokinetic IEMG/W value. Additionally, the IEMG/W relationship did not appear to be affected by sex or individual muscle tested. CONCLUSIONS: Per unit of work performed, the isotonic contractions resulted in greater motor unit recruitment or an increased rate of firing, or both. This finding may have implications for the early phase of rehabilitation, when goals include complete motor unit recruitment of injured or atrophied muscles.

Journal Article↗
PubMed1991

Torque potentiation and myosin light-chain phosphorylation in human muscle following a fatiguing contraction.

Indices of electrically stimulated and maximal voluntary isometric muscle torgue and the phosphate content of myosin phosphorylatable light chains (P light chains) were studied during recovery following a 60-s maximal voluntary isometric contraction (MVC) in 21 human subjects. Analysis of muscle biopsy samples revealed that immediately after the 60-s MVC there were significant decreases in ATP (-15%) and phosphocreatine (-82%), and lactate concentration increased by 17-fold. All indices of muscle torque production were reduced by the 60-s MVC, but the twitch torque and torque at 10 Hz were relatively less reduced compared with the torque at 20 and 50 Hz or a 1-s MVC. Between 3 and 6 min of recovery, twitch torque and torque at 10 Hz stimulation were significantly potentiated, reaching peak values of 125 and 134%, respectively, compared with rest. Phosphate content of the fast and two slow P light chains was significantly increased over rest levels immediately after and 4 min after the 60-s MVC. These results suggest that myosin P light-chain phosphorylation could provide a mechanism to increase human muscle torque under conditions of submaximal contractile element activation following fatigue.

Adenosine Triphosphate↗
PubMed1995

Relative degree of stimulation-evoked glycogen degradation in muscle fibres of different type in rat gastrocnemius.

1. The relative degree of glycogen degradation, caused in different fibre types by supramaximal electrical activation of the muscle nerve, was investigated in m. gastrocnemius medialis of young adult rats under general pentobarbitone anaesthesia. Four different protocols of intermittent maximal tetanic activation were used, each lasting 6 s (33% duty cycle; fast and slow isovelocity concentric (shortening) contractions, brief- and long-burst isometric contractions; 6 rats per group). All contractions were evoked under ischaemic conditions. 2. Work output finally dropped to 29% of the initial value for the fast concentric and to 87% for the slow concentric contractions. In isometric protocols evoked by the same stimulation patterns, the force x time area rose to 110% for brief-burst contractions and dropped to 95% for the long-burst contractions. 3. Following the physiological procedures, the experimental muscle and its contralateral control were removed and prepared for histochemical analysis. Serial sections were stained for glycogen (periodic acid-Schiff (PAS) method) and myofibrillar ATPase (mATPase), the latter reactions being used for classifying the fibres as types I, IIA, IIBd and IIBm. 4. For deep 'red' regions of non-stimulated contralateral control muscles the optical density of PAS staining was ranked between fibre types such that I < IIA < IIBd < IIBm. In superficial 'white' regions of the same muscles, no significant difference in PAS staining density was found between IIBd and IIBm fibres (types I and IIA not present). 5. All contractile protocols produced a significant glycogen degradation in IIBm fibres, and the fast concentric activation procedure was associated with a significant decline of PAS staining in all fibre types. For all activation protocols, the relative degree of glycogen degradation within a given region was ranked such that IIBm > IIBd > IIA > I. For IIBm vs. IIBd fibres, the differences in relative degradation were greater and more consistently significant for superficial white regions than in the deeper red muscle portions. 6. The results are discussed in relation to glycogen degradation measurements in studies of motor unit recruitment. Furthermore, the results from red vs. white muscle regions underline that fibres of seemingly the same mATPase type may differ considerably in other properties.

Adenosine Triphosphatases↗
PubMed2002

Electromyographic Analysis of Single-Leg, Closed Chain Exercises: Implications for Rehabilitation After Anterior Cruciate Ligament Reconstruction.

OBJECTIVE: Many knee rehabilitation studies have examined open and closed kinetic chain exercises. However, most studies focus on 2-legged, closed chain exercise. The purpose of our study was to characterize 1-legged, closed chain exercise in young, healthy subjects. SUBJECTS: Eighteen normal subjects (11 men, 7 women; age, 24.6 +/- 1.6 years) performed unsupported, 1-legged squats and step-ups to approximately tibial height. MEASUREMENTS: Knee angle data and surface electromyographic activity from the thigh muscles were recorded. RESULTS: The maximum angle of knee flexion was 111 +/- 23 degrees for squats and 101 +/- 16 degrees for step-ups. The peak quadriceps activation was 201 +/- 66% maximum voluntary isometric contraction, occurring at an angle of 96 +/- 16 degrees for squats. Peak quadriceps activation was 207 +/- 50% maximum voluntary isometric contraction and occurred at 83 +/- 12 degrees for step-ups. CONCLUSIONS: The high and sustained levels of quadriceps activation indicate that 1-legged squats and step-ups would be effective in muscle rehabilitation. As functional, closed chain activities, they may also be protective of anterior cruciate ligament grafts. Because these exercises involve no weights or training equipment, they may prove more cost effective than traditional modes of rehabilitation.

Journal Article↗
PubMed1996

Length-specific impairment of skeletal muscle contractile function after eccentric muscle actions in man.

1. The effects of maximum voluntary eccentric muscle actions on forearm flexor strength were studied at three different elbow joint angles (0.87, 1.57 and 2.79 rad) to examine whether subsequent impairment of contractile function is muscle length-specific. 2. A bout of 70 maximum voluntary eccentric muscle actions performed with the forearm flexors elicited delayed muscle soreness, efflux of creatine kinase into the blood, loss of elbow joint range of motion and a prolonged decline in maximum voluntary isometric contraction torque at the three elbow angles monitored (P < 0.01) in 30 subjects. 3. The relative decline in maximum voluntary isometric contraction torque after eccentric exercise differed between elbow angles (P < 0.01). The greatest decline in strength relative to baseline was observed at the most acute elbow angle of 0.87 rad, followed by 1.57 and 2.79 rad respectively. Superimposed electrical stimulation in a subgroup of eight subjects did not increase the torque elicited by the forearm flexors during maximum voluntary contraction tests at the most acute elbow angle (0.87 rad) at any time-point after eccentric exercise, suggesting the disproportionate loss of strength at short muscle length was not due to the inhibitory effects of muscle soreness. 4. Measures of arm circumference and ability to fully flex the elbow (in the same subgroup of eight subjects) suggested the greater decline in strength at the acute elbow angle was not due to the possible confounding influences of muscle swelling and/or impaired muscle shortening ability on strength measurements at short muscle length. 5. These data suggest a shift in the forearm flexor length-tension relationship could account for the disparate decline in strength between elbow angles after eccentric exercise. The disproportionate loss of strength at short muscle length suggests that eccentric exercise evoked a subtle increase in muscle length, perhaps attributable to the cumulative effects of regions of lengthened sarcomeres and/or series elastic elements.

Adolescent↗
PubMed2004

Differences in the force/endurance relationship between young and older men.

The aim of the present study was to ascertain if in six young (23-35 years) and in six older (70-72 years) healthy men matched for comparable absolute and specific maximal force of the dominant elbow flexors, differences in isometric endurance, myoelectrical fatigability, and shortening velocity are still recognizable. To assess the specific force, the muscle cross sectional area (CSA) was determined from magnetic resonance imaging (MRI) scans. The performance of the elbow flexors was studied by assessing the isometric endurance times (ET) at different percentages of maximal isometric contraction (MVC), the average muscle fibre conduction velocity of action potentials (CV), and the median frequency (MDF) of the surface electromyogram (sEMG) of the biceps brachii. Finally, the torque-velocity curve was assessed by means of maximal isokinetic contractions at six fixed angular velocities. All data were expressed as the mean (SD). The results showed that: (1) the ET was longer in the older subjects at the highest levels of isometric contraction, independently from the absolute force; (2) the modifications of muscle fibre CV during isometric effort progressed less rapidly in the older than the younger groups, as did those of MDF; and (3) at the same angular velocity, the older subjects exerted less absolute force than the younger subjects. These results suggest an impairment of the neuromuscular system of older men, which is less powerful and less fatigable than that of young men.

Adult↗
PubMed1983

Quantitative estimation of anaerobic and oxidative energy metabolism and contraction characteristics in intact human skeletal muscle in response to electrical stimulation.

A set up for electrical stimulation of the human quadriceps femoris muscle and registration of tension is described. Normal values for the frequency-tension relations and relaxation time are presented. There was no relationship between contraction characteristics and fibre type distribution. Muscle tissue was sampled after electrical stimulation by percutaneous biopsy technique. Phosphocreatine (PCr) decreased during a 75 s isometric contraction from 76 mmol per kg dry muscle down to a mean value of 9 mmol. Lactate increased during the same time period from 5 mmol per kg dry muscle to 100 mmol. At end of contraction there was a rapid resynthesis of PCr with a half time of about 20 s while the lactate content decreased slowly. The relaxation time of the muscle was prolonged from 38 ms, in non-fatigued muscle, to 128 ms after 75 s of isometric contraction. The relaxation time was normalized after the contraction at the same rate as the resynthesis of PCr. It is proposed that the relationship between PCr and lactate of contracting muscle can be used as an index of glycolytic capacity and that the rate of resynthesis of PCr after contraction is a measure of oxidative capacity. Relaxation time measurements alone may be used as a non-invasive estimation of the oxidative capacity.

Adenosine Diphosphate↗
PubMed1998

Contraction properties of the superior pharyngeal constrictor muscle.

OBJECTIVE: The mechanical contraction property of the superior pharyngeal constrictor (PC) muscle was analyzed and compared with the levator veli palatini (LVP) muscle. DESIGN: Twenty adult dogs anesthetized with sodium pentobarbital were used. RESULTS: The isometric contraction curves of LVP and PC were recorded after direct electric stimulation to each muscle. The contraction time of isometric twitch contraction of the superior PC muscles was 30.3+/-5.25 msec, and the half relaxation time was 22.97+/-5.44 msec. The summation curve was observed at a stimulus frequency above 20 Hz of a repetitive pulse stimulus frequency of 85 Hz. CONCLUSIONS: The mechanical contraction properties of the PC muscle are similar to those of the LVP, but with more aspects that are characteristic of a fast twitch muscle.

Animals↗
PubMed2003

Angle-specific impairment of elbow flexors strength after isometric exercise at long muscle length.

In this study, we examined the long-term reductions in maximal isometric force (MIF) caused by a protocol of repeated maximal isometric contractions at long muscle length. Furthermore, we wished to ascertain whether the reductions in MIF are dependent on muscle length--that is, are the reductions in MIF more pronounced when the muscle contracts at a short length. The MIF of the elbow flexors of seven young male volunteers was measured at five different elbow angles between 50 degrees and 160 degrees. On a separate day, the participants performed 50 maximal voluntary isometric muscle contractions with the elbow flexors at a lengthened position; that is, with the shoulder hyperextended at 45 degrees and the elbow joint fixed at 140 degrees. Following this exercise, the MIF at the five elbow angles, range of motion, muscle soreness and plasma creatine kinase activity were measured at 24 h intervals for 4 days. On day 1, the decline in MIF was higher at the more acute elbow angles of 50 degrees (42 +/- 8%) and 70 degrees (39 +/- 8%; both P<0.01) than at 90 degrees (26 +/- 4%) and 140 degrees (16 +/- 3%; both P<0.01). No significant reduction in MIF was evident at an elbow angle of 160 degrees. Maximal isometric force at an elbow angle of 140 degrees was fully restored on day 3, whereas at an angle of 50 degrees it remained depressed for the 4 day observation period. Restoration of MIF was a function of the elbow angle, with force recovery being less at the smaller angles. The range of motion was decreased by 14 +/- 2 degrees on day 1 (P<0.01) and did not return to baseline values by day 4. Muscle soreness ratings remained significantly elevated for the 4 day period. Serum creatine kinase peaked on day 1 (522 +/- 129 IU, P<0.01) and decreased thereafter. We conclude that the disproportionate decrease in MIF at the small elbow angles and the length-specific recovery in MIF after repeated maximal isometric contractions at long muscle length may be explained by the presence of overstretched sarcomeres that increased in series compliance of the muscle, therefore causing a rightward shift of the force-length relationship.

Adult↗
PubMed1996

Effects of fatigue and sprint training on electromechanical delay of knee extensor muscles.

Electromechanical delay (EMD) of knee extensors in isometric contraction was investigated in six healthy men before and after four periods of 30-s allout sprint cycling exercise, conducted pre and post a 7-week sprint cycling training programme. The EMD was lengthened from 40.4 (SEM 3.46) ms at rest to 63.4 (SEM 7.80) ms after the fatiguing exercise (P < or = 0.05) in the pre-training test. During maximal voluntary contractions (MVC) conducted after the fatiguing exercise, the peak contraction force (Fpeak) and peak rate of force development (RFDpeak) were reduced by 51%-56% and 38%-50%, respectively (both P < or = 0.05). The mechanisms of EMD lengthening during fatigue could have been due to the deterioration in muscle conductive, contractile or elastic properties and require further study. The training programme increased the total work performed during the four periods of sprint exercise (P < or = 0.05). However, no significant training effects were found in the resting or postexercise EMD, Fpeak and RFDpeak during isometric MVC. These unchanged isometric contraction variables but enhanced dynamic performance suggest that isometric tests of muscle are insensitive to the neuromuscular adaptations to sprint training.

Adult↗