ISOTONIC AND ISOMETRIC THERMAL CONTRACTION OF HUMAN DERMIS. I. TECHNIC AND CONTROLLED STUDY.
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Collagen↗
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Quasi-elastic light-scattering studies of single skeletal muscle fibers.
Measurements were made of the intensity autocorrelation function, g(2)[tau], of light scattered from intact frog muscle fibers. During the tension plateau of an isometric tenanus, scattered field statistics were approximately Gaussian and intensity fluctuations were quasi-stationary. The half time, tau 1/2, for the decay of g(2)[tau] was typically 70 ms at a scattering angle of 30 degrees. The decay rate, 1/tau 1/2, of g(2)[tau] varied roughly linearly with the projection of the scattering vector on the fiber axis. 1/tau 1/2 was greater during the tension creep phase of tetani of highly stretched fibers, but was roughly independent of sarcomere length during the tension plateau. g(2)[tau] measured during rest or on diffraction pattern maxima during isometric contraction were flat with low amplitudes. These results are consistent with a model of a 200-mu m segment of an isometrically contracting fiber in which scattering material possesses relative axial velocities of 1-2 mu m/s accompanied by relative axial displacements greater than 0.1 mu m. The slow (1-2 mu m/s) motion of one portion of the fiber relative to another observed under the microscope (500X) during isometric contraction is consistent with the light-scattering results. Structural fluctuations on the scale of the myofibrillar sarcomere which may arise from asynchronous cycling of cross-bridges must involve relative axial velocities less than 3 mu m/s or relative axial displacements less than 0.05 mu m.
Animals↗
Regulation of arterial blood pressure in humans during isometric muscle contraction and lower body negative pressure.
Previous studies have shown that the blood pressure response to isometric handgrip remains unchanged during reductions in preload induced by lower body negative pressure (LBNP). The purpose of the present study was to assess the beat-by-beat haemodynamic mechanisms allowing for precise control of mean arterial pressure (MAP). We have followed the cardiovascular variables involved in the regulation of MAP during isometric handgrip with and without additional application of LBNP during defined periods of the ongoing contraction. Sixteen subjects participated. Mean arterial blood pressure (MAP), heart rate (HR), stroke volume (SV), cardiac output (CO), blood flow velocity in the brachial artery, acral skin blood flow, as well as total (TPR) and local (LPR) peripheral resistance were continuously recorded/calculated before, during and after 2 min of handgrip both with and without concomitant LBNP. The main finding was that MAP increased at the same rate and to the same absolute level whether or not LBNP was applied. A uniform increase in MAP was observed even though the cardiovascular variables evolved differently in the periods with and without LBNP. At the onset of LBNP at -20 mmHg, there was a transient drop in MAP and a transient increase in HR, but within seconds, MAP was regulated back to the slope caused by the isometric handgrip proper. CO and SV, which were declining gradually, showed an additional marked but gradual reduction upon LBNP application. At the same time, both LPR and TPR increased markedly and continuously. In summary, the increase in MAP during isometric handgrip remained essentially unchanged by LBNP-induced alterations in preload. The increase in MAP was caused by a marked increase in peripheral resistance. This supports the concept of a central set point, continuously regulated upwards as long as the isometric handgrip persists. Furthermore, it reveals a considerable flexibility in the cardiovascular control mechanisms used to achieve the desired arterial pressure.
Adaptation, Physiological↗
Myocardial energetics during isometric twitch contractions of cat papillary muscle.
During myocardial tetanus, when activation is maximum and constant, there is a linear relationship throughout contraction between oxygen consumption (MVo2) and the cumulative product of active tension and time (integral of AT). The goal of this study was to determine the relation of MVo2 to integral of AT during isometric myocardial twitch contractions. Ten right ventricular cat papillary muscles were studied in a flow respirometer. MVo2 was determined during contractions unloaded from Lmax to a slack length at successive 100-ms intervals after stimulation. In contrast to the linear relationship observed during tetanus, MVo2/integral of AT varied during twitch contractions: when the muscles were made slack 100 ms after stimulation MVo2/integral of AT was 389 +/- 51 (SE) (nl of O2/mg of dry muscle)/(N of active tension/mm2.s of active tension). This value was 94 +/- 7 at peak active tension and was constant thereafter. There was a continuous increase in cumulative MVo2 as integral of AT increased; before integral of AT began, MVo2 was 0.41 +/- 0.04 (nl of O2/mg)/contraction at Lmax and 0.22 +/- 0.04 at a slack length; at peak isometric tension MVo2 was 1.84 +/- 0.19; for a complete contraction MVo2 was 2.89 +/- 0.25. These data support two concepts 1) activation energy is small and dependent on initial length and tension; and 2) integral of AT is variably energy dependent throughout the entire isometric twitch contraction.
Animals↗
Changes in pennation with joint angle and muscle torque: in vivo measurements in human brachialis muscle.
1. Estimates of pennation in human muscles are usually obtained from cadavers. In this study, pennation of human brachialis was measured in vivo using sonography. Effects of static and dynamic changes in elbow angle and torque were investigated. 2. Pennation was measured in eight subjects using an 80 mm, 5 MHz, linear-array ultrasound transducer to generate sagittal images of the brachialis during maximal and submaximal isometric contractions at various elbow angles. It was shown that estimates of pennation were reproducible, representative of measurements made throughout the belly of the muscle and not distorted by compression of the muscle with the transducer or rotation of the muscle out of the plane of the transducer. 3. Mean resting pennation was 9.0 +/- 2.0 deg (S.D., range 6.5-12.9 deg). When the muscle was relaxed there was no effect of elbow angle on pennation. However, during a maximal isometric contraction (MVC), with the elbow flexed to 90 deg, pennation increased non-linearly with elbow torque to between 22 and 30 deg (mean 24.7 +/- 2.4 deg). The effect of increasing torque was small when the elbow was fully extended. The relationship between elbow angle, elbow torque and brachialis pennation suggests that the relaxed brachialis muscle is slack over much of its physiological range of lengths. 4. There was no hysteresis in the relationship between torque and pennation during slow isometric contractions (0.2 MVC s-1), and the relationship between elbow angle and pennation was similar during slow shortening and lengthening contractions. 5. Two consequences follow from these findings. Firstly, intramuscular mechanics are complex and simple planar models of muscles underestimate the increases in pennation which occur during muscle contraction. Second, spindle afferents from relaxed muscles may not encode joint angle over the full range of movement.
Adult↗
Electromagnetic stimulation blocks isometric twitch contraction in the frog sciatic nerve-gastrocnemius muscle preparation.
The effect of electromagnetic stimulation (EMS) on nerve conduction and muscle twitch contraction was studied in isolated sciatic nerve-gastrocnemius muscle of the frog. Electrical stimulation (ES) of the sciatic nerve produced twitch contractions in the gastrocnemius muscle and these responses were reduced and eventually blocked by EMS, applied to the nerve simultaneously with ES, from a d.c. source at a certain frequency and duration of the induced current. The EMS-induced inhibition of the twitch contractions was reversible, and this depended on the induced current and its duration. The possibility that other factors may have contributed to the inhibition of twitch contractions, such as a rise in temperature, was also investigated. It was concluded that EMS inhibited indirectly-elicited twitch contractions produced by ES in the frog nerve-muscle preparation.
Animals↗
Joint position dependence of weakness during maximum isometric voluntary contractions in subjects with hemiparesis.
OBJECTIVE: To determine the distribution of weakness across elbow range of motion (ROM) in subjects with hemiparesis. DESIGN: A detailed analysis of elbow torque and associated electromyographic signals of 5 prime elbow muscles generated during maximum isometric voluntary flexion (MIVF) and extension (MIVE) at 8 different elbow positions. SETTING: Rehabilitation center research laboratory. PARTICIPANTS: Convenience samples of 5 controls and 10 subjects with hemiparesis with sufficient passive (>90 degrees ) and active (>60 degrees ) ROM on their paretic side. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Measured and normalized MIVF and MIVE torques and normalized moving average electromyographic signals of each muscle at each testing position. RESULTS: Measured MIVF and MIVE torques generated by the hemiparetic group were marginally and significantly smaller than those of the control group (2-factor repeated-measures analysis of variance [ANOVA]: P=.053 for MIVF, P=.011 for MIVE). Distribution of weakness was nonuniform across elbow positions, as shown by normalized torque-position curves. Normalized MIVE torque of the hemiparetic group was significantly and marginally smaller than that of the control group at 15 degrees and 30 degrees (Student t test: P<.0001, P=.054), respectively. Although statistically not significant, the normalized MIVF torque of the hemiparetic group was slightly larger than that of the control group but became smaller than the control group's as the elbow flexed beyond 90 degrees. Our electromyographic recordings supported the normalized MIVF torque findings, showing a significant increase in brachioradialis activation in the control group at flexed positions during MIVF (1-factor repeated-measure ANOVA, P=.003), but not in the hemiparetic group (P=.392). CONCLUSION: Our findings suggest that measuring the strength in multiple joint positions is useful for characterizing the basic changes in muscle activation strategies and properties and provides a relevant measure of elbow weakness from a clinical and functional perspective. Various mechanisms of action are discussed to better understand the relation between joint position and weakness.
Adult↗
Involvement of membrane excitation failure in fatigue induced by intermittent submaximal voluntary contraction of the first dorsal interosseous muscle.
Factors involving muscle fatigue were studied at intermittent isometric contraction of the first dorsal interosseous muscle (FDI). Subjects made repeated contraction of 6 s, 40% of maximal voluntary contraction (40% MVC) (= target force) followed by 4 s rest until the target force could no longer be maintained. Measurement of MVC, recording of M wave evoked from the relaxed muscle, force measurement during tetanic electrical stimulation and measurement of serum K+ concentration were performed every 2 min during the fatiguing exercise and after 10 min of recovery. The declining rate of MVC force was always smaller than that of the force generated by 50 Hz stimulation, suggesting that no central nervous system (CNS) failure was involved. The amplitude and the area of the M wave declined while the duration of the wave increased, accompanied by the rise in serum K+ concentration. After 10 min of recovery, all parameters except the MVC force were restored. Thus we concluded that the failure in muscle membrane excitation, as well as the failure in excitation/contraction coupling, is involved in the deteriorating force generating capacity of FDI during intermittent isometric contraction.
Adult↗
[Changes in the morphology of the normal left ventricle during the phases of isovolumic contraction and relaxation. Consequences on the calculation of the volume and cardiac output by cineangiocardiographic methods].
It is well known that the left ventricular volume, as measured by the cineangiographic method, decreases during the phase of isometric contraction. What is more, the cardiac index and the ejection fraction measured by this method are definitely larger than those derived from dilution methods. These discrepancies can be explained by movements of the mitral valve during the phases of isometric contraction and relaxation. The systolic ejection volume (SEV) was measured by three different methods: 1. End-diastolic volume (EDV) -end-systolic volume (ESV) ; 2. EDV - pre-filling volume (PFV) ; 3. Pre-ejection volume (PEV) - ESV. It has emerged that the results given by the methods (2) and (3) correspond closely, and differ significantly from those given by method (1); they are also close to those obtained by the dilution method. This difference seems to arise from the fact that the movements of the mitral valve during the phase of isometric relaxation are diametrically opposite to those which occur during isometric contraction; thus, when the values EDV-ESV are used in the calculation of SEV, an overestimate is made because the mitral valve is not to be found in the same position within the ventricular cavity for both values.
Adolescent↗
ISOTONIC AND ISOMETRIC THERMAL CONTRACTION OF HUMAN DERMIS. 3. SCLERODERMA AND CICATRIZING LESIONS.
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Cicatrix↗
Phosphagen and metabolite content during contraction in porcine carotid artery.
Previous studies (Paul, R. J. Chemical energetics of vascular smooth muscle. In: Handbook of Physiology: The Cardiovascular System. Bethesda, MD: Am. Physiol. Soc., 1980, p. 201-235) have shown that vascular oxygen consumption reaches a steady state at approximately twice the basal rate during maintenance of isometric contraction. The time course of the attainment of a metabolic steady state, the metabolic signal for the observed increase in respiration, and the contribution of endogenous phosphagens to the energetics of isometric contraction are not known with certainty. To this end, the time course of the tissue content of ATP, ADP, AMP, phosphocreatine (PCr), inorganic phosphate (Pi), and lactate were measured during a KCl-induced isometric contraction in porcine carotid artery and compared with values in the basal state. Oxygenated unpoisoned strips were frozen at 0, 0.5, 1, and 15 min of contraction, and tissue extracts were analyzed using analytical isotachophoresis. No statistically significant changes from the basal levels of ATP and PCr were measured. A small but significant increase in ADP was seen at all times. An increase in Pi of 1.25 mumol/g was observed at 0.5 min, which decreased in time. Tissue lactate content increased by 1.79 mumol/g after 1 min of contraction. The calculated range of cellular free ADP (ADPfree), 44-123 microM, may be sufficient to saturate oxidative phosphorylation. This and the apparent lack of change of ADPfree from basal during contraction suggest that it does not play a role in the coordination of metabolism and contractility. From as early as 0.5 min, when less than 40% of peak isometric force is attained, intermediary metabolism provides the total ATP required for contraction.
Adenine Nucleotides↗
An evaluation of temporomandibular joints and jaw muscles after orthodontic treatment involving premolar extractions.
Experimental subjects (n = 29) were patients who had undergone orthodontic treatment in combination with extraction of maxillary or mandibular premolar teeth, or both. Control subjects (n = 29) were healthy dental students with no orthodontic or extraction experience. Sagittal (corrected axis) tomograms of the TMJs were used to determine the narrowest linear distances between the anterior and posterior outlines of the TMJ condyle and the TMJ fossa, expressed as the joint space ratio. There were no significant (p greater than 0.05) differences between the control and experimental ratios. Bipolar surface electromyograms of the masseter and anterior temporalis muscles were used to determine the isometric contraction velocities of these muscles until 50% and 100% voluntary isometric contraction effort (teeth clenching) was achieved. There were no significant (p greater than 0.05) differences between the control and experimental subjects. Electromyograms were also used to determine the relative contribution of the masseter and anterior temporalis muscles to the bite force developed during brief maximum voluntary tooth clenching, expressed as the activity index. There were no significant (p greater than 0.05) differences between the control and experimental subjects.
Adolescent↗
Sarcomere length dependence of muscle stiffness changes during contraction recorded using ultrasonic waves.
We have developed a technique with which muscle stiffness changes during isometric contraction can be continuously recorded by measuring the propagation velocity of ultrasonic waves with negligibly small perturbations to the contractile system, and obtained an unexpected result that, during isometric contraction, muscle stiffness decreased in the transverse direction while it increased in the longitudinal direction. In the present study, we measured the stiffness of frog skeletal muscle with ultrasonic waves at various sarcomere lengths from 2.2 to more than 3.6 microns, and found that (1) the resting muscle stiffness is insensitive to the resting force development in both the longitudinal and the transverse directions, and (2) the absolute amount of both the longitudinal and the transverse stiffness changes during isometric tetanus decreased linearly with increasing sarcomere length, approaching zero at 3.6-3.8 microns sarcomere lengths. These results indicate that the stiffness changes measured with ultrasonic waves reflect the changes in the number of cross-links between the myofilaments.
Animals↗
The relationship of serum creatine kinase, fiber type, and isometric exercise.
In 11 untrained subjects (mean age = 22.5 yr) serum creatine kinase (CK) was measured before and after two types of knee extension exercise regimens. One regimen consisted of 35 10-s maximal isometric contractions separated by a 20-s rest (10:20). This regimen provided adequate recovery time between trials so that strength loss amounted to only 23.4% over the 35 contractions. The other exercise regimen consisted of the same 35 maximal isometric contractions but separated by 5 s between trials (10:5), resulting in a 54.6% strength loss. Muscle fiber type was also determined to assess the relationship of fiber type with serum CK and strength loss. The fast-twitch (FT)/slow-twitch (ST) area ratio correlated with resting CK. Baseline strength correlated with strength loss over the 10:5 condition but not with strength loss over the 10:20 condition suggesting different mechanisms responsible for strength decline for the two exercise conditions. Although a greater strength loss was found for the 10:5 condition, serum CK levels were significantly higher following the 10:20 exercise. An analysis of covariance showed that the mean strength level over the 35 contractions was significantly related to CK increase in the two exercise conditions. Results suggest that mechanical factors associated with high tension levels may be responsible for CK efflux following isometric exercise.
Adult↗
Cruciate ligament loading during isometric muscle contractions. A theoretical basis for rehabilitation.
A model of the knee in the sagittal plane was used to investigate the ligament forces resulting when an external load applied to the tibia resisted either extension or flexion of the knee under increasing isometric quadriceps or hamstrings contractions, respectively. An elementary mechanical analysis showed which ligament, the anterior or posterior cruciate, was loaded at a given flexion angle and known line of action of the external load. Ligament force, as a proportion of the external load, was also calculated. The results serve as guidelines for the design of injury-specific physical therapy techniques for use after cruciate ligament reconstruction.
Anterior Cruciate Ligament↗
NMR and analytic biochemical evaluation of CrP and nucleotides in the human calf during muscle contraction.
This study compared biochemical and 31P-nuclear magnetic resonance (NMR) determinations of energy metabolites during isometric contractions of the human calf muscle at various exercise intensities. Seven male subjects performed one-legged isometric contractions at a work load of 28, 64, and 90% of maximal voluntary contraction force (28-, 64-, and 90%-CON, respectively) for 3 min, 40 s, and 40 s, respectively, in a magnet and in an exact model of the magnet with an arrangement for rapid muscle biopsy sampling from the gastrocnemius. The decrease in phosphocreatine (CrP) determined by NMR was 20, 33, and 71% for 28%-, 64%-, and 90%-CON, respectively. These decreases were the same as those determined biochemically (25, 34, and 61%, respectively). Muscle CrP 1 min after 90%-CON was also found to be similar between NMR and biochemical determinations (88 and 74% of resting value, respectively). Although no significant change in muscle ATP was found by NMR, a decrease of 29% was observed biochemically at 90%-CON. The ratio between muscle CrP and ATP was the same between NMR and biochemical determinations except for 90%-CON (1.98 and 0.78, respectively). The increase in muscle ADP determined by NMR was two-, five-, and eightfold higher than that found biochemically for 28%-, 64%-, and 90%-CON, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Lower limb performance in older female patients with Parkinson's disease.
AIMS: This study examined lower limb performance in older sedentary patients with Parkinson's disease (PD). METHODS: Fourteen female patients with mild to moderate PD and 12 age-matched controls were included in this study. The force preparation and production of the knee extensor muscles during maximal isometric contraction were measured by dynamometric chair. Two force plates were used to measure the chair rising performance. RESULTS: PD patients had longer visual reaction time during performing maximal isometric contraction, and lower maximal isometric force (MF) and rate of force development of the knee extensor muscles compared with controls. However, MF relative to body weight (BW) did not differ significantly in PD patients and controls. A longer chair rising time and lower maximal rate of vertical ground reaction force (VGRF) development while rising from a chair were found in PD patients compared with controls. No significant differences in maximal VGRF, and the sum of maximal VGRF of the right and left legs relative to the BW while rising from a chair were observed between the groups. In PD patients, chair rising time correlated negatively with MF of the knee extensor muscles. PD subjects also showed a positive correlation between the BW-related maximal VGRF while rising from a chair and MF of the knee extensor muscles relative to BW. CONCLUSIONS: These data suggest that subjects with PD are more deficient in the regulation of force-time parameters, rather than simply in force production of the knee extensor muscles.
Aged↗
[Effects during isometric voluntary contractions of elbow flexion muscles on EMG-reaction time (EMG-RT)].
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Acoustic Stimulation↗