PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Isometric Contraction”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 667 records · Page 37Linked to original sources
PubMed2001

Lengthening contractions are not required to induce protection from contraction-induced muscle injury.

We tested the hypothesis that lengthening contractions and subsequent muscle fiber degeneration and/or regeneration are required to induce exercise-associated protection from lengthening contraction-induced muscle injury. Extensor digitorum longus muscles in anesthetized mice were exposed in situ to repeated lengthening contractions, isometric contractions, or passive stretches. Three days after lengthening contractions, maximum isometric force production was decreased by 55%, and muscle cross sections contained a significant percentage (18%) of injured fibers. Neither isometric contractions nor passive stretches induced a deficit in maximum isometric force or a significant number of injured fibers at 3 days. Two weeks after an initial bout of lengthening contractions, a second identical bout produced a force deficit (19%) and a percentage of injured fibers (5%) that was smaller than those for the initial bout. Isometric contractions and passive stretches also provided protection from lengthening contraction-induced injury 2 wk later (force deficits = 35 and 36%, percentage of injured fibers = 12 and 10%, respectively), although the protection was less than that provided by lengthening contractions. These data indicate that lengthening contractions and fiber degeneration and/or regeneration are not required to induce protection from lengthening contraction-induced injury.

Animals↗
PubMed1978

Catenoid shape of the interventricular septum: possible cause of idiopathic hypertrophic subaortic stenosis.

Previous studies have shown that asymmetric septal hypertrophy (ASH) may occur in embryonic and malformed hearts and that muscle cell disarray is found in myocardium that contracts isometrically. To account for the characteristic ASH and septal muscle fiber disarray of idiopathic hypertrophic subaortic stenosis (IHSS), we postulated that a catenoid shape of the septum, i.e., net zero curvature, would have the mechanics required to produce IHSS. Accordingly, hearts from eight autopsied patients with IHSS were studied for curvature and thickness of free walls and septum, and they were compared to similar measurements in 80 other hearts. In all eight hearts with IHSS the septum was concave to the left in the transverse plane but convex to the left in the apex-to-base plane. Such a catenoid configuration of the septum was not observed in any of the other 80 hearts. The distinctive shape of the septum in IHSS would account for isometric contraction, since adjacent fiber tracts with opposite curvatures would develop maximum tension but would not have motion. Fiber disarray and local hypertrophy would result from such isometric contraction. Since ventricular configuration is acquired early in cardiogenesis, IHSS might therefore result from a genetic or embryonic determination of a catenoid septum.

Adolescent↗
PubMed1982

Contractile force of canine tracheal smooth muscle during continuous stretch.

Canine tracheal smooth muscle strips were mounted horizontally in a tissue bath between a force transducer and a motor-driven movable steel rod, which was used to change muscle length. Muscle length and force were continuously measured during stretch and simultaneously plotted on an X-Y recorder. Active force during stretch was investigated as follows: an initial length was set with the muscle relaxed, where it was contracted isometrically with acetylcholine. After active force reached a steady state, muscle length was decreased until the total tension was equal to zero. The muscle was then stretched slowly to obtain a continuous length-force curve. Results show that force during stretch increases as the length at which the initial isometric contraction is elicited, is decreased. A possible interpretation is that during tonic muscle contraction, the contractile element is able to shorten very slowly relative to the rate at which the muscle was retracted. Thus, the contractile element length established during isometric contraction would affect the muscle force obtained during subsequent stretch of the muscle.

Acetylcholine↗
PubMed1987

Correlation of force-length area with oxygen consumption in ferret papillary muscle.

The ventricular systolic pressure-volume area correlates well with myocardial oxygen consumption. However, in isolated muscle preparations, there are experimental data based on both mechanical and energetic measurements that suggest that the pressure-volume area concept may not obtain. In the present study, force-length area, the analog of pressure-volume area for a linear muscle, was examined in the ferret papillary muscle preparation under a wide range of loading conditions. There were two major findings: first, force-length area is closely correlated with oxygen consumption (r = 0.94-0.98); this correlation is better than those for such other indexes as peak force and force-time integral. Furthermore, this relation of oxygen consumption with force-length area is independent of the mode of contraction (isometric or shortening), while the relations with the other indexes are not. Second, quick release imposed after end-systole during isometric contraction was found to curtail oxygen consumption. The first finding, the optimal correlation of force-length area with oxygen consumption, suggests both that the correlation of pressure-volume area with oxygen consumption on the ventricular level arises from a basic property of cardiac muscle and that force-length area may be the best mechanical index to use in calculating regional oxygen consumption for a ventricular segment. The second finding, however, suggests that the time-varying elastance model, on which the concepts of pressure-volume area and force-length area are based, may not provide a complete description of the mechanical basis of cardiac muscle energetics, especially during the isometric contraction.

Animals↗
PubMedDate not supplied

Relationship between the in-situ activity of ornithine decarboxylase and contractile function of the rabbit papillary muscle.

The relationship between isometric contraction and myocardial ornithine decarboxylase (ODC; EC.4.1.1.17) activity was studied in right ventricular papillary muscles isolated from rabbits. ODC specific activity and polyamine content were significantly increased in papillary muscles contracting isometrically 90 times per minute at the apex of the length-tension relationship for 4 to 5 hours when compared with paired non-contracting muscles or isometrically contracting muscles stimulated at 30 times per min. The increase in ODC activity appeared to be due to new protein synthesis since cycloheximide blocked the increase in ODC activity without affecting isometric function. Thus, the present results suggest that increased contractile demands of the heart may stimulate the synthesis of myocardial ODC, increase ODC activity and polyamine content.

Animals↗
PubMed1997

Changes in the mechanical properties of human and amphibian muscle after eccentric exercise.

Following a series of eccentric contractions, that is stretching of the muscle while generating active tension, the length-tension relationship of isolated amphibian muscle has been shown to shift towards longer muscle length (Katz 1939; Wood et al. 1993). Here we report observations of electrically stimulated ankle extensor muscles of nine human subjects, demonstrating a similar shift in optimum angle for torque generation [3.9 (1.5) degrees] following exercise on an inclined treadmill that involved eccentric contractions in one leg. (All values are means with the SEMs in parentheses). The shift in the unexercised, control leg was significantly less [mean 0.4 (0.7) degree P < 0.05]. Correlated with this shift was a drop in torque [25.1 (5.6)% for the experimental leg; 1.6 (0.7)% for the control leg, P < 0.002]. Optimum angles returned to pre-exercise values by 2 days post-exercise, while torque took a week to recover. A similar shift in optimum length [12 (1.3)% of rest length] was obtained for five toad (Bufo marinus) sartorius muscles subjected to 25 eccentric contractions. Isometrically contracted control muscles showed a smaller shift [3.5 (1.6)%, n = 5]. Accompanying the shift was a drop in tension of 46 (3)% after the eccentric contractions [control isometric, 23 (6)%, P < 0.0001]. By 5 h after the eccentric contractions the shift had returned to control values, while tension had not recovered. When viewed with an electron microscope, sartorius muscles fixed immediately after the eccentric contractions exhibited many small, and a few larger, regions of myofilament disruption. In muscles fixed 5 h after the contractions, no small regions of disruption were visible, and the number of large regions was no greater than in those muscles fixed immediately after the eccentric contractions. These disruptions are interpreted as the cause of the shift in length-tension relationship.

Adult↗
PubMed2002

Muscle and tendon relations in humans: power enhancement in counter-movement exercise.

To clarify the mechanisms of power enhancement during counter-movement exercise, in vivo muscle fibre behavior during plantar flexion exercise was estimated by real time ultrasonography. Six healthy male subjects were requested to perform ankle plantar flexion exercise with counter-movement (CM, plantar flexion preceded by dorsiflexion) and without counter-movement (noCM, plantar flexion only) on a specially designed dynamometer. In CM, in the dorsiflexion phase, muscle fascicle length was initially lengthened, following which its length remained unchanged while the whole muscle-tendon unit was still lengthened, and decreased in the plantar flexion phase. In noCM, fascicle length decreased throughout the movement and it was longer at the onset of movement than in CM. During dorsiflexion phase in CM, muscle fascicles were not actively lengthened, but contracted isometrically at near optimum length of fibre; thus the increase in muscle-tendon unit length was taken up by elongation of the tendinous tissues. These results demonstrate that power enhancement during CM is due to higher force production by isometric contraction at optimal fibre length.

Achilles Tendon↗
PubMed2003

Kinetic effects of fiber type on the two subcomponents of the Huxley-Simmons phase 2 in muscle.

The Huxley-Simmons phase 2 controls the kinetics of the first stages of tension recovery after a step-change in fiber length and is considered intimately associated with tension generation. It had been shown that phase 2 is comprised of two distinct unrelated phases. This is confirmed here by showing that the properties of phase 2(fast) are independent of fiber type, whereas those of phase 2(slow) are fiber type dependent. Phase 2(fast) has a rate of 1000-2000 s(-1) and is temperature insensitive (Q(10) approximately 1.16) in fast, medium, and slow speed fibers. Regardless of fiber type and temperature, the amplitude of phase 2(fast) is half (approximately 0.46) that of phase 1 (fiber instantaneous stiffness). Consequently, fiber compliance (cross-bridge and thick/thin filament) appears to be the common source of both phase 1 elasticity and phase 2(fast) viscoelasticity. In fast fibers, stiffness increases in direct proportion to tension from an extrapolated positive origin at zero tension. The simplest explanation is that tension generation can be approximated by two-state transition from attached preforce generating (moderate stiffness) to attached force generating (high stiffness) states. Phase 2(slow) is quite different, progressively slowing in concert with fiber type. An interesting interpretation of the amplitude and rate data is that reverse coupling of phase 2(slow) back to P(i) release and ATP hydrolysis appears absent in fast fibers, detectable in medium speed fibers, and marked in slow fibers contracting isometrically. Contracting slow and heart muscles stretched under load could employ this enhanced reversibility of the cross-bridge cycle as a mechanism to conserve energy.

Animals↗