Eccentric Form Research Articles

Metabolic reaction after concentric and eccentric endurance-exercise of the knee and ankle.

Power training plays an essential part in many sport disciplines. The importance of eccentric power training remains a matter of controversial discussion. The objective of this study was therefore to investigate the difference in metabolic reaction between eccentric and concentric stress in comparable work. Sixty-four men between 22 and 60 yr of age performed maximum isokinetic 1-min endurance tests of the knee and ankle each in concentric (180 degrees.s-1) and eccentric (60 degrees.s-1) modes with comparable total area of contraction-time curve (NS). Higher strength values (mean peak torque, P < 0.01), lower fatigue (fatigue index, P < 0.001), lower increase in lactate (P < 0.01), and lower ammonia production (P < 0.01) were found in eccentric than in concentric exercise, independent of the joint. The eccentric form of stress showed lower decrease and thus age-dependence in maximum strength and in fatigue than the concentric form. The results permit the conclusion that eccentric exercise leads to less fatigue and lower lactate and ammonia reaction than concentric exercise in comparable work levels. Variable visco-elastic properties of the muscle fibers themselves with additive passive strength in eccentric mode is considered as the cause. It remains uncertain whether the lower metabolic stress might be useful during the training process. A greater scope of training and increased number of training stimuli might be applied in primarily eccentric forms of exercise.

Alpha- and beta-adrenoceptor blockade fail to prevent high sodium diet-induced left ventricular hypertrophy.

High sodium diet (HS, 8% NaCl) induces left ventricular hypertrophy (LVH) in normotensive rats without an increase in pressure or volume load or in resting cardiac sympathetic activity. HS may affect LV adrenoceptors density or affinity or their postreceptor pathways, thereby causing LVH. We therefore assessed the effects of HS with and without blockade of alpha1- or beta-adrenoceptors by terazosin or nadolol, alone or in combination, on resting hemodynamics, LV and right ventricular (RV) weights, and LV dimensions of male WKY rats. HS increased LV weight by 14% to 17%, and the ratio of LV wall thickness to radius by 18% to 23%. Singly or in combination, the adrenoceptor antagonists did not prevent HS-induced LVH, but instead aggravated it. The increased ratio of LV wall thickness to radius and of LV to RV were attenuated by terazosin or nadolol alone. Neither the resting LV peak-systolic or end-diastolic pressures nor the right atrial pressure was changed by HS, either alone or in combination with the blockers. The failure of chronic alpha1- or beta-blockade to prevent HS-induced LVH suggests that adrenoceptor activation is not important in evoking the LVH. However, the blockers shifted the LVH from a concentric to an eccentric form, suggesting an involvement of additional trophic factors during adrenoceptor blockade.

Instabilities in Accretion Disks of Cataclysmic Variables: A Unification Model for Dwarf Nova Outburst

AbstractInstabilities of accretion disks in cataclysmic variable stars are reviewed in relation to dwarf nova outbursts. Two different kinds of instabilities of accretion disks are now known: the thermal instability and the tidal instability. The thermal instability is produced by hydrogen ionization-recombination transition, which gives rises to a thermal limit-cycle oscillation in accretion disks and it is thought to be responsible for outbursts of U Gem-type dwarf novae. The tidal instability is produced by the tidal effects of the secondary star on accretion disks, by which the disk is deformed to eccentric form and it slowly precesses in the inertial frame of reference. The tidal instability is thought to be responsible for the superhump phenomenon observed during superoutbursts of SU UMa-type dwarf novae. There is a rich variety in outburst behaviors of non-magnetic cataclysmic variables, starting from non-outbursting nova-like stars to various sub-classes of dwarf novae. A unification model for dwarf nova outbursts is then proposed based on these two instabilities. In this model, the non-magnetic cataclysmic variables are classified in the orbital-period versus mass-transfer-rate diagram into four regions depending on different combination to these two instabilities, and their observed outburst behaviors are basically understood on this diagram.

Exploration of Mechanical and Electromyographic Responses of Trunk Muscles to High-Intensity Resistive Exercise

The purposes of this study were to determine the effects of high intensity exercise on fatigue of the trunk muscles within a test session, and on multiple kinetic and electromyographic (EMG) variables over a 6-week training period. Fourty-five normal men and women (20-40 years of age) completed the study. The KIN/COM trunk testing unit (Chattecx Corporation, Chattanooga, Tennessee) was used for both testing and training. The results of the study follow: 1) The KIN/COM trunk testing system was very accurate, and the method used was highly reproducible for the kinetic variables. Reproducibility for the endurance variables was mixed, and isolated EMG variables were poor. 2) Kinetic and EMG decrements associated with fatigue did occur in the trunk muscles with ten continuous cycles of maximal concentric and eccentric contractions. 3) Trunk muscle strength gains were highest for the same mode of exercise used in training (specificity), but significant strength gains also were seen in different modes of muscle contraction (transfer of training). For the trunk extensors, the eccentric form of exercise was superior. 4) The rate of isometric torque development and decay was increased by exercise in men. 5) Trunk muscle endurance was retained when gains in strength occurred. 6) The majority of variables reflecting strength and endurance were retained. The methods and results can serve as guidelines for the evaluation of trunk muscle function and resistive exercise in the clinic.

Diastolic characteristics and cardiac energetics of isolated hearts exposed to volume and pressure overload.

The relation between diastolic dimensions and systolic function was studied in isolated rat hearts exposed to pressure (primary hypertension) and to volume load (hyperthyroidism). The hearts were arrested in diastole and cardiac dimensions analysed. Cardiac function was determined using an anterograde working heart preparation. Both models of cardiac overload produced significant left ventricular hypertrophy, however with different design. One concentric and one eccentric form of left ventricular hypertrophy were found in the spontaneously hypertensive rat obtained from two different breeders. An even more pronounced form of eccentric left ventricular hypertrophy was seen in hyperthyroid rats. The hearts with an eccentric form of hypertrophy had a higher maximal stroke volume when perfused at a high aortic pressure than those with a concentric form. At a low aortic pressure and hence a limited coronary perfusion cardiac performance was diminished in both types of spontaneously hypertensive rats but remained normal in hyperthyroid rats. Furthermore, oxygen consumption was reduced in all hypertrophied hearts compared with non-hypertrophied hearts. These data therefore suggest (a) that hearts having an eccentric type of hypertrophy may be in a more favourable situation, delivering a higher stroke volume for a given degree of myocardial fibre shortening; and (b) that the development of coronary vascular structural changes in spontaneously hypertensive rats, thereby increasing vascular resistance, leads to a decrease in left ventricular function at a low coronary perfusion pressure, whereas no such reduction was observed in hyperthyroid hearts, probably owing to a normal vascular resistance.

Pellucid Marginal Corneal Degeneration

Pellucid marginal corneal degeneration is a bilateral disorder characterized by thinning of the cornea in the inferior periphery. The ectatic cornea remains clear and develops high, irregular astigmatism. We report the clinicopathologic features of three cases and review the clinical, histopathologic, and electron microscopic features of previously reported cases. Pellucid marginal corneal degeneration may represent an eccentric form of keratoconus and, in the setting of healed hydrops, may resemble closely Terrien's marginal degeneration clinically and histopathologically

The coronary arteries in early life in three different ethnic groups.

The histologic changes in the coronary arteries in full-term fetuses, infants, and children of 211 consecutive necropsy specimens from Ashkenazy, Yemenite, and Bedouin groups were studied, excluding cardiac deaths. The developmental structural pattern of the coronary arteries is similar in the three ethnic groups. Differences in the intensity and quantity of the structural findings between the sexes and among various ethnic groups are found in early life. The intimal tissue in the Ashkenazy male develops in an eccentric form, has more collagen tissue components, and is more highly developed than in the Ashkenazy female. Structural findings in the internal elastic membrane and the elastic fibers of the intima are less apparent in the Bedouin group, particularly in the female, than in the Ashkenazy and Yemenite groups. Statistical analysis of the quantitative data showed the intima and musculo-elastic layers to be more developed in the Ashkenazy male than in the Yemenite and Bedouin males. However, Ashkenazy males clearly have more intima and musculo-elastic tissue than do the Ashkenazy females. This was not true for Yemenites and was found in only one of three age groups among Bedouins. The relationship between the structural findings in coronary arteries of children under 10 years and the reported prevalence of coronary heart disease in the corresponding adult population in these three different ethnic groups has been pointed out.

Cornish Promontory Forts

INTEREST in the promontory forts of Cornwall has been much stimulated by the results of Dr. Mortimer Wheeler's excavations in Brittany. One of them, the large and evidently important fort of Trevelgue Head and Porth Island, Newquay, has been under excavation since July 3. Its investigation is being carried on under the direction of Mr. C. K. Croft Andrew on behalf of the Cornwall Excavations Committee. Excavation is still in progress, though much hampered through lack of funds; but the finds reported to date (The Times, Aug. 15), ranging from Neolithic to Early Iron Ago, fully bear out anticipation of the importance of the site, based partly on its superficial resemblance to Hengistbury Head, Hampshire, partly on the imposing character of its septuple line of defences. The main defences are now assigned to the third century B.C., when there supervened an occupation rich in artistic and metallurgical attainments. The pottery is akin to that of Glastonbury Lake Village, displaying curvilinear and lenticular decoration, as well as naturalistic leaf and vegetable forms. It would appear that in order that the outermost defences should include a native iron mine, they were given an eccentric form. At the back of the sixth, the innermost, rampart was banked the refuse of a considerable Iron Ago town. This consisted of houses, or large huts, arranged terrace-wise on the slope rising from the back of the sixth bank to the apex of the island. The best example of a house cleared as yet was occupied from about 200 B.C. to A.D. 100. It is nearly circular and 46 ft. across, the upper sector being sunk two feet deep in the soft slate rock. It shows some fine examples of dry-walling. The wall was probably never more than 4 ft. or 5 ft. high, but it was 6 ft. thick. The roof ran up from eaves which were supported on a ring of external posts, while the span, being too great for early carpenters, was supported by rings of inner posts.