Effect Of Contraction Frequency Research Articles

The Effect of Contraction Frequency on the Central and Peripheral Blood Flow / VO2 Relationship

The Effect of Contraction Frequency on the Central and Peripheral Blood Flow / VO2 Relationship

Effect of contraction frequency on the contractile and noncontractile phases of muscle venous blood flow.

The purpose of this study was to test the hypothesis that increasing muscle contraction frequency, which alters the duty cycle and metabolic rate, would increase the contribution of the contractile phase to mean venous blood flow in isolated skeletal muscle during rhythmic contractions. Canine gastrocnemius muscle (n = 5) was isolated, and 3-min stimulation periods of isometric, tetanic contractions were elicited sequentially at rates of 0.25, 0.33, and 0.5 contractions/s. The O2 uptake, tension-time integral, and mean venous blood flow increased significantly (P < 0.05) with each contraction frequency. Venous blood flow during both the contractile (106 +/- 6, 139 +/- 8, and 145 +/- 8 ml x 100 g-1 x min-1) and noncontractile phases (64 +/- 3, 78 +/- 4, and 91 +/- 5 ml x 100 g-1 x min-1) increased with contraction frequency. Although developed force and duration of the contractile phase were never significantly different for a single contraction during the three contraction frequencies, the amount of blood expelled from the muscle during an individual contraction increased significantly with contraction frequency (0.24 +/- 0.03, 0.32 +/- 0.02, and 0.36 +/- 0.03 ml x N-1 x min-1, respectively). This increased blood expulsion per contraction, coupled with the decreased time in the noncontractile phase as contraction frequency increased, resulted in the contractile phase contribution to mean venous blood flow becoming significantly greater (21 +/- 4, 30 +/- 4, and 38 +/- 6%) as contraction frequency increased. These results demonstrate that the percent contribution of the muscle contractile phase to mean venous blood flow becomes significantly greater as contraction frequency (and thereby duty cycle and metabolic rate) increases and that this is in part due to increased blood expulsion per contraction.

Effect of contraction frequency on leg blood flow during knee extension exercise in humans

Previous studies in isolated muscle preparations have shown that muscle blood flow becomes compromised at higher contraction frequencies. The purpose of this study was to examine the effect of increases in contraction frequency and muscle tension on mean blood flow (MBF) during voluntary exercise in humans. Nine male subjects [23.6 +/- 3.7 (SD) yr] performed incremental knee extension exercise to exhaustion in the supine position at three contraction frequencies [40, 60, and 80 contractions/min (cpm)]. Mean blood velocity of the femoral artery was determined beat by beat using Doppler ultrasound. MBF was calculated by using the diameter of the femoral artery determined at rest using echo Doppler ultrasound. The work rate (WR) achieved at exhaustion was decreased (P < 0.05) as contraction frequency increased (40 cpm, 16.2 +/- 1.4 W; 60 cpm, 14.8 +/- 1.4 W; 80 cpm, 13.2 +/- 1.3 W). MBF was similar across the contraction frequencies at rest and during the first WR stage but was higher (P < 0.05) at 40 than 80 cpm at exercise intensities >5 W. MBF was similar among contraction frequencies at exhaustion. In humans performing knee extension exercise in the supine position, muscle contraction frequency and/or muscle tension development may appreciably affect both the MBF and the amplitude of the contraction-to-contraction oscillations in muscle blood flow.

Sugar transport in the perifused left atrium: Effects of contraction frequency, digitalis and ionic alterations

The activity of the sugar transport system in the rat left atrium was studied by measuring the distribution of 3-methylglucose. Sugar transport increased progressively with the rate of muscle contraction, from rest to 240 beat/min. This effect persisted for up to 15 min after contraction had ceased. Hyperosmolarity increased sugar transport in parallel with cell shrinkage, expansion of extracellular space and increase in intracellular Na + and ionic strength; opposite changes were induced by hypo-osmolarity. Anoxia, uncouplers of oxidative phosphorylation, K +-free medium, as well as 10 −5 g/ml ouabain or 1.0 m m diphenylhydantoin (DPH) stimulated sugar transport and inhibited the Na + pump. In contrast, 10 −9 g/ml ouabain or 0.5 m m DPH decreased sugar transport and intracellular Na + and increased intracellular K +. In all these respects sugar transport in atria resembled that in skeletal muscle. The data are consistent with the proposed role of Ca 2+ as regulator of sugar transport but exclude cytoplasmic Ca 2+ from this function. The effect of 10 −9 g/ml ouabain appears not to be related to the inotropic effect of the drug.

The Influence of Contraction Frequency and of a Local Anesthetic (Mepivacaine) on Human Fetal Myocardium

AbstractThe relation between contraction frequency and mechanical performance was investigated in isolated perfused heart preparations and in papillary muscles from human fetuses at mid‐gestation. The influence of mepivacaine on the isometric force and the action potential of the papillary muscles and on the contractility of the whole hearts was also studied. Under the experimental conditions used, the isometric force of the papillary muscles increased with frequency within the range 60 to 180 contractions per min. The right intraventricular pressure of the isovolumetrically contracting hearts was influenced only to a minor degree by changes in contraction rate between 60 and 150 contractions per min and decreased at higher frequencies. Mepivacaine (0.625–10 μg/ml) caused a dose‐dependent decrease of the active force and a slight reduction of the duration of the action potential in the papillary muscle. The effects of contraction frequency and of mepivacaine are discussed in relation to the asynchrony of the ventricular contraction.