It is feasible to reduce gutters in CG configurations with the use of endoanchors in an in vitro juxtarenal aneurysm model.

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Devrome AN, MacIntosh BR. The biphasic force-velocity relationship in whole rat skeletal muscle in situ. J Appl Physiol 102: [2294][2295][2296][2297][2298][2299][2300] 2007. First published April 5, 2007; doi:10.1152/japplphysiol.00276.2006.-Edman has reported that the force-velocity relationship (FVR) departs from Hill's classic hyperbola near 0.80 of measured isometric force (J Physiol 404: 301-321, 1988). The purpose of this study was to investigate the biphasic nature of the FVR in the rested state and after some recovery from fatigue in the rat medial gastrocnemius muscle in situ. Force-velocity characteristics were determined before and during recovery from fatigue induced by intermittent stimulation at 170 Hz for 100 ms each second for 6 min. Force-velocity data were obtained for isotonic contractions with 100 ms of 200-Hz stimulation, including several measurements with loads above 0.80 of measured isometric force. The force-velocity data obtained in this study were fit well by a double-hyperbolic equation. A departure from Hill's classic hyperbola was found at 0.88 Ϯ 0.01 of measured isometric force, which is higher than the ϳ0.80 reported by Edman et al. for isolated frog fibers. After 45 min of recovery, maximum shortening velocity was 86 Ϯ 2% of prefatigue, but neither curvature nor predicted isometric force was significantly different from prefatigue. The location of the departure from Hill's classic hyperbola was not different after this recovery from the fatiguing contractions. Including an isometric point in the data set will not yield the same values for maximal velocity and the degree of curvature as would be obtained using the double hyperbola approach. Data up to 0.88 of measured isometric force can be used to fit data to the Hill equation.fatigue; contractile properties; double hyperbola; maximal velocity THE RELATIONSHIP BETWEEN MUSCLE shortening velocity and the load that is imposed on muscle is known as the force-velocity relationship (FVR), where velocity of shortening decreases for progressively higher loads. In 1938, A. V. Hill reported the classic equation that is most often used by researchers to characterize the FVR in skeletal muscle (17)where P is force at any velocity of shortening, V; P o * is predicted isometric force, and a and b are constants. The maximal velocity of shortening (V max ) can be estimated by solving the equation for P ϭ 0, once the constants are known. The ratio a/P o *, describes the magnitude of curvature of the relationship, with a higher value indicating a lesser curvature.Although Hill's equation is used most frequently when force-velocity data are fit to an equation, several studies have shown that the force-velocity properties of muscle do not fit the simple rectangular hyperbola over the full range of values for force and velocity (1,(12)(13)(14)(15). Rather, there is a departure of measured values from the predicted hyperbola at high forces where velocity of shortening is low. According to Edman et al. (14), this departure from the traditional rectang...

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Fatiguing contractions change the force-velocity relationship, but assessment of this relationship in fatigue has usually been obtained after isometric contractions. We studied fatigue caused by isometric or isotonic contractions, by assessment of the force-velocity relationship while the contractions maintaining fatigue were continued. This approach allowed determination of the force-velocity relationship during a steady condition of fatigue. We used the in situ rat medial gastrocnemius muscle, a physiologically relevant preparation. Intermittent (1/s) stimulation at 170 Hz for 100 ms resulted in decreased isometric force to ~35% of initial or decreased peak velocity of shortening in dynamic contractions to ~45% of initial. Dynamic contractions resulted in a transient initial increase in velocity, followed by a rapid decline until a reasonably steady level was maintained. Data were fit to the classic Hill equation for determination of the force-velocity relationship. Isometric and dynamic contractions resulted in similar decreases in maximal isometric force and peak power. Only V was different between the types of contraction ( P < 0.005) with greater decrease in V during isotonic contractions to 171.7 ± 7.3 mm/s than during isometric contractions to 208.8 mm/s. Curvature indicated by a/Po (constants from fit to Hill equation) changed from 0.45 ± 0.04 to 0.71 ± 0.11 during isometric contractions and from 0.51 ± 0.04 to 0.85 ± 0.18 during isotonic contractions. Recovery was incomplete 45 min after stopping the intermittent contractions. At this time, recovery of low-frequency isometric force was substantially less after isometric contractions, implicating force during intermittent contractions as a determining factor with this measure of fatigue. NEW & NOTEWORTHY The force-velocity relationship was captured while fatigue was maintained at a constant level during isometric and dynamic contractions. The curvature of the force-velocity relationship was less curved during fatigue than prefatigued, but within 45 min this recovered. Low-frequency fatigue persisted with greater depression of low-frequency force after isometric contractions, possibly because of higher force contractions during intermittent contractions.