The biphasic force-velocity relationship in whole rat skeletal muscle in situ

Abstract

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...

Characteristics of Tetanic Force Produced by the Sternomastoid Muscle of the Rat

“…Our results from the rat SM muscle are in agreement with those from other muscles or species used in previous studies. For instance, Devrome and MacIntosh [45] analyzed the force-frequency relationship for a rat gastrocenemius muscle with sciatic nerve stimulation using a 100 ms train of 0.05 ms pulses at a frequency up to 200 Hz. They found the shape of the muscle force curve, which is similar to that observed in the present study with the highest muscle force at 200 Hz.…”

Contractile Performance of Striated Muscle

“…3. The biphasic shape of the force-velocity relationship, with a breakpoint near 0.8 P 0 , also appears in a similar way in mammalian muscle fibres (Edman, 2005;Devrome & MacIntosh, 2007) and in isolated muscle spindles of the frog (Edman et al, 2002). It is worth pointing out that the high-force deviation of the force-velocity curve has been shown to exist also in skinned muscle fibres and to be unrelated to the state of activation of the contractile system (Lou & Sun, 1993).…”

Hill’s equation of muscle performance and its hidden insight on molecular mechanisms

“…The Hill hyperbola also failed to accurately describe the force–velocity relationship at loads greater than ∼80% of isometric force (Edman et al, 1976; Lännergren, 1978). Studies specifically designed to examine the deviation of force–velocity data at high loads from Hill’s hyperbola have revealed double hyperbolic features (Edman, 1988; Edman et al, 1997) and reversal of curvature (Wang et al, 1994; Devrome and MacIntosh, 2007). Theoretical models of cross-bridge cycling (Edman et al, 1997; Negroni and Lascano, 2008; Månsson, 2010) were able to simulate the nonhyperbolic features of the force–velocity relationship, suggesting that the deviation from Hill’s hyperbola has its origin in the kinetics of interaction between myosin cross-bridges and the actin filaments.…”

“…But when V approaches zero, overestimation of force by the Hill equation becomes obvious. This may account for, at least partially, the deviation of force–velocity data from the Hill hyperbola in the low velocity region (Edman, 1988; Wang et al, 1994; Devrome and MacIntosh, 2007).…”