Papier 1. Modèle mécanique de la contraction musculaire. 1. Relation force-vitesse

Abstract : The two parameters that determine the functionality of a muscle fibre are the tension (T) exerted at both ends and the velocity of shortening (V), two mechanical characteristics. We established a relationship between T and V by developing a theoretical model of muscular contraction based on the swinging lever arm assumption. At the nanoscale, force and motion are generated by myosin II heads during the working stroke (WS). The change in conformation of a myosin head during the WS is characterized by the rotation of the lever correlated to the linear displacement of the motor domain. The position of the lever is marked by the angle θ. The maximum variation of θ between the two extremes θup and θdown relating to the 2 positions up and down is usually given as 70°. When the angle θ is between θup and θdown , the WS is triggered in 3 modes, fast, slow or very slow. In tetanus isometry, θ is uniformly distributed between the two angles θup and θT separated by a conventional 50° interval. Consequently in tetanus isometry there is a 20° gap between θT and θdown where no head is in WS. We link this absence to the slow detachment of myosin heads. The equation between T and V refers to these 4 occurrences: fast, slow and very slow initiations of WS between θup and θdown , then slow detachment between θT and θdown. The equation is constructed from the geometric data of the myosin head and the time constants of the cross-bridge cycle reactions associated with these 4 events. The biphasic aspect of the curve is explained by the slow detachment which only occurs at very slow speeds. An additional term, derived from the viscosity present as soon as the velocity increases, completes the equation. An adequate fit between the model and examples from the physiological literature is found (r² > 99%).
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Submitted on : Tuesday, August 13, 2019 - 12:31:02 AM
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Sylvain Louvet. Papier 1. Modèle mécanique de la contraction musculaire. 1. Relation force-vitesse. 2019. ⟨hal-01965922v2⟩

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