1. Experimental Procedures in the Study of Muscle Mechanics

This chapter describes the laboratory procedures classically used to analyze the fundamental properties of muscular contraction. These procedures include the characteristics of the bath in which the specimen, isolated muscle or muscle fiber, is immersed during the experiment, its electrical stimulation and the setups used to record with a minimum of error the force exerted by muscle at a constant length (isometric contraction), during shortening against a constant load (isotonic contraction) and at a constant speed (isovelocity contraction). Isometric contractions at different muscle lengths allow the determination of the force-length relation, which will be described in Chap. 3. Isotonic contraction at a given length allows the determination of the force-velocity relation (Chap. 3) and can be attained mechanically on the whole muscle by means of an isotonic lever (whose physical principle and an example of the apparatus used are described) or electronically on a single muscle fiber and on a tendon-free fiber segment, by means of a feed-back system (isotonic release). An example is shown of the mechanical system (the Levin and Wyman ergometer) used to measure the work done by a muscle during an isovelocity contraction (Chap. 4). The physical response of a system to an action, i.e. the difference between input to a system (both mechanical and electrical) and output of the system, is analyzed with the aim to understand and minimize the distortion of the input signal and to define the ‘time constant’ of several trends of physiological processes reported in this book.