Viscous properties of human muscle during contraction

The purpose of this study was to determine viscous properties of human musc le during plantarflexion efforts. Experiments were performed on 17 subjects with an ankle ergometer allowing sinusoidal oscillations during isometric contractions and isokinetic movements. Sinusoidal oscillations led to the e xpression of (i) Bode diagrams of the: musculo-articular system allowing th e determination of a damping coefficient (B-bode), and (ii) a viscous coeff icient (B-sin) using an adaptation of Hill's equation to sinusoidal oscilla tions. Isokinetic movements led to torque-velocity relationships. They show ed a fall in torque associated to an increase in angular velocity what was quantified by calculating a damping coefficient (B-iso). Both experiments g ave consistent results indicating that B-bode was the lowest viscous parame ter. This difference is discussed in terms of (i) "analog' viscosity origin ating from muscle cross-bridges; and (ii) real mechanical damping of passiv e structures. (C) 1999 Elsevier Science Ltd. All rights reserved.