In vivo force–velocity relation of human muscle: a modelling from sinusoidal oscillation behaviour

Isokinetic tests performed on human muscle in vivo during plantar flexion contractions lead to torque–angular velocity relationships usually fitted by Hillʹs equation expressed in angular terms. However, such tests can lead to discrepant results since they require maximal voluntary contractions performed in dynamic conditions. In the present study, another way to approach mechanical behaviour of a musculo-articular structure was used, i.e. sinusoidal oscillations during sub-maximal contractions. This led to the expression of (i) Bode diagrams allowing the determination of a damping coefficient (Bbode); and (ii) a viscous parameter (Bsin) using an adaptation of Hillʹs equation to sinusoidal oscillations. Then torque–angular velocity relationships were predicted from a model based on the interrelation between Bbode and Bsin and on the determination of optimal conditions of contraction. This offers the possibility of characterizing muscle dynamic properties by avoiding the use of isokinetic maximal contractions