VISCOSITY OF THE ELBOW FLEXOR MUSCLES DURING MAXIMAL ECCENTRIC AND CONCENTRIC ACTIONS

The aim of the present study was to estimate the damping coefficient ( B factor) of the elbow flexor muscles during both eccentric and concen tric muscle actions. We used a muscle model consisting of a viscous da mper associated in parallel with a contractile component, both in seri es with an elastic component. The viscous damper allowed the concentri c loss and the eccentric gain of force to be modelled. Eight volunteer subjects performed maximal eccentric and concentric elbow movements o n an isokinetic dynamometer at angular velocities of 0.52, 1.04 and 2. 09 rad . s(-1). Torques at an elbow joint angle of 90 degrees were rec orded. Electromyogram (EMG) signals from the belly of the right elbow flexor and from the long head of the triceps brachia muscles were reco rded using two pairs of bipolar surface electrodes. The root mean squa re (rms) of the EMG was determined. Eccentric and concentric rms were not significantly different (P >0.05). The B factor was higher in the concentric than in the eccentric conditions (P <0.05), and, whatever t he muscle action type it decreased as the velocity increased. These re sults indicated that the concentric loss and the eccentric gain of for ce were attributable to the behaviour of the contractile machinery. Fu rthermore, whatever the exact cause of loss and gain of tension, our s tudy showed that the total effect can be modelled by the viscous dampe r of a three-component muscle model.