IN-VIVO MEASUREMENT OF THE SERIES ELASTICITY RELEASE CURVE OF HUMAN TRICEPS SURAE MUSCLE

The force-extension characteristic of the series-elastic component of the human triceps surae muscle has been measured in vivo by means of a hydraulic controlled-release ergometer in 12 subjects. The SEC charac teristic can be described by a linear relation between muscle moment a nd extension, with a stiffness K-1, preceded by a quadratic 'toe' regi on at low moments. Stiffness K-1 increases with the level of activatio n of the muscle. At an ankle moment of 100 N m, values range between 2 50 and 400 N m rad(-1). The elastic stretch corresponds then to about 30 degrees, which is considerable compared with the total ankle moveme nt range. At moments of 150 and 180 N m, which correspond to the peak moments in walking and running, respectively, the elastic energy store d in the SEC was 23-37 and 31-57 J. These energy values are amply suff icient to enable the conservation of negative (eccentric) work into a subsequent phase of positive (concentric) work in both walking and run ning. (C) 1998 Elsevier Science Ltd. All rights reserved.