Representative muscle work loops (shown as in vivo muscle stress
plotted versus fascicle strain) of the LG, MG and SDF for a single
stride cycle during decline, level and incline trotting (2.5
ms–1). Thicker portions of the line in each work loop denote
the period of muscle activation. Arrows denote the direction of changes in
muscle stress versus fascicle strain (strain=1.0 denotes the resting
length of the fascicles recorded during quiet stance). Net work per cycle is
denoted by the area within the work loop (here normalized as muscle stress and
strain), with counter-clockwise loops denoting net positive work. In all three
muscles, muscle stress (force) and net shortening strain increase as animals
move from decline to level, to incline conditions.