Fig. 6. Red fibre preparations: work loops (force versus length change) during movement at 1Hz and with a stimulation duty cycle of 0.4 at four different stimulation phases, as shown in the diagrams on the left. Fibres were taken from four different positions along the body, as shown in the diagram at the bottom. BL, body length. The scale for the different work loops is given on the left of the loop: vertical, 10mN; horizontal, 0.1 mm. The arrow on each work loop indicates the movement direction. The sign in the loop indicates whether the net work was positive or negative. The ripple on the force recordings from 0.2 and 0.8BL, where BL is body length, is noise from the recording circuit. It is prominent in these recordings because these muscle preparations were small and therefore produced low active force. All recordings are from fibre preparations from the same eel.