Fig. 3. Twitch force (A) and length (B) of a muscle fibre bundle preparation from the transverse muscle mass of the tentacle of Loligo pealei. The recordings of twitch force and length are superimposed after a stimulus at time zero. The highest force recording was obtained during an isometric (constant-length) twitch, and the others (a, b, c, d) were obtained during isotonic twitch with the force clamped to four different levels. The vertical lines mark the point at which force was measured. The slopes of the dashed lines on the length recordings give the velocity of shortening, and the vertical lines are the same times at which force was measured and mark the centre of the section from which the slopes were measured.