Fig. 2. Mechanical performance of a bluegill sunfish abductor superficialis muscle fascicle in vivo. (A) Fascicle stress production during an applied sinusoidal length change. The broken trace shows fascicle length, and the unbroken line fascicle stress. The bold line shows the timing of the applied stimulus. (B) Work loop obtained from the data in A by plotting fascicle stress against fascicle length. The area enclosed by the loop indicates the net work done by the fascicle. Stresses are shown relative to maximal isometric tetanic stress, P₀, and strains relative to L₀, the length at which maximum isometric tetanic stress was measured.