Fig. 3. Examples of the four protocols used to measure work done and cost of the different contractions, as described in Materials and methods. (A) Muscle length (upper traces) and force (lower traces) during shortening contractions preceded by either an isometric phase (protocol i) or stretch (protocol ii). Triangles indicate onset (up) and termination (down) of stimulation. (B) Muscle length (upper) and force (lower) during either a purely isometric contraction (protocol iii) or an isometric contraction preceded by a stretch (protocol iv). L_o is muscle length giving maximal, isometric twitch force. Scale bars indicate muscle length (mm), force (mN) and time (ms).