Fig. 2. Example of raw data for stress against time (A) and length against time (B) for one set of three contractions with a shortening distance equal to 100% of stretch distance. L_opt=optimal length. Isometric-shortening contraction–thick, solid, light-grey line; purely isometric contraction–thick, broken, dark-grey line; stretch-shortening contraction–thin, solid, black line. Force is transiently negative after shortening because of damped oscillations, which may have been caused by vibrations in the wire hook attached to the force transducer. Vertical broken lines indicate the period over which mean force was calculated before the stiffness test. Inset shows expansion of force records between broken lines, with double-headed arrows indicating the force enhancement calculated by two different methods (rFE1,rFE2) and the force depression (FD).