Fig. 3. Mean ascending limb portion of the force–length relationship (gray circles, solid line) and steady-state forces (mean ±1 S.D.) following stretch tests (black squares, connected to initial lengths by broken lines) in lumbrical fibres. Forces were normalized with respect to the maximal isometric force (dotted line) for comparison across fibres. Fibre lengths were normalized relative to the optimal fibre length (0%), i.e. the length at which the isometric force was greatest. Note that steady-state force enhancement for stretches beginning at lengths –10 and –15% produced average forces greater than the isometric force at optimal length (0%). Optimal average sarcomere length was based on Lutz and Rome (1994), who demonstrated that maximal force in single frog fibres for fixed-end contractions (as produced here) correspond to an average sarcomere length of 2.1 µm. The remaining average sarcomere lengths were calculated proportionally to the fibre length change.