Fig. 4. Residual force enhancement remaining after rapid shortening by various distances (shortening distance expressed as a percentage of stretch distance). Force enhancement is calculated in two different ways: (A) relative to a contraction without stretch but with shortening (solid line); and (B) relative to a purely isometric contraction (broken line). These two methods represent maximum and minimum bounds, respectively, for the true residual force enhancement. In both cases, force enhancement was significantly greater than zero when shortening distance was 100% of stretch distance. The first data point shows the residual force enhancement without shortening. Top axis gives corresponding final fibre length relative to optimal length (L_opt). Error bars indicate means ± s.e.m. Labels give number of fibres (N) when this was less than six. ^*Different from zero, P<0.05.