A, force relative to the isometric value. B, force in kPa. Negative velocities refer to lengthening. Circles: sf-1, n = 8; squares, sf-2, n = 5; triangles: 2A, n = 6; diamonds: 2A/2X, n = 11. Bars are ± s.e.m.. Data are grouped in classes of velocity. The sample number in each class varies between 2 and 14. Lines are Hill's equations fitted to the pooled force–shortening velocity data. Continuous lines, sf-1; dashed lines, sf-2; dotted lines, 2A; dot–dashed lines, 2A/2X.