Figure 5. Stiffness measurements with 4 kHz length oscillations.

Force response (a) to a 6 nm hs⁻¹ stretch (c) with (continuous lines) and without (dashed lines) superimposed 1 nm hs⁻¹ peak-to-peak 4 kHz length oscillations. Traces b and d were obtained after subtracting the responses without oscillations from those with oscillations. Half-sarcomere stiffness for four step sizes (1.6 nm hs⁻¹, circles; 3.1 nm hs⁻¹, triangles; 4.9 nm hs⁻¹, squares; 6 nm hs⁻¹, diamonds) is shown in e. The first stiffness points after the step (filled symbols at 625 μs) are obtained from the three cycles as indicated by the thicker parts of traces in b and d. Data are mean ±s.e.m. from four fibres, except diamonds, which are from the fibre in a–d.