Fig. 1. (A) Force recording of a skinned fibre bundle of anterior byssus retractor muscle (ABRM) of common muscle Mytilus edulis. The spikes represent the force responses following repetitive stretches (0.2 Hz, 0.2% of the fibre length in amplitude and 0.2 s in duration), which serve as a measure of stiffness. The solution sequence is indicated. (B) Force-stiffness diagram of another ABRM fibre bundle undergoing the protocol shown in A. The stiffness (mN/%L₀) was calculated by relating the maximal positive amplitude of the stretch-induced force peaks (mN) to the (constant) relative length change (%L₀). Open circles, activation solution at pH 6.7; open triangles, relaxation solution at pH 6.7; filled triangles, relaxation solution at pH 7.4.