History‐dependence of muscle slack length following contraction and stretch in the human vastus lateralis

摘要

Key points class="unordered" style="list-style-type:disc" id="tjp12935-list-0001">In reduced muscle preparations, the slack length and passive stiffness of muscle fibres have been shown to be influenced by previous muscle contraction or stretch. In human muscles, such behaviours have been inferred from measures of muscle force, joint stiffness and reflex magnitudes and latencies.Using ultrasound imaging, we directly observed that isometric contraction of the vastus lateralis muscle at short lengths reduces the slack lengths of the muscle–tendon unit and muscle fascicles. The effect is apparent 60 s after the contraction.These observations imply that muscle contraction at short lengths causes the formation of bonds which reduce the effective length of structures that generate passive tension in muscles.