Figure 1. Experimental protocol for the main experiment and supplementary experiment.

For the main experiment there were four conditions: contract‐short (A), contract‐long‐weak (B), contract‐long (C), and stretch (D). For the supplementary experiment there were three conditions: contract‐short (A), contract‐long (C), and hold‐short (E). In each panel, time proceeds from left to right. The vertical axis indicates knee angle. Thick coloured lines show the knee angle as a function of time. ‘Weak’ and ‘strong’ refer to weak contractions and strong contractions, respectively. The arrow indicates the transducer placement, which took ∼5 s. ‘Test image’ indicates the period over which the test image sequence was recorded. Subjects were asked to remain relaxed except when performing the weak or strong contractions. Note that all conditions began with a weak contraction with the knee flexed (i.e. with the vastus lateralis muscle in the lengthened position).