Movie S1.

High speed video showing an isolated semimembranosus muscle squeezed mid-contraction at 1.15 L₀. Contraction is initiated at the start of the video. Once an isometric force plateau is reached, a squeeze is applied via inflation of a pneumatic pressure cuff fit about the muscle belly. The muscle relaxes after a period of squeeze. Text animations denote the onset of contraction, squeezing, and relaxation.