Before revision:  However, current rheological methods assume approximately invariant mechanical properties during measurement, and thus cannot be used for characterizing the rheology of tunable materials. Here, we develop a geometric framework for characterizing tunable materials by combining classical oscillatory rheology that uses Lissajous force-length loops to characterize non-tunable materials, with the technique of work loops that is used to study muscle's work output under varying stimulation.
After revision:  However, current rheological methods assume approximately invariant mechanical properties during measurement, and tests it using published datasets and simulations. Skeletal muscle's rheology, how it deforms under forces, is neurally modulated and crucial for animal movement. Muscle's force-length loops to characterize non-tunable materials, with the technique of work loops that is used to study muscle's work output under varying stimulation.