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To study the muscular mechanics, researchers have employed two standard methods of measuring the force-length relations of muscles. The first is to measure the muscle forces during an isometric contraction state, in which the length is kept unchanged. The second is to make these measurements during an isotonic contraction state, in which the force is kept constant and the length of the muscle allowed to change. Certain muscle groups, such as cardiac tissues, perform auxotonic contractions, which are neither isometric nor isotonic. In this study, a new type of force-clamp system has been developed to use realistic waveforms for studying the auxotonic contraction state of muscles. The system provides digital feedback controls of the length such that the contraction force can follow the time course of a prescribed waveform. The prescribed waveform can be set to various percentages of a previous recorded force waveform, thereby exploring the different states of auxotonic contraction.