Fig. 2. Load-clamp recordings at four different force levels during tetanus of a mouse single muscle fiber. (A-D) In each set of records traces represent (from the top): fiber length (puller signal), tetanic force and base line of force. Calibrations of time and force are the same in A-D. A downward deflection of puller signal (FL = fiber length) denotes shortening. Note the different calibrations of puller signal in A-D. The resting fiber length was 0.58 mm. Temperature, 23.5°C.