Figure 2: The schematic for the stimulation and recording system. The SM muscle is illustrated in the center. An Aurora Servomotor unit (305-LR) was used to stretch the SM muscle to optimal length and record muscle force. Electrical stimulation (200 ms trains of 200 Hz biphasic pulses) was generated by a National Instruments multifunction board (NI USB 6251). The stimulation trains were optically isolated from ground with an Optical Isolation Unit (A-M 2200) and directed to the SM nerve or directly to SM muscle. A Dell laptop with user-written LabView software was used to control the output signals (intensity of electrical stimulation and position of the servomotor lever) and to record the input signal (muscle force). Data were analyzed offline with National Instruments DIAdem software.