Fig. 5. A representative series of force traces during the 4 min fatigue test is shown for a male FCR. (A) The first 24 s of the intermittent, sub-maximal tetani (1 train/2 s; 200 ms duration, 30 pulses s^-1; sweep speed=2.5 s cm^-1). Note that the tetanic traces fall back to baseline (arrows) during the 2 s intervals between tetanic trains. By 2 mins into the test (B), the rate of relaxation of the muscle has slowed so that the trace returns only part way to baseline, resulting in sustained force between stimulus trains. By the last 20 s of the fatigue test (C), sustained force comprises approximately 70% of the total force at maximum stimulation. Note that the trace had not returned to baseline within this panel even after more than 8 s following the last stimulus train. In most cases it took from 10-15 s for the force to relax completely to baseline. The tick marks on the lower trace indicate the points of stimulation once every 2 s.