Subjecting a muscle to a series of eccentric contractions, where the contracting muscle is lengthened, results in a number of changes in its mechanical properties. These include a fall in isometric tension which is particularly pronounced during low frequency stimulation, a phenomenon known as low frequency depression (LFD). Reports of LFD have not taken into account the shift in optimum length for active tension generation to longer muscle lengths that takes place after eccentric contractions. Given the length dependence of the stimulation frequency-tension curve, we have tested the hypothesis that the change in this relationship after eccentric exercise is due to the shift in optimum length. We have measured LFD by recording tension in response to a linearly increasing rate of stimulation of the nerve to medial gastrocnemius of anaesthetised cats, over the range 0-100 pulses per second. Tension responses were measured before and after 50 eccentric contractions consisting of 6 mm stretches starting at 3 mm below optimum length, and finishing at 3 mm above it. An index of LFD was derived from the tension responses to ramp stimulation. It was found that LFD after the eccentric contractions was partly, but not entirely, due to changes in the muscle's optimum length. An additional factor was the effect of fatigue. These observations led to the conclusion that the muscle length dependence of LFD was reduced by eccentric contractions. All of this means that after eccentric exercise the tension deficit at low rates of muscle activation is likely to be less severe than first thought.