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When step current is injected into the soma of a mammalian motoneuron, the motoneuron fires initially with a very high instantaneous rate which then declines.This phenomenon of decrease in firing rate with stimulus kept constant is called adaptation.In motor control the term fatigue is used for the muscle and the central nervous system but never for the motoneuron.We have shown before that when motoneurons have discharged for a few minutes, they can be substituted by recruitment of new motoneurons, while the discharging motoneurons rest.After rest, these motoneurons resume firing while some of the discharging motoneurons drop out.When input to the motoneuron pool is kept constant, there is rotation among discharging motoneurons in order to maintain force.When a motoneuron is resting we show that initially it is neither responsive to synaptic inputs nor to noise.But after some time, it responds with spikes both to synaptic inputs and noise until it resumes tonic discharge.A constant discharge followed by inability to discharge given the same input, which, after rest, is followed by slow recovery to resumption of tonic firing is reported for mammalian limb motoneurons.Such behaviour is akin to the definition of fatigue used for other cells or systems rather than to adaptation defined for step injected currents.Acknowledgements: Work was supported by a grant from National Science and Engineering Research Council of Canada.