In the speech Sherrington notes the importance of fatigue as a factor affecting competition between rival reflexes for control over the final common path (ie. set of motor neurones relating to a specific action):

'Whatever be the nature of the physiological processes in the conflict between the competing reflexes, the issue of that conflict - namely, the determination of which competing arc shall for the time being reign over the final common path - is largely determined by three factors. One of these is the relative intensity of the stimulation of rival the reflexes. An arc strongly stimulated is ceritus paribus more likely to capture the common path than one which is excited feebly...

A second main determinant for th issue of the conflict between the rival reflexes is the functional species of those reflexes. Arcs belonging to species of receptors which, considered as sense-organs, provoke strongly affective sensation - e.g. pain, sexual feeling, &c. - with the final common path with remarkable facility...

A third main factor... is "fatigue." An arc under long continuous stimulation of its receptor tends, even when it holds the common path, to retain its hold less well. Other arcs can then more readily dispossess it. A stimulus to a fresh arc has, in virtue of its mere freshness, a better chance of capturing the common path... This waning of a reflex under long-maintained excitation is one of the many phenomena that pass in physiology under the name "fatigue." Its place of incidence lies at the synapse. It seems a process elaborated and preserved in the selective evolution of the neural machinery. It prevents long continuous possession of a common path by any ne reflex of considerable intensity. It favours receptors taking turn about. It helps to ensure serial variety of reaction. The organism, to be successful in a million-sided environment, must in its reactions be many-sided. Were it not for such so-called "fatigue," an organism might, in regard to its receptivity, develop an eye, or an ear, or a mouth, or a hand or leg, but it would hardly develop the marvellous congeries of all those sense-organs which it actually does.' (466)