Abstract
Publisher Summary The central nervous system (CNS) recruits spinal motoneurons in an orderly fashion under most of the tested experimental paradigms. Experimental observations suggesting selective excitation/recruitment of larger motor units during the electrical stimulation of cutaneous nerves, electrical stimulation of the rubrospinal tract, and lengthening contractions have been reported. The results utilizing synchronous electrical stimulation of cutaneous nerves, or the red nucleus, have to be interpreted as nonphysiological. Instead, under physiological activation of these pathways, the preferential inhibition of small motoneurons by these pathways would change the slope of the recruitment curve instead of causing selective recruitment of large motoneurons. The implications and mechanisms for the selective recruitment reported during lengthening contractions have to be reconsidered. This chapter presents the data obtained with two different experimental paradigms, both of which result in lengthening of active muscles. These observations do not support selective recruitment of fast twitch motor units during lengthening contractions. Two main papers where single motor unit data have been produced and interpreted to suggest selective recruitment of large motor units are central to the discussion in the chapter.
Published Version
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