Motor unit physiology: Some unresolved issues

The purpose of this review was to examine three issues that limit our under standing of motor unit physiology: (1) the range and distribution of the in nervation ratios in a muscle; (2) the association between discharge rate an d force; and (3) the variation in motor unit activity across contractions t hat differ in speed and type. We suggest that if more data were available o n these issues, the understanding of neuromuscular function would be enhanc ed substantially, especially with regard to plasticity in the motor neuron pool, adequacy of the neural drive to muscle, and flexibility of activation patterns across various types of contractions. Current data are limited an d these limitations influence our ability to interpret adaptations in muscl e function in health and disease, (C) 2001 John Wiley & Sons, Inc.