“…It should be noted that motoneurones destined to be fast are then developed into a less excitable state by the reduction in input resistance, due to resistivity, size and geometry changes, and possibly also by other intrinsic differences making F motoneurones less excitable than S motoneurones (Burke & Nelson, 1971;Fleshman, Munson, Sypert & Friedman, 1981;Kernell & Monster, 1981;Gustaffson & Pinter, 1984b). As suggested by the results of Gallego, Huizar, Kudo & Kuno (1978), a quiescent motoneurone would lead to a speeding of its muscle unit from the slow contraction present at birth. One may then surmise that a post-natal differentiation into type F motoneurones, leading into a developing decrease in their excitability and a reduction in their motor activity, would result in the observed muscle unit speeding (cf.…”