Staircase Phenomenon of Human Muscle : Relation to the Active State

Abstract

Desmedt and Hainaut¹ have interpreted their findings on the staircase phenomenon of normal human muscle in situ in terms of the “kinetics of myofilament activation”, and find themselves at variance with the current explanation of the phenomenon according to which the potentiation of the twitch force is due to a prolongation of the “active state”² as defined by Hill³. The disagreement is based on the finding of a shortening of the contraction time of the isometric twitch in staircase potentiation^4–6. Desmedt and Hainaut¹ argue that this finding rules out (a) that the potentiation is caused by a prolongation of the decay of the “active state”, and (b) that the “active state” reaches maximum in a single twitch. Instead, they suggest that the staircase phenomenon is a result of an intensification of the “active state”⁷, early in the contraction cycle of the twitch.