Voluntary strength and fatigue

In voluntary efforts it is not known for certain whether the force that can be exerted is limited by the capacity of the nervous centres and conducting pathways to deliver motor impulses to the muscle fibres or by the intrinsic contractile properties of the fibres themselves; whether, in fact, a voluntary effort can be bettered by maximal tetanic stimulation of the muscle electrically, or not. Again in fatigue it is undecided whether tension falls because the degree of voluntary innervation drops or because the fibres are biochemically incapable of maintaining their contraction. The experiments described here attempt to settle these questions by comparing directly voluntary tension with that resulting from electrically excited motor volleys. To make a valid comparison in an intact human subject is difficult, but it will be argued that it can be achieved by using a particularly convenient muscle, the adductor of the thumb, and special apparatus. The paper falls into three parts: the first shows that a maximal voluntary effort develops the same tension as a maximal tetanus artificially excited; in the second part the same equality is found to persist during fatigue, implying that in fatigue, too, the limitation of strength is peripheral; finally the effect of ischaemia is described. Preliminary accounts have already appeared (Merton & Pampiglione, 1950; Merton, 1950).