The role of sub-maximal force production in the enslaving phenomenon

When individuals perform a force task involving only one finger, they involuntarily move other fingers as well. This phenomenon is referred to as the enslaving force or the interdependency of fingers. Given that previous literature on the enslaving force has focused on maximal isometric force production, the present research was designed to study the role of sub-maximal force production in the enslaving phenomenon. To this end, we examined behaviorally three levels of force production with a constant rate of force development. We also examined the temporal organization of enslaving separating the achievement of the desired force (ramp phase) and its maintenance (static phase). During the static phase we found: (i) the amount of enslaving increased with the increment of nominal force level whether the index, middle, ring or little fingers were used as the master finger; (ii) enslaving is strongest in the finger directly adjacent to the master finger; and (iii) in terms of enslaving, the index finger was more 'independent' than the other three fingers, regardless of nominal force produced, followed by the little, middle, and ring fingers. In terms of temporal organization, we found that the time-lag of activation of 'slave fingers' during the ramp phase was reduced as the amount of force level increased. Overall, our data suggest that enslaving effect is a task specific phenomenon and depends on the amount of force produced by the master finger.