Properties of postural adjustments associated with rapid arm movements

摘要: 1. We have examined rapid postural adjustments associated with a class of voluntary movements that disturb equilibrium. In the text follows, these motor activities are termed and focal movements, respectively. Standing human subjects performed variety movement tasks on hand-held manipulandum, resulting in disturbances to their The experimental use interact subject's environment relatively simple was permitted more precise comparison movements. 2. Subjects either pulled or pushed stiff interface (the handle) they responded predetermined way handle perturbations. These were carried out various degrees steady-state stability. Prior during support surface forces, electromyographic (EMG) signals, body sway monitored. 3. addition previously shown reaction-time armed we demonstrated occur concept segmental stretch reflexes self-initiated (untriggered) Postural initiated shortly before all tested except short-latency component biceps reflex (25- 30-ms latency). However, this rarely elicited by perturbations free-standing subjects; therefore, usually preceded any activity under condition. 4. By varying degree equilibrium, reciprocal gain/threshold relationship between components documented, i.e., when stability high, reduced absent enhanced. Conversely, difficult elicit condition where not fully supported direction reaction times prolonged. 5. found share number organizational properties automatic Specifically, muscle synergies equivalent composition, relative activation magnitudes, temporal sequencing. Furthermore, both types highly specific locus magnitude quality equilibrium (e.g., "set"). 6. A conceptual model is proposed suggests one which influence set sequencing might be accomplished. propose common central organization those support-surface