Impaired proactive and reactive grip force control in chronic hemiparetic patients

Objectives: The aim of the study was to test manipulative capacities of hem iparetic patients with partial recovery in a drawer task. The main objectiv e was to assess adjustments of grip force in the face of load perturbations . Methods: The task was to pull and to hold the drawer manipulandum during pr edictable or unpredictable perturbations with short (90 ms) load pulses (fa ctor set). Results: The following novel observations were made. (1) Load pulses elicit ed, at a latency of about 70 ms, a transient grip force response and a corr esponding phasic EMG response. These reactive adjustments were larger durin g holding than during pulling (factor task). In patients, the reactive grip force adjustments and the EMG response in the grip muscles were reduced. ( 2) The above deficit was set dependent. (3) With regular perturbations, gri p force was scaled already before perturbation onset. This proactive adjust ment was greatly reduced in the patient group. (4) Coordination between gri p force and pull for ce before onset of the perturbation was also disturbed in the patients who generated less Slip force per unit pull force than con trol subjects. Conclusions: It is concluded that the patients had difficulties ill adaptin g proactively and reactively to external load disturbances, in addition to their hand weakness. (C) 2000 Elsevier Science Ireland Ltd. All rights rese rved.