Mechanical perturbation of the wrist during one-handed catching

In the present study, the co-ordination of grasp and transport components o f one-handed catching was examined following mechanical perturbations appli ed to the wrist. Six skilled catchers (mean age = 27.5 years) performed 64 trials in which tennis balls were projected at approximately 8 m s(-1). The trial blocks consisted of 10 non-perturbed trials (NPTs) (baseline), and a block of 54 trials of which 20 trials were perturbed. The perturbation was in the form of a resistive force (12 N) applied via a piece of cord attach ed to a mechanical brake. In baseline trials participants reached maximal w rist velocity closer to the time of hand-ball contact (237 ms +/- 68) than in the perturbed (309 ms +/- 61) condition. Furthermore the wrist velocity profile of five out of six participants exhibited a double peak immediately after a perturbation. However, aperture variables such as the relative mom ent of final hand closure (approximately 70% of overall movement time) were not typically affected. The stability of grasp and transport coupling for one-handed catching was shown to vary from trial to trial. Skilled performe rs exploited redundant degrees of freedom in the motor system when faced wi th a sudden, unexpected change in task constraints. (C) 2000 Elsevier Scien ce B.V. All rights reserved. PsycINFO classification: 2330.