Variability of Positioning Accuracy following a Maximum Isometric Contraction

Abstract

The purpose of this study was to examine the effects of different contraction times and delay times prior to a positioning task. While blindfolded, each of 25 subjects learned to produce elbow-extension movements to a short and a long target using a kinesthesiometer. The subject then produced 30 trials without feedback to each target. These control trials were preceded by a foreperiod of 0-, 3-, or 6-sec. delay. The 60 experimental trials were identical to control trials except the subject isometrically contracted elbow extensor muscles for 3 or 6 sec. prior to each trial. Following each isometric contraction the subject delayed movement for 0, 3, or 6 sec. The 3-sec. and 6-sec. prepositioning contractions produced greater undershooting and variability than no prepositioning contractions, and the 0-sec. delay produced less constant error than either the 3- or 6-sec. delay. It was concluded that following isometric contraction, undershooting a target occurred and this effect did not dissipate within a 6-sec. period.