Control of Rapidly Executed Forces to a Target

Abstract

The purpose of the present study was to determine whether initial measures of impulse (i.e., area under the force-time curve) could be used to predict peak force (PF) in hand grip responses of 5- and 10-kg amplitude executed as rapidly as possible. 12 subjects performed 75 practice and 25 test contractions in each condition, with and without visual feedback. The time to peak (PT) for the 5-kg responses was 41 msec., while the 10-kg condition averaged 56 msec. Analyses demonstrated no effect for visual feedback. Correlational analyses of cumulative impulse sections from 5 msec., to PF within conditions showed that early measures of force within a response were not very good predictors of final force amplitude. Indeed, for both conditions upwards of 85% of a reponse needed to have occurred before 50% of PF variance could be predicted. Analyses across conditions demonstrated that 50% of PF variance could be predicted between 15 and 20 msec. PT was also an important predictor variable. By using PT along with cumulative impulse 50% of the variance in PF could be predicted prior to 10 msec., at 5 kg (25% of PT) and at about 15 msec., for 10 kg (27% of PT). Across conditions, 85% of the variance in PF was predictable by 5 msec. Such results suggest that either more refined response indices are needed in predicting response outcome or that even for very rapid responses some lower level “tuning” probably occurs after initiation.