Modulation of anticipatory postural adjustments in a reactive and a self-triggered mode in humans

Five subjects raised their preferred arm until horizontal in one of two exp erimental conditions: (1) in response to a visual signal (reactive conditio n), and (2) in a self-triggered condition. In both conditions, subjects wer e instructed to execute the movement at approximately 80% of their maximal velocity, such that all movements were nearly similar. EMG activity was rec orded in a focal muscle (Anterior Deltoidus) and in three postural muscles (ipsi-lateral Gastrocnemius, contra-lateral Tensor Fascia Latae and ipsi la teral Semitendinosus) known to be activated prior to the focal muscle. Resu lts showed greater anticipatory postural adjustments in the self-triggered than in the reactive condition for the three postural muscles. It is sugges ted that similar intentional movements can be triggered by different timing strategies. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.