Abstract
Muscles involved in rapid, targeted movements often display a triphasic (Agonist-Antagonist-Agonist) EMG pattern. Some authors have suggested the entire pattern is programmed in advance and initiated as a unit (e.g. Wadman et al., 1979). However evidence from TMS studies has suggested that the Antagonist (ANT) may be prepared separately from Agonist-1 (AG1) (MacKinnon & Rothwell, 2000) with execution of the bursts occurring serially (Irlbacher et al., 2006). Using a startling acoustic stimulus (SAS), which triggers prepared motor commands at short latency (Carlsen et al., 2012), we previously showed independent ANT triggering for a short amplitude movement by presenting the SAS at AG1 onset (Forgaard et al., 2012). Triggering by startle did not occur for longer movements, presumably because the ANT was not sufficiently prepared at this relatively early time point. In the present study we further investigated the time course of ANT readiness by presenting a SAS later in a longer movement. Eleven participants performed ballistic elbow extensions to a 60° target. In 21% of trials a SAS was delivered randomly either with the “go” signal, at AG1 onset, or 70 ms before estimated ANT onset. ANT was triggered early when the SAS was delivered 70 ms prior to its normal onset (p < .05), but not when it was presented with the “go” signal, or at AG1 onset. The present data support the suggestion that components of the triphasic pattern are generated serially and the time at which the ANT burst is fully prepared depends on movement amplitude.Acknowledgments: NSERC