The aim of this study was to investigate the electromyographical basis of inaccurate movement by identifying the variate and invariate characteristics of a ballistic, isometric precision-grip skill. Our results have shown that in most subjects investigated, IEMG, discharge rate and the patterns of muscle synergy were variate movement parameters while the sequence of muscle activation, the relative duration of muscle activity and the time to peak force (rise-time) remained essentially invariate. Based on these results, we can conclude that inaccurate performance of this skill, in most of the subjects investigated, was more dependent upon changes in muscle IEMG than in alterations in the temporal sequencing of muscle activity. It was apparent that from trial to trial, subjects had more difficulty in reproducing the appropriate levels of muscle contraction and synergy than in reproducing the required periods of action.