RESUMO
The relationships were examined between the relative force level and exertion strategy during rapid isometric contractions. Thirteen subjects exerted isometric pinchings as fast as possible at various force levels. Force curves and surface EMGs from the first dorsal interosseous muscle were obtained during the contractions. While the single-peaked force curves remained analogous up to a certain force level, they changed to multi-peaked ones at higher force levels. The critical force level, which could be determined in all subjects as relative force level to MVC, was positively correlated with the %MVC EMG magnitude for unit time, obtained below the critical level. EMG durations were significantly shorter blow than above the critical level. These results suggest that different exertion strategies are utilized in rapid contractions at different force levels, and that individual differences in the critical force level are related to difference in the manner of motor unit activation.