Asymmetry of force fluctuation in knee extension.

The purpose of this study was to investigate the asymmetry of force fluctuation and mechanomyogram (MMG) signal during low intensity isometric knee extension. Twelve healthy males (21+/-1 years) performed unilateral force matching tasks; sustained isometric knee extension for 15 s at levels corresponding to 10% and 20% maximal voluntary contraction (MVC) with the visual feedback of force. During the force matching tasks, MMG was detected by an accelerometer arrangement placed on the vastus lateralis. Power spectrum density of the MMG was obtained by the fast Fourier transformation method, and mean power frequency (MPF) was calculated. Force fluctuation, amplitude of MMG and MPF of MMG were significantly increased in 20% MVC task compared to the 10% MVC task in both limbs. Significant differences between stronger MVC limb and weaker MVC limb were not observed in force fluctuation, amplitude of MMG and MPF of MMG during 10% and 20% MVC tasks. These results suggest that the asymmetry of force steadiness during low intensity isometric knee extension was not observed because there was no difference regarding mechanical characteristics in active muscle between stronger and weaker limbs.