The linearity and reliability of the mechanomyographic amplitude versus submaximal isometric force relationship

The purpose of this study was to investigate the linearity and reliability of the mechanomyographic (MMG) amplitude versus submaximal isometric force relationship for the vastus lateralis. Twenty healthy subjects (mean +/- SD age = 24.0 +/- 4.3 years) volunteered to perform submaximal isometric muscle actions of the dominant leg extensors from 10 to 50% of the maximum voluntary contraction (MVC) on two separate occasions. During each muscle action, the surface MMG signal was detected from the vastus lateralis. The coefficients of determination for the MMG amplitude versus isometric force relationship ranged from r(2) = 0.001 to 0.962, thus indicating a wide range of linearity between subjects. In addition, the linear MMG amplitude versus force slope coefficient was not particularly reliable, with an intraclass correlation coefficient of 0.743 and a standard error of the measurement of 50.66% of the mean value. These findings indicated that the MMG amplitude versus submaximal isometric force relationship did not demonstrate sufficient linearity and reliability to be used for examining the effects of interventions (e.g. training, detraining, stretching, etc). Future studies need to be done to determine the cause(s) for this lack of linearity and reliability and possible techniques that can be used to improve it.