Comparison of a piezoelectric contact sensor and an accelerometer for examining mechanomyographic amplitude and mean power frequency versus torque relationships during isokinetic and isometric muscle actions of the biceps brachii

The purpose of this study was to compare a piezoelectric contact sensor with an accelerometer for measuring the mechanomyographic (MMG) signal from the biceps brachii during submaximal to maximal isokinetic and isometric forearm flexion muscle actions. Following determination of isokinetic peak torque (PT) and the isometric maximum voluntary contraction (MVC), 10 adults (mean ± SD age = 22.8 ± 2.7 yrs) performed randomly ordered, submaximal step muscle actions of the dominant forearm flexors in 20% increments from 20% to 80% PT and MVC. Surface MMG signals were recorded simultaneously from a contact sensor and an accelerometer placed over the belly of the biceps brachii muscle. During the isokinetic and isometric muscle actions, the contact sensor and accelerometer resulted in linear increases in normalized MMG amplitude with torque (r2 range = 0.84–0.97) but the linear slope of the normalized MMG amplitude versus isokinetic torque relationship for the accelerometer was less (p < 0.10) than that of the contact sensor. There was no significant (p > 0.05) relationship for normalized MMG mean power frequency (MPF, %max) versus isokinetic and isometric torque for the contact sensor, but the accelerometer demonstrated a quadratic (R2 = 0.94) or linear (r2 = 0.83) relationship for the isokinetic and isometric muscle actions, respectively. There were also a number of significant (p < 0.05) mean differences between the contact sensor and accelerometer for normalized MMG amplitude or MPF values. These findings indicated that in some cases involving dynamic and isometric muscle actions, the contact sensor and accelerometer resulted in different torque-related responses that may affect the interpretation of the motor control strategies involved.