H-13P Free Communication/Poster Skeletal Muscle Physiology
The purpose of this study was to examine the mechanomyographic (MMG) amplitude-isometric torque relationship of the biceps brachii at three different joint angles.
Twelve adult females (21±2 yrs) performed isometric muscle actions of the dominant forearm flexors on a Cybex II Dynamometer at 25, 50, 75, and 100% maximal voluntary contraction at joint angles of 30, 60, and 90° above the horizontal plane. MMG and EMG signals were recorded from the mid-portion of the biceps brachii using a piezoelectric contact sensor and a bipolar surface electrode arrangement, respectively.
Initial examination of the maximal isometric torque data suggested the presence of two different groups based on angle where maximal torque was produced. A one-way mixed factorial ANOVA indicated significant (p < 0.05) differences between the subjects such that six subjects (group A) recorded the highest maximal torque at 60° while the remaining six (group B) at 90°. Further, in comparison to group B, the maximal torque at 30 and 60° was significantly (p < 0.05) greater for group A. Examination of the EMG and MMG amplitude patterns across level of force indicated the EMG amplitude patterns for both groups increased up to 100%MVC at each joint angle. The MMG amplitude pattern increased up to 100% MVC at each jont angle for group A. For group B, however, the MMG amplitude decreased or plateaued between 75 and 100% MVC at 30 and 60° and increased up to 100% MVC at 90°.
These findings suggest that the amplitude patterns of the MMG signal from the biceps brachii may be joint angle dependent and associated with the variations in the magnitude of isometric torque production at multiple joints angles. Future investigations should consider evaluating the MMG amplitude-isometric torque relationship for unique groups based on angle of maximal torque production.