Influence of knee joint angle change to the electromyogram and mechanomyogram

The present study was aimed at the elucidation of the effect of a change in knee joint angle on activities of quadriceps muscles of thigh using electromyogram (EMG) and mechanomyogram (MMG). Of 9 healthy adult males, the maximum voluntary contraction (MVC) of rectus femoris (RF), vastus lateralis (VL) and vastus medialis (VM) was measured during knee joint extension. Then, surface EMG and MMG were recorded when 20, 40, 50, 60, 70, and 80% of MVC were induced for a specified period. Subjects positioned themselves with their knee joint flexed at 90 or 60 degrees. Both EMG and MMG tended to indicate greater value in the position with the knee joint flexed at 90 degrees than at 60 degrees. Integrated MMG showed a decrease during 80%MVC in a position with the knee joint flexed at 90 degrees, but not at 60 degrees. The results suggest that muscular activities may be influenced by a change in knee joint angle, and that MMG may be affected more by the change compared with EMG.