The present investigation aimed to clarify the effect of muscle length on the mechanomyogram (MMG) during isometric twitch contraction of quadriceps femoris muscle. Single twitch contraction of quadriceps femoris muscle was elicited electrically. The muscle length was identically represented using different combinations of hip and knee joint angle. The MMGs were recorded by small accelerometers over each muscle belly of rectus femoris, vastus medialis and vastus lateralis muscle. The electromyograms (EMGs) of same muscles were recorded simultaneously with bipolar surface electrodes placed at both sides of the accelerometer. The twitch force of quadriceps femoris muscle was measured as knee extension force. There was no significant change in the EMG amplitude with muscle length. The MMG demonstrated the greatest amplitude at intermediate length and decreased with muscle shortening as well as lengthening. The behavior in the MMG associated with muscle length was similar to that in force production. The present results suggest that the MMG reflects interaction between actin and myosin filaments of skeletal muscle fibers.
