Technique for interpretation of electromyography for concentric and eccentric contractions in gait.

We present a technique to combine muscle shortening and lengthening velocity information with electromyographic (EMG) profiles during gait. A biomechanical model was developed so that each muscle's length could be readily calculated over time as a function of angles of the joints it crossed. The velocity of shortening and lengthening of the muscle fiber was then calculated, and with computer graphics this information was overlaid on the EMG profiles. Thus, researchers and clinicians were not only able to interpret the processed EMG signal as level of activity (tension) but also to gain insight as to the muscles' role as generators (muscle shortening) or absorbers (muscle lengthening) of energy. Six common muscles are documented, using database profiles; soleus (SOL), medial gastrocnemius (MG), tibialis anterior (TA), vastus lateralis (VL), rectus femoris (RF), and semitendinosus (ST). The protocol thus demonstrates a relatively simple technique for calculating muscle fiber velocity and for combining that velocity information with EMG activity profiles.