The normal peak of electromyographic activity of the quadriceps femoris muscle in the stair cycle.

The quadriceps femoris muscles of 18 subjects with no history of knee joint pathology were analysed climbing stairs. Temporal data was obtained from bilateral contact closing footswitches. Knee joint data was measured using a specially constructed flexible linkage-bar electrogonimeter. Electromyographic activity was obtained from bipolar Beckman surface electrodes placed on four components of the quadriceps femoris, vastus medialis oblique, vastus medialis longus, vastus lateralis and rectus femoris. Results showed that within the stair cycle, stance occupied 60% and swing 40%. Cadence values were greater during descending than ascending stairs. Joint angle data demonstrated 2 changes in direction of the angular motion of the knee joint in both ascending and descending. Electromyographic analysis identified a peak of EMG activity for each component of the quadriceps femoris in both ascending and descending stairs. Results identified the location of peak EMG activity at specific knee joint angles. The quadriceps components also demonstrated a regular sequence of recruitment. EMG amplitude levels obtained were higher in ascending than descending stairs. The results have clinical implications in the design of lower extremity prostheses and in the application of functional electrical stimulation.