Upper leg EMG activation during walking. Vastus Lateralis (VL), Rectus Femoris (RF), Biceps Femoris (BF), Gluteus Medius (GME). Raw EMG signals from the vastus lateralis, rectus femoris, biceps femoris, and gluteus medius muscles for a single stride (1.0 m/s). Data is shown for one exemplary control subject and twelve amputee subjects. EMG signals are high-pass filtered and demeaned. Vertical lines show toe-off. Median frequency is shown above each plot in gray. Many EMG patterns of amputee subjects are different from the control and there is a large amount of variability in EMG patterns across amputees. (B) Empirical cumulative density function of EMG power spectrum. Lines are shown for group means and boundaries indicate group range.