Lower leg EMG maximum voluntary activation. Tibialis Anterior (TA), Gastrocnemius Medial Head (GASM), Gastrocnemius Lateral Head (GASL). (A) EMG during maximum voluntary activation of the tibialis anterior and gastrocnemii muscles during seated dorsiflexion and plantar flexion. Data is shown for one exemplary control subject and twelve amputee subjects. Signals are high-pass filtered, demeaned, and rectified (for visualization). Signals in black indicate that the muscle is expected to act as an agonist to the ankle movement. Signals in gray indicate that the muscle is expected to act as an antagonist to the ankle movement. Median frequency during maximum voluntary activation (agonist or antagonist depending on which activation had the greatest amplitude) is shown above each plot in gray. In control subjects, there was high agonist muscle activation (black) and low antagonist muscle activation (gray). This activation pattern was not consistent in amputee subjects. Amputee subjects A02 and A08 had little to no lower leg muscle activation during dorsiflexion and high activation of both the tibialis anterior and gastrocnemii muscles during plantar flexion. A01 had activation of all lower leg muscles for both dorsiflexion and plantar flexion, but the activation level was not well sustained. Some amputee subjects had activation patterns similar to controls (A05, A06, A07, A09, A10). (B) Empirical cumulative density function of EMG power spectrum. Lines are shown for group means and boundaries indicate group range.