Fig. 6. Mean electromyographic (EMG) activity normalized to walking at PTS for three muscles: (A) tibialis anterior (TA), (B) rectus femoris (RF), (C) medial gastrocnemius (MGAS) during normal walking (filled squares), normal running (filled circles) and walking with an assistive device: (A) dorsiflexor assist (DFA; open squares)), (B) leg swing assist (LSA; open squares), (C) aiding horizontal force (AHF; open squares) at preferred walking speed (PWS; 1.25 m s^–1), preferred transition speed (PTS; 1.94±0.03 m s^–1), at speeds less than PTS (–0.3, –0.2, –0.1 m s^–1) and speeds greater than PTS (+0.1, +0.2 m s^–1).