Mean rectified EMG of vastus lateralis, soleus, rectus femoris and gastrocnemius lateralis during gait in a stroke participant and a healthy participant. Tracing of averaged rectified EMG activities of knee extensors (continuous line) and ankle extensors (dotted line) are presented for the paretic (upper panel) and non-paretic (middle panel) sides of a stroke participant (# 4 in Table 1) and a healthy participant (lower panel) walking at 0.99 m/s and 1.04 m/s, respectively. Tracing are averaged for 9 cycles, expressed as a percentage of maximal EMG. The duration (length of time) of the first double-support (DS1), single-support (SS), second double-support (DS2) sub-phases of stance and of the swing phase (SW) are presented in relation to the entire gait cycle. Co-activation of vastus lateralis (VL) and soleus (Sol) is presented in the left panel. Co-activation of rectus femoris (RF) and gastrocnemius lateralis (GL) is presented in the right panel. Arrows represent the latencies in maximal activation of vastus lateralis (VLmax), soleus (Solmax) rectus femoris (RFmax) and gastrocnemius lateralis (GLmax). Circles represent the amplitude of the soleus co-activation index during peak activation of VL (CAISol/Vlmax). Squares represent the amplitude of vastus lateralis co-activation during peak activation of Sol (CAIVL/Solmax). Lozenges represent the amplitude of gastrocnemius lateralis co-activation during peak activation of RF (CAI GL/RFmax). Triangles represent the amplitude of rectus femoris co-activation during peak activation of GL (CAI RF/GLmax).