Group comparisons of co- activation indexes in 13 stroke and 10 healthy participants. Mean peak activation intervals (PAI) and co-activation amplitude indexes (CAI) measured during the stance phase are presented for the paretic (black bars) and non-paretic (grey bars) sides of stroke participants and for control participants (white bars). PAIs between knee extensors (vastus lateralis: VL or rectus femoris: RF) and ankle extensors (soleus: Sol and gastrocnemius lateralis: GL) are expressed as a percentage of the gait cycle duration (upper panel). CAI of knee extensors (VL and RF), expressed as a percentage of their maximal EMG activation during peak activation of ankle extensors (at Solmax and GLmax), are also presented (middle panel). CAI of ankle extensors (Sol and GL), expressed as a percentage of their maximal EMG activation, during peak activation of knee extensors (at VLmax and RFmax) are presented (lower panel). Vertical bars =1 SEM. Asterisks represent significant differences between groups (* p ≤0.05; ** p ≤0.01; *** p ≤0.001).