The aim of this study was to assess, via an electromyographic (EMG) biofeedback method, the mechanical contribution of both agonist and antagonist muscles during maximal voluntary contraction (MVC). We compared this original method with the MVC-EMGmax ratio and the torque/EMG relationship method, both of which are commonly used to estimate antagonist torque. The plantarflexion (PF) and dorsiflexion (DF) MVCs were measured simultaneously with EMG activity of triceps surae (TS) and tibialis anterior in 15 young adults (mean age 23 years). Antagonist torques obtained from the torque/EMG relationship and EMG biofeedback methods appeared to be similar. TS antagonist torque had a major mechanical impact on DF MVC ( approximately 42%). EMG coactivation is significantly different than normalized antagonist torque. TS antagonist torque is not negligible when maximal DF is assessed, and the EMG biofeedback method is a simple method to estimate antagonist torque.