Study of the nonlinear dynamics of muscles interaction within a single joint is complicated by hysteresis phenomena. Here, we investigate the activation of the flexor and extensor muscles of the elbow joint under conditions when they functioned as antagonists in motor tasks involving the primary activation of agonists. Flexors and extensors were alternately activated through visual biofeedback and therefore successively act as agonists and antagonists. When muscle length and force were altered trapezoidally, the electromyograms of both the initially activated and co-activated muscle groups aligned accordingly. Sinusoidal changes also produced similar electromyographic responses, with asymmetry attributed to the muscles’ hysteresis properties. Statistical analysis confirmed the overall asymmetry in electromyograms of initially activated and coactivated muscles, suggesting a supportive antagonists’ role.