Resumo. Background: In the dynamic knee extension (DKE), a metal bar is positioned parallel to bicycle frame, replacing the pedal of a cycle ergometer, which allow consecutives extensions instead of pedaling movement. Considering the fixed ratchet of cycle ergometer, the knee joint returns to its initial position passively, isolating the quadriceps group during the exercise. Thus, DKE can be used to investigate the role of the anterior thigh muscles for the locomotion or balance, for example. However, the DKE ergometer is not commercially available. Aim: to describe the construction of a prototype ergometer for DKE and characterize the force signal and electromyography responses. Methods: Six participants underwent a progressive effort to exhaustion. The electromyography signal of Vastus Lateralis and Biceps Femoris were monitored. The last 10 extensions of each stage were used for analyzes. Results: the force signal has three phases: I: knee extension moment; II: crank draws the metal rod back; III: rapid compression of the load cell by the leg. In addition, Vastus Lateralis activation was higher than Biceps Femoris in all stages (p<0.02). Interpretation: These results demonstrated that is possible to construct an ergometer for DKE, which increase the possibilities of research in motor behavior.