This study aimed to examine the effects of different voluntary forces of dynamic stretching (DS) on the maximal dorsiflexion angle of the ankle joint, passive torque, and subjective fatigue. Eleven healthy male participants were included in this study. Ankle angle and passive torque were measured before and after DS, which involved four sets of ankle plantarflexion-dorsiflexion performed for 30 s while sitting on an isokinetic machine with the knees fully extended. Although ankle plantarflexion was passively performed via an isokinetic machine, participants were instructed to perform the active ankle dorsiflexion under either of the following two conditions: with maximal voluntary contraction (MVC) (DSmax) or with submaximal voluntary contraction (DSsub). In DSsub, 80% MVC was set as the target voluntary force. Subjective fatigue during DS was measured using the visual analogue scale. In DSsub, participants actually demonstrated 87.0 ± 5.8% MVC. The maximal ankle dorsiflexion angle significantly increased after DS in both conditions. Subjective fatigue was significantly greater after two, three, and four sets of DSmax than after the corresponding repetitions of DSsub. Although passive torque at the maximal dorsiflexion angle tended to increase after stretching, no significant changes were observed in the passive torque from before to after DS. These results compared MVC with approximately 87% MVC, indicating that the voluntary force of DS did not influence the increment of the maximal dorsiflexion angle after DS. Our study findings also suggested that 80–90% MVC is recommended during DS to increase the maximal dorsiflexion angle without excessive subjective fatigue.