The aim of this study was to measure maximum isometric force under two different conditions: active and passive conditions. The electromyograms (EMGs) were also measured. The elbow flexors of healthy subjects were studied. Six healthy subjects took part in this study. The isometric maximum force and the EMGs of the elbow flexors were measured under two contrasting conditions. The first was a standard isometric measurement in which a subject actively pulled a fixed wire using their elbow flexor at 100% effort (active). In the second case, the subject tried to keep their elbow at 90 degrees of flexion for as long as possible against external forces produced by an electric motor (passive). The highest force values were extracted during the isometric phase when the elbow angles were kept constant. Hence, the elbow angles were also monitored by an electric goniometer in the later measurement. The passive condition resulted in higher forces than the active condition in 4 of 6 subjects. For a subject who showed different maximum forces under the two conditions, the mean (standard deviation) measured maximum forces under active and passive conditions were 285.2 (11.0) N and 300.2 (14.1) N, respectively (p < 0.01). For the EMG, there were no significant differences between the two conditions. In conclusion, the passive condition used in this study enhanced isometric maximum forces compared to that obtained under standard isometric conditions.