We developed a family of human‐body finite‐element models named THUMS Version 6 by incorporating one‐dimensional multiple‐muscle models into a family of detailed models of THUMS Version 4 based on medical image data for the prediction of occupant posture changes before a vehicle crash and injury risks during the crash. THUMS Version 6 has three body sizes: AM50, AF05, and AM95. A muscle‐activation controller was applied in THUMS Version 6 for representing the muscle conditions of sleeping, relaxed, and braced drivers. The direct impact and compression response characteristics of the models were validated by comparison with cadaver test data, and the kinematic response characteristics considering muscle activation were validated by comparison with sled test data using volunteers. We performed simulations of a frontal collision with a velocity of 55 km/h after a deceleration of 0.8 G by autonomous emergency brakes for 300 ms, and the results showed that injury outcomes differed among the three muscle conditions and three body sizes. In addition, the effect of seatbelt pre‐pretension was discussed in comparison with the braced condition. The simulation results obtained using THUMS Version 6 suggest the importance of considering muscle activity in injury prediction through simulated vehicle collisions.