Walking and running, the two most basic and functional gait modes, have been often addressed through EMG, kinematics and biomechanical modelling, however, there is no consensus in the literature on which factors trigger the transition from walking to running. Ankle plantarflexors and dorsiflexor were found to play an important role in gait transition due to higher muscular activation to propel the body forward to run. We tested these muscles activation during walking and running at the same speeds, through a musculoskeletal model derived from subjects' kinematic and kinetic data. Compared to EMG data frequently reported in the literature, the results yielded similar activation patterns for all muscles analyzed. Besides, across speeds, dorsiflexor activation kept increasing in walking, especially after PTS (preferred transition speed), which may indicate its contribution to gait transition, as an effort to bring the foot forward to keep up with the unnatural condition of walking at high speeds.