Personnel onboard high-speed marine craft are exposed to eccentric slam impacts of up to 20 g due to hull separation from the water during operation. To maintain postural stability, occupants adopt a semi-squatted position to attenuate the highacceleration loading, which leads to severe acute and chronic musculoskeletal injuries, and hinders post-transit performance. The harsh environment warrants a thorough understanding of human-body behaviour in order to predict responses under specific conditions, and quantify energy expenditure in maintaining postural stability.A comprehensive, three degree-of-freedom sagittal-plane musculoskeletal dynamic modelling framework was developed to estimate musculotendon forces from neuromuscular stimuli and joint kinematics to provide estimates of joint torques and muscle energetics. The model was calibrated and validated through experimental trials with seven participants in the laboratory and indicates good agreement with torque profiles obtained through inverse dynamics. The framework provides general applicability to postural stability in a wide range of motion environments and supports future investigation of injury criteria and occupant-seat interaction on high-speed craft.ii For Mom, Dad, Ibrahim, and Huseina.iii