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Interactions between trunk orientation and gait kinetics are proposed to be inevitable for maintaining dynamic balance, and these interactions are unknown for walking on uneven ground. The purpose of this study was to investigate the interaction effects of posture (regular erect, 30°, 50° and 70° trunk flexion) and step category (unperturbed, perturbation, pre- and post-perturbation) on able-bodied walking kinetics. Statistical analysis revealed interactions posture×step: with increased trunk flexion, walking on uneven ground exhibited less changes in GRF kinetic parameters relative to upright walking. Pre-adaptations were more pronounced in the approach step to the drop in regular erect gait. It seems that in trunk-flexed gaits trunk is used in a compensatory way during the step-down to accommodate changes in ground level. In conclusion, exploitation of this mechanism resembles the ability of small birds in adjusting their zigzag- like configured legs to cope with changes in ground level.