An example method may include i) determining, by a robot having at least one foot, a representation of a coefficient of friction between the foot and a ground surface; ii) determining, by the robot, a representation of a gradient of the ground surface; iii) based on the determined representations of the coefficient of friction and the gradient, determining a threshold orientation for a target ground reaction force on the foot of the robot during a step; iv) determining the target ground reaction force, where the target ground reaction force comprises a magnitude and an orientation; v) determining an adjusted ground reaction force by adjusting the orientation of the target ground reaction force to be within the determined threshold orientation; and vi) causing the foot of the robot to apply a force on the ground surface equal to and opposing the adjusted ground reaction force during the step.