Final answer:
The midstance phase of gait requires the greatest amount of ankle dorsiflexion to keep the sole of the foot in contact with the ground while supporting body weight (option a).
Step-by-step explanation:
The phase of gait that requires the greatest amount of ankle dorsiflexion range of motion is the midstance phase. During midstance, the foot is flat on the ground, supporting the body's weight as it moves over the foot, and the ankle must dorsiflex to accommodate this position.
Dorsiflexion in this phase involves lifting the front of the foot upwards as the body moves forward, which is necessary to keep the sole of the foot in contact with the ground for stability and to prepare for the next stage of gait, the propulsion phase. The phase of gait and the associated ankle motion can be understood by considering the anatomical position, where dorsiflexion corresponds with decreasing the angle between the dorsal (top) of the foot and the shin.
Hence, the answer is option a.