Final answer:
The knee requires a 60-90 degree range of motion during the swing phase of gait to ensure efficient leg swing and ground clearance, as well as preparation for heel strike.
Step-by-step explanation:
The required range of motion for the knee during the swing phase of gait is 60-90 degrees. This range allows the leg to swing through and clear the ground efficiently without dragging the toes and prepares the leg for the heel strike at the beginning of the next stance phase. Adequate motion is crucial for a fluid and natural gait pattern.