Umirrat yadāhā conveys the firmness and tension of the forelegs. The associated notion of imrār belongs to the action of twisting a rope securely; the rope supplies the comparison rather than a literal component of the camel.
Fatl shazr indicates an angled or side-directed manner of tight twisting. The essential point is not merely “like a rope,” but controlled tension, close twisting, and strength transferred from rope-making to the forelegs.